SolarElectricityHandbookAsimple,practicalguidetosolarenergy:howtodesignandinstallphotovoltaic

solarelectricsystems

2012Edition

MichaelBoxwell

www.GreenstreamPublishing.com

GreenstreamPublishing12 Poplar Grove, Ryton on Dunsmore, Warwickshire, CV8 3QE. UnitedKingdom

Copyright©MichaelBoxwell2009–2012PublishedbyGreenstreamPublishing2012

SmashwordsEdition:ISBN978-1-907670-23-7KindleEdition:ISBN978-1-907670-22-0

FirstEdition–publishedApril2009SecondEdition–publishedNovember2009

ThirdEdition–publishedMarch2010FourthEdition–publishedJanuary2011FifthEdition–publishedOctober2011SixthEdition–publishedFebruary2012

Editor:SheilaGlasbeyMichaelBoxwellassertsthemoralrighttobeidentifiedastheauthorofthis

work.AcataloguerecordforthisbookisavailablefromtheBritishLibrary.

Whilstwehavetriedtoensuretheaccuracyofthecontentsinthisbook,theauthororpublisherscannotbeheldresponsibleforanyerrorsoromissionsfound

therein.Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmitted,inanyformorbyanymeans,electronic,

mechanical,photocopying,recordingorotherwise,withoutthepriorpermissionofthepublishers.

TableofContents

TableofContentsIntroducingSolarEnergy

WhothisbookisaimedatTherapidlychangingworldofsolarenergySolarelectricityandsolarheatingThesourceofsolarpowerTheprinciplesofsolarelectricityUnderstandingtheterminologySettingexpectationsforsolarelectricityWhychooseasolarelectricsystem?Cost-justifyingsolarSolarpowerandwindpowerFuelcellsGrid-tiedsolarelectricsystemsSolarelectricityandtheenvironmentEnvironmentalefficiency:comparingsupplyanddemandInconclusion

ABriefIntroductiontoElectricityDon’tpanicAbriefintroductiontoelectricityHowtomeasureelectricityTherelationshipbetweenvolts,amps,ohms,wattsandwatt-hoursVoltsPowerEnergyAwordfornon-electriciansInconclusion

TheFourConfigurationsforSolarPowerStand-alone/off-gridExamplesofsimplestand-alonesystemsGrid-tieAnexampleofagrid-tiesystem

Grid-tiewithpowerbackup(gridinteractive)AnexampleofagridinteractivesystemGridfallbackAnexampleofagridfallbacksystemGridfailoverHowgrid-tiesystemsdifferfromstand-aloneInconclusion

ComponentsofaSolarElectricSystemSolarpanelsBatteriesControllerInverterElectricaldevicesConnectingeverythingtogetherAstand-alonesystemAgrid-tiesystemusingasinglecentralinverterAgrid-tiesystemusingmultiplemicro-invertersInconclusion

TheDesignProcessShort-cuttingthedesignworkSolarenergyandemotionsInconclusion

ScopingtheProjectDesigninggrid-tieorgridfallbacksystemsComparingsupplywithdemandFleshingoutthescopeProducingapoweranalysisAwordofwarningWhenyouarereadytoproceedCalculatinginefficienciesAddingtheinefficienciestoourpoweranalysisWhendoyouneedtousethesolarsystem?KeepingitsimpleImprovingthescopeInconclusion

CalculatingSolarEnergyWhatissolarenergy?

Whyisthisuseful?CalculatingsolarirradianceCapturingmoreofthesun’senergyTheimpactoftiltingsolarpanelsonsolarirradianceCalculatingtheoptimumtiltforsolarpanelsGettingthebestfromsolarpanelsatdifferenttimesoftheyearPositioningyoursolarpanelsUsing solar irradiance to work out how much energy a solar panel willgenerateUsing solar irradiance to give you an approximate guide for the requiredpowercapacityofyoursolararraySolarpanelsandshadeSolararraypowerpointefficienciesTheeffectsoftemperatureonsolarpanelsTemperature impact on solar performance in Austin, Texas during thesummermonthsWorkingoutanapproximatecostWhatifthefiguresdonotaddup?WorkingoutdimensionsInconclusion

SurveyingYourSiteWhatwewanttoachieveWhatyouwillneedFirstimpressionsDrawingaroughsketchofthesitePositioningthesolararrayRoof-mountingGround-mountingPole-mountingSplittingthesolararrayintoseveralsmallerarraysIdentifyingthepathofthesunacrosstheskyShadingProfessionaltoolsforobstacleanalysisCellphoneapplicationsUsingpaperandpencilFutureproofyoursystemWhatifthereareshadingobstructions?Positioningbatteries,controllersandinverters

CablingSitesurveyfortheholidayhomeInconclusion

UnderstandingtheComponentsHowtousethesechaptersCommoncomponentsforallsystemsSolarpanelsAmorphoussolarpanelsPolycrystallinesolarpanelsMonocrystallinesolarpanelsWhichsolarpaneltechnologyisbest?WhattolookforwhenchoosingasolarpanelBuyingcheapsolarpanelsSecond-handsolarPVpanelsFresnellensesandmirrorsSolarpanelmountingsSolartrackersSolararraycablesFusesandisolationswitchesGroundfaultprotection

ComponentsforGrid-TiesystemsHighvoltagein-seriesLowvoltagesystemsMicro-invertersystemsGrid-tiesolarpanelsGrid-tieinvertersInputvoltagePowerratingPowertrackingMultiplestringsDiagnosticsandreportinginformationBuilt-insafetyInstallationoptionsandoperatingenvironmentBuyingfromeBay

ComponentsforStand-AloneSystemsCalculateyouroptimumvoltageVoltagesandcurrentsWhatvoltagescanIrunat?

HowtoworkoutwhatvoltageyoushouldberunningatHowtocalculateyourcurrentCalculatingcablethicknessesConvertingwiresizes:MixingandmatchingsolarpanelsBatteriesTypesofbatteriesBatteryconfigurationsBatterylifespanHoldoverCalculatinghowlongasetofbatterieswilllastSecond-handbatteriesBuildingyourbatterybankBatterysafetySolarcontrollerBalancingthebatteriesAllowforexpansionMaximumpowerpointtrackingGroundfaultprotectionBackuppowerUsingmultiplecontrollersInvertersBatterybankvoltagePowerratingWaveformInstallationoptionsandoperatingenvironmentGroundfaultprotectionCablesBatterycablesAppliancecablingPlugsandsocketsAppliancesLightingRefrigerationMicrowaveovensTelevisions,DVDs,computergamesconsolesandmusicMusicsystemsDishwashers,washingmachinesandtumbledryersAirconditioningsystems

ReputablebrandnamesSolarpanelmanufacturersandbrandsSolarcontrollerandinvertermanufacturersandbrandsBatterymanufacturersandbrandsShoppinglistfortheholidayhomeInconclusion

Planning,regulationsandapprovalsNationalandinternationalstandardsforsolarcomponentsInstallationregulationsGettingyourelectricitysupplierinvolvedSolargrantsandsellingyourpowerGeneralinformationaboutgrants,taxcreditsandfeed-intariffsInconclusion

DetailedDesignSafetyisdesignedinWhatistheworstthatcanhappenwithasolarinstallation?GroundingyourelectricsDCElectricsACelectricsHightemperaturesThinksafetySolararraydesignSolararraydesign–stand-alonesystemsSolararraydesign–grid-tiesystemswithmicro-invertersSolararraydesign–grid-tiesystemswithasingleinverterBatteriesControllerInverterDevicesSpecificsforagridfallbacksystemCircuitprotectionEarthing(grounding)DCcircuitprotectionACcircuitprotectionCablesizingandselectionSizingyourcablesProtectingcablerunsDesigningyoursystemtokeepyourcablesrunsasshortaspossible

SelectingsolarcableControllercableBatteryinterconnectioncablesSomesamplewiringdiagramsTheholidayhomewiringdiagramThenextstepSolarframemountingPositioningbatteriesPlanningtheinstallationInconclusion

InstallationHaveyoureadtheinstructions?SafetyYourFirstAidkitChemicalclean-upkitConsideringthegeneralpublicWorkingatheightHandlingWorkingwithbatteriesGlovesElectricalsafetyAssemblingyourtoolkitPreparingyoursiteTestingyoursolarpanelsInstallingthesolararrayCleaningthepanelsAssemblyandconnectionsRoof-mountingasolararrayFinalwiringInstallingthebatteriesPre-installationPositioningthebatteriesVentilationAccessInsulationConnectionsInstallingthecontrolequipmentInstallingagrid-tiesystem

CommissioningthesystemProgrammingyoursolarcontrollerTestingyoursystemChargingupyourbatteriesConnectingyourdevicesInconclusion

TroubleshootingKeepsafeCommonfaultsExcessivepowerusageSolutionsInsufficientpowergenerationSolutionsDamagedwiring/poorconnectionsWeakbatteryChangingbatteriesInverterissues

MaintainingYourSystemAsrequiredEverymonthEverythreemonthsEverysixmonthsEveryyearAtthestartofeachwinter

InternetSupportToolsavailableonthewebsiteOnlineprojectanalysisMonthlyinsolationfiguresSolaranglecalculatorSolarresourcesQuestionsandanswersAuthoronline!Solararticles

AFinalWordAppendixA–CrystallineSolarPanelsandShading

TypesofobstructionDesigningshade-tolerantsolarsystems

TracktheshadeIncreasingthenumberofsolarpanelsPanelorientationChoiceofsolarpanelUsemicro-invertersDesignaparallelsolararrayDesignamulti-stringsolararrayOtheroptionsIfallelsefails...Inconclusion

AppendixB–SolarInsolationUnderstandingthisinformationSolarinsolationvalues–AustraliaSolarinsolationvalues–CanadaSolarinsolationvalues–IrelandSolarinsolationvalues–NewZealandSolarinsolationvalues–UnitedKingdomSolarinsolationvalues–UnitedStatesofAmerica

AppendixC–TypicalPowerRequirementsHouseholdandofficeGardenandDIYCaravans,boatsandrecreationalvehicles

AppendixD–LivingOff-GridAsolarelectricsysteminconjunctionwithgridelectricity

AppendixE–OtherSolarProjectsGridfallbacksystem/gridfailoversystemPortablesolarpowerunitSolarboatSolarshedlightSolarelectricbikes

AppendixF–BuildingYourOwnSolarPanels(andWhyYouShouldn’t)

IntroducingSolarEnergy

Ninety-threemillionmilesfromEarth,oursunis333,000timesthesizeofourplanet.Ithasadiameterof865,000miles,asurfacetemperatureof5,600°Canda core temperature of 15,000,000°C. It is a huge mass of constant nuclearactivity.Directly or indirectly, our sun provides all the power we need to exist andsupportsall lifeforms.Thesundrivesourclimateandourweather.Withoutit,ourworldwouldbeafrozenwastelandofice-coveredrock.Solarelectricityisawonderfulconcept.Takingpowerfromthesunandusingittopowerelectricalequipmentisaterrificidea.Therearenoongoingelectricitybills,norelianceonapowersocket:afreeandeverlastingsourceofenergythatdoesnotharmtheplanet!Ofcourse,therealityisalittledifferentfromthat.Yetgeneratingelectricityfromsunlightaloneisapowerfulresource,withapplicationsandbenefitsthroughouttheworld.Buthowdoes itwork?Forwhat is it suitable?Whatare the limitations?Howmuchdoesitcost?Howdoyouinstallit?Thisbookanswersallthesequestionsandshowsyouhowtousethepowerofthesuntogenerateelectricityyourself.Alongtheway,Iwillalsoexposeafewmythsaboutsomeofthewilderclaimsmadeabout solar energy and Iwill showyouwhere solarpowermayonlybepart of the solution. Although undoubtedly there are some significantenvironmentalbenefitsofsolarelectricity,Iwillalsobetalkingaboutwhereitsenvironmentalcredentialshavebeenoversold.I will keep the descriptions as straightforward as possible. There is somemathematicsandscienceinvolved.Thisisessentialtoallowyoutoplanasolarelectric installation successfully.However, none of it is complicated and thereareplentyofshort-cutstokeepthingssimple.Thebookincludesanumberofexampleprojectstoshowhowyoucanusesolarelectricity.Someof theseareverystraightforward,suchasprovidingelectricallight forashedorgarage, forexample,or fittingasolarpanel to theroofofacaravan or boat. Others aremore complicated, such as installing photovoltaicsolarpanelstoahouse.

I also show some rathermore unusual examples, such as the possibilities forsolarelectricmotorbikesandcars.Theseareexamplesofwhatcanbeachievedusingsolarpoweralone,alongwithalittleingenuityanddetermination.I haveusedonemain example throughout thebook:providing solar-generatedelectricityforaholidayhomewhichdoesnothaveaccesstoanelectricitysupplyfromthegrid.Ihavecreatedthisexampletoshowtheissuesandpitfallsthatyoumayencounteralongtheway,basedonreallifeissuesandpracticalexperience.Awebsiteaccompanies thisbook. Ithas lotsofuseful information,alongwithlistsofsuppliersandasuiteofonlinesolarenergycalculatorsthatwillsimplifythecostanalysisanddesignprocesses.Thewebsiteisatwww.SolarElectricityHandbook.com.

WhothisbookisaimedatIfyousimplywant togainanunderstandingabouthowsolarelectricityworksthenthishandbookwillprovideyouwitheverythingyouneedtoknow.If you are planning to install your own stand-alone solar power system, thishandbook is a comprehensive source of information that will help youunderstandsolarandguideyouinthedesignandinstallationofyourownsolarelectricsystem.Solar has a big application for integrating into electrical products: mobilephones,laptopcomputers,portableradios.Evenlightelectriccarscanusesolarenergy to provide some or all of their power requirements, depending on theapplication.Ifyouareadesigner,lookingtoseehowyoucanintegratesolarintoyourproduct,thisbookwillgiveyouagroundinginthetechnologythatyouwillneedtogetyoustarted.If you are specifically looking to install a grid-tie system, i.e. a solar energysystemthatwillfeedelectricitybackintoyourlocalpowergrid,thisbookwillprovideyouwithagoodfoundationandwillallowyoutocarryoutthedesignofyoursystem.Youwillstillneedtocheckthelocalplanninglawsandanyotherlocal legislation surrounding the installation of solar energy systems, and youwillhavetounderstandthebuildingofelectricalsystems.Insomecountries,youspecificallyneedtobecertifiedinordertocarryoutthephysicalinstallationofagrid-tiesystem.If you are planning to install larger, commercial–size systems, or if you arehopingtoinstallgrid-tiesolarsystemsprofessionally, thenthisbookwillserveasagoodintroduction,butyouwillneedtogrowyourknowledgefurther.Thisbookgivesyouthefoundationsyouneedinorder tobuild thisknowledge,butthere are special skills requiredwhendesigningand implementing larger scalesolar systems that go far beyondwhat is required for smaller systems and arebeyondthescopeofthisbook.Ifyouareplanningyourownsolarinstallation,itwillhelpifyouhavesomeDIYskills. Whilst I include a chapter that explains the basics of electricity, afamiliaritywithwiringisalsoofbenefitforsmallerprojectsandyouwillrequirea thorough understanding of electrical systems if you are planning a largerprojectsuchaspoweringahousewithsolar.

TherapidlychangingworldofsolarenergyIwrotethefirsteditionofthisbookearlyin2009.Itisnotalongtimeago.Yetthis 2012 issue is the sixth edition. In every edition, I have had to rewritesignificantsectionsofthebookandsignificantlyupdatethewebsiteinordertokeepupwiththerapidpaceofchange.The rapid improvement in the technology and the freefall in costs since early2009havetransformedtheindustry.Systemsthatwerecompletelyunaffordableorimpracticaljusttwoorthreeyearsagoarenowcost-effectiveandachievable.Solarpanelsavailabletodayaresmaller,morerobustandbettervalueformoneythan ever before. For many more applications, solar is now the most cost-effectivewaytogenerateelectricity.Overthecomingyears,allthesignsarethatthetechnologyandtheindustrywillcontinuetoevolveatasimilarpace.By2015,solarwillbethecheapestformofelectricity generator, undercutting traditionally low-cost electricity generatorssuchascoal-firedpowerstations.Wearelikelytoseesolarenergyincorporatedintomoreeverydayobjectssuchaslaptopcomputers,mobilephones,backpacksandclothing.Meanwhile,solarenergyiscausingarevolutionforlargeareasofAsiaandAfrica,whereentirecommunitiesarenowgainingaccesstoelectricityforthefirsttime.As an easy-to-use and low-carbon energygenerator, solar iswithout equal. Itspotentialforchangingthewaywethinkaboutenergyinthefutureishuge.Forfamilies and businesses in rural African and Asian villages, it is creating arevolution.

SolarelectricityandsolarheatingSolarelectricityisproducedfromsunlightshiningonphotovoltaicsolarpanels.Thisisdifferenttosolarhotwaterorsolarheatingsystems,wherethepowerofthesunisusedtoheatwaterorair.Solarheatingsystemsarebeyondtheremitofthisbook.Thatsaid,thereissomeusefulinformationonsurveyingandpositioningyoursolarpanelslateronthatisrelevanttobothsolarphotovoltaicsandsolarheatingsystems.Ifyouareplanningtousesolarpowertogenerateheat,solarheatingsystemsarefarmoreefficient thansolarelectricity,requiringfarsmallerpanels togeneratethesameamountofenergy.Solar electricity is often referred to as photovoltaic solar, or PV solar. Thisdescribesthewaythatelectricityisgeneratedinasolarpanel.For the purposes of this book, whenever I refer to solar panels I am talkingaboutphotovoltaic solarpanels forgeneratingelectricity, andnot solarheatingsystems.

ThesourceofsolarpowerDeepinthecentreofthesun,intensenuclearactivitygenerateshugeamountsofradiation. In turn, this radiation generates light energy called photons. Thesephotonshavenophysicalmassoftheirown,butcarryhugeamountsofenergyandmomentum.Differentphotonscarrydifferentwavelengthsoflight.Somephotonswillcarrynon-visiblelight(infraredandultra-violet),whilstotherswillcarryvisiblelight(whitelight).Over time, these photons pushout from the centre of the sun. It can takeonemillionyears foraphoton topushout to thesurface fromthecore.Once theyreach the sun’s surface, these photons rush through space at a speed of 670millionmilesperhour.Theyreachearthinaroundeightminutes.Ontheirjourneyfromthesuntoearth,photonscancollidewithandbedeflectedbyother particles, and are destroyedon contactwith anything that can absorbradiation,generatingheat.Thatiswhyyoufeelwarmonasunnyday:yourbodyisabsorbingphotonsfromthesun.Ouratmosphereabsorbsmanyofthesephotonsbeforetheyreachthesurfaceoftheearth.Thatisoneofthetworeasonsthatthesunfeelssomuchhotterinthemiddleoftheday.Thesunisoverheadandthephotonshavetotravelthroughathinnerlayerofatmospheretoreachus,comparedtotheendofthedaywhenthesun is setting and the photons have to travel through amuch thicker layer ofatmosphere.Thisisalsooneofthetworeasonswhyasunnydayinwinterissomuchcolderthanasunnydayinsummer.Inwinter,whenyourlocationontheearthistiltedawayfromthesun, thephotonshave to travel throughamuchthicker layerofatmospheretoreachus.

(Theotherreasonthatthesunishotterduringthemiddleofthedaythanattheendisbecausetheintensityofphotonsismuchhigheratmidday.Whenthesunislowinthesky,thesephotonsarespreadoveragreaterdistancesimplybytheangleofyourlocationonearthrelativetothesun.)

TheprinciplesofsolarelectricityAsolarpanelgenerateselectricityusing thephotovoltaiceffect, a phenomenondiscoveredintheearly19centurywhenscientistsobservedthatcertainmaterialsproducedanelectriccurrentwhenexposedtolight.Twolayersofasemi-conductingmaterialarecombinedtocreatethiseffect.Onelayerhastohaveadepletednumberofelectrons.Whenexposedtosunlight,thelayersofmaterialabsorbthephotons.Thisexcitestheelectrons,causingsomeofthemto‘jump’fromonelayertotheother,generatinganelectricalcharge.Thesemi-conductingmaterialusedtobuildasolarcell issilicon,cutintoverythinwafers.Someofthesewafersarethen‘doped’tocontaminatethem,therebycreating an electron imbalance in the wafers. The wafers are then alignedtogethertomakeasolarcell.Conductivemetalstripsattachedtothecellstaketheelectricalcurrent.Whenaphotonhitthesolarcell,itcandooneofthreethings:itcanbeabsorbedbythecell,reflectedoffthecellorpassstraightthroughthecell.It is when a photon is absorbed by the silicon that an electrical current isgenerated.Themorephotons(i.e.thegreaterintensityoflight)thatareabsorbedbythesolarcell,thegreaterthecurrentgenerated.Solarcellsgeneratemostoftheirelectricityfromdirectsunlight.However,they

also generate electricity on cloudy days and some systems can even generateverysmallamountsofelectricityonbrightmoonlitnights.Individual solarcells typicallyonlygenerate tinyamountsofelectricalenergy.Tomakeusefulamountsofelectricity,thesecellsareconnectedtogethertomakea solar module, otherwise known as a solar panel or, to be more precise, aphotovoltaicmodule.

UnderstandingtheterminologyIn this book, I use various terms such as ‘solar electricity’, ‘solar energy’ and‘solarpower’.HereiswhatImeanwhenIamtalkingabouttheseterms:Solarpower isageneraltermforgeneratingpower,whetherheatorelectricity,fromthepowerofthesun.Solarenergyreferstotheenergygeneratedfromsolarpower,whetherelectricalorasheat.Solar electricity refers to generating electrical power using photovoltaic solarpanels.Solar heating refers to generating hot water or warm air using solar heatingpanelsorground-sourceheatpumps.

SettingexpectationsforsolarelectricitySolarpowerisausefulwayofgeneratingmodestamountsofelectricity,solongas there is agoodamountof sunlight available andyour location is free fromobstaclessuchas treesandotherbuildings thatwillshadethesolarpanelfromthesun.Solar expertswill tell you that solar electricity is normally only cost-effectivewherethereisnoothersourceofelectricityavailable.Whilst this is often the case, there are plenty of exceptions to this rule.Oftensolar electricity can be extremely practical and can save youmoney over themoretraditionalalternatives.Someexamplesmightinclude:

Installingalightorapowersourcesomewherewhereitistrickytogetastandardelectricitysupply,suchasinthegarden,shedorremotegarage Creating a reliable and continuous power source where the standardelectricitysupplyisunreliablebecauseofregularpowercuts Buildingamobilepowersource thatyoucan takewithyou,suchasapowersourceforusewhilstcamping,workingonoutdoorDIYprojectsorworkingonabuildingsite Creating green energy for your own use and selling surplus energyproductionbacktotheelectricitysuppliersthroughafeed-intariff

Theamountofenergyyouneedtogeneratehasadirectbearingonthesizeandcostofasolarelectricsystem.Themoreelectricityyouneed,themoredifficultandmoreexpensiveyoursystemwillbecome.If your requirements for solar electricity are to run a few lights, to run somerelativelylow-powerelectricalequipmentsuchasalaptopcomputer,asmallTV,a compact fridge and a few other small bits and pieces, then if you have asuitablelocationyoucanachievewhatyouwantwithsolar.Ontheotherhand,ifyouwanttorunhigh-powerequipmentsuchasfanheaters,washing machines and power tools, you are likely to find that the costs willrapidlygetoutofcontrol.As I mentioned earlier, solar electricity is not well suited to generating heat:heating rooms, cooking and heating water all take up significant amounts ofenergy.Usingelectricitytogeneratethisheatisextremelyinefficient.Insteadofusing solar electricity to generate heat, you should consider a solar hotwaterheatingsystem,andheatingandcookingwithgasorsolidfuels.

It is possible to power the average family home purely on solar electricitywithoutmakinganycutsinyourcurrentelectricityconsumption.However,itisnotcheap,andyouwillneedalotofroofspacetofitallthepanels!Itisusuallyagoodideatocarefullyevaluateyourelectricityusageandmakesavingswhereyoucanbeforeyouproceed.Mosthouseholdsandbusinessesareveryinefficientwiththeirelectricalusage.Spendingsometimefirstidentifyingwhereelectricityiswastedandeliminatingthis waste is an absolute necessity if you want to implement solar electricitycost-effectively.Thisisespeciallytrueifyouliveincoolerclimates,suchasNorthernEuropeorCanada,wherethewintermonthsproducemuchlowerlevelsofsolarenergy.IntheUnitedKingdom,forinstance,theroofoftheaverage-sizedhomeisnotlargeenough to hold all the solar panels that would be required to provide theelectricityusedby theaveragehousehold throughout theyear. In this instance,makingenergysavingsisessential.Forotherapplications,asolarelectric installation ismuchmorecost-effective.For instance, nomatter which country you live in, providing electricity for aholidayhomeiswellwithinthecapabilitiesofasolarelectricsystem,solongasheatingandcookingarecateredforusinggasorsolidfuelsandthesite is inasunnypositionwith little or no shade. In this scenario, a solar electric systemmaybemorecost-effectivethaninstallingaconventionalelectricitysupplyifthehouseisoff-gridandisnotclosetoagridelectricityconnection.If your requirements are more modest, such as providing light for a lock-upgarage, for example, there are off-the-shelf packages to do this for a veryreasonablecost.Around£70–£100($110–$160)willprovideyouwithalightingsystemforashedorsmallgarage,whilst£200($300)willprovideyouwithasystembigenoughforlightinglargestablesoraworkshop.This is far cheaper than installing a conventional electricity supply into abuilding, which can be expensive even when a local supply is available justoutsidethedoor.Low-cost solar panels are also ideal for charging up batteries in caravans andrecreationalvehiclesoronboats,ensuringthatthebatteriesgetatricklechargebetweentripsandkeepingthebatteriesintip-topconditionwhilstthecaravanorboatisnotinuse.

Whychooseasolarelectricsystem?Thereareanumberofreasonstoconsiderinstallingasolarelectricsystem:

Wherethereisnoothersourceofelectricalpoweravailable,orwherethecostofinstallingconventionalelectricalpoweristoohigh Whereothersourcesofelectricalpowerarenot reliable.Forexample,whenpowercutsareanissueandasolarsystemcanactasacost-effectivecontingencyWhenasolarelectricsystemisthemostconvenientandsafestoption.Forexample, installing low voltage solar lighting in a garden or providingcourtesylightinginaremotelocationYoucanbecomeentirelyselfsufficientwithyourownelectricalpower Once installed, solar power provides virtually free power withoutdamagingtheenvironment

Cost-justifyingsolarCalculatingthetruecostofinstallingasolarelectricsystemdependsonvariousfactors:

ThepowerofthesunatyourlocationatdifferenttimesoftheyearHowmuchenergyyouneedtogenerateHowgoodyoursiteisforcapturingsunlight

Compared to other power sources, solar electric systems typically have acomparativelyhighcapitalcost,butalowongoingmaintenancecost.Tocreate a comparisonwith alternativepower sources, youwill oftenneed tocalculateapaybackofcostsoveraperiodofafewyearsinordertojustifytheinitialcostofasolarelectricsystem.Onallbut thesimplestof installations,youwillneed tocarryouta surveyonyour site and carry out some of the designwork before you can ascertain thetotal cost of installing a photovoltaic system. Do not panic: this is not asfrighteningasitsounds.ItisnotdifficultandIcoveritindetailinlaterchapters.Wecanthenusethisfiguretoputtogetheracost-justificationonyourprojecttocomparewiththealternatives.

SolarpowerandwindpowerWind turbines can be a good alternative to solar power, but probably achievetheirbestwhenimplementedtogetherwithasolarsystem:asmallwindturbinecangenerateelectricityinabreezeevenwhenthesunisnotshining.Small wind turbines do have some disadvantages. Firstly, they are very site-specific, requiring higher than average wind speeds and minimal turbulence.Theymustbehigherthansurroundingbuildingsandawayfromtalltrees.Ifyouliveonawindsweptfarmorclosetothecoast,awindturbinecanworkwell.Ifyouliveinabuilt-upareaorclosetotreesormainroads,youwillfindawindturbineunsuitableforyourneeds.Comparedtothelargewindturbinesusedbythepowercompanies,smallwindturbinesarenotparticularlyefficient.Ifyouareplanningtoinstallasmallwindturbineincombinationwithasolarelectricsystem,asmallerwindturbinethatgenerates a fewwatts of power at lowerwind speeds is usually better than alargewindturbinethatgenerateslotsofpowerathighwindspeeds.

FuelcellsFuel cells can be a goodway to supplement solar energy, especially for solarelectricprojectsthatrequireadditionalpowerinthewintermonths,whensolarenergyisatapremium.A fuel cell works like a generator. It uses a fuel mixture such as methanol,hydrogenorzinctocreateelectricity.Unlikeagenerator,afuelcellcreatesenergythroughchemicalreactionsratherthanthroughburningfuelinamechanicalengine.Thesechemicalreactionsarefarmorecarbon-efficientthanagenerator.Fuel cells are extremely quiet, although rarely completely silent, and producewaterastheironlyemission.Thismakesthemsuitableforindoorusewithlittleornoventilation.

Grid-tiedsolarelectricsystemsGrid-tiedsolarelectric systemsconnectdirectly into theelectricitygrid.Whenthesun is shiningduring theday,excesselectricity feeds into thegrid.Duringtheeveningandnight,whenthesolarpanelsarenotprovidingsufficientpower,electricityistakenfromthegridasrequired.Grid-tied solar electric systems effectively create a micro power station.Electricitycanbeusedbyotherpeopleaswellasyourself. In somecountries,ownersofgrid-tiedsolarelectricsystemsreceivepayment foreachkilowattofpowertheyselltotheelectricityproviders.Because a grid-tied solar electric system becomes part of the utility grid, thesystemwillswitchoffintheeventofapowercut.Itdoesthistostopanycurrentflowingbackintothegrid,whichcouldbefatalforengineersrepairingafault.

SolarelectricityandtheenvironmentOnceinstalled,asolarelectricsystemisalow-carbonelectricitygenerator: thesunlightisfreeandthesystemmaintenanceisextremelylow.Thereisacarbonfootprintassociatedwiththemanufactureofsolarpanels,andinthepastthisfootprinthasbeenquitehigh,mainlyduetotherelativelysmallvolumes of panels being manufactured and the chemicals required for the‘doping’ofthesiliconinthepanels.Thanks to improvedmanufacturing techniquesandhighervolumes, thecarbonfootprintofsolarpanelsisnowmuchlower.Youcantypicallyoffsetthecarbonfootprintofbuildingthesolarpanelsbytheenergygeneratedwithin2–5years,and someof the very latest amorphous thin-film solar panels can recoup theircarbonfootprintinaslittleassixmonths.Therefore,asolarelectricsystemthatrunsasacompletestand-alonesystemcanreduceyourcarbonfootprint,comparedtotakingthesamepowerfromthegrid.Grid-tiedsolarsystemsareslightlydifferentintheirenvironmentalbenefit,andtheir environmental payback varies quite dramatically from region to region,dependingonanumberoffactors:

Howgridelectricity isgeneratedbythepowercompanies inyourarea(coal,gas,nuclear,hydro,windorsolar) Whether or not your electricity generation coincides with the peakelectricity demand in your area (such as air conditioning usage in hotclimates,orhighelectricalusagebynearbyheavyindustry)

It is therefore much more difficult to put an accurate environmental paybackfigureongrid-tiedsolarsystems.It isundeniably true that somepeoplewhohavegrid-tiedsolarpoweractuallymakenodifferencetothecarbonfootprintoftheirhome.Incolderclimates,themajorityofelectricityconsumption is in theeveningsandduring thewinter. Ifyou have grid-tie solar but sell most of your energy to the utility companiesduringthedayinthesummerandthenbuyitbacktoconsumeintheeveningsand in thewinter, you aremaking little or no difference to the overall carbonfootprintofyourhome.Ineffect,youaresellingyourelectricitywhenthereisasurplusandbuyingitbackwhenthereishighdemandandallthepowerstationsareworkingatfullload.In warmer climates, solar energy can make a difference. In a hot area, peak

energyconsumptiontendstooccuronsunnydaysaspeopletrytokeepcoolwithair conditioning. In this scenario, peak electricity demand occurs at the sametimeaspeak energyproduction froma solar array, and agrid-tie solar systemcanbeaperfectfit.If you live in a colder climate, this does not mean that there is no point ininstallingagrid-tiesolarsystem.Itdoesmeanthatyouneedtotakeagoodhardlookathowandwhenyouconsumeelectricity.Donotjustassumethatbecauseyou can have solar panels on the roof of your house, you are automaticallyhelpingtheenvironment.From an environmental perspective, if youwish to get the very best out of agrid-tiesystem,youshouldtrytoachievethefollowing:

UsethepoweryougenerateforyourselfUsesolarenergyforhighloadapplicationssuchasclotheswashingReduceyourownpowerconsumptionfromthegridduringtimesofpeakdemand

Environmentalefficiency:comparingsupplyanddemandThere is anonlinecalculator thatwill allowyou tomapyourelectricityusageoveraperiodofayearandcompareitwiththeamountofsunlightavailabletoyourhome.Designedspecificallyforgrid-tieinstallations,thiscalculatorallowsyoutoseehowcloseafitsolarenergyisintermsofsupplyanddemand.Whilstthisonlinecalculatorisnosubstituteforadetailedelectricalusagesurveyand research into the exact source of the electricity supplied to you at yourlocation, it will give you a good indication of the likely environmentalperformanceofasolarenergysystem.To use this online calculator, youwill need to collate information about yourelectricity usage for each month of the year. You will usually find thisinformation on your electricity bill or by contacting your electricity provider.Thenvisitwww.SolarElectricityHandbook.com,followthelinkstotheGrid-TieSolar Calculator in the Online Calculators section and fill in the onlinequestionnaire.

Inconclusion Solar electricity can be a great source of power where your powerrequirements are modest, there is no other source of electricity easilyavailableandyouhaveagoodamountofsunshineSolarelectricityisnotthesameassolarheatingSolarpanelsabsorbphotonsfromsunlighttogenerateelectricity Direct sunlight generates themost electricity.Dull days still generatesomepower Solarelectricity isunlikely togenerateenoughelectricity topower theaverage family home, unless major economies in the household powerrequirementsaremadefirst Largersolarelectricsystemshaveacomparativelyhighcapitalcost,buttheongoingmaintenancecostsareverylow Smallersolarelectricsystemcanactuallybeextremelycost-effectivetobuyandinstall,evenwhencomparedtoaconventionalelectricitysupplyItcanbemuchcheaperusingsolarelectricityataremotebuilding,ratherthanconnectingittoaconventionalgridelectricitysupplyStand-alonesolarenergysystemscanhaveabigenvironmentalbenefitiftheynegatetheneedforaconnectiontogridpower Grid-tie solar energy systemshave an environmental benefit in sunnyclimateswheretypicalelectricityusagepatternsaresimilartothesupplyofsunlight Incolderregions,whereelectricityusageishighestwhensunlightisinshortsupply,theenvironmentalbenefitsarelesscertain

ABriefIntroductiontoElectricity

Beforewecanstartplayingwithsolarpower,weneedtotalkaboutelectricity.Tobemoreprecise,weneedtotalkaboutvoltage,current,resistance,powerandenergy.Having these terms clear in your headwill help you to understand your solarsystem.Itwillalsogiveyouconfidencethatyouaredoingtherightthingwhenitcomestodesigningandinstallingyoursystem.

Don’tpanicIf you have not looked at electrics since youwere learning physics at school,someof theprinciplesofelectricitycanbeabitdaunting tostartwith.Donotworryifyoudonotfullygraspeverythingonyourfirstreadthrough.ThereareafewcalculationsthatIshowonthenextfewpages,butIamnot

expectingyoutorememberthemall!WheneverIusethesecalculationslateronin thebook,Ishowallmyworkingsand,ofcourse,youcanreferbackto thischapterasyougainmoreknowledgeonsolarenergy.Furthermore, the website that accompanies this book includes a number ofonlinetoolsthatyoucanusetoworkthroughmostofthecalculationsinvolvedindesigningasolarelectricsystem.Youwillnotbespendinghourswithaslide-ruleandreamsofpaperworkingallthisoutbyyourself.

AbriefintroductiontoelectricityWhenyouthinkofelectricity,whatdoyouthinkof?Doyouthinkofabatterythat is storing electricity?Do you think of giant overhead pylons transportingelectricity?Doyouthinkofpowerstationsthataregeneratingelectricity?Ordoyou think of a device like a kettle or television set or electric motor that isconsumingelectricity?Thewordelectricityactuallycoversanumberofdifferentphysicaleffects,allofwhicharerelatedbutdistinctfromeachother.Theseeffectsareelectriccharge,electriccurrent,electricpotentialandelectromagnetism:

Anelectriccharge isabuild-upofelectricalenergy. It ismeasured incoulombs.Innature,youcanwitnessanelectricchargeinstaticelectricityorinalightningstrike.Abatterystoresanelectriccharge Anelectriccurrentistheflowofanelectriccharge,suchastheflowofelectricitythroughacable.ItismeasuredinampsAnelectricpotentialreferstothepotentialdifferenceinelectricalenergybetweentwopoints,suchasbetweenthepositivetipandthenegativetipofabattery. It ismeasured involts.Thegreater theelectricpotential (volts),thegreatercapacityforworktheelectricityhasElectromagnetismistherelationshipbetweenelectricityandmagnetism,which enables electrical energy to be generated frommechanical energy(such as in a generator) and enables mechanical energy to be generatedfromelectricalenergy(suchasinanelectricmotor)

HowtomeasureelectricityVoltagereferstothepotentialdifferencebetweentwopoints.AgoodexampleofthisisanAAbattery:thevoltageisthedifferencebetweenthepositivetipandthenegativeendofthebattery.Voltageismeasuredinvoltsandhasthesymbol‘V’.Currentistheflowofelectronsinacircuit.Currentismeasuredinamps(A)andhas the symbol ‘I’. If you check a power supply, it will typically show thecurrentonthesupplyitself.Resistanceistheoppositiontoanelectricalcurrentinthematerialthecurrentisflowingthrough.Resistanceismeasuredinohmsandhasthesymbol‘R’.Powermeasurestherateofenergyconversion.Itismeasuredinwatts(W)andhas the symbol ‘P’. You will see watts advertised when buying a kettle orvacuum cleaner: the higher thewattage, themore power the device consumesandthefaster(hopefully)itdoesitsjob.Energyreferstothecapacityforwork:powermultipliedbytime.Energyhasthesymbol ‘E’. Energy is usually measured in joules (a joule equals one watt-second),butelectricalenergyisusuallyshownaswatt-hours(Wh),orkilowatt-hours(kWh),where1kWh=1,000Wh.

The relationship between volts, amps, ohms,wattsandwatt-hoursVolts

CurrentxResistance=VoltsIxR=V

Voltageisequaltocurrentmultipliedbyresistance.ThiscalculationisknownasOhm’s Law. As with power calculations, you can express this calculation indifferentways. If you knowvolts and current, you can calculate resistance. Ifyouknowvoltsandresistance,youcancalculatecurrent:Volts÷Resistance=Current

V÷R=IVolts÷Current=Resistance

V÷I=R

PowerVoltsxCurrent=Power

VxI=PPowerismeasuredinwatts.Itequalsvoltstimescurrent.A12-voltcircuitwitha4-ampcurrentequals48wattsofpower(12x4=48).Basedonthiscalculation,wecanalsoworkoutvoltageifweknowpowerandcurrent,andcurrentifweknowvoltageandpower:

Power÷Current=VoltsP÷I=V

Example:A48-wattmotorwitha4-ampcurrentisrunningat12volts.48watts÷4amps=12voltsCurrent=Power÷Volts

I=P÷VExample:a48-wattmotorwitha12-voltsupplyrequiresa4-ampcurrent.

48watts÷12volts=4ampsPower (watts) is also equal to the square of the current multiplied by the

resistance:Current²xResistance=Power

I²xR=P

EnergyEnergy is ameasurementofpowerover aperiodof time. It showshowmuchpowerisused,orgenerated,byadevice, typicallyoveraperiodofanhour.Inelectricalsystems,itismeasuredinwatt-hours(Wh)andkilowatt-hours(kWh).Adevicethatuses50wattsofpower,hasanenergydemandof50Whperhour.A solar panel that can generate 50 watts of power per hour, has an energycreationpotentialof50Whperhour.However,becausesolarenergygenerationissovariable,basedontemperature,weatherconditions,thetimeofdayandsoon,anewfigureisnowoftenshownspecificallyforsolarsystems:awatt-peak(Wp)rating.Awatt-peakratingshowshowmuchpowercanbegeneratedbyasolarpanelatits peak rating. It has been introduced to highlight the fact that the amount ofenergy a solar panel can generate is variable and to remind consumers that asolarpanelratedat50wattsisnotgoingtobeproducing50watt-hoursofenergyeverysinglehourofeverysingleday.

Awordfornon-electriciansRealistically,ifyouarenewtoelectricalsystems,youshouldnotbeplanningtoinstallabigsolarenergysystemyourself. Ifyouwanta low-voltagesystemtomounttotheroofofaboat,gardenshedorbarn,orifyouwanttoplaywiththetechnologyandhavesomefun,thengreat:thisbookwilltellyoueverythingyouneedtoknow.However,ifthelimitofyourelectricalknowledgeiswiringaplugor replacing a fuse, you should not be thinking of physically wiring andinstallingasolarenergysystemyourselfwithoutlearningmoreaboutelectricalsystemsandelectricalsafetyfirst.Furthermore,ifyouareplanningtoinstallasolarenergysystemtotheroofofahouse, be aware that in many parts of the world you need to have electricalqualificationsinordertocarryoutevensimplehouseholdwiring.Thatdoesnotmeanthatyoucannotspecifyasolarenergysystem,calculatethesizeyouneedandbuythenecessaryhardwareforabigproject.Itdoesmeanthatyouaregoingtoneedtoemployaspecialisttocheckyourdesignandcarryouttheinstallation.

Inconclusion Understandingthebasicrulesofelectricitymakesitmucheasiertoputtogetherasolarelectricsystem Aswithmanythingsinlife,abitoftheorymakesalotmoresensewhenyoustartapplyingitinpracticeIfthisisyourfirstintroductiontoelectricity,youmayfinditusefultorunthroughitacoupleoftimesYoumayalsofinditusefultobookmarkthissectionandreferbacktoitasyoureadon Youwill also find that, onceyouhave learned abitmore about solarelectricsystems,someofthetermsandcalculationswillstarttomakeabitmoresense.Ifyouarenotanelectrician,berealisticinwhatyoucanachieve.Electricscanbedangerousandyoudonotwanttogetitwrong.Youcandomostofthedesignworkyourself,butyouaregoingtoneedtogetaspecialistintocheckyourdesignandcarryouttheinstallation.

TheFourConfigurationsforSolarPower

There are four different configurations you can choose from when creating asolarelectricityinstallation.Thesearestand-alone(sometimesreferredtoasoff-grid),grid-tie,grid-tiewithpowerbackup(alsoknownasgridinteractive)andgridfallback.Hereisabriefintroductiontothesedifferentconfigurations:

Stand-alone/off-gridWorldwide,stand-alonesolarphotovoltaicinstallationsarethemostpopulartypeofsolarinstallationthereis.Itiswhatsolarphotovoltaicswereoriginallycreatedfor: to provide power at a location where there is no other source easilyavailable.Whetheritispoweringashedlight,providingpowerforapocketcalculatororpoweringacompleteoff-gridhome,stand-alonesystemsfundamentallyallworkin the same way: the solar panel generates power, the energy is stored in abatteryandthenusedasrequired.Ingeneral,stand-alonesystemsarecomparativelysmallsystems,typicallywithapeakpowergenerationofunderonekilowatt.Almost everyone can benefit from a stand-alone solar system for something,even if it is something asmundane as providing an outside light somewhere.Even if you are planningon somethingmuchbigger andgrander, it is often agoodideatostartwithaverysmallandsimplestand-alonesystemfirst.Learnthebasicsandthenprogressfromthere.

Examplesofsimplestand-alonesystemsThevendingmachineByBoxisamanufacturerofelectroniclockers.Thesearetypicallyusedforleftluggageat railway stationsor at airports, or situated at shoppingmallsor fuelstations and used as part of a delivery service for people to collect internetdeliveries,sotheydonotneedtowaitathome.Oneofthebiggestissueswithelectroniclockershasoftenbeenfindingsuitablelocationstoplacethemwhereapowersourceisavailable.ByBoxovercamethisissue by building an electronic locker with a solar roof to provide permanentpowertothelocker.Thesolarroofprovidespowertoasetofbatteriesinsidethelocker.Whennotinuse, the locker itself is in standby mode, thereby consuming minimal power.Whenacustomerwishestousethelocker,theypresstheSTARTbuttonandusethelockerasnormal.Thebenefit toByBoxhas been twofold: they can install a locker bank in anylocation,withoutanydependenceonapowersupply.Secondly, thecostof thesolar panels and controllers is often less than the cost of installing a separateelectricitysupply,evenifthereisonenearby.

RecreationalvehiclesHolidayingwith recreational vehiclesor caravans is on the increase, and solarenergyischangingthewaypeoplearegoingonholiday.In the past, most RV owners elected to stay on larger sites, which providedaccess to electricity and other facilities. As recreational vehicles themselvesbecomemore luxurious, however, people are now choosing to travel tomoreremote locations and live entirely ‘off-grid’, using solar energy to provideelectricitywherever they happen to be. Solar is being used to provide all thecomfortsofhome,whilstofferingholidaymakers thefreedomtostaywherevertheywant.

Grid-tieGrid-tieisgainingpopularityinEuropeandtheUnitedStates.Thisisduetotheavailability of grants to reduce the installation costs and the ability to earnmoneybysellingelectricitybackintotheelectricitycompaniesthroughafeed-intariff.Feed-intariffschemesvaryaroundtheworldandarenotavailableeverywhere.Where they exist, your local electricity company buys electricity from solarproducersatanagreedrateperkilowatt-hour. Insomecountries, thispricehasbeensetataninflatedratebygovernmentinordertoencouragepeopletoinstallsolar. In other countries and regions, the price is agreed by the electricitycompaniesthemselves.Inagrid-tiesystem,yourhomerunsonsolarpowerduringtheday.Anysurplusenergy thatyouproduce is thenfed into thegrid. In theeveningsandatnight,whenyour solarenergysystem isnotproducingelectricity,you thenbuyyourpowerfromtheelectricitycompaniesintheusualway.Thebenefitofgrid-tiesolarinstallationsisthattheyreduceyourrelianceonthebigelectricitycompaniesandensurethatmoreofyourelectricityisproducedinanenvironmentallyefficientway.Onedisadvantageofmostgrid-tiesystemsisthatifthereisapowercut,powerfromyoursolararrayisalsocut.Grid-tiecanworkespeciallywellinhot,sunnyclimates,wherepeakdemandforelectricityfromthegridoftencoincideswiththesunshining,thankstothehighpower demand of air conditioning units. Grid-tie also works well where theownersusemostofthepowerthemselves.

Anexampleofagrid-tiesystemSi Gelatos is a small Florida-based ice-cream manufacturer. In 2007, theyinstalled solar panels on the roof of their factory to provide power and offsetsomeoftheenergyusedinrunningtheircoldstoragefacility.“Running industrial freezers is extremely expensive and consumes a lot ofpower,”explainsDanFosterofSiGelatos.“Realistically,wecouldnothopetogenerateallofthepowerfromsolar,butwefeltitwasimportanttoreduceouroverallpowerdemandandsolarallowedustodothat.”Cold storage facilities consume most of their power during the day in thesummer, when solar is running at its peak. Since installing solar power, Si

Gelatoshas seen itsoverall energyconsumptiondropby40%andnowhardlytakesanypowerfromtheutilitiesduringpeakoperatingtimes.“Solar has done three things for our business,” saysDan. “Firstly, it is a veryvisiblesignforourstaffthatweareseriousabouttheenvironment.Thisinturnhasmadeour employeesmoreaware that theyneed todo theirbit bymakingsurelightsandequipmentareswitchedoffwhentheyarenotneeded.Secondly,it showsour customers thatwecare for the environment,whichhasdefinitelybeen good for goodwill and sales. Thirdly, and most importantly, we’regenuinely making a real contribution to the environment, by reducing ourelectricity demand at the time of day when everyone else’s demand forelectricityishighaswell.”

Grid-tiewithpowerbackup(gridinteractive)Grid-tie with power backup – also known as a grid interactive system –combinesagrid-tieinstallationwithabankofbatteries.Aswithgrid-tie,theconceptisthatyouusepowerfromyoursolararraywhenthe sun shines and sell the surplus to thepower companies.Unlike a standardgrid-tiesystem,however,abatterybankprovidescontingencyforpowercutssothatyoucancontinuetousepowerfromyoursystem.Typically, youwould set up ‘protected circuits’within your building thatwillcontinue to receive power during a power outage. This ensures that essentialpowerremainsavailableforrunninglights,refrigerationandheatingcontrollers,for example, whilst backup power is not wasted on inessential items such astelevisionsandradios.If there is a potential for main power to be lost for several days, it is alsopossible to design a system to incorporate other power generators into a gridinteractive system, such as a generator. This would allow a grid interactivesystem to work as a highly efficient uninterruptable power supply (UPS) forextendedperiodsoftime.Thecostofagrid-tiesystemwithpowerbackupishigherthanastandardgrid-tie system, because of the additional cost of batteries and battery controllers.Typically, having power backup will add 12–20% of additional costs over astandardgrid-tiesystem.Aswithnormalgrid-tiesystems,itispossibletosellsurpluspowerbacktotheutilitycompaniesinsomecountries,allowingyoutoearnanincomefromyoursolarenergysystem.

AnexampleofagridinteractivesystemGrid interactive systems are gaining popularitywith rural farms in theUnitedKingdom,whereevenshortpowerblackoutscancausesignificantdisruption.Traditionally,farmshavecounteredthisbyusinggeneratorstoprovidelightandpower. However, between 2009 and 2011, when the UK Government wereoffering large incentives for installing solar power, many farmers fitted gridinteractivesystemsontotheirbuildings,providingthemselveswithanincomebyselling electricity to the electricity utility companies and giving themselvesbackuppowerincaseofapowerblackout.Theadditionalcostofinstallingagridinteractivesystemoverastandardgrid-tie

system is more than offset by the low running costs and ease of use of thesystem.Farmersdonotneedtobuyandrungeneratorsandthesystemisalmostentirelymaintenance-free.This isabigcontrastwithgeneratorsystems,whichneed to be tested and run regularly in order to ensure they are workingeffectively.

GridfallbackGrid fallback is a lesser-known system that makes a lot of sense for smallerhousehold solar power systems. For most household solar installations wheresolar is being installed for technical or environmental reasons, grid fallback ismypreferredsolution.Operationally it iseffective, it iscost-effectiveand it isenvironmentallyextremelyefficient.With a grid fallback system, the solar array generates power, which in turncharges a battery bank. Energy is taken from the battery and run through aninvertertopoweroneormorecircuitsfromthedistributionpanelinthehouse.When thebatteries runflat, thesystemautomaticallyswitchesback to thegridpower supply. The solar array then recharges the batteries and the systemswitchesbacktosolarpower.With a grid fallback system, you do not sell electricity back to the electricitycompanies.All thepower thatyougenerate,youuseyourself.Thismeans thatsomeofthegrantsthatareavailableforsolarinstallationsinsomecountriesmaynotbeavailabletoyou.Italsomeansthatyoucannotbenefitfromsellingyourelectricitybacktotheelectricitycompanies.For this reason,grid fallbackmakesmoresense incountrieswhere there isnofeed-in tariff available, such as India, or in countries like Australia that havefinancialincentivesavailableforbothgrid-tiedandoff-gridsystems.Gridfallbacksystemsprovidemostofthebenefitsofagridinteractivesystem,withtheadditionalbenefitthatyouuseyourownpowerwhenyouneedit,ratherthanwhenthesunisshining.Thisreducesyourrelianceonexternalelectricitysuppliesduringpeakloadperiods,whichensuresthatyoursystemhasanoverallenvironmentalbenefit.Theothersignificantbenefitofagridfallbacksystemiscost:youcangenuinelybuildausefulgridfallbacksystemtopoweroneormorecircuitswithinahousefor a very small investment and expand it as budget allows. I have seen gridfallbacksystemsinstalledforunder£400($680),providingausefulamountofpower for a home. In comparison, even a very modest grid-tie system costsseveralthousandsofpounds.Thereisacrossoverpointwhereagrid-tiesystemworksoutmorecost-effectivethanagridfallbacksystem.Atpresent,thatcrossoverpointisaroundthe1kWhmark:ifyoursystemiscapableofgeneratingmorethan1kWofelectricityperhour,agrid-tiesystemmaybemorecost-effective.Ifyoursystemgeneratesless

than 1kW of electricity per hour, a grid fallback system is almost certainlycheaper.Unlessyouarelookingtoinvestasignificantamountofmoneyonalargergrid-tiesysteminordertoproducemorethan1kWofpowerperhour,orifyouwantto take advantage of feed-in tariffs, a grid fallback solution is certainlyworthinvestigatingasanalternative.

AnexampleofagridfallbacksystemBackin2001,ColinMetcalfeinstalledasolarpanelontotheroofofhisgarage,inordertochargeanoldcarbattery,whichinturnpoweredasinglelightandasmallinverter.Afterapowercutthatwinter,Colindecidedtoexpandhissysteminordertoprovidebasicpowertohishouse.“IwantedtoensureIalwayshadenoughpowerinmyhometopowerlightsandtoensuremyheatingsystemwouldwork,”explainedColin.“Ihavegasheating,but the controllers are all electric,whichmeans that if there is a power cut, Ihavenoheating at all. In addition, I liked the idea of free electricity thatwasgeneratedinanenvironmentallyfriendlyway.”Colinupgradedhissystembitbybit,asfundsallowed.“Anelectricianfittedanew distribution panel (consumer unit) formy essential circuits, and thiswasconnectedupto themainpanelviaanautomatic transferswitch.ThenIaddedadditionalsolarpanelsandbatteriesovertheyearsasIcouldaffordthem.”Thisautomatictransferswitchmeanttheessentialcircuitswouldreceivepowerfromthesolararrayorthebatterieswhilepowerwasavailable,butswitchbackto utility power when the batteries ran flat. Originally, the system providedaroundhalf thepowerheneeded,butashehasaddedtothesystem,moreandmoreofhispowernowcomesfromhissolararray.“TodayIhavearound1.4kWofsolarpanelsontheroofofmygarage,”saysColin.“Theylookabitoddasnotwopanelsarealike,as Ihavebought thembitbybitas fundsallow,but theynowprovideallthepowerIneedaroundtheyearforallmyessentialcircuits.”

GridfailoverAlternatively,youcanconfigureagridfallbacksystemasagridfailoversystem.Agrid failover systemkicks inwhen there is a power failure fromyourmainelectricitysupply.Ineffect,itisanuninterruptablepowersupply,generatingitspowerfromsolarenergy.The benefit of this configuration is that if you have a power cut, you have

contingency power. The disadvantage of this configuration is that you are notusingsolarpowerforyourday-to-dayuse.Although rare in Europe andAmerica, grid failover systems used to bemorecommon incountrieswherepower failuresarecommonplace. InAfricaand inmany parts of Asia, grid failover systems reduce the reliance on powergeneratorsforlightingandbasicelectricityneeds.However, in most cases, customers have found that a grid fallback or gridinteractive system is more suitable for their needs. I am aware of two gridfailover systems that have been installed in the past: both of these have sincebeenreconfiguredasgridfallbacksystems.

Howgrid-tiesystemsdifferfromstand-aloneGenerally, stand-alone and smaller grid fallback systems run at low voltages,typicallybetween12and48volts.Thisisbecausebatteriesarelow-voltageunitsandsobuildingastand-alonesystemata lowvoltage isasimple, flexibleandsafeapproach.Grid-tiesystemstendtobelargerinstallations,oftengeneratingseveralkilowattsofelectricityeachhour.Astheelectricityisrequiredasahigh-voltagesupply,itis more efficient to connect multiple solar panels together to produce a highvoltage circuit, rather than use an inverter to step up the voltage. This high-voltageDC power is then converted into anAC current by a suitable grid-tieinverter.Grid-tie systems either link multiple solar panels together to produce a solararrayvoltageofseveralhundredvoltsbeforerunningto the inverter,orhaveasmallinverterconnectedtoeachsolarpaneltocreateahigh-voltageACsupplyfromeachpanel.Thebenefitof thishighvoltage isefficiency.There is lesspower loss runninghigh-voltage,low-currentelectricitythroughcablesfromthesolararray.For stand-alone battery-based systems, low-voltage is the best solution, as thebattery banks tend to work better as low-voltage energy stores. For grid-tiesystems where the energy is not being stored in a battery bank, the higher-voltagesystemsarethebestsolution.Neitherapproachisinherently‘better’:italldependsonthetypeofsystemyouaredesigning.

Inconclusion SolarcanbeusedinanumberofdifferentwaysandformanydifferentapplicationsStand-alonesystemsarethesimplestandeasiesttounderstand.Theytendtobecomparativelysmallsystems,providingpowerwherenootherpowersourceiseasilyavailable Withgrid-tie,yoursolarenergysystemgenerateselectricitythatisthenusednormally.AnyexcesselectricityproductionisexportedontothegridGrid-tiewithpowerbackup(alsoknownasgridinteractive)providesyouwith the benefits of a grid-tie system with the added benefit that powerremainsavailableevenifelectricitytoyourareaiscutoff Gridfallbacksystemshavemore incommonwithstand-alonesystemsthan grid-tie systems. In design they are very similar to stand-alonesystems,withaninverterrunningfromabankofbatteriesandanautomatictransfer switch to switch power between the solar energy system and thegridpowersupply Grid failover systems are comparatively rare now, but provideuninterruptablepowersuppliesusingsolarasthebackupsourceGrid-tiesystemshaveadifferentdesigntostand-alonesystems.Theytendtobehigh-voltagesystems,whereasstand-alonesystemsrunatmuchlowervoltages

ComponentsofaSolarElectricSystem

BeforeIgetintothedetailaboutplanninganddesigningsolarelectricsystems,itisworthdescribingallthedifferentcomponentsofasystemandexplaininghowthey fit together.Once you have read this chapter, youwill have a reasonablegraspofhowasolarenergysystemfitstogether.Ideliberatelydonotgointomuchdetailatthisstage:allIamdoingisprovidinganoverviewfornow.Thedetailcancomelater.

SolarpanelsTheheart of a solar electric system is the solar panel itself.There are varioustypesofsolarpanelandIwilldescribethemallindetaillateron.Solarpanelsor,moreaccurately,photovoltaic solar panels, generate electricityfrom the sun. The more powerful the sun’s energy, the more power you get,although solar panels continue to generate small amounts of electricity in theshade.Most solarpanels aremadeupof individual solar cells, connected together.Atypical solar cellwill only produce aroundhalf a volt, so by connecting themtogetherinseriesinsidethepanel,amoreusefulvoltageisachieved.Most solar panels are rated as 12-volt solar panels, although higher-voltagepanels are also available. A 12-volt solar panel produces around 14–18 voltswhen put under load. This allows a single solar panel to charge up a 12-voltbattery.Incidentally,ifyouconnectavoltmeteruptoasolarpanelwhenitisnotunderload,youmaywellseevoltagereadingsofupto26volts.Thisisnormalinan‘open circuit’ on a solar panel.As soon as you connect the solar panel into acircuit,thisvoltagelevelwilldroptoaround14–18volts.Solarpanelscanbelinkedtogethertocreateasolararray.Connectingmultiplepanels together allows you to produce a higher current or to run at a highervoltage:

Connecting thepanels inseries allowsa solararray to runat ahighervoltage. Typically, 24 volts or 48 volts in a stand-alone system, or up toseveralhundredvoltsinagrid-tiesystem Connectingthepanels inparallelallowsasolararray toproducemorepowerwhilemaintainingthesamevoltageastheindividualpanels When you connectmultiple panels together, the power of the overallsystemincreases,irrespectiveofwhethertheyareconnectedinseriesorinparallel

Inasolararraywherethesolarpanelsareconnectedinseries(asshowninthefollowing diagrams), you add the voltages of each panel together and add thewattageofeachpaneltogethertocalculatethemaximumamountofpowerandvoltagethesolararraywillgenerate.

Asolararraymadeoffoursolarpanelsconnectedinseries.Ifeachindividualpanelisratedasa12-volt,12-wattpanel,thissolararraywould

beratedasa48-volt,48-wattarraywitha1ampcurrent.In a solar array where the panels are connected in parallel (as shown in thediagrambelow),youtaketheaveragevoltageofallthesolarpanelsandyouaddthewattageofeachpaneltocalculatethemaximumamountofpowerthesolararraywillgenerate.

Asolararraymadeoffoursolarpanelsconnectedinparallel.Witheachpanelratedasa12-volt,12-wattpanel,thissolararraywouldberatedasa

12-volt,48-wattarraywitha4ampcurrent.I will go into more detail later about choosing the correct voltage for yoursystem.

BatteriesExceptinagrid-tiesystem,wherethesolararrayconnectsdirectlytoaninverter,solar panels rarely power electrical equipment directly. This is because theamount of power the solar panel collects varies depending on the strength ofsunlight.Thismakesthepowersourcetoovariableformostelectricalequipmenttocopewith.In a grid-tie system, the inverter handles this variability: if demand outstripssupply,youwillgetpowerfromboththegridandyoursolarsystem.Forastand-aloneoragridfallbacksystem,batteriesstoretheenergyandprovideaconstantpowersourceforyourelectricalequipment.Typically, this energy is stored in ‘deep cycle’ lead acid batteries. These looksimilar to carbatteriesbuthaveadifferent internaldesign.Thisdesignallowsthemtobeheavilydischargedandrechargedseveralhundredtimesover.Most lead acid batteries are 6-volt or 12-volt batteries and, like solar panels,thesecanbeconnectedtogethertoformalargerbatterybank.Likesolarpanels,multiplebatteriesusedinseriesincreasethecapacityandthevoltageofabatterybank. Multiple batteries connected in parallel increase the capacity whilstkeepingthevoltagethesame.

ControllerIf you are using batteries, your solar electric system is going to require acontrollerinordertomanagetheflowofelectricity(thecurrent)intoandoutofthebattery.Ifyoursystemoverchargesthebatteries,thiswilldamageandeventuallydestroythem. Likewise, if your system completely discharges the batteries, this willquiterapidlydestroythem.Asolarcontrollerpreventsthisfromhappening.Thereareafewinstanceswhereasmallsolarelectricsystemdoesnotrequireacontroller.Anexampleofthisisasmall‘batterytop-up’solarpanelthatisusedto keep a car battery in peak conditionwhen the car is not being used.Thesesolar panels are too small to damage the battery when the battery is fullycharged.In the majority of instances, however, a solar electric system will require acontroller in order to manage the charge and discharge of batteries and keepthemingoodcondition.

InverterThe electricity generated by a solar electric system is direct current (DC).Electricityfromthegridishigh-voltagealternatingcurrent(AC).Ifyouareplanningtorunequipmentthatrunsfromgrid-voltageelectricityfromyoursolarelectricsystem,youwillneedaninvertertoconvertthecurrentfromDCtoACandconvertthevoltagetothesamevoltageasyougetfromthegrid.Traditionally, there is usually one central inverter in a solar system, eitherconnectingdirectlytothesolararrayinagrid-tiesystem,ortothebatterypackin an off-grid system. A more recent invention has been the micro inverter.Micro-invertersareconnectedtoindividualsolarpanelssothateachindividualpanelprovidesahigh-voltagealternatingcurrent.Solarpanelswithmicro-inverters are typicallyonlyusedwithgrid-tie systemsandarenotsuitableforsystemswithbatterybackup.Forgrid-tiesystems,theydo offer some significant benefits over themore traditional ‘big box’ inverter,althoughtheup-frontcostiscurrentlyhigher.Invertersareabigsubjectallontheirown.Iwillcomebacktodescribetheminmuchmoredetaillateroninthebook.

ElectricaldevicesThefinalelementofyoursolarelectricsystemisthedevicesyouplantopower.Theoretically, anything thatyoucanpowerwith electricity canbepoweredbysolar. However,many electrical devices are very power hungry, whichmakesrunningthemonsolarenergyveryexpensive!Ofcourse, thismaynotbe somuchof an issue ifyouare installingagrid-tiesystem:ifyouhaveveryenergy-intensiveappliancesthatyouonlyuseforshortperiods, the impact to your system is low. In comparison, runninghigh-powerappliancesonanoff-gridsystemmeansyouhavetohaveamorepowerfuloff-gridsolarenergysystemtocopewiththepeakdemand.Low-voltagedevicesMostoff-gridsolarsystemsrunatlowvoltages.Unlessyouareplanningapuregrid-tie installation, you may wish to consider running at least some of yourdevicesdirectlyfromyourDCsupplyratherthanrunningeverythingthroughaninverter.Thishasthebenefitofgreaterefficiency.Thanks to the caravanning and boating communities, lots of equipment isavailable to run from a 12-volt or 24-volt supply: light bulbs, refrigerators,ovens, kettles, toasters, coffee machines, hairdryers, vacuum cleaners,televisions, radios, air conditioning units, washing machines and laptopcomputersareallavailabletorunon12-voltor24-voltpower.In addition, thanks to the recent uptake in solar installations, some specialistmanufacturers are building ultra low-energy appliances, such as refrigerators,freezersandwashingmachines,specificallyforpeopleinstallingsolarandwindturbinesystems.You can also charge upmost portable items such asMP3 players andmobilephonesfroma12-voltsupply.High-voltagedevicesIfrunningeverythingatlowvoltageisnotanoption,orifyouareusingagrid-tiesystem,youuseaninvertertorunyourelectricaldevices.

ConnectingeverythingtogetherAstand-alonesystem

The simplified block diagram above shows a simple stand-alone solar electricsystem.Whilst the detailwill vary, this design forms the basis ofmost stand-alonesystemsandistypicaloftheinstallationsyouwillfindincaravans,boatsandbuildingsthatdonothaveaconventionalpowersupply.Thisdesignprovidesbothlow-voltageDCpowerforrunningsmallerelectricaldevices and appliances such as laptop computers and lighting, plus a higher-voltage AC supply for running larger devices such as larger televisions andkitchenappliances.In thisdiagram, thearrowsshowtheflowofcurrent.Thesolarpanelsprovidetheenergy,whichisfedintothesolarcontroller.Thesolarcontrollerchargesthebatteries. The controller also supplies power to the low-voltage devices, usingeitherthesolarpanelsorthebatteriesasthesourceofthispower.TheACinvertertakesitspowerdirectlyfromthebatteryandprovidesthehigh-voltageACpowersupply.

Agrid-tiesystemusingasinglecentralinverter

Thissimplifiedblockdiagramshowsasimplegrid-tiesystem,typicalofthetypeinstalled inmany homes today. The solar panels are connected to the grid-tieinverter,whichfeedstheenergyintothemainsupply.Electricitycanbeusedbydevicesinthebuildingorfedbackoutontothegrid,dependingondemand.Thegrid-tieinvertermonitorsthepowerfeedfromthegrid.Ifitdetectsapowercut,italsocutspowerfromthesolarpanelstoensurethatnoenergyisfedbackoutontothegrid.Thegrid-tiemetermonitorshowmuchenergy is taken from thegridandhowmuchisfedbackintothegridusingthesolarenergysystem.

Agrid-tiesystemusingmultiplemicro-invertersAgrid-tiesystemusingmicro-inverters issimilar to theoneabove,except thateachsolarpanelisconnectedtoitsowninverter,andtheinvertersthemselvesaredaisy-chained together, converting the low-voltageDC power from each solarpanelintoahigh-voltageACpowersupply.

InconclusionTherearevariouscomponentsthatmakeupasolarelectricsystem Multiplesolarpanelscanbe joined together tocreateamorepowerfulsolararray.Inastand-alonesystem,theelectricityisstoredinbatteriestoprovideanenergy store and provide a more constant power source. A controllermanagesthebatteries,ensuringthebatteriesdonotgetoverchargedbythesolararrayandarenotover-dischargedbythedevicestakingcurrentfromthem An inverter takes the DC current from the solar energy system andconverts it into a high-voltage AC current that is suitable for runningdevicesthatrequiregridpowerGenerally,itismoreefficienttousetheelectricityasaDCsupplythananACsupply

TheDesignProcess

Nomatter what your solar energy system is for, there are seven steps in thedesignofeverysuccessfulsolarelectricinstallation:

ScopetheprojectCalculatetheamountofenergyyouneedCalculatetheamountofsolarenergyavailableSurveyyoursiteSizeupthesolarelectricsystemSelecttherightcomponentsandworkoutfullcostsProducethedetaileddesign

Thedesignprocesscanbemademorecomplicated,orsimplified,basedonthesize of the project. If you are simply installing an off-the-shelf shed light, forinstance,youcanprobablycompletethewholedesigninaroundtwentyminutes.If, on the other hand, you are looking to install a solar electric system in abusinesstoprovideemergencysitepowerinthecaseofapowercut,yourdesignworkislikelytotakeconsiderablymoretime.Whetheryoursolarelectricsystemisgoingtobelargeorsmall,whetheryouarebuyinganoff-the-shelfsolarlightingkitordesigningsomethingfromscratch,itisworthfollowingthisbasicdesignprocesseverytime.Thisistrueevenifyouareinstallinganoff-the-shelfsystem.Thisensuresthatyouwillalwaysget thebestfromyoursystemandwillprovideyouwiththereassurancethatyoursolarenergysystemwillachieveeverythingyouneedittodo.

Short-cuttingthedesignworkHaving said that doing the design work is important, there are some usefulonlinetoolstohelpmaketheprocessaseasyaspossible.Once you have scoped your project, the Solar Electricity Handbook website(www.SolarElectricityHandbook.com) includes a number of online tools andcalculatorsthatwillhelpyoucarryoutmuchofthedesignwork.Thesolarirradiancetablesandsolaranglecalculatorswillallowyoutoworkouthowmuchsolarenergyisavailableatyourlocation,whilst theoff-gridprojectanalysis and grid-tie project analysis questionnaires will each generate and e-mailtoyouafullreportforyourproposedsystem,includingcalculatingthesizeofsystemyourequireandprovidingacostestimate.Ofcourse,thereisalimittohowmuchasetofonlinesolartoolscanhelpyouinisolation, so you will still need to carry out a site survey and go throughcomponentsselectionanddetaileddesignyourself,butthesetoolswillallowyouto try several different configurations and play out ‘what if’ scenarios quicklyandeasily.Incidentally,whilstsomeofthesetoolsaskyouforane-mailaddress(inordertosendyouyourreport),youre-mailaddressisnotstoredanywhereonthesystem.Otherthanthereportthatyourequest,youwillneverreceiveunsolicitede-mailsbecauseofenteringyoure-mailaddress.

SolarenergyandemotionsDesigncanoftenseemtobeapurelyanalyticalandrationalprocess. Itshouldnotbe.Allgreatdesignsstartwithadream.For many people, choosing solar energy is often an emotional decision: theywantasolarenergysystemforreasonsotherthanjustthepurelypractical.Somepeoplewantsolarenergybecausetheywantto‘dotheirbit’fortheenvironment,otherswanttheverylatesttechnology,orwanttousesolarsimplybecauseitcanbe done. Others want solar energy because they see the opportunity to earnmoney.Isuspectthatformosthomeowners,thereasonsareacombinationoftheabove.It is so important that the emotional reasons for wanting something are notignored.Wearenotrobots.Ouremotionsshouldbecelebrated,notsuppressed:theWrightbrothersbuiltthefirstaircraftbecausetheywantedtoreachthesky.NASAsentaman to themoonbecause theywanted togofurther thananyonehad ever done before.Neither undertaking could be argued as purely rational;theyweretheresultsofbigdreams.It is important to acknowledge that there areoftenhidden reasons forwantingsolar energy. Sadly, these reasons often do notmake it down onto a sheet ofpaper in a design document or onto a computer spreadsheet. Sometimes, thepersonmaking the decision for buying solar energy is secretlyworried that iftheyvoicetheirdreams,theywillappearinsomewayirrational.The reality is that it is often a good thing if there is an emotional element towantingasolarenergysystem.Bydocumentingthesereasons,youwillendupwithabettersolution.Forinstance,iftheenvironmentalbenefitsaretopofyouragenda,youwilluseyoursolarenergysysteminadifferentway tosomebodywhoislookingatsolarpurelyasabusinessinvestment.Byacknowledgingthesereasonsandincorporatingthemintothedesignofyoursystem, you will end up with a far better system. Not only will you have asystemthatworksinapracticalsense,itwillalsoachieveyourdream.

Inconclusion Nomatter how big or small your project, it is important to design itproperly Thereareonlinetoolsavailabletohelpyouwiththecalculationsandtospeedupthework Donotignoretheemotionalreasonsforwantingasolarenergysystem.Youareahumanbeing:youareallowedtodream

ScopingtheProject

As with any project, before you start, you need to know what you want toachieve.Infact,itisoneofthemostimportantpartsofthewholeproject.Getitwrongandyouwillendupwithasystemthatwillnotdowhatyouneeditto.Itisusuallybesttokeepyourscopesimpletostartwith.Youcanthenfleshit

outwithmoredetaillater.Herearesomeexamplesofasuitablescope:

TopoweralightandaburglaralarminashedonanallotmentToprovidepowerforlighting,akettle,aradioandsomehandheldpowertoolsinaworkshopthathasnoconventionalelectricalconnectionToprovideenoughpowerforlighting,refrigerationandaTVinaholidaycaravan To provide lighting and power to run four laptop computers and thetelephonesysteminanofficeduringapowercutTochargeupanelectricbikebetweenuses To provide an off-grid holiday home with its entire electricityrequirements ToreducemycarbonfootprintbyproducingelectricityforallmyhomerequirementsTorunanelectriccarentirelyonsolarenergy

Fromyourscope,youcanstartfleshingthisouttoprovidesomeinitialestimatesonpowerrequirements.Asmentionedinthepreviouschapter,IhavecreatedtwoonlineSolarProject

Analysis tools, one for grid-tie systems andone for off-grid systems.You canfindbothofthesetoolsonmywebsitewww.SolarElectricityHandbook.com.Youwillstillneedtocollectthebasicinformationtoworkwith,butallthehardworkisdoneforyou.This toolwillproduceacompleteprojectscope,workout thelikelyperformanceofyoursolarenergysystemandprovidesomeballparkcostestimates.For the purposeof these next fewchapters, I amgoing to use the example of

providingasmalloff-gridholidayhomewithitsentireelectricityrequirements.Thisisabigproject.Inrealityifyouhavelittleornoexperienceofsolarelectricsystems or household electrics you would be best starting with somethingsmaller.Goingcompletelyoff-gridisanambitiousproject,butforthepurposesof teaching solar electric system design, it is a perfect example: it requires adetaileddesignthatcoversalloftheaspectsofdesigningasolarenergysystem.

Designinggrid-tieorgridfallbacksystemsForoursampleproject,grid-tieisnotanoptionasweareusingsolarpowerasanalternativetoconnectingoursitetotheelectricitygrid.However,grid-tieisbecomingapopularoption,especiallyinthesouthernstatesof the United States and in European countries like Spain, Germany and theUnitedKingdomwhere generous government subsidies and feed-in tariffs areavailable.In terms of scoping the project, it makes little difference whether you areplanning a grid-tie or grid fallback system or not: the steps you need to gothrougharethesame.Theonlyexception,ofcourse,isthatyoudonotneedtotakeintoaccountbatteryefficiencieswithgrid-tie.Thebiggestdifferencewithagrid-tieorgridfallbacksystemisthatyoudonothave to rely on your solar system providing you with all your electricityrequirements:youwillnotbeplungedintodarknessifyouusemoreelectricitythanyougenerate.Thismeans thatyoucanstartwithasmallgrid-tieorgridfallbacksystemandexpanditlateronasfundsallow.Despitethat,itisstillagoodideatogothroughapoweranalysisaspartofthedesign.Evenifyoudonotintendtoproduceallthepoweryouneedwithsolar,havingapoweranalysiswillallowyoutobenchmarkyoursystemandwillhelpyou size your grid-tie system if you aim to reduce your carbon footprint byprovidingtheelectricitycompanieswithasmuchpowerasyoubuyback.Mostgrid-tiesystemsaresizedtoprovidemorepowerthanyouneedduringthesummerand less thanyouneedduring thewinter.Overaperiodofayear, theaim is to generate asmuch power as you use, although on amonth-by-monthbasisthismaynotalwaysbethecase.Manysolarcompaniesclaimthatthisthenprovidesyouwitha‘carbonneutral’system:youaresellingyourexcesspowertotheelectricitycompaniesandthenbuyingthesameamountofelectricitybackwhenyouneedit.If this iswhatyouareplanning todowithyourgrid-tie system,your scope ismuchsimpler.Youneedtogetyourelectricitybillsforthepastyearandmakeanote of how much electricity you have used over the year. Then divide thisfigurebythenumberofdaysintheyear toworkoutadailyenergyusageandensureyoursystemgeneratesthisasanaverageovertheperiodofayear.

Becauseyouarenotgeneratingenoughelectricityduringthewintermonthsinacarbonneutralgrid-tiesystem,youneedfewersolarpanelsthanyouwouldneedtocreateanentirelystand-alonesystem.

ComparingsupplywithdemandIfyouaredesigningagrid-tiesystem,itcanbeinterestingtocomparethesupplyof solar energywith your electricity usage pattern.By comparing supplywithdemand, you can see how closely solar energy productionmatches your ownusage and this, in turn, can be used as an indicator to identify howenvironmentallybeneficialsolarenergyisforyou.To do this, youwill need to ascertain yourmonthly electricity usage for eachmonthof theyear.Yourelectricity suppliermayalreadyprovideyouwith thisinformation on your electricity bill. If not, you should be able to request thisfromthem.Once you have this information, visitwww.SolarElectricityHandbook.com andfill in the Grid-Tie Solar Project Analysis, including your individual monthlyconsumptionfigures. In thereport that ise-mailed toyou,youwillseeachartthatallowsyoutoseehowcloselyyourelectricityusagemapsontosolarenergyproduction.This reportwill alsoprovideyouwith an approximate estimate for the carbonfootprintforeachkilowatt-hourofelectricityyouproducefromyoursolararray,based on the production and installation of your solar array and the likelyamountofenergythatitwillgenerateduringitslifetime.Based on this, it is possible to seewhether installing solar energy is likely toproducereal-worldenvironmentalsavings.

FleshingoutthescopeNowweknowtheoutlinescopeofourproject,weneedtoquantifyexactlywhatweneedtoachieveandworkoutsomeestimatesforenergyconsumption.Ourholidayhomeisasmalltwo-bedroomcottagewithasolidfuelcookerandboiler.Thecostofconnectingthecottagetothegridis£4,500(around$7,200)andIsuspectthatsolarelectricpowercouldworkoutsignificantlycheaper.Thecottageismainlyusedinthespring,summerandautumn,withonlyafewweekendvisitsduringthewinter.Electricity is required for lighting in each room, plus a courtesy light in theporch,a fridge in thekitchenanda small television in the sitting room.Therealso needs to be surplus electricity for charging up a mobile phone or MP3playerandfortheoccasionaluseofalaptopcomputer.Nowwehavedecidedwhatdevicesweneedtopower,weneedtofindouthowmuchenergyeachdeviceneeds,andestimatethedailyusageofeachitem.Inordertokeepefficiencyhighandcostslow,wearegoingtoworkwithlow-voltageelectricswhereverpossible.Thebenefitsofusinglow-voltdevicesratherthanhighergrid-voltagearetwofold:

Wearenotlosingefficiencybyconvertinglow-voltDCelectricstogrid-voltageACelectricsthroughaninverter. Manyelectronicdevices that plug into agrid-voltage socket require atransformer to reduce thepowerbackdown toa lowDCcurrent, therebycreatingasecondlevelofinefficiency

Many household devices, like smaller televisions, music systems, computergamesconsolesandlaptopcomputers,haveexternaltransformers.Itispossibletobuy transformers that runon12-voltor24-volt electrics rather than theACvoltagesweget fromgridpower, andusing these is themost efficientwayofprovidinglow-voltagepowertothesedevices.Therecanbedisadvantagesoflow-voltageconfigurations,however,andtheyarenottherightapproachforeveryproject:

If running everything at 12–24 volts requires a significant amount ofadditional rewiring, the cost of carrying out the rewiring can be muchhigherthanthecostofaninverterandaslightlylargersolararray Ifthecablerunningbetweenyourbatteriesandyourdevicesistoolong,

youwillgetgreaterpowerlossesthroughthecableat lowervoltagesthanyouwillathighervoltages

If you already havewiring in place towork at grid-level voltages, it is oftenmore appropriate to runa systematgridvoltageusingan inverter, rather thanrunningthewholesystematlowvoltage.Ifyouhavenowiringinplace,runningthesystemat12or24voltsisoftenmoresuitable.

ProducingapoweranalysisThenextstepistoinvestigateyourpowerrequirementsbycarryingoutapoweranalysis,whereyoumeasureyourpowerconsumptioninwatt-hours.Youcanfindoutthewattageofhouseholdappliancesinoneoffourways:

Checktherearoftheappliance,oronthepowersupplyChecktheproductmanualMeasurethewattsusingawattmeterFindaballparkfigureforsimilaritems

Often a power supply will show an output current in amps rather than thenumberofwattsthedeviceconsumes.Ifthepowersupplyalsoshowstheoutputvoltage,youcanworkoutthewattagebymultiplyingthevoltagebythecurrent(amps):Power(watts)=VoltsxCurrent(amps)

P=VxIForexample,ifyouhaveamobilephonechargerthatuses1.2ampsat5volts,youcanmultiply1.2ampsby5volts toworkout thenumberofwatts: in thisexample,itequals6wattsofpower.IfIpluggedthischargerinforonehour,Iwoulduse6watt-hoursofenergy.A watt meter is a useful tool for measuring the energy requirements of anydevicethatrunsonhigh-voltageACpowerfromthegrid.Thewattmeterplugsintothewallsocketandtheapplianceplugsintothewattmeter.AnLCDdisplayonthewattmeterthendisplaystheamountofpowerthedeviceisusing.Thisisthemostaccuratewayofmeasuringyourtruepowerconsumption.Findingaballparkfigureforsimilardevicesistheleastaccuratewayoffindingout the power requirement and should only be done as a last resort.A list ofpowerratingsforsomecommonhouseholdappliancesisincludedinAppendixC.Onceyouhavealistofthepowerrequirementsforeachelectricaldevice,drawupa table listingeachdevice,whether thedeviceuses12-voltorgridvoltage,andthepowerrequirementinwatts.Thenputanestimateinhoursforhowlongyouwilluseeachdeviceeachdayandmultiply thewattsbyhours tocreatea totalwatt-hourenergy requirementforeachitem.Youshouldalsofactorinany‘phantomloads’onthesystem.Aphantomloadis

the name given to devices that use power even when they are switched off.Televisions in standbymode are one such example, but any device that has apowersupplybuiltintotheplugalsohasaphantomload.Theseitemsshouldbeunplugged or switched off at the switchwhen not in use. However, youmaywishtofactorinasmallamountofpowerforitemsinstandbymode,totakeintoaccountthetimesyouforgettoswitchsomethingoff.Ifyouhaveagas-poweredcentralheatingsystem, remember thatmostcentralheating systems have an electric pump and the central heating controller willrequireelectricityaswell.Atypicalcentralheatingpumpusesaround60wattsof power a day, whilst a central heating controller can use between 2 and 24wattsaday.Oncecomplete,yourpoweranalysiswilllooklikethis:

Device

Voltage

Power(watts)

Hoursofuse

perday

Watt-hoursenergy

Livingroomlighting

12V

11W

5

55Wh

Kitchenlighting

12V

11W

2

22Wh

Hallwaylighting

12V

8W

½

4Wh

Bathroomlighting

12V

11W

1½

17Wh

Bedroom1lighting

12V

11W

1

11Wh

Bedroom2lighting

12V

11W

1½

17Wh

Porchlight

12V

8W

½

4Wh

Smallfridge

12V

12W

24

288Wh

TV

12V

40W

4

160Wh

Laptopcomputer

12V

40W

1

40Wh

Chargingcellphonesand

MP3players

12V

5W

4

20Wh

Phantomloads

12V

1W

24

24Wh

TotalEnergyRequirementaday(watt-hours)

662Wh

AwordofwarningIn theheadlongenthusiasmfor implementingasolarelectricsystem, it isveryeasytounderestimatetheamountofelectricityyouneedatthisstage.Tobesurethatyoudonotleavesomethingoutwhichyouregretlater,Isuggestyouhaveabreakatthispoint.Thenreturnandreviewyourpoweranalysis.Itcanhelptoshowthislisttosomebodyelseinordertogettheirinputaswell.Itis very easy to get emotionally involved in your solar project, and having asecondpairofeyescanmakeaworldofdifferencelateron.

WhenyouarereadytoproceedWenowknowexactlyhowmuchenergyweneedtostoreinordertoprovideonedayofpower.Forourholidayhomeexample,thatequatesto662watt-hoursperday.Thereisonemorethingtotakeintoaccount:theefficiencyoftheoverallsystem.Batteries,invertersandresistanceinthecircuitsallreducetheefficiencyofoursolarelectricsystem.Wemustconsidertheseinefficienciesandaddthemtoourpoweranalysis.

CalculatinginefficienciesBatteries do not return 100% of the energy used to charge them. TheChargeCycleEfficiencyofthebatterymeasuresthepercentageofenergyavailablefromthebatterycomparedtotheamountofenergyusedtochargeit.Charge cycle efficiency is not a fixed figure, as the efficiency can vary

dependingonhowquicklyyouchargeanddischargethebattery.However,mostsolar applications do not overstress batteries and so the standard charge cycleefficiencyfiguresareusuallysufficient.Approximate charge cycle efficiency figures are normally available from thebattery manufacturers. However, for industrial quality ‘traction’ batteries, youcanassume95%efficiency,whilstgelbatteriesandleisurebatteriesareusuallyintheregionof90%.If you are using an inverter in your system, you need to factor in theinefficienciesoftheinverter.Again,theactualfiguresshouldbeavailablefromthe manufacturer but typically, you will find that an inverter is around 90%efficient.

AddingtheinefficienciestoourpoweranalysisInourholidayhomeexample,thereisnoinverter.Iftherewere,wewouldneedtoadd10%forinverterinefficienciesforeverygrid-powereddevice.We are usingbatteries.Weneed to add5% to the total energy requirement totakechargecycleefficiencyintoaccount.5%of662equals33watts.Addthistoourpoweranalysis,andourtotalwatt-hourrequirementbecomes695watt-hoursperday.

Whendoyouneedtousethesolarsystem?It is important toworkout atwhat timesofyearyouwill beusingyour solarelectric systemmost.For instance, ifyouareplanning touseyour systemfulltimeduringthedepthsofwinter,yoursolarelectricsystemneedstobeabletoprovideallyourelectricityevenduringthedulldaysofwinter.Aholidayhomeisofteninregularuseduringthespring,summerandautumn,butleftemptyforperiodsoftimeduringthewinter.This means that, during winter, we do not need our solar electric system to

provideenoughelectricity for fulloccupancy.Weneedenoughcapacity in thebatteriestoprovideenoughelectricityfor,say,theoccasionallongweekend.Thesolararraycanthenrechargethebatteriesagain,oncethehomeisempty.Wemightalsodecidethat,ifweneededadditionalelectricityinwinter,wecouldhaveasmallstandbygeneratoronhandtogivethebatteriesaboostcharge.For the purposes of our holiday home, our system must provide enoughelectricity for full occupancy fromMarch toOctober and occasionalweekendusefromNovemberuntilFebruary.

KeepingitsimpleYou have seen what needs to be taken into account when creating a poweranalysisandcalculatingtheinefficiencies.Ifyouareplanningtousetheonlinetoolstohelpyou,nowisthetimetousethem.Visitwww.SolarElectricityHandbook.comandfollowthelinkstoeithertheOff-GridorGrid-TiedSolarProjectAnalysistools,whichcanbefoundintheOnlineCalculators section. This will allow you to enter your devices on the poweranalysis, select the months you want your system to work and select yourlocation from a worldwide list. The system will automatically e-mail you adetailedsolaranalysisreportwithallthecalculationsworkedoutforyou.

ImprovingthescopeBased on the work done, it is time to put more detail on our original scope.Originally,ourscopelookedlikethis:

Provideanoff-gridholidayhomewithitsentireelectricityrequirements.

Nowtheimprovedscopehasbecome:Provide an off-grid holiday home with its entire electricityrequirements, providing power for lighting, refrigeration, TV, laptopcomputer and various sundries, which equals 695 watt-hours ofelectricityconsumptionperday.The systemmust provide enough power for occupation fromMarchuntilOctober,plusoccasionalweekenduseduringthewinter.

There isnowa focus for theproject.Weknowwhatweneed toachieve forasolarelectricsystemtowork.Nowweneedtogotothesiteandseeifwhatwewanttodoisachievable.

InconclusionGettingthescoperightisimportantforthewholeproject StartbykeepingitsimpleandthenfleshitoutbycalculatingtheenergyrequirementsforallthedevicesyouneedtopowerIfyouaredesigningagrid-tiesystem,youdonotneedtogointosomuchdetail:youcangettheusageinformationfromyourelectricitycompany.ItisprobablyincludedonyourelectricitybillIfyouaredesigningagrid-tiesystem,youcanmakeareasonableestimateof its environmental benefit by comparing solar energy supplywith yourdemandonamonth-by-monthbasisDonotforgettofactorin‘phantomloads’ Becausesolarelectricsystemsrunatlowvoltages,runningyourdevicesatlowvoltageismoreefficientthaninvertingthevoltagetogridlevelsfirst Thankstothepopularityofcaravansandboats,thereisalargeselectionof 12-volt appliances available. If you are planning a stand-alone or gridfallback system, youmaywish to use these in your solar electric systemratherthanlessefficientgrid-voltageappliances Evenifyouareplanningagrid-tiesystem,itisstillusefultocarryoutadetailedpoweranalysisDonotforgettofactorininefficienciesforbatteriesandinvertersTakeintoaccountthetimesofyearthatyouneedtouseyoursolarelectricsystem Once you have completed this stage, youwill knowwhat the projectneedstoachieveinordertobesuccessful

CalculatingSolarEnergy

Thenexttwochaptersarejustasusefulforpeoplewishingtoinstallasolarhotwatersystemastheyareforpeoplewishingtoinstallsolarelectricity.WheneverIrefertosolarpanelorsolararray(multiplesolarelectricpanels)inthesetwochapters,theinformationisequallyvalidforsolarelectricityandsolarhotwater.

Whatissolarenergy?Solarenergyisacombinationof thehoursofsunlightyougetatyoursiteandthe strength of that sunlight. This varies depending on the time of year andwhereyoulive.Thiscombinationofhoursandstrengthofsunlightiscalledsolar insolationorsolar irradiance, and the results can be expressed as watts per square metre(W/m²) or, more usefully, in kilowatt-hours per square metre spread over theperiodofaday(kWh/m²/day).Onesquaremetreisequalto9.9squarefeet.

Whyisthisuseful?Photovoltaicsolarpanelsquotetheexpectednumberofwattsofpowertheycangenerate,basedonasolarirradianceof1,000wattspersquaremetre.Thisfigureisoftenshownasawatts-peak(Wp)figureandshowshowmuchpowerthesolarpanel can produce in ideal conditions. A solar irradiance of 1,000 watts persquaremetreiswhatyoucouldexpecttoreceiveatsolarnooninthemiddleofsummer at the equator. It is not an average reading that you could expect toachieveonadailybasis.However, onceyouknow the solar irradiance for your area, quoted as a dailyaverage (i.e. the numberof kilowatt-hours per squaremetre per day), you canmultiplythisfigurebythewattageofthesolarpaneltogiveyouanideaofthedailyamountofenergyyoucanexpectyoursolarpanelstoprovide.

CalculatingsolarirradianceSolar irradiance varies significantly from one place to another and changes

throughout theyear. Inorder to comeupwith some reasonable estimates, youneedirradiancefiguresforeachmonthoftheyearforyourspecificlocation.Thanks to NASA, calculating your own solar irradiance is simple. NASA’snetworkofweathersatelliteshasbeenmonitoringthesolarirradianceacrossthesurfaceoftheearthformanydecades.Theirfigureshavetakenintoaccounttheupperatmosphericconditions,averagecloudcoverandsurfacetemperature,andarebasedonsamplereadingseverythreehoursforthepastquarterofadecade.Theycovertheentireglobe.Forreference,Ihavecompiledthis informationfordifferentregionsacross theUnitedStates,Canada,Australia,NewZealand,theUnitedKingdomandIrelandinAppendixB.Thewebsitegoesfurther.Wehaveincorporatedsolarirradiancechartsforeverymajor townandcity ineverycountry in theworld:simplyselectyour locationfrom a pull-down list of countries and cities and you can view the irradiancefiguresforyourexactarea.Using the information inAppendixB,here are the solar irradiance figures forLondonintheUnitedKingdom,shownonamonth-by-monthbasis.Theyshowthe average daily irradiance, based on mounting the solar array flat on theground:

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

0.75 1.37 2.31 3.57 4.59 4.86 4.82 4.20

Thesefiguresshowhowmanyhoursofequivalentmiddaysunwegetovertheperiodofanaveragedayofeachmonth.Inthechartabove,youcanseethatinDecemberwegettheequivalentof0.6ofanhourofmiddaysun(36minutes),whilst inJuneweget theequivalentof4.86hoursofmiddaysunlight(4hoursand50minutes).

Capturingmoreofthesun’senergyThetiltofasolarpanelhasanimpactonhowmuchsunlightyoucapture:mountthesolarpanelflatagainstawallorflatonthegroundandyouwillcapturelesssunlightthroughoutthedaythanifyoutiltthesolarpanelstofacethesun.ThefiguresaboveshowthesolarirradianceinLondon,basedontheamountofsunlightshiningonasinglesquaremetreoftheground.Ifyoumountyoursolarpanel at an angle, tilted towards the sun, you can capture more sunlight andtherefore generate more power. This is especially true in the winter months,

whenthesunislowinthesky.The reason for this is simple:when the sun is high in the sky the intensity ofsunlight is high.When the sun is low in the sky the sunlight is spreadover agreatersurfacearea:

Thisdiagramshowsthedifferentintensityoflightdependingontheangleofsuninthesky.Whenthesunisdirectlyoverhead,a1m-wideshaftofsunlightwillcovera1m-wideareaontheground.Whenthesunislowinthesky–inthisexample,Iamusinganangleof30°towardsthesun–a1m-wideshaftofsunlightwillcovera2m-wideareaontheground.Thismeanstheintensityofthesunlightishalfasmuchwhenthesunisatanangleof30°comparedtotheintensityofthesunlightwhenthesunis

directlyoverhead.

TheimpactoftiltingsolarpanelsonsolarirradianceIfwetiltoursolarpanelstowardsthesun,itmeanswecancapturemoreofthesun’senergytoconvertintoelectricity.Oftentheangleofthistiltisdeterminedforyouby theangleofanexistingroof.However, forevery location thereareoptimalanglesatwhichtomountyoursolararray,inordertocaptureasmuchsolarenergyaspossible.Using London as an example again, this chart shows the difference inperformanceofsolarpanels,basedontheangleatwhichtheyaremounted.TheanglesIhaveshownareflatontheground,uprightagainstawall,andmountedat different angles designed to get the optimal amount of solar irradiance atdifferenttimesoftheyear(Iexplaintherelevanceofthesespecificanglesina

moment):

FlatJan

Feb

Mar

Apr

May

Jun

Jul

Aug

0.75 1.37 2.31 3.57 4.59 4.86 4.82 4.20

UprightJan

Feb

Mar

Apr

May

Jun

Jul

Aug

1.20 1.80 2.18 2.58 2.70 2.62 2.71 2.80

38°angle-Bestyear-roundtiltJan

Feb

Mar

Apr

May

Jun

Jul

Aug

1.27 2.04 2.76 3.67 4.17 4.20 4.25 4.16

23°angle-BestwintertiltJan

Feb

Mar

Apr

May

Jun

Jul

Aug

1.30 2.03 2.62 3.34 3.66 3.69 3.76 3.73

53°angle-BestsummertiltJan

Feb

Mar

Apr

May

Jun

Jul

Aug

1.19 1.95 2.77 3.84 4.52 4.63 4.66 4.41

AdjustingthetiltmanuallyeachmonthJan

Feb

Mar

Apr

May

Jun

Jul

Aug

1.3022°tilt

2.0530°tilt

2.7838°tilt

3.8646°tilt

4.7054°tilt

4.9162°tilt

4.9054°tilt

4.4646°tilt

Note:Allanglesaregivenindegreesfromverticalandarelocationspecific.

Lookatthedifferenceintheperformancebasedonthetiltofthesolarpanel.Inparticular, lookat thedifference inperformance in thedepthsofwinterand intheheightofsummer.It is easy to see that someanglesprovidebetterperformance inwinter; othersprovidebetterperformanceinsummer,whilstothersprovideagoodcompromiseall-year-roundsolution.

CalculatingtheoptimumtiltforsolarpanelsBecauseofthe23½°tiltoftheearthrelativetothesun,theoptimumtiltofyoursolar panelswill vary throughout the year, depending on the season. In someinstallations,itisfeasibletoadjustthetiltofthesolarpanelseachmonth,whilstinothersitisnecessarytohavethearrayfixedinposition.

To calculate the optimum tilt of your solar panels, you can use the followingsum:

90°–yourlatitude=optimumfixedyear-roundsettingThis angle is the optimum tilt for fixed solar panels for all-year-round powergeneration. This doesnot mean that youwill get themaximum power outputeverysinglemonth:itmeansthatacrossthewholeyear,thistiltwillgiveyouthebestcompromise,generatingelectricityalltheyearround.

GettingthebestfromsolarpanelsatdifferenttimesoftheyearDependingonwhenyouwanttouseyoursolarenergy,youmaychoosetouseadifferenttiltinordertoimprovepoweroutputatagivenpointintheyear.Eachmonthoftheyear,theangleofthesunintheskychangesby7.8°–higherinthesummerandlowerinthewinter.Byadjustingthetiltofyoursolarpaneltotrackthe sun, you can tweak the performance of your system according to yourrequirements.Youmaywanttodothisforanumberofreasons:

Forastandalone,off-gridsystem,youoftenneedtogetasmuchpowergenerationduringthewintermonthsaspossibletocounterthereductioninnaturallightWheninstallingagrid-tiesysteminacoolclimate,wherethefocusisonreducing your carbon footprint, you can choose to boost your electricityproduction inwinter, to offset the amount of electricity you need to buywhendemandisatitshighest Wheninstallingagrid-tiesystemwherethefocusisonmakingthemostprofitbysellingyourpower,youcanchoose to tiltyoursolarpanelsatasummer setting and thereby produce the maximum amount of energypossibleoverthecourseoftheyear

Youcanseethismonthlyoptimumangle(roundedtothenearestwholedegree)onthebottomrowoftheprevioustable.OptimumwintersettingsHereisanexampleofhowyoucouldtweakyoursystem.Performanceofasolarsystemisatitsworstduringthewintermonths.However,bytiltingyourpanelsto capture as much of the sunlight as possible during the winter, you cansignificantlyboosttheamountofpoweryougenerateatthistime.BasedontheNorthernHemisphere,anoptimumwintertiltforsolarpanelsisthe

optimum angle for November and January. For the SouthernHemisphere, theoptimumwinter tilt isMayandJuly:90°–your latitude–15.6°=optimumwintersettingAsyoucanseefromtheprevioustable,ifyoutiltyoursolarpanelsatthisangle,youwillsacrificesomeofyourpowergenerationcapabilityduringthesummermonths. However, as you are generating so much more power during thesummerthanyouareinthewinter,thismaynotbeanissue.More importantly, compared to leaving the panels on a flat surface, you arealmostdoublingtheamountofpoweryoucangenerateduringthethreebleakestmonthsoftheyear.Thismeansyoucanreducethenumberofsolarpanelsyouneedtoinstall.OptimumsummersettingsIfyouwishtogetthebestoutputofyoursystemoverall,youwillfindthatyouwillgetslightlymoreenergy,whenmeasuredoverthecourseofthewholeyear,byanglingyoursolarpanelstoanoptimumsummertimetilt.Inwarmclimates,wheremaximumenergyconsumption isduringhotweather,anglingyourpanelstogetthemaximumamountofsunlightduringtheheightofsummercanbethebestsolution,bothfinanciallyandenvironmentally.For Northern Hemisphere countries, the optimum summer time tilt is theoptimum angle for May and July. For Southern Hemisphere countries, theoptimumsummertimetiltistheoptimumangleforNovemberandJanuary:90°–yourlatitude+15.6°=optimumsummersetting

PositioningyoursolarpanelsRegardlessofwhereyoulive,thesunalwaysrisesfromtheeastandsetsinthewest.IfyouliveintheNorthernHemisphere,solarpanelswillalwaysworkbestif theyaresouth-facing.In theSouthernHemisphere,solarpanelsworkbest iftheyarenorth-facing.However, it is not always possible to position your solar panels so they arefacingexactlytherightway.Forinstance,ifyouwanttoinstallsolarpanelsontheroofofthehouse,andtherooffaceseast/west,thenitmaynotbepracticaltoinstallsolarpanelsinanyotherlocation.Thankstoimprovedsolarpaneldesignoverthepastdecade,thisisnotasbigaproblemaswasoncethecase.Whilstthefigurevariesslightlyindifferentpartsof the world, from one solar panel manufacturer to another and during thedifferent seasons of the year, the average efficiency drop of a solar panel

mountedawayfromduesouth(duenorthintheSouthernHemisphere)isaround1.1%foreveryfivedegrees.Thismeansthatifyourpanelsfacedueeastorduewest,youcanexpectaround20%lossofefficiencycomparedtofacingyourpanelsintheoptimumposition.Youcanevenfaceyourpanelsinthecompletelyoppositedirection–northintheNorthernHemisphereorsouthintheSouthernHemisphere–losingaround40%oftheefficiencyofyoursolararraybydoingso.

FortheNorthernHemisphere,thischartshowstheapproximateefficiencylossbynotfacingyourpanelsdirectlysouth.ForSouthernHemisphere

countries,thechartshouldbereversed.

UsingsolarirradiancetoworkouthowmuchenergyasolarpanelwillgenerateBasedonthesefigures,wecancalculateonamonthlybasishowmuchpowerasolar panel will give us per day, by multiplying the monthly solar irradiancefigure by the statedwattage of the panel: Solar Irradiance x PanelWattage =Watt-hoursperdayAswenowknow,thesolarirradiancefiguredependsonthemonthandtheangleforthesolarpanel.Assumingwehavea20-wattsolarpanel,mountedflatonthe

ground, here are the calculations for London in December and June:

Flat

DecemberJune

0.60x20W=12Whofenergyper

day

4.86x20W=97Whofenergyper

day

As you can see, there is a big difference in the amount of energy you cangenerate in themiddle of summer, compared towinter. In the example above,over eight times the amount of energy is generated in the height of summercomparedtothedepthsofwinter.Herearethesamecalculationsagain,butwiththesolarpanelsangledat38°forbest all-year-round performance. Note the significant improvement in winter

performanceandtheslightlyreducedsummerperformance:38°angle

December

June

1.05x20W=21Whofenergyper

day

4.20x20W=84Whofenergyper

day

Using solar irradiance to give you an approximate guide for therequiredpowercapacityofyoursolararrayIn the same way that you can work out howmuch energy a solar panel willgenerateperday,youcanusesolarirradiancetogiveyouanapproximateguide

fortherequiredcapacityofsolararraythatyouneed.I sayanapproximateguide,because theactual capacitywill alsoneed to takeintoaccount:

ThepeculiaritiesofyoursiteThelocationandanglesofyoursolarpanelsAnyobstaclesblockingthesunlightatdifferenttimesofyear

IcoverallthisinthenextchapterwhenIlookatthesitesurvey.Nevertheless,itcanbeusefultocarryoutthiscalculationinordertoestablishaballparkcost foryoursolarelectricsystem.Thecalculation is simple: take thefigureyoucalculatedforyourtotalnumberofwatt-hoursperdayanddivideitbythesolarirradiancefigurefortheworstmonththatyourequireyoursystemtowork.Usingourholidayhomeasanexample,wecanlookatourwatt-hoursperdayfigure of 695Wh/day and then divide this number by theworstmonth on ourirradiancechart(December).Itisworthdoingthisbasedonmountingthesolarpanelatdifferentangles,toseehowtheperformancescompare:

Flat

695÷0.6=1159watts

Ifwehaveoursolarpanelslaidflat,wewouldneeda1,159-wattsolararraytopowerourhomeinDecember.

Upright

695÷1.01=688watts

Ifwemountthesolarpanelsverticallyagainstawall,wecouldgeneratethesameamountofpowerwitha688-wattsolararray.

38°angleBest

year-roundtilt

695÷1.05=661watts

Angledtowardstheequator,wecouldgeneratethesameamountofpowerwitha661-wattsolararray.

23°angleBest

wintertilt

695÷1.08=643watts

Withtheoptimumwintertilt,wecanusea643-wattsolararray.

53°angleBest

summertilt

695÷0.97=716watts

Angledtowardsthesummersun,wewouldrequirea716-wattsolararraytoprovidepowerinDecember

Tiltadjustedeach

month

695÷1.08=643watts

Withthetiltofthesolarpaneladjustedeachmonth,wecanusea643-wattsolararray,thesameasthebestwintertiltsettings.

ThischarttellsusthattoprovidefullpowerforourholidayhomeinDecember,we require a solar arraywith a generation capacity of between 643watts and1159watts,dependingonthetiltofthesolarpanels.Butrememberourscope.WeonlywanttousethehomefulltimefromMarchtoOctober.Thesolarelectricsystemonlyneedstoprovideenoughelectricityforalongweekendduringthewinter.Thismeans that, so long as our batteries are big enough to provide electricalpower for a few days, it does not matter if the solar power in winter is notenough toprovide for constantuse.As soonaswecloseup theholidayhomeagain,thesolarpanelswillrechargethebatteries.Herearemycalculationsagain,thistimeusingOctoberasourworstmonth:

Flat

695÷1.69=411watts

Ifwehaveoursolarpanelslaidflat,wewouldneeda411-wattsolararraytopowerourhomeinOctober.

Upright

695÷2.07=335watts

Ifwemountthesolarpanelsverticallyagainstawall,wecouldgeneratethesameamountofpowerwitha335-wattsolararray.

38°angleBest

year-roundtilt

695÷2.41=288watts

Angledtowardstheequator,wecouldgeneratethesameamountofpowerwitha288-wattsolararray.

23°angleBest

wintertilt

695÷2.37=293watts

Withtheoptimumwintertilt,wecanusea293-wattsolararray.

53°angleBest

summertilt

695÷2.33=298watts

Angledtowardsthesummersun,wewouldrequirea298-wattsolararraytoprovidepowerinOctober

Tilt

695÷2.41=288watts

Withthetiltofthesolarpaneladjustedeachmonth,wecanusea288-wattsolararray,thesameasthebestyear-roundtiltsettings.

adjustedeach

month

This chart tells us thatwe require a solar arraywith a generation capacity ofbetween 288 watts and 411 watts, depending on the tilt of the solar panels.Comparedtoourearliercalculationsforgeneratingpowerthroughouttheyear,itismuchlower.Wehavejustsavedourselvesasignificantamountofmoney.Youcanalsoseethatduringthesummermonths, thesolarelectricsystemwillgenerate considerably more electricity than we will need to run our holidayhome. That is fine. Toomuch is better than not enough and it allows for theoccasionswhenalightisleftswitchedonoraTVisleftonstandby.

SolarpanelsandshadeThebiggestnegativeimpactonsolarenergyproductionisshade.Evenifonlyaverysmallamountofyoursolararrayisinshade,theimpactontheperformanceofyourwholesystemcanhaveaverybigeffect.Unlikesolar thermal (hotwater)systems, the lossofpower throughshading ismuchgreater than theamountof thepanel that is inshade.Withsolar thermalsystems, if 5% of the panel is in shade, you lose around 5% of the powerproduction.Dependingontheexactcircumstances,evenifonly5%ofaphotovoltaicsolarpanelisinshade,it ispossibletolose50–80%ofpowerproductionfromyourentiresolararray.Forthisreason,itishugelyimportantthatyoursolarenergysystemremainsoutof shade throughout the day. Sometimes this is not possible, and this requiressomeadditionaldesignworkinordertokeeptheeffectofshadeonyoursystemtoaminimum.Icovershadeinmuchmoredetail inAppendixA, includinganexplanationofwhy shade has such a big impact on energy production. For now, it is justimportanttoknowthatshadingcansignificantlyaffecttheamountofenergyyoucangetfromyoursolarenergysystem.

SolararraypowerpointefficienciesNowwe know the theoretical size of our solar panels.However,we have nottakenintoaccounttheefficienciesofthepanelsthemselvesortheefficienciesofthecontrollerorinverterthathandlesthem.Solarpanelsareratedontheir‘peakpoweroutput’.Peakpoweronasolarpanelinbrightsunlightisnormallygeneratedatbetween14and20volts.Thisvoltagecan go up and down quite significantly, depending on the amount of sunlightavailable.This swing in voltage gets much higher if you have multiple solar panelsconnectedtogetherinseries–orifyouareusingahigher-voltagesolarpanel.Itiscommonforasolararraywithfifteenortwentypanelsconnectedinseriestohavevoltageswingsofseveralhundredvoltswhenacloudobscuresthesunforafewseconds!Managing thisvoltage swingcanbedone inoneof twoways.The cheap andsimplemethod is to cut the voltagedown to a setting that the solar panel caneasilymaintain.Forinstance,asolarpanelratedat12voltswillusuallymaintainavoltagelevelofatleast14voltsduringdaylighthours.Achargecontrollerorinverterthatcutsthevoltagedowntothislevelwillthenalwaysbeabletousethispower.Thedisadvantageofthisapproachisthat,asyoucutthevoltage,thewattagedropswithit,meaningyoucanloseasignificantamountofenergy.Intermsoftheamountofenergyyoucancapture,asopposedtowhatthesolararraycollects, thismethodcanreducetheefficiencyofasolararraybyaround25%.Abetter solution is to use controllers and inverters that incorporateMaximumPower Point Tracking (MPPT). Maximum power point tracking adjusts thevoltagefromthesolararraytoprovidethecorrectvoltageforthebatteriesorfortheinverterinordertoremovethisinefficiency.Maximum power point trackers are typically 90–95% efficient. Over the pastthree years, the price ofMPPT controllers and inverters has dropped and theavailabilityhasincreasedtothepointwhereitisalmostalwaysworthbuyinganMPPT controller and inverter for all but the very smallest and simplest solarinstallations.Incidentally,youonlyneedanMPPTinverterforgrid-tiesystemswhereyouarepowering the inverter directly from the solar panels. You do not require anMPPTinverterifyouareplanningtoruntheinverterthroughabatterybank.

To take into account power point efficiencies, you need to divide yourcalculationby0.9ifyouplantouseaMPPTcontrollerorinverter,andby0.75ifyouplantouseanon-MPPTcontrollerorinverter:

NonMPPTcontroller/invertercalculation

MPPTcontroller/inverter

calculations

Flatsolarpanel

Solarpanelat38°tilt

Flatsolarpanel

Solar

panelat38°tilt

411watts÷0.75=

548wattsolarpanel

288watts÷0.75=

384wattsolarpanel

411

watts÷0.9=

456wattsolarpanel

288watts÷0.9=320wattsolarpanel

TheeffectsoftemperatureonsolarpanelsSolar panels will generate less power when exposed to high temperaturescompared to when they are in a cooler climate. Solar PV systems can oftengeneratemoreelectricityonadaywithacoolwindandahazysunthanwhenthesunisblazingandthetemperatureishigh.When solar panels are given a wattage rating, they are tested at 25°C (77°F)againsta1,000W/m²lightsource.Atacoolertemperature,thesolarpanelwillgeneratemoreelectricity,whilst at awarmer temperature the same solarpanelwillgenerateless.Assolarpanelsareexposedtothesun,theyheatup,mainlyduetotheinfraredradiation they are absorbing.As solar panels are dark, they can heat up quiteconsiderably.Inahotclimate,asolarpanelcanquiteeasilyheatupto80–90°C(160–175°F).Solar panel manufacturers provide information to show the effects oftemperatureontheirpanels.Calledatemperaturecoefficientofpower rating, itis shown as a percentage of total power reduction per 1°C increase intemperature.Typically,thisfigurewillbeintheregionof0.5%,whichmeansthatforevery1°Cincreaseintemperature,youwilllose0.5%efficiencyfromyoursolararray,whilstforevery1°Cdecreaseintemperatureyouwillimprovetheefficiencyofyoursolararrayby0.5%.Assumingatemperaturecoefficientofpowerratingof0.5%,thisis theimpactonperformancefora100Wsolarpanelatdifferenttemperatures:

5°c/

41°F

15°c/

59°F

25°c/

77°F

35°c/

95°F

45°c/

113°F

55°c/

131°F

Paneloutputfora100W

solarpanel

110W

105W

100W

95W

90W

85W

Percentagegain/loss

10%

5%

0%

-5%

-10%

-15%

InnorthernEuropeandCanada,hightemperatureisnotasignificantfactorwhendesigningasolarsystem.However,insouthernstatesofAmericaandinAfrica,India,AustraliaandtheMiddleEast,wheretemperaturesaresignificantlyabove25°C(77°F)formuchoftheyear,thetemperatureofthesolarpanelsmaybeanimportantfactorwhenplanningyoursystem.Ifyouaredesigningasystemforall-year-rounduse,theninallfairnessaslightdipinperformanceattheheightofsummerisprobablynotanissueforyou.Ifthat is the case, youdo not need to consider temperaturewithin the design ofyoursystemandyoucanskipthisinformation.If your ambient temperature is high during the times of year you need to getmaximumperformancefromyoursolarpanels,thenyouwillneedtoaccountfortemperatureinyourdesign.Youcanhelpreducethetemperatureofyoursolarpanelsbyensuringafreeflowofairbothaboveandbelowthepanels.Ifyouareplanningtomountyoursolarpanelsonaroof,makesurethereisagapofaround7–10cm(3–4")belowthepanels, to allow a flow of air around them. Alternatively, you can considermountingthepanelsonapole,whichwillalsoaidcooling.Fora rooftop installation, if theaverageair temperatureataparticular timeofyearis25°C/77°Forabove,multiplythistemperatureinCelsiusby1.4inordertogetalikelysolarpaneltemperature.Forapole-mountedinstallation,multiplyyour air temperature by 1.2 in order to calculate the likely solar paneltemperature. Then increase your wattage requirements by the percentage lossshowninthetemperaturecoefficientofpowerratingshownonyoursolarpanels,inordertoworkoutthewattageyouneedyoursolarpanelstogenerate.

TemperatureimpactonsolarperformanceinAustin,TexasduringthesummermonthsBywayofanexample,hereisatableforAustininTexas.Thisshowsaverageair temperatures for each month of the year, the estimated solar paneltemperatureforthehottestmonthsoftheyearandtheimpactontheperformanceonthesolararray,assumingatemperaturecoefficientofpowerratingof0.5%.

Jan

Feb

Mar

Apr

May

Averagemonthly

49°F10°C

53°F12°C

62°F16°C

70°F21°C

76°F24°C

temperature

Likelyroof-mounted

temperatureofsolararray

(Celsiusx1.4)

93°F34°C

Performance

impactforroof-mountedsolar:

-4½%

Likelypole-mounted

temperatureofsolararray

(Celsiusx1.2)

84°F29°C

Performanceimpactfor

pole-mountedsolar:

-2%

ThePerformance Impact calculations in rows 3 and 5 of the above table arecalculatedusingthefollowingformula:(EstimatedSolarPanelTemp°C–25°C)x(–TempCoefficientofPowerRating)So,forJuly,thecalculationforroof-mountedsolarwas(41°C–25°C)x(–0.5)=–8%Foraroundfivemonthsoftheyear,theambienttemperatureinAustinisgreaterthan25°C/77°F.During thesemonths, thehigher temperaturewillmean lowerpoweroutputfromasolararray.Ifyouaredesigningasystemthatmustoperateatmaximumefficiencyduring theheightofsummer,youwillneed to increasethe size of your solar array by the percentages shown, in order to handle thisperformancedecrease.Youcan find theaverageambientair temperature foryour locationbyvisitingTheWeatherChannelwebsiteatwww.weather.com.Thisexcellentsiteprovidesaveragemonthly temperatures for towns and cities across theworld, shown in

yourchoiceofFahrenheitorCelsius.Our example holiday home project is in the United Kingdom, where thetemperatureisbelow25°Cformostoftheyear.Inaddition,oursolardesignwillproducemorepower thanweneedduring thesummermonths.Asaresult,wecanignoretemperatureinourparticularproject.

WorkingoutanapproximatecostIt isworthstressingagainthat thesefiguresareonlyapproximateat thisstage.We have not yet taken into account the site itself and we are assuming thatshadingwillnotbeanissue.If you are planning to do the physical installation yourself, a solar electricsystemconsistingofsolararray,controllerandbatterycostsaround£4.00($6.20US)perwatt,+/–15%.Agrid-tiesystemischeapertoinstall thanastand-alonesystem,asyoudonotneed tobudget forbatteries.Youwill, however,needaqualifiedelectrician tocertify the system before use. In most countries, you will also need all thecomponents used in your solar installation to be certified as suitable for gridinstallation. If you are planning grid-tie, budget around £2.00–£3.00 ($3.10–$4.60US)perwatt,+/–15%.Forourholidayhomeinstallation,weneed320wattsofsolarelectricityifwetiltthesolarpanelstowardsthesun,or456wattsifwemountthepanelsflat.Ourroughestimatesuggestsa totalsystemcostofaround£1,280($1,970US),+/–15% for tilted panels, or £1,824 ($2,800 US) +/– 15% for a flat panelinstallation.If you remember, the cost to connect this holiday home to a conventionalelectricitysupplywas£4,500($7,200).Therefore, installingsolarenergyis thecheaperoptionforprovidingelectricityforourhome.

Whatifthefiguresdonotaddup?Insomeinstallations,youwillgettothisstageandfindoutthatasolarelectricsystemsimplyisunaffordable.Thisisnotuncommon.Iwasaskedtocalculatetheviabilityforusing100%solarenergyatanindustrialunitonce,andcameupwithaballparkfigureof£33½m(around$54m)!Whenthishappens,youcandooneoftwothings:walkaway,orgobacktoyouroriginalscopeandseewhatcanbechanged.The best thing to do is go back to the original power analysis and see whatsavingsyoucanmake.Lookattheefficienciesoftheequipmentyouareusingandseeifyoucanmakesavingsbyusinglower-energyequipmentorchangingthewayequipmentisused.Ifyouare absolutelydetermined to implement a solar electric system, there isusually away to do it.However, youmayneed to be ruthless as towhat you

havetoleaveout.Intheexampleoftheindustrialunit,theunderlyingrequirementwastoprovideemergency lightingandpower for a clusterof computer servers if therewasapower cut. The cost for implementing this system was around £32,500($52,000): comparable in cost to installing andmaintaining on-site emergencygeneratorsandUPSequipment.

WorkingoutdimensionsNowweknowthecapacityofthesolarpanels,wecanworkoutanapproximatesizeofoursolararray.Thisisextremelyusefulinformationtoknowbeforewecarryoutoursitesurvey:thesolarpanelshavetogosomewhere.Weneedtobeabletofindenoughsuitablespaceforthemwheretheywillreceiveuninterruptedsunshineinasafelocation.Therearetwomaintechnologiesofsolarpanelsonthemarket:amorphousandcrystallinesolarpanels.Iwillexplainthecharacteristicsandtheadvantagesanddisadvantagesofeach,lateron.Forthepurposesofworkingouthowmuchspaceyou’regoingtoneedtofitthesolar panels, you need to know that a 1m² (approximately 9.9 square feet)amorphous solar panel generates in the region of 60 watts, whilst a 1m²crystallinesolarpanelgeneratesintheregionof160watts.Therefore,forourholidayhome,wearelookingforalocationwherewecanfitbetween5and7.6m² (49–75 square feet)of amorphous solarpanelsor2–3m²(20–29squarefeet)ofcrystallinesolarpanels.

Inconclusion Bycalculatingtheamountofsolarenergytheoreticallyavailableatoursite,wecancalculateballparkcostsforoursolarelectricsystem Therearevariousinefficienciesthatmustbeconsideredwhenplanningyour system. If you do not take these into account, your systemmaynotgenerateenoughpower Itisnotunusualfortheseballparkcoststobefartooexpensiveonyourfirstattempt.Theanswer is to lookcloselyatyouroriginalscopeandseewhatcanbecutinordertoproduceacost-effectivesolution Aswell asworkingout ballpark costs, these calculations alsohelpuswork out the approximate dimensions of the solar array. This means weknow howmuch spacewe need to findwhenwe are carrying out a sitesurvey

SurveyingYourSite

Thesite survey isoneof themost importantaspectsofdesigninga successfulsolarsystem.Itwillidentifywhetherornotyoursiteissuitableforsolar.Ifitis,thesurveyidentifiestheidealpositiontoinstallyoursystem,ensuringthatyougetthebestvalueformoneyandthebestpossibleperformance.

WhatwewanttoachieveForasolarelectricsystemtoworkwell,weneedthesitesurveytoanswertwoquestions:

Is there anywhere on the site that is suitable for positioningmy solararray? Do nearby obstacles such as trees and buildings shade out toomuchsunlight?

Thefirstquestionmightatfirstsounddaftbut,dependingonyourproject,itcanmakethedifferencebetweenasolarenergysystembeingviableornot.Byansweringthesecondquestion,youcanidentifyhowmuchoftheavailablesunlightyouwillbeabletocapture.It isvitallyimportantthatyouanswerthisquestion.Thenumberonereasonforsolarenergyfailingtoreachexpectationsisobstaclesblockingoutsunlight,whichdramaticallyreducestheefficiencyofthesystem.Toanswerthissecondquestion,weneedtobeabletoplotthepositionofthesunthroughtheskyatdifferenttimesoftheyear.Duringthewinter,thesunismuchlowerintheskythanit isduringthesummermonths.It is important toensurethat the solar array can receive direct sunlight throughout the day during thewinter.

WhatyouwillneedYouwillneedacompass,aprotractor,aspiritlevelandatapemeasure.Inevitablyaladderisrequiredifyouareplanningtomountthesolararrayonaroof.Acameracanalsobeextremelyuseful forphotographing thesite. Ifyouhavean iPhoneor anAndroidcellphone,youcanalsodownload somecheapsoftwarethatwillhelpyouidentifythepathofthesunacrosstheskyandassistwithobstacleanalysis.Ialsofindituseful togetsomelargecardboardboxes.Openthemoutandcutthemintotheroughsizeofyourproposedsolararray.Thiscanhelpyouwhenfinding a location for your solar panels. It is far easier to envisage what theinstallationwill look like and it can help highlight any installation issues thatyoumightotherwisehavemissed.Ifyouhaveneverdoneasolarsitesurveybefore,itdoeshelpifyouvisitthesiteonasunnyday.

Onceyouhavemoreexperiencewithdoingsolar site surveys,youwill find itdoesnot actuallymakemuchdifferencewhetheryoudoyour site surveyonasunnydayoranovercastday.Aspartof thesitesurvey,wemanuallyplot thesun’spositionacrossthesky,soonceyouhavemoreexperience,sunnyweatheractuallymakeslittledifferencetothequalityofthesurvey.

FirstimpressionsWhenyoufirstarriveonthesite,thefirstthingtocheckisthatthelayoutofthesitegivesitaccesstosunlight.Wewilluseamorescientificapproachforcheckingforshadelater,butaquicklookfirstoftenhighlightsproblemswithoutneedingtocarryoutamorein-depthsurvey.IfyouareintheNorthernHemisphere,lookfromeast,throughsouthandtothewest to ensure there are no obvious obstructions that can block the sunshine,such as trees andother buildings. If you are in theSouthernHemisphere, youneed to check from east, through north to west for obstructions. If you arestandingontheequator,thesunpassesoverhead,soonlyobstructionsintheeastandwestareimportant.Beverycarefulnottolookdirectlyatthesun,evenforafewmoments,whilstyouarecarryingout thissurvey.Even in themiddleofwinter, retinaburncancausepermanentdamagetoyoureyesight.Look around the site and identify all the different options for positioning thesolar array. If you are considering mounting your solar array on a roof,remember that the world looks a very different place from a rooftop, andobstructionsthatareaproblemstandingonthegroundlookverydifferentwhenyouareatroofheight.

DrawingaroughsketchofthesiteIt canbehelpful todrawupa rough sketchof the site. It doesnothave tobeaccurate, but it can be a useful tool to have, both during the site survey andafterwardswhenyouaredesigningyoursystem.Includeallpropertiesandtrees thatareclosetoyoursiteandnot just thoseonyourland.Includetreesthataretoosmalltoworryaboutnow,butmaybecomeaprobleminafewyears’time.Alsomakeanoteofwhichwayisnorth.

PositioningthesolararrayYournexttaskistoidentifythebestlocationtopositionyoursolararray.Whilstyoumayalreadyhaveagoodideawhereyouwanttoinstallyoursolarpanels,itisalwaysagoodideatoconsiderallthedifferentoptionsavailabletoyou.As we discovered in the last chapter, solar arrays perform at their best whentiltedtowardsthesun.If you are planning to install solar energy for a building, then the roof of thebuildingcanoftenbeasuitableplacetoinstallthesolararray.Thisiseffectivewheretheroofissouth-facingorwheretheroofisflatandyoucanfitthepanelsusingangledmountings.Otheralternativesaretomountsolarpanelsonawall.Thiscanworkwellwithlonger,slimmerpanels thatcanbemountedatananglewithoutprotruding toofaroutfromthewallitself.Alternatively,solarpanelscanbeground-mountedormountedonapole.Whenconsideringapositionforyoursolararray,youneedtoconsiderhoweasyitisgoingtobetocleanthesolarpanels.Solarpanelsdonotneedtobespotless,butdirtandgrimewillreducetheefficiencyofyoursolarsystemovertime,sowhile you are looking atmounting solutions it is definitelyworth consideringhowyoucanaccessyourpanelstogivethemaquickwasheveryfewmonths.

Roof-mountingIfyouareplanningtomountyoursolararrayonaroof,youneedtogainaccesstotherooftocheckitssuitability.Useacompasstocheckthedirectionoftheroof.Ifitisnotdirectlyfacingsouth,youmayneed toconstructanangledsupport inorder toget thepanelsangledcorrectly.You will also need to find out the pitch of the roof. Professionals use a toolcalled a Roof Angle Finder to calculate this. Roof angle finders (also calledMagnetic Polycast Protractors) are low-cost tools available from builders’merchants.Youpresstheanglefinderupagainsttheraftersunderneaththeroofandtheanglefinderwillshowtheangleindegrees.Alternatively,youcancalculatetheangleusingaprotractoratthebaseofaroofrafterunderneaththeroofitself.Solar panels in themselves are not heavy: 15–20kilograms (33–44pounds) at

most.Yetwhenmultiple panels are combinedwith a frame, especially if thatframeisangled,theoverallweightcanbecomequitesignificant.Checkthestructureoftheroof.Ensurethatitisstrongenoughtotakethesolararrayandtoascertainwhatfixingsyouwillneed.Itisdifficulttoprovidegeneraladviceonroofstructuresandfixings.Therearesomanydifferentroofdesignsitisnotpossibleformetoprovidemuchusefulinformationonthissubject.Ifyouarenotcertainaboutthesuitabilityofyourroof,askabuilderoranarchitecttoassessyourroofforyou.Roof-mountingkitsareavailable fromsolarpanelsuppliers.Alternatively,youcanmakeyourown.Ifitdoesnotcompromiseyoursolardesign,itcanbequiteusefultomountyoursolarpanelsatthelowestpartoftheroof.Thiscanmakeitconsiderablyeasiertokeepthepanelsclean:mostwindowcleanerswillhappilywasheasily-accessiblesolarpanelsiftheyaresituatedatthebottomoftheroof,andtelescopicwindowcleaner kits are available to reach solar panels at the lower end of a roofstructure.Measureandrecordtheoverallroof-spaceavailableforasolararray.Itisalsoagoodideatousethecardboardcut-outsyoumadeearlierandplacetheseontheroof to give a ‘look and feel’ for the installation and help you identify anyinstallationissuesyoumayhavewithpositioningandmountingthesolararray.

Ground-mountingIfyouwanttomountyoursolararrayontheground,youwillneedaframeontowhichyoucanmountyoursolarpanels.Mostsolarpanelsupplierscansupplysuitableframesoryoucanfabricateyourownonsite.There are benefits for a ground-mounted solar array: you can easily keep thepanelscleanandyoucanuseaframetochangetheangleofthearrayatdifferenttimesofyeartotracktheheightofthesuninthesky.Takeanoteofgroundconditions,asyouwillneedtobuildfoundationsforyourframe.Incidentally,youcanbuyground-mountedsolar frames thatcanalsomove thepanel to track thesunacross theskyduring theday.TheseSolarTrackerscanincreasetheamountofsunlightcapturedbyaround15–20%inwinterandupto55%insummer.Unfortunately,atpresent,commercialsolartrackersareexpensive.Unlessspaceisatanabsolutepremium,youwouldbebettertospendyourmoneyonabigger

solararray.However, for a keenDIY engineer who likes the idea of a challenge, a solartrackerthatmovesthearraytofacethesunasitmovesacrosstheskyduringthedaycouldbeausefulandinterestingprojecttodo.Therearevarioussitesontheinternet, suchas instructables.com,where keenhobbyists have built their ownsolartrackersandprovideinstructionsonhowtomakethem.

Pole-mountingAnotheroptionformountingasolarpanelistoaffixoneonapole.Becauseofthe weight and size of the solar panel, you will need an extremely goodfoundationandaheavyweightpole,inordertowithstandthewind.Youcanmountupto600-wattarraysusingsingle-polemountings.Largerarrayscanbepole-mountedusingframesconstructedusingtwoorfourpoles.Most suppliers of solar panels and associated equipment can provide suitablepoles.

SplittingthesolararrayintoseveralsmallerarraysIt may be that when you get to the site, you find that there is no one spaceavailablethatwillallowyoutoinstallallthesolarpanelsyouneed.Ifthisisthecase,itispossibletosplityoursinglesolararrayintoseveralsmallerarrays.Thismeans,forinstance,thatyoucouldhavetwosetsofpanelsmountedondifferentroofpitches,orsomemountedonaroofandsomefromapole.Ifyoudo this,youarecreating twoseparate solar energy systems,whichyouthen have to link together. For a grid-tie system, you would require either amicro-invertersystemoraninverterthatcanacceptinputsfrommorethanonesolararray.Forastand-alonesystem,youwouldrequireabatterycontrollerforeachseparatesolararray.

IdentifyingthepathofthesunacrosstheskyOnceyouhaveidentifiedasuitablepositionforyoursolararray,itistimetobealittlemorescientificinensuringtherearenoobstructionsthatwillblocksunlightatdifferenttimesoftheday,oratcertaintimesoftheyear.The path of the sun across the sky changes throughout the year. This is whycarryingoutasitesurveyissoimportant:youcannotjustchecktoseewherethesun is shining today. The height and position of the sun constantly changesthroughouttheyear.Eachyear,therearetwodaysintheyearwhenthedayisexactlytwelvehourslong.Thesetwodaysare21Marchand21September,thesolarequinoxes.Onthese equinoxes the sun rises due east of the equator and sets duewest of theequator.Atsolarnoonontheequinox,exactlysixhoursafterthesunhasrisen,theangleofthesunis90°minusthelocallatitude.In theNorthernHemisphere (i.e. north of the equator), the longest day of theyearis21Juneandtheshortestdayoftheyearis21December.Thesetwodaysarethesummerandwintersolsticesrespectively.On the summer solstice, the angle of the sun is 23.5° higher than it is on theequinox, whilst on the winter solstice the angle is 23.5° lower than on theequinox.Thesetwoextremesareduetothetiltoftheearth,relativetoitsorbitaroundthesun. In theNorthernHemisphere, the summer solstice occurswhen theNorthPoleistiltedtowardsthesun,andthewintersolsticeoccurswhentheNorthPoleistiltedawayfromthesun.

Figure4:ThischartshowsthedifferentpathsofthesunfromsunrisetosunsetatdifferenttimesoftheyearfromtheNorthernHemisphere.The

intersectionbetweenN,S,EandWisyourlocation.WewilltakeLondonintheUnitedKingdomasanexample.London’slatitudeis51°.Ontheequinox,theangleofthesunatnoonwillbe39°(90°–51°).Onthesummersolstice,theanglewillbe62.5°(39°+23.5°)andonthewintersolstice,itwillbe15.5°(39°–23.5°).

Londoninmid-summer,comparedtoLondoninmid-winterAswellasthesolarirradiancefigures,AppendixBshowstheheightofthesunintheskyatnoonatdifferenttimesoftheyearandtheoptimumtiltsforsolarpanelsfortheUnitedStates,Canada,Australia,NewZealand,UnitedKingdomandIreland.

For more detailed information on sun heights on a monthly basis, or forinformation for other countries, visit www.SolarElectricityHandbook.com andfollowthelinktothesolarpanelanglecalculator.

ShadingAsmentionedinapreviouschapter,shadingcanhaveaverysignificantimpactontheperformanceofyoursolarenergysystem.Evenatinyamountofshadingcan have a huge impact on the amount of energy that your system is able togenerate. Therefore, it is important that your solar array remains shade-freewheneverpossible.You can carry out this analysis in various ways. You can use a professionalobstacleanalysistool,youcandownloadanobstacleanalysistoolontoyourcellphoneoryoucanusepaperandpenciltocomeupwitharoughplan.

ProfessionaltoolsforobstacleanalysisIn the past, a product called aSolarPathfinderwas one of the best tools youcouldget.Thiswasaplasticunitwithananglechartmountedonthetop.Aglassdomewas then placed on top of the chart. Youwouldmount the unit onto atripodat thedesired location.Obstacleswere reflected in theglassbubbleandthis would allow you to manually plot the obstacles on the chart and thenmanuallyworkoutyourshadingissues.TheSolarPathfinderissurprisinglyeffective,asitcanbeeasilymovedaroundin order to find the best location for solar panels. Many professional solarinstallers still use a Solar Pathfinder for quick checks, despite also using themoreexpensiveandadvancedelectronicequipment toprovideamoredetailedanalysis.SomesolarsupplierscanrentyouaSolarPathfinderforasmalldailyorweeklyfee and can do the manual calculations for you once you have plotted theobstacles.TodaythereareelectronicsystemsthatuseGPS,tiltswitchesandaccelerometerstodothisworkelectronically.Theyareexpensivetobuyorrentonadailybasis.Theydoprovide extremely comprehensive solar analysis, however, and if youplan to take up solar installations professionally, they are a worthwhileinvestment.The best known is the Asset from Wiley Electronics and the SunEye fromSolmetric.MypersonalpreferenceisSunEye,asIfindtheunitsimpler,butbothproductsdoasimilarjob.

Cellphoneapplications

Whilsttheyareverygood,thesetoolsareoverkillforsmallersolarinstallationsandareoftenverycomplicatedtouse.Thankfully,modernsmartphonesprovidethe processing power and functionality to do a similar job. A few companieshave now developed solar shade analysis software to run on these mobilephones.Theseusethephone’sbuilt-inGPS,compass,accelerometerandcameratorecordacompleteshadeanalysisinamatterofafewmoments.If you have an iPhone, you can download a product called Solmetric IPV.Costing $29.99, this application handles your obstacle tracking, automaticallyprovidingchartsshowingyourshadinganalysisthroughouttheyear.Thedetailof reporting isnotasgreatassomeof theotherelectronic tools,butmoreandmoreprofessionalsarenowusingthissoftware.Itprovidesmostofthefunctionsthatyougetwithamoreexpensivesystem,butinapackagethatiseasiertouseandfarcheapertobuy.You can find outmore about Solmetric IPV fromwww.solmetric.com and thesoftwarecanbedownloadedfromtheiTuneswebsite.Alternatively, there is an Android phone download called Solar Shading,produced by Comoving Magnetics. Costing $15 on the Android Market, thisapplicationprovidesyouwithacompleteshadinganalysisthroughouttheyear,presentingtheinformationineasy-to-readcharts.

Above:Examplesofon-screenreportsfromSolmetricIPVrunningontheiPhone.

Below:Screen-shotsfromSolarShading,runningonAndroidphones.

UsingpaperandpencilFinally, if you do not have access to a professional tool or a suitablemobilephone, you can use the old-fashionedmethod of paper and pencil. Go to thepositionwhereyouareplanningtoputyoursolararrayandfindduesouthwithacompass.Lookingfromthesameheightasyourproposedlocation,andworkingfromeast towest,checktherearenoobstacles,suchas treesorbuildings, thatcanshadethesunatdifferent timesof thedayorwhenthesunisat its lowestwinterheight.To do this, you will need to find out what position the sun rises and sets atdifferent timesof theyear.Thankfully, this iseasy tofindout.Thesolaranglecalculator which you can find atwww.SolarElectricityHandbook.com includesthisinformation,makingiteasytoidentifythepathofthesunatthesedifferenttimesoftheyear.Forasimpleone-offsitesurvey,theeasiestwaytoidentifypotentialobstructionsis touseaprotractorandpencil.Tapethepencil to thecentreof theprotractorwhereall the linesmeet, insuchaway that theotherendof thepencilcanbemoved across the protractor.You can use this protractor to check the field ofview,usingthepencilasan‘aimer’toshowtheangleofthesunintheskybasedondifferenttimesoftheyear.

Beverycarefulnottolookdirectlyatthesun,evenforafewmoments,whilstyouarecarryingout thissurvey.Even in themiddleofwinter, retinaburncancausepermanentdamagetoyoureyesight.Yoursurveyneedstoensuretherearenoobstaclesinthedepthsofwinter,whenthesunisonlyafewdegreesupinthesky.In thecaseofLondon,on the21December thesunwillbeonly15½°highatmidday(atduesouth)andlowerthanthatfortherestoftheday.Ifthereareobstaclesthatareblockingvisibilityofthesun,findanotherlocation.Alternatively, findotherways around theobstacle, such asmounting the solararrayhigheruponaframe.Ofcourse,ifyoudonotneedyoursolarsystemtoproducemuchpowerduringthe winter months this may not be a problem for you. However, make sureobstaclesdonotshadeyoursystemforthetimesofyearwhenyouneedpower.

FutureproofyoursystemYoudoneedtoconsiderthefuturewheninstallingasolarelectricsystem.Thesystemwillhavealifetimeofatleast20years,soasfaraspossibleyouneedtoensurethatthesystemwillbeeffectiveforthatlengthoftime.When scanning thehorizon, take into account that trees andhedgeswill growduringthelifetimeofthesystem.Asmallspruceinanearbygardencouldgrowintoamonsterinthespaceofafewyears,andifthatisarisk,itisbesttoknowaboutitnow,ratherthanhaveanastysurpriseafewyearsdowntheline.Seeifthereisanyplannedbuildingworknearbythatmayovershadowyoursiteandtrytoassessthelikelihoodoffuturebuildingworkthatcouldhaveanimpactonshading.Itisalsoworthfindingoutiffogorheavymistisaproblematcertaintimesoftheyear.Theefficiencyofyoursolararraywillbecompromisedifthesitehasregularproblemswithheavymist.

Whatifthereareshadingobstructions?Ifthereareobstructionsthatshadeyourproposedlocation,andtherearenootherlocations that are suitable for solar,youneed toascertainatwhatpointduringthedaytheobstructionsoccur.Anything due south (or due north in the Southern Hemisphere) is a major

problem,asthiswillbethepositionofthesunwhentheintensityofthesunlightis at its highest.Core power generation occurs between 9am and 3pm. If youhaveshadingeitherbefore9amorafter3pm,youwilllosearound20%ofyourcapability in the summer, or 40%of your capability if you have shading bothbefore9amandafter3pm.During thewinter, thedifference isnotsogreat. Ifyouhaveshadingbefore

9amorafter3pmduringthewinter,youwillprobablyloseonlyaround5–10%ofyourgeneratingcapabilitiesduringthistime.If you have shading during your core power generation times, you need to

give serious thought as to whether you should continue with a solarimplementation: the performance of your solar system will be severelycompromised.Ifyoudohavesignificantshadingissuesandyouwant tofindout theexact

impactoftheseobstructionsonyoursolararray,youaregoingtoneedtouseaprofessional tool for obstacle analysis. The electronic tools will be able to

quantify exactly what the impact of the shade is on your system at differenttimesoftheyear.Ifobstructionsoccurforpartoftheday,suchasduringthemorningorduringtheafternoon,youcanconsiderincreasingthenumberofsolarpanelsyoupurchaseandanglingthemawayfromtheobstructioninordertoincreasetheircollectionofsunlightduringtheunobstructedpartsoftheday.Alternatively,youmaybebetteroff investigatingotherenergyoptions,such

aswindpowerorfuelcells,eitherinsteadofusingsolarorincombinationwithasmallersolarelectricsystem.AppendixAlooksattheissueofshadinginalotmoredetailandexplainshow

youcanworkaroundobstructionissues.Itisalwaysbesttoavoidshadeasfaraspossible, because workarounds can become costly. However, if you cannoteliminateshadealtogether,itneednotwriteoffsolarasasolutionthatcanworkforyou.

Positioningbatteries,controllersandinvertersYou need to identify a suitable location for batteries. This could be a roomwithin a building, in a garage or garden shed, or in a weatherproof batteryhousing.Itisimportanttotrytokeepallthehardwareclosetogether,inordertokeepthecable lengths as short as possible. By ‘hardware’, I am referring to the solararrayitself,batteries,controllerandinverter.Forthebatteries,inverterandcontroller,youarelookingforalocationthatfitsthefollowingcriteria:

Water-andweatherproofNotaffectedbydirectsunlightInsulatedtoprotectagainstextremesoftemperatureFacilitiestoventilategasesfromthebatteriesProtectedfromsourcesofignitionAwayfromchildren,petsandrodents

Lead acid batteries give off very small quantities of hydrogenwhen charging.Hydrogenisexplosive.Youmustensurethat,whereveryourbatteriesarestored,theareareceivesadequateexternalventilationtoensurethesegasescannotbuildup.Because of the extremely high potential currents involved with lead acidbatteries,thebatteriesmustbeinasecureareaawayfromchildrenandpets.Foralloftheabovereasons,batteriesareoftenmountedonheavy-dutyracking,which is then made secure using an open-mesh cage. Alternatively, you canpurchasepurpose-builtbatteryenclosuresfromsolarorbatterysuppliers.Controllersandinvertersneedtobemountedasclosetothebatteriesaspossible.Theseareoftenwall-mounted,butcanalsobemountedtoracking.Large inverters can be extremely heavy, so if you are planning towall-mountone,makesurethatthewallisload-bearingandabletotaketheweight.

CablingWhile you are on site, consider likely routes for cables, especially the heavy-duty cables that link the solar array, controller, batteries and inverter together.Try to keep cable lengths as short as possible, as longer cables mean lowerefficiency. Measure the lengths of these cables so that you can ascertain thecorrectspecificationforcableswhenyoustartplanningtheinstallation.

SitesurveyfortheholidayhomeBack to our holiday home example: based on our previous calculations, ourholiday home needs a solar array capable of generating 320 watt-hours ofenergy, if we angle the array towards the sun. This solar array will take upapproximately2m²(18sq.ft)ofsurfacearea.Oursitesurveyfortheholidayhomeshowedthemainpitchoftheroofisfacingeasttowest.Thisisnotidealforasolararray.Theeasternsideoftheroofhasachimney.Thereisshadefromatalltreethatobscurespartofthewest-facingpartoftheroof.Thereisnospaceonthegableendoftherooftofittherequiredsolarpanels.

Mapoftheholidayhome,identifyinglikelyobstaclesandasuitablepositionforthesolararray

Anoldshedclosetothehousehasasouth-facingroof,butonlya20°pitch.Atree shades the shed for most of the mornings for nine months of the year.Furthermore, the condition of the shed means that it would need significant

remedialworkshouldwedecidetouseit.Thereisafarmtotheeastofthehouse,withalargebarnandanumberoftreesborderingthehouse,thetallestofwhichisapproximately30feet(10m)tall.Oneofthesetreesprovidesshadetotheshedandpartoftherearofthehouseduringthewinter,andmayprovidemoreshadeduringtherestoftheyearifitcontinuestogrow.Thegardenissouth-facingandreceivessunlightthroughouttheyear.We decide to install the solar array in the rear garden, constructing a suitable1.2m(4feet)tallgardenstorewithasouth-facingpitchedroofofapproximately52° (allowingus to tilt the solararrayat38° fromvertical forbestyear-roundsunshine).Oursolarhousewillhold thebatteriesandcontrollerandwillhaveadequateventilationtoensurethatthesmallamountsofhydrogengeneratedbythebatteriescanescape.Bybuildingourownstructure,wecaninstallthesolararrayattheoptimumtilttocaptureasmuchsunlightaspossible.Thismeansoursolararrayiscompactandkeepsourcoststoaminimum.The solar house will be located around 10m (33 feet) from the house andshieldedfromthehousebyanewshrubbery.The cable lengths between the solar array and the solar controller areapproximately2m(6½feet).Thecable lengthbetweenthesolarcontrollerandthebatteries is less than1m(3feet).Thecable lengthbetweenthesolarhouseandthehomeis12m(40feet).Thereisafurther10m(33feet)ofcablinginsidethehouse.These longer cable lengths are not ideal. Cable runs should be as short aspossibleinordertoreducepowerlossesthroughthecable.However,wecannotposition the solar array any nearer to the house.Wewill have to address thisparticularproblemthroughourdesign.

Inconclusion There isa lot todoonasitesurvey.It is important.Spendtime;get itright.Drawingamapandtakingphotographscanhelpwiththesitesurveyandareinvaluableforthenextstage,whenwestartdesigningournewsystem.Solarpanelscanberoof-mounted,mountedwithaframeonthegroundoronapole.Onceyouhaveidentifiedalocationforthepanels,checkforobstructionsthatwillshadethepanelsthroughouttheyear. These obstructions are most likely to be an issue during the wintermonths,whensolarenergyisatapremium.Identifyasuitablespaceforbatteries,controllerandinverter.Planthecablerunsandthemeasurethelengthoftherequiredcables.Cablesshouldbeasshortaspossible,inordertoreducethevoltagelossesthroughthesystem.Iflongcablelengthsarenecessitatedbythepositioningof the solar array,wemay need to run our system at a higher voltage tocompensate.

UnderstandingtheComponents

Onceyouhavecompletedyour site survey,youknowall the facts:howmuchpoweryouneedtogenerate,thesuitabilityofyoursiteandapproximatelyhowmuchitisgoingtocostyou.Now you need to look at the different technologies and products that areavailable,toseewhatbestsuitsyouandyourapplication.Your choice of components and the design of your system will depend onwhether you are designing a stand-alone system (which also includes gridfallbackandgrid failover systems), or agrid-tie system that exports energy tothegrid.Becausetherearedifferencesinthedesignofstand-aloneandgrid-tiesystems,Ihavesplitthissectionintofourchapters.Thischapterlooksatcomponentsthatarecommontobothgrid-tiesystemsandstand-alonesystems.Thenextchapterlooks specifically at what you require for grid-tie systems. The third chapterlooksspecificallyatstand-alonesystemsandsystemsthatincorporatetheirownbatterystore,whilstthefourthchapterlooksatthecomponentcertificationandregulations that you need to take into account when selecting solar energyequipment.

HowtousethesechaptersThese next three chapters will go into much more detail about the differentoptionsavailabletoyou.Thereisabewilderingchoiceofsolarpanels,batteries,controllers,invertersandcables.Thesechapters explain the technology in a lotmoredetail, soyoucangoandtalksensiblytosuppliersandunderstandwhattheyaresaying.

CommoncomponentsforallsystemsCore to all solar energy systems are the solar panels themselves. Most solarpanelscanbeusedforeithergrid-tieorstand-aloneuse,andalthoughrecentlysome manufacturers have released higher-voltage solar panels designedspecifically for grid-tie applications, the criteria for choosing one solar paneloveranotherremainthesame.

SolarpanelsTherearethreedifferenttechnologiesusedforproducingsolarpanels.Eachhasitsownsetofbenefitsanddisadvantages.For thepurposeof thishandbook,Iamignoringtheexpensivesolarcellsusedonsatellitesandinresearchlaboratoriesandfocusingonthephotovoltaicpanelsthatareavailablecommerciallyatreasonablecosttoday.

AmorphoussolarpanelsThe cheapest solar technology is amorphous solar panels, also known as thin-filmsolarpanels.Thesepanelshavehadabadreputationinthepast,withpoorproductreliabilityandquestionable lifespan.Thishasoftenbeendownto thechemistriesused inolder designs of panel breaking down under extremes of temperature over aperiodofafewyears,orthepoorqualityofmaterialsusedintheproductionofcheappanels.Thankfully, this technology hasmatured significantly over the past five yearsand amorphous solar is now regarded as being highly reliable, with somesignificantbenefitsover traditional solarpanels.Bignamemanufacturers suchasMitsubishi,SanyoandSharpnowmanufacturehigh-qualityamorphoussolarpanels, along with some exceptionally good specialist manufacturers such asSolar Frontier and Uni-Solar. Some manufacturers now even offer a ten-ortwenty-yearwarrantyontheiramorphouspanels.On paper, amorphous solar panels are the least-efficient panels available,typicallyconvertingaround6–8%ofavailablesunlighttoelectricity.Thismeansthat you need twice as much space available for installing amorphous solarpanelscomparedtocrystallinepanels.However,amorphouspanelsaregoodatgeneratingpowerevenonovercastandextremelydulldays.Ingeneral, theyarealsofarbetter inextremetemperatureconditions,withsignificantly lesspower lossathigher temperatures thanothersolarpaneltechnologies.Unlikeothersolarpaneltechnologies,amorphoussolarpanelsprovideexcellentperformance even when partially shaded. Whilst a best-case scenario is toeliminateshadingwheneverandwhereverpossible,amorphouspanelscontinuetooperateatahighlevelofefficiencyevenifpartofthearrayisinshade.Amorphous panels can also be manufactured into a shape or mounted on a

curvedsurface.Theycanbemadetobehard-wearingenoughtobefittedontosurfaces that can be walked on. A few solar manufacturers have startedmanufacturingamorphoussolarrooftiles(orshingles),sothatnew-buildhousescanincorporatesolarintothestructureoftheroof.This combination makes amorphous panels suitable for integration intoconsumerproductssuchasmobilephonesandlaptopcomputers,andformobileproductssuchas theroofofanRVorcaravan,where themanufacturerhasnocontroloverwheretheproductsareplacedorhowtheyareused.Amorphous panels are the cheapest panels to manufacture and a number ofmanufacturersarenowscreen-printinglow-costamorphoussolarfilms.Overthepastthreeyears,amorphoussolarpanelcostshavedroppedbyaround30%eachyear.Theyareexpectedtodroptoaroundhalftheircurrent(2012)costby2015.Because of their lower efficiency, an amorphous solar panel has to be muchlarger than the equivalent polycrystalline solar panel. As a result, amorphoussolarpanelscanonlybeusedeitherwherethereisnosizerestrictiononthesolararrayorwheretheoverallpowerrequirementisverylow.Intermsofenvironmentalimpact,amorphouspanelstendtohaveamuchlowercarbonfootprintatpointofproduction,comparedtoothersolarpanels.Atypicalcarbonpaybackforanamorphoussolarpanelwouldbein theregionof12–30months.Most amorphous solar panels have comparatively low power outputs. Thesepanelscanworkwellforsmallerinstallationsofuptoaround300-wattoutputs,butnotsowellforlargerinstallations:largernumbersofpanelswillberequiredandtheadditionalexpenseinmountingandwiringtheseadditionalpanelsstartstooutweightheircostadvantage.Consequently, amorphous solar panels are often more suited to OEMapplications,asanenergysourcebuiltintoamanufacturedproduct,orforlarge-scale commercial installations where the panels are incorporated into thestructureofaroof-spaceonanewbuild.Some of themost exciting advances in solar technologies over the past threeyears have come from amorphous technology. Products as diverse as mobilephones, laptop computers, clothing and roofing materials have all hadamorphous solar panels built into them. An exciting technology, amorphoussolarisgoingtogetbetterandbetteroverthecomingyears.

Polycrystallinesolarpanels

Polycrystallinesolarpanelsaremadefrommultiplesolarcells,eachmadefromwafers of silicon crystals. They are far more efficient than amorphous solarpanelsindirectsunlight,withefficiencylevelsof13–18%.Consequently, polycrystalline solar panels are often around one third of thephysicalsizeofanequivalentamorphouspanel,whichcanmakethemeasiertofitinmanyinstallations.Polycrystallinesolarpanels typicallyhavea lifeexpectancyofabout25years.Thiscanoftenbeexceeded:commercial solarpanelsonlybecameavailable inthe late 1970s and early 1980s and many of these panels are still perfectlyfunctionalandinusetothisday.Themanufacturingprocessforpolycrystallinesolarpanelsiscomplicated.Asaresult,polycrystallinesolarpanelsareexpensivetopurchase,oftencosting20–30% more than amorphous solar panels. The environmental impact ofproductionisalsohigherthanamorphouspanels,withatypicalcarbonpaybackof3–5years.Pricesforpolycrystallinesolarpanelsaredropping,thankstoboththeincreaseinmanufacturingcapacityoverthepastfewyearsandtheincreasingpopularityforlargerscreentelevisions,whichusethesamespecificationglass.Forthepastfive years, prices have been dropping by around 25% per year. They willundoubtedly continue to reduce in price as the cost of amorphous solartechnologycontinuestodrop.

MonocrystallinesolarpanelsMonocrystalline solar panels aremade frommultiple smaller solar cells, eachmade froma singlewaferof siliconcrystal.These are themost efficient solarpanelsavailabletoday,withefficiencylevelsof15–24%.Monocrystalline solar panels have the same characteristics as polycrystallinesolarpanels.Becauseoftheirefficiencies,theyarethesmallestsolarpanels(perwatt)available.Monocrystallinesolarpanelsarethemostexpensivesolarpanelstomanufactureand therefore to buy. They typically cost 35–50% more than the equivalentpolycrystallinesolarpanels.

Whichsolarpaneltechnologyisbest?For most applications, polycrystalline panels offer the best solution, withreasonablevalueformoneyandacompactsize.

Amorphouspanelscanbeagoodchoiceforsmallerinstallationswherespaceisnot an issue. They are usually not practical for generating more than a fewhundred watts of power because of their overall size, unless you have anextremelylargeareathatyoucancoverwithsolarpanels.

WhattolookforwhenchoosingasolarpanelNotallsolarpanelsarecreatedequal,andit isworthbuyingaqualitybrandedproductoveranunbrandedone.Cheaper,unbrandedsolarpanelsmaynotliveuptoyourexpectations,especiallywhencollectingenergyoncloudydays.Ifyouarespendinga lotofmoneybuyingasolarenergysystemthatneeds tolastmanyyears,itisadvisabletopurchasefromaknownbrandsuchasKyocera,Panasonic,ClearSkies,Hyundai,Sanyo,Mitsubishi,SolarFrontierorSharp.MypersonalrecommendationisKyocerapolycrystallinesolarpanels,orMitsubishiorSolarFrontieramorphouspanels.Ihavefoundthesetobeparticularlygood.

BuyingcheapsolarpanelsNotallsolarenergysystemshavetolasttenortwentyyears.Ifyouarelookingfor a small, cheap system to provide power to an RV or caravan, or yourrequirements are modest, such as installing a light in a shed, buying a cheapsolarpanelmaywellbetherightoptionforyou.Thequalityofthecheapersolarpanelshasimprovedsignificantlyoverthepastfew years. Six or seven years ago, buying a cheap, unbranded Chinese-madeproductwas a recipe for disaster.Many of the panelswere poorly assembled,allowingwatertoseepthroughtheframesanddamagingthesolarcells.Alotofthemusedplateglass,oftena thin, low-gradeglass thatbecomescloudedovertimeandiseasilychippedorbroken.Thecellsusedbythesemanufacturerswereoftensub-standardrejectcellsandoftendegradedveryquickly.Thankfully,most of these problems are now resolved and if you buy a cheapsolar panel on eBay, you are likely to have a good product that will reliablygeneratepowerforfivetotenyears,andinallprobabilityalotlonger.Ifyouarebuying a solar panel from amanufacturer you have never heard of, here is achecklistofthingstolookfor:Buybiggerthanyouthinkyou’llneedIfyouarebuyingaverycheapsolarpanel,youarelikelytobesavingasmuchas 50% of the price when compared to buying a branded product. However,expectittodegradeslightlymorequicklythanabrandedunit,anddonotexpectittobequitesoefficient.To counter this, buy a solar panelwith a higherwatt rating (often shownas a

wattpeak,orWp,rating)thanyouactuallyneed,orbuyadditionalsolarpanelsifyouarepurchasinganentirearray.Aimfor15%morepowerthanyouwouldotherwisehavebought.Youwillstillsavealotofmoney,butyouwillhaveanextrabitofassurancethatthesystemwillbeuptothetask.WarrantyWith cheap solar panels, you’re not going to get a five-, ten-or twenty-yearwarranty,butyoushouldstillexpectaone-ortwo-yearwarrantywithanysolarpanelyoubuy.Checktoseeexactlywhatthewarrantyoffers.You are looking for a warranty that guarantees a minimum output undercontrolled conditions.The standard across the industry is toguarantee80%ofthequotedoutputundercontrolledconditions.If you have a warranty claim, also check to see how you can claim on thatwarranty.Shippingabrokensolarpanelhalfwayaroundtheworldandpayingforreturncarriageislikelytocostasmuchasbuyinganewsolarpanel.GlassIfyouarebuyingasolarpanelthatisgoingtobefittedtoamovingvehicle,orifyouarebuyingaphysicallylargesolarpanel,makesurethatthesolarpanelusestemperedglass.Tempered, or toughened, glass is around eight times stronger than plate glass.Thismakesitfarmorerobust.Ifyourglassischippedonyoursolarpanel,youwill immediately see a significantdrop inpoweroutput. Ifwatergets into thesolarpanel itself, itcancreateashortcircuitandbecomesafirehazard.Waterandelectricitydonotmix.It isworthnotingthatsomeamorphoussolarpanelscannotusetemperedglassbecause of theway the thin film is applied to the glass. Somemanufacturersreducethisproblembyusingthickerplateglass.

Second-handsolarPVpanelsFrom time to time, second-hand solar panels appear for sale. They appear oneBayoraresoldbysolarequipmentsuppliersorbuildingsalvageyards.Solongastheycomefromareputablebrand,second-handsolarpanelscanbeextremelygoodvalue formoneyandevenoldpanels thatare25–30yearsoldmaystillgivemanymoreyearsofuseful service.Althoughgoodquality solarpanelsshouldprovideatleast25yearsservice,nobodyknowshowmuchlongerthey will last. The early commercially available solar panels (which are now

over30yearsold)arestillworkingextremelywell,typicallyworkingataround80–90%oftheiroriginalcapacity.Thereare,however,afewpoints to lookoutfor ifyouareconsideringbuyingsecond-handsolarPVpanels:

Neverbuysecond-handsolarPVpanelsunseen.Takeamulti-meterwithyouandtestthemoutsidetomakesureyouaregettingareasonablevoltageandwattagereadingCheckthepanelsandrejectanywithchippedorbrokenglass.Alsorejectanypanelswherethesolarcellsthemselvesarepeelingawayfromtheglassorhavecondensationbetweentheglassandthesolarcell TheefficiencyofoldersolarPVpanelsissignificantlylowerthannewpanels.30yearsago,themostefficientsolarpanelswereonlyaround5–6%efficient, compared to 13–24% efficiency levels today. 10–15 years ago,mostsolarpanelswerearound10–12%efficient Consequently,asolarPVpanelfromtheearly1980sislikelytobethreetimesthesizeandweightofanequivalentmoderncrystallinepanel Thesesecond-handpanelswillnothaveanyof the safetycertificationratings that you get with new solar panels. This may cause issues withbuildingregulationsorbuildinginsurance,ifyouareinstallingtheseontoabuildingaspartofanewsolarinstallation

FresnellensesandmirrorsAverybriefwordhereaboutFresnel lensesandmirrors.TheFresnel lenswasinventedfor lighthouses,asawayofprojectinga lightovera longdistance. Itdoesthisbyrefractingthelighttomakeitaconcentratedbeam.Scientistshavebeen experimenting with Fresnel lenses in conjunction with solar panels forconcentratingthepowerofthesunlightandfocusingitonasolarpanel.In effect, by concentrating the sunlight into a smaller area and increasing thesolar irradiance, significantlymore energy can be captured by the solar panel,therebyimprovingitsefficiencyquiteimpressively.However, there are problemswith this technology.Most specifically, the heatbuild-up is quite considerable and, in testing, many solar panels have beendestroyedbytheexcessiveheatgeneratedbytheFresnellens.ThisisespeciallytrueofFresnellensesbuiltbyenthusiasticamateurs.There are one or two companies now promoting Fresnel solar panels. These

panelstendtobequitelargeandbulky.Duetotheheatbuild-up,theyalsoneedtobeverycarefullymounted,withadequateventilationaroundthepanel.Thereare also questions about the long-term reliability of Fresnel solar panels. Myadvicewouldbetoavoidtheseuntilotherpeoplehavetriedthemforanumberofyearsandfoundouthowreliabletheyreallyare.As an alternative,mirrors or polishedmetal can be a usefulway of reflectingadditional sunlight back onto solar panels and therefore increasing the solarirradiance.However,youmust takecare toensure that the reflected lightdoesnot dazzle anyone. The practicalities of mounting, safety and ensuring thatpeoplearenotdazzledbythereflectedsunlightnormallydissuadepeoplefromusingmirrorsinthisway.

SolarpanelmountingsYoucaneitherfabricateyourownmountingforyoursolarpanels,orpurchaseaready-mademodularsystem.Thedesignof thesystemmust takeintoaccountwindloading,sothat it isnotdamagedordestroyedinhighwinds.Ifyouareinstallingsolarinahotclimate,yourmountingmustalsoensurethereisadequateventilationbehindthepaneltoavoidexcessiveheatbuild-up.Your support structure needs to be able to set the angle of the solar array foroptimalpositioningtowardsthesun.Ifyouhavenotinstalledsolarelectricsystemsbefore,itisusuallyagoodideatobuy amodular support structure from the same supplier as your solar panels.Onceyouhavemoreexperience,youcanthenchoosetofabricateyourown,ifyouprefer.

SolartrackersForground-orpole-mountedsolararrays,youcanbuysolar trackers that trackthepathofthesunacrosstheskyandmovethesolarpanelssotheyarefacingthesunatalltimes.Thebenefitsofsolar trackersare that they increase theamountofsunlight thesolarpanelscancapture.Theyincreaseenergycapturebyupto55%duringthesummermonthsandbyaround15–20%duringthewintermonths.Unfortunately, the cost of these solar trackersmeans that they are rarely cost-effective.Itisusuallyfarcheapertobuyalargersolararraythanitistobuyasolartracker.Onlyifspaceisatapremiumaresolartrackerscurrentlyviable.

SolararraycablesSolar array cables connect your solar panels together and connect your solararraytothesolarcontroller.These cables are often referred to as ‘array interconnects’. You can purchasethemalreadymadeuptospecifiedlengthsormakethemupyourself.Thecablesare extremely heavy duty and resistant to high temperatures and ultra-violetlight.Theyalsohaveatough,extra-thickinsulationtomakethemlesspronetoanimaldamage.Ifyouareplanningtowireyoursolararrayinparallelratherthaninseries,youneedtoensurethatyoursolararraycablescancopewiththecurrentthatyouaregoingtobegeneratingthroughyoursolararray.Ifyouaredesigningaparalleldesignsystem,Iexplainhowyoucancalculatethesizeofcablerequiredinthechapteronstand-alonesystemcomponents.

FusesandisolationswitchesTheabilitytoisolatepartsofthesystemisimportant,especiallywhileinstallingthesystemandcarryingoutmaintenance.Evencomparativelylowvoltagescanbedangeroustoworkon.Even small systems should incorporate a fuse between the batteries and thecontrollerand/orinverter.Ifsomethinggoeswrongwiththesystem,farbettertoblowacheapfusethanfryabatteryorasolarcontroller.For all but the smallest systems, you will also need to incorporate isolationswitches into your solar design. This will allow a battery bank to bedisconnectedformaintenancepurposes.Foranyinstallationwithmorethanonesolarpanel,andforallgrid-connectedsystems,anisolationswitchtodisconnectthe solar array should also be installed: I would recommend installing anisolationswitchonthesolararrayforallsolararrayscapableofgeneratingover100wattsofpower.Ifyoursolarpanelsaremountedsomewayfromyour inverterorcontroller, itcanalsobeagoodideatohaveanisolationswitchfittednexttothesolarpanels,as well as one fitted next to the inverter or controller. You can then easilydisconnectthesolarpanelsfromtherestofthesystemformaintenanceorincaseofanemergency.Ensurethattheisolationswitchyouchooseiscapableofhandlinghigh-currentDC circuits, with contacts that will not arc. Suitable isolation switches areavailablefromanysolarsupplier.If you are planning a grid-connected system, youwill also needAC isolationswitchestoallowyoutodisconnecttheinverterfromthegridsupply.Youwillrequire an isolation switch next to the inverter, and a second one next to thedistributionpanel.

GroundfaultprotectionGroundfaultprotectionensuresthatifthereisashortwithinthesolararray,thecurrentflowiscutoffimmediately.Thisavertstheriskofdamagetoeitherthecontrollerorthesolararray,andsignificantlyreducestheriskofelectrocution.Ground faultprotectionworksbymeasuring thecurrententeringandexitingacircuit.Ifeverythingisworkingcorrectly,thecurrentinshouldequalthecurrentout.However,ifthereisa‘leak’orapartialshortcircuit,thesystemwillseeadifference in current and immediately shut down.A partial short circuit couldoccurifasolarpanelwasbrokenorifsomebodytouchedanexposedcable.Most solar inverters and solar controllers incorporate ground fault protection,using a Residual Current Device (RCD) built into the unit (note: RCDs areknownasGroundFaultInterrupters–GFIs–intheUnitedStatesandCanada).Manyexperts say that it isprudent to install a separateground faultprotector,evenifthecontrollerorinverterhasgroundfaultprotectionbuiltin.Asthecostof anRCDorGFI is low and the benefits theyprovide are high, this is goodadvice.YouwillrequireseparategroundfaultprotectionforyourDCandACcircuits:

Foranythinglargerthan100-wattsolarpanelsystems,andforallsystemsmounted toabuilding,youshould installgroundfaultprotectionbetweenyoursolarpanelsandyourcontrollerorinverter If you are installing a DC power supply into a building for runningappliances,youmustinstallgroundfaultprotectionbetweenyourcontrollerandthispowersupply Ifyouareusingan inverter,youshould installground faultprotectionbetweenyourinverterandanyload

There are specific RCD units for DC circuits and these are stocked by solarpanelsuppliers.

ComponentsforGrid-Tiesystems

Beforediscussingthecomponentsrequiredforagrid-tiesysteminmoredetail,itisusefultolookathowagrid-tiesystemisconfigured.Therearethreebasicdesignsforgrid-tiesolarenergysystems:

High-voltagein-seriessystemsLow-voltagesystemsMicro-invertersystems

Highvoltagein-seriesThisis themostpopularconfigurationforagrid-tiesystemtoday.Solarpanelsare connected together in series, producing a high-voltage DC power. This isthenfedintoacentralinvertertoconvertthepowerintoanACsource,whichinturnisconnectedintothestandardbuildingelectricalsystem:

Asimplifiedblockdiagramshowingthebasiclayoutofahighvoltagein-seriessolarenergysystem

Thisdesignisthemostcost-effectivedesignforgrid-tiesystems.Itisrelativelystraightforward to install, simple to maintain, and components are readilyavailable.Byrunningthesolararrayathighvoltage,itisalsoveryefficient,withminimallossesthroughthearrayitselfandallowingtheinvertertorunataveryhighlevelofefficiency.Thisiswhythisdesigniscurrentlysopopularwithinthegrid-tiesolarindustry.Thishigh-voltageDCpowerhasthebenefitofgreatefficiency,butcomeswithanumberofverysignificant safety risks.Voltagesashighas600volts inNorthAmericaand1,000voltsinEuropearecommon:voltagesthatcanveryeasilybefataloncontact.Thesehighvoltagescanalsocausesignificantproblemsifthereisdamagetothewiringbetweensolarpanels,eitherduetoamistakeduringinstallation,through

animaldamage,orsimplythroughwearovertime.Ifadamagedcablegeneratesahigh-voltage,directcurrentelectricarcwhilstthepanelsareindirectsunlight,the immenselyhigh temperaturescaneasilymeltmetalandareapotential firehazard.Connecting solar panels in series also has a significant disadvantage: whenconnectedinseries, thesolararrayisonlyasstrongas itsweakest link.Ifyouhave a damaged solar panel, shade blocking light to a few solar cells, or adamaged cable, the output of the entire solar array drops to the output of thatweakestlink.

LowvoltagesystemsIt is for these reasons that, inpreviouseditionsof thisbook, Ihaveadvocatedlower-voltage solar arrays for many grid-tie systems. This was achieved byrunning shorter series of solar panels and having multiple strings running inparallel. These are much safer than the very high voltage systems usuallyinstalled,loselittleinefficiencyandareinherentlymoretolerantofshade.

Asimplifiedblockdiagramshowingthebasiclayoutofalow-voltagesolarenergysystemwheremultiplestringsofsolarpanelsareconnectedin

parallelThisdesigntendstobemoreexpensiveto install thananin-seriesdesign.Youwilleitherneedtobuyagrid-tieinverterthatcanacceptmultiplestringsofsolarpanels,orbuyaseparateinverterforeachstring.I no longer advocate this approach, because there is now another alternativeavailable that, in my opinion, renders both high-voltage in-series and low-voltagesystemsredundant:

Micro-invertersystemsMicro-inverter systems have been around for a few years now, but until veryrecentlyhadnotgainedpopularity,mainlyduetotheirhighercost.

However,withthehugegrowthinthepopularityofgrid-tiesystemsaroundtheworld,micro-invertersystemshavebecomefarmorewidespreadasthebenefitsof this technology have become more apparent. Prices for micro-invertersystems are dropping fast and are now comparable to high-voltage in-seriessystems.Inamicro-invertersystem,eachsolarpanelhasitsowninverter,convertingitsoutput toAC power. In effect, each solar panel becomes its own independentsolarenergysystem.Inthemajorityofmicro-invertersystems,theinverteritselfismountedoutside,boltedtotheframethatalsoholdsthesolarpanelinplace.Theindividualsolarpanelsareconnected toanACpowercable that runsalongside thesolararrayandthenfeedsdirectlyintothebuilding’selectricalsystem.

Asimplifiedblockdiagramshowingthebasiclayoutofamicro-invertersystem

There are some very significant benefits ofmicro-inverter systems over otherformsofgrid-tiesystems:

As each solar panel runs as an independent unit, if one panel isunderperforming,eitherbecauseofdamageorsimplybecauseitisshaded,itdoesnotaffecttheoutputfromanyoftheotherpanelsBecausethereisnohigh-voltageDCpowerrunningfromonepaneltothenext,safetyislessofanissue Installation, fault-finding and maintenance also become significantlyeasierItiseasytoexpandyourgrid-tiesysteminthefuture,asbudgetallowsMoreflexiblesolarpanelinstallation–youcanhavesolarpanelsmountedindifferentlocationsandfacingindifferentdirections

Whilsttoday,series-connectedsolarsystemswithacentralinverterarestillthe

standardmodel for installing grid-tie systems, the industry ismoving towardsmicro-invertertechnologyasafarbettermodel.

Nowyouhaveaclearerideaofhowagrid-tiesystemisputtogether,itistimetolookatthecomponentsavailableinmoredetail.

Grid-tiesolarpanelsIn thepast,whenmost solar energy systemswere stand-alone systems, almosteverysolarpanelyoucouldbuywasratedfora12-voltoutput.Whilstthisisstilltrueforsmallerpanels,therearenowhigher-voltageconfigurationsavailableforlargersolarpanels.Asgrid-tiesystemshavebecomemorepopular,higher-voltagesolarpanelshavebecomeavailable.Manysolarpanelsof150Wpcapacityandoverareratedfora24-voltoutputandsomemanufacturersarenowbuildingsolarpanelswithratedoutputsofbetween48voltsand120volts.Thesehighervoltagesarewell suited togrid-tie installations.By runningyoursolar array at a higher voltage, you can keep the current flow low, whichimproves the efficiencyof theoverall system.Usinghigh-voltage solar panelsalsogivesyoutheoptiontoconnectmultiplesolarpanelsinparallelratherthaninseries,whilstretainingthebenefitofthehigh-voltagecurrent.The 24-volt and 48-volt solar panels can work with many micro-invertersystems, too. Theoretically, this would allow a micro-inverter system to runmoreefficiently,althoughinpracticethedifferencesseemtobemarginal.

Grid-tieinvertersGrid-tieinvertersconverttheDCpowerfromyoursolarenergysystemintoACpower, and convert the voltage to the same as the grid. This allows you toconnectyoursystemintothegrid,enablingyoutobecomeaminipowerstationandsupplyyourelectricitytotheelectricitycompanies.Youcannotuseanordinaryinverterforgrid-tieapplications.Thereareanumberofreasonsforthis:

Grid-tieinvertershavetoworkinconjunctionwiththegrid,inordertobeabletoexportelectricitytoit.TheACpuresinewaveformgeneratedbytheinverterhastobeperfectlycoordinatedwiththewaveformfromthegrid There is an additional safety featurewith grid-tie inverters to cut offpowerfromthesolararrayifthegridshutsdownGrid-tieinvertersareconnecteddirectlytothesolarpanels.Inanin-seriessystem, thismeans the inputvoltage fromthepanelscan fluctuatewildly,oftenjumpingordroppingbyseveralhundredvoltsinaninstant.Nongrid-tieinverterscannotcopewithsuchmassivevoltagejumps Inmanycountries,grid-tieinvertershavetobecertifiedforusewiththegrid

Thereareanumberofthingstoconsiderwhenpurchasingagrid-tieinverter:InputvoltagePowerratingPowertrackingHowmanystringstheinvertercansupportDiagnosticsandreportinginformationInbuiltsafetysystemsInstallationoptionsandoperatingenvironmentCertificationandlocalregulations

InputvoltageYourchoiceofinverterwillhavealargevoltagerangeinordertocopewiththehuge fluctuation of voltage that a solar array can provide. From this voltagerange,youwillbeabletoidentifyhowmanysolarpanelstheinvertercancope

with,whenconnectedinseries.Youneedtorememberthattheratedvoltageofasolarpanelisnotthemaximumvoltagethatthesolarpanelcangenerate.Thevoltagefromasingle12-voltsolarpanelcanfluctuateanywherefrom12voltsonaverydullday,uptoaround20voltsinintenseoverheadsunlight.Ifyouhavea48-voltsolarpanel,orfour12-voltsolarpanelsconnectedtogetherinseries,thevoltageswingcanbebetween48voltsand88volts.Inadditiontothis,asolarpanelcanproducesignificantlyhighervoltagesinanopencircuit–i.e.whenthesolararrayisgeneratingpowerbutthepowerisnotbeing used.Depending on your solar panel, it is possible for a single 12-voltsolarpaneltogenerate26voltsinanopencircuit.Asyoucanseefromthetablebelow,thehigherthenominalvoltagefromyoursolararray,thegreaterthevoltagefluctuationcanbe:Numberof12-

voltsolarpanels

Nominalsolararrayvoltage

Low

voltageondullday

Peakvoltageinintensesunlight

Maximumopen-circuitvoltage

1

12-volt

12volts

20volts

26volts

2

24-volt

24volts

40volts

52volts

4

48-volt

48volts

80volts

104volts

6

72-volt

72volts

120volts

156volts

8

96-volt

96volts

160volts

208volts

10

120-volt

120volts

200volts

260volts

15

180-volt

180volts

300volts

390volts

20

240-volt

240volts

400volts

520volts

25

300-volt

300volts

500volts

650volts

30

360-volt

360volts

600volts

780volts

35

420-volts

420volts

700volts

910volts

40

480-volts

480volts

800volts

1,040volts

Note:themaximumopen-circuitvoltageallowableintheUnitedStatesforgrid-tiedsystemsis600volts,whilstinEuropeitisadvisablethatyoursystemdoesnotexceed1,000volts.Youmustensurethatyoursystemneverexceedsthis.Asyoucanseefromthistable,ifaheavycloudblocksthesunonanotherwiseclear day, you can see a voltage drop of several hundred volts in an instant.Whenthecloudpassesover,thevoltageshootsbackupagain.Itisimportanttoensurethatthesolarpanelwillworkwiththepeakvoltageofyoursolararrayandnotjustthenominalvoltageofyourarray.Ifyouexceedthepeakvoltageofyour inverter, the inverterwill shutdown toavoiddamage. Inextremecases,youcoulddamageordestroyyourinverterbyexceedingtheinputvoltagerating.In addition to the standard input voltage range, your inverterwill also showamaximumvoltagerating.Thismaximumvoltageratingrelatestothemaximumopencircuit voltageofyour solar array.Youmust ensure that theopencircuitvoltageofyourarraydoesnotexceedthemaximumvoltageofyourinverter.

PowerratingTherearetwopowerratingsonagrid-tieinverter:

Inputpowerrating–theminimumandmaximumamountofpowertheinvertercanacceptfromthesolararray Outputpowerrating– themaximumamountofpowerandcurrent theinvertercangenerateasanACoutput

InputpowerratingThe input power rating shows theminimum andmaximumwattage range theinvertercanworkwith.Inthemain,thewidertherange,themoreefficientyourinverteris.Thespecificationonaninverterwilltypicallyshowthreefiguresforinputpowerrating:

Anominalpowerrating,showninwattsAminimumandmaximumpowerrange

Astart-uppowerratingThe nominal power rating shows the maximum amount of power that theinvertercanconvert intoanACoutput.Ifyouexceedthisfigureonyoursolararray, the additional power will be lost and converted into heat. Exceed thisfigureforlongandyourinvertermayshutdowntoavoidoverheating.Theminimumpowerratingshowstheminimumamountofpowerthatyoursolararray must generate in order for the inverter to start producing power. Themaximumpower rating shows themaximumamountofpower that canbe fedintotheinverterbeforeyouriskdamagingyourinverter.The start-up power rating is theminimum amount of power the solar inverterrequires to power itself. If the solar array produces less than this amount ofpower,theinverterwillswitchoff.Becauseofthewidevariationinthepowerasolarpanelcanproduce,itisgoodpracticetobuyabiggergrid-tieinverterthanyouactuallyneed.Rememberthatwhilst a solarpanelhas awatt-peak (Wp) rating, in ideal conditions thepanelitselfmayslightlyexceedthisratinginarealworldenvironment.OutputpowerratingTheoutputpowerratingisthemaximumcontinuousACpowerthattheinvertercangenerate.Theoutputpower informationwillshowvoltage,nominaloutputpowerinwatts,themaximumoutputcurrentinampsandthealternatingcurrentfrequency.For North America, the grid voltage is nominally set at 110 volts, with afrequencyof60Hz.Forthemajorityoftherestoftheworld,thegridvoltageisnominallysetat230volts,withafrequencyof50Hz.Inbothcases,itisnormaltogetsomevariationinvoltageandfrequency.The output power ratingwill also show themaximum efficiency rating of theinverter,givenasapercentage.This rating isusually in the regionof90–94%withmoderngrid-tieinverters.Ifyouareshoppingonabudget,youmustcheckthisrating:someverycheapgrid-tieinvertersmaybesignificantlylessefficient.

PowertrackingAs discussed on previously, the efficiency of the solar array depends on howefficientlythefluctuatingvoltageishandledbyyourinverter.If you are purchasing a grid-tie inverter, you should invest in one thatincorporates maximum power point tracking (MPPT).Maximum power point

trackingcanprovideanadditional15–20%ofenergywhencomparedtoanon-MPPTinverter.Today,MPPTisthenorm,butthereareafewolderdesignsofinverterstillonthe market, often sold at bargain prices online. No matter how cheap theseinvertersare,theperformancelossrarelymakesthemaworthwhileinvestment.

MultiplestringsA‘string’ofsolarpanelsissimplyanarrayofsolarpanelsconnectedinseries.Someinvertersallowyoutoconnectmorethanonestringofsolarpanels.Thesetwostrings thenworkas separatearrays,but feed thepower through thesameinverter.

Withmultiplestrings,youcanmixandmatchsolarpanelsandlocatetheminphysicallyseparateareasifyousowish.Thetwostringsruncompletely

independentlyofeachotherWithamultiple string system,your two solar arrayswork independently fromeach other. This means that you can have two different sizes of array withdifferentsolarpanels,orhavethetwoarraysmountedatdifferentorientations.Ifonearrayispartiallyshaded,theperformancedoesnotaffectthesecondarray.Thisisdifferenttoconnectingmultiplestringstogethertocreateaserial/parallelhybrid.Ifyouhavemultiplestringsconnectedtogether,thetwostringsarestilllinked.Youneedtohaveidenticalsetupsonbothstringsandthepanelsneedtobefacingthesameway.Failuretodothiswillresultinlowersolarperformance.

Herewehavetwostringsofsolarpanels,connectedtogetherinparalleltofeedasinglestringinverter.Thetwostringshavetomatcheachother.Ifonestringiscompromised,forinstanceduetoshading,thesecondstringisalsoaffected.(Note:youwouldnotnormallywireagrid-tiesolararrayin

thisway.Instead,youwouldconnecteverythinginseriesonasinglestring.)

Multiplestringsareofbenefitinthefollowingsituations:Whereyouwishtofittwodifferentsizesofsolarpanel Fittingsolarpanelsfacingatdifferentorientations,suchasonaroofthathastwodifferentpitchesResolvingshadingissues.Solarpanelsthatareinshadeatcertaintimesofthedaycanbeputontoaseparatestringsoasnottoaffecttheoutputoftherestofthesystem

Whilstaninverterthatcanhandlemultiplestringsdoeshaveitsbenefits,thereisusually an additional cost for multi-string inverters. If you are considering amulti-string inverter, you are probably better off choosing a micro-invertersystemwhereeverysolarpanelhasitsowninverter.

DiagnosticsandreportinginformationAlmost all inverters provide a level of diagnostics and reporting information,eitherusingasmalldisplaybuiltintotheinverteritself,aseriesofLEDsonthefrontpaneloftheinverter,aseparatemonitoringunitthatplugsintotheinverter,orbyallowingyoutoconnectaPCtotheinverter.Some inverters even have a built-in internet connection, allowing them toconnect to awireless network. Thismeans your system can provide youwithupdatesviae-mail,viaabuilt-inwebsite,orevensendupdates toyourmobilephone. In some cases, these systems can be remotely monitored by the solarinvertersupplier,whocanthennotifyyouifthereareanypotentialissueswithyoursystem.Ifyouhaveamicro-invertersystemwithmultipleinverters,thediagnosticsandreportingsystemisusuallyaseparatebox,whichiseitherconnectedtotheACpoweratthepointwherethesolararrayconnectstoyourdistributionpanel,oritcommunicateswirelesslywith themicro-inverters. This ensures that you haveonecentralinformationpointforyourinverters.As a bareminimum, youwant an inverter that can tell you if your system isworking and provide youwith an indication ofwhatmay be the problem if afaultisdetected.Thediagnosticsshouldbeabletogiveyouenoughinformationtoenabletoyouidentifyafaultwithyoursystem,suchas:

Insufficientorexcesspowerfromthesolararray

GridconnectionissuesGridvoltageorfrequencyissuesOverheating

Mostsolarinverterswillprovideyouwithmuchmoreinformation,allowingyoutoseethevoltageandcurrentfromyoursolararrayandtheamountofACpowerbeinggeneratedat thatmoment.Theywillalsobeable toshowtheamountofenergy generated by the system, both for that day and since the system wasinstalled.

Built-insafetyMostinvertersincorporatesafetyshutdownsystemsaspartoftheinverteritself.Itiscommonforinverterstohavegroundfaultprotectionbuiltin.Asmentionedin theprevious chapter, even ifyour inverterdoesprovide this, it is still goodpractice to install additional ground fault protection when you design yoursystem.This is incorporated intoyoursystemusingaResidualCurrentDevice(RCD). RCDs are known asGround Fault Interrupters (GFIs) in the UnitedStatesandCanada.Agrid-tieinverterwillalsomonitorthepowerfromthegridandshutdownifitdetectsapowercut(sometimesreferredtoas‘IslandProtection’).Thispowershutdownensuresthatyoursolarenergysystemdoesnotcontinuetofeed power into the grid if there is a power cut. This is a necessary safetyrequirement: if workers are attempting to repair a power outage, they riskelectrocutionifpowerisbeingfedintothegridfromyoursolararraywhiletheyareworking.Inverters should also shut down or derate if the internal temperature gets toohigh,inordertoavoidpermanentdamage.

InstallationoptionsandoperatingenvironmentInverterstendtobeheavyunits.Theyneedtobemountedsecurelyonawallorbolted to the floor.They can generate a significant amount of heat, especiallywhen running close to their rated output, and require good airflow around theunitstokeepthemcool.Youcanpurchase inverters foreither indoororoutdoor installation. Ifyouarelookingatinstallinganinverteroutdoors,checkthattheinverterissealedagainstdustandwateringress,ratedtoatleastIP64.Overheating inverters is thenumberonereasonforgrid-tiesystemsfailing.As

aninvertergetshotter,itprovideslesspower,andifthetemperaturecontinuestorise,itwilleventuallyshutdowntoavoidpermanentdamage.Whenchoosinganinverter,checkitsoperatingtemperaturesandconsiderhowyoucanensureyoursystemremainswithintheselimits.Inverters should always be installed in a well-ventilated area, away from theceiling and with a clearance around each side, the top and the bottom. Theycannotbe installed inasealedcupboard.Some invertershave theoptionofanexternal heat sink or temperature-controlled cooling fans to help keep theinvertercool.Mostinvertersdomakeasmallamountofnoise.Thisistypicallyacontinuouslow-level hum. It is usually only noticeable if the surrounding area is quiet.However, for this reason, inverters are not usually installed inside the livingspace in a homeor in an office environment. Instead, consider installing yourinverterinagarageoronanoutsidewallofyourbuilding.Occasionally, thesoundmadeby the inverterhasbeenknowntoresonatewiththewall,amplifyingthesoundandmakingitquiteunpleasanttolivewith.Thiscanoccureveniftheinverterismountedtoanoutsidewall.Thisisaveryrareoccurrence,butismostlikelytooccurifyouareplanningtomountyourinverteronto a wall made of solid concrete. The solution is to dampen the mountingbetweentheinverterandthewallorfloorthattheinverterismountedon.Thereis a very effective product called Green Glue, produced by the Green GlueCompany(www.GreenGlueCompany.com) that isappliedbetween thewallandtheinverter.Whenitiscompressedbyremountingtheinverter,thegluespreadsouttoformasoundisolationbarrierthatisparticularlyeffectiveatblockingoutlow-resonancevibrations.

BuyingfromeBaySome companies and individuals have been selling non-approved grid-tieinverters online, most commonly on eBay. These are often sold at a bargainprice,bundledwithacheapsolarpanelandoftenadvertisedasa‘microgrid-tiesystem’.The sellers claim that these systemsaredesigned for amateur installation.Theinverterplugs into thehouseholdelectricity supply throughanormaldomesticpower socket, and the systems look exceptionally easy to install and use.Thesellersoftenclaimthatyoucanusethesesystemstosellpowerbacktotheutilitycompaniesandthattheycanbeusedtorunthemeterbackwards.These systems are highly dangerous and must be avoided. For a start, the

equipmenthasinevitablynotbeencertifiedforgrid-tieuseinanycountry.Moreimportantly, the use of these systems is illegal in the United States, Canada,AustraliaandmostoftheEuropeanCommunity,becauseofthewaytheinvertersconnect to the household electricity supply, using a domestic power plug inreverse.Thismeansthatthehouseholdplughasgrid-levelACpowerrunningthroughit.This is extremely high risk and directly contravenes basic electrical safetylegislation. In the UK, for instance, this is directly in contravention withBS7671:2008(amd1,2011)551.7.2 (ii).Thecatastrophicandpotentially fatalresultsshouldsomebodyunplugthecableandaccidentallytouchtheunshieldedplugdonotbearthinkingabout.Never design any electrical system that risks grid-level AC power runningthroughexposedconnectors.The livesof thepeople aroundyouareworth farmorethansavingafewpounds.

ComponentsforStand-AloneSystems

Ifyouaredesigningastand-alonesystem, there isa lotmoredesignworkandplanning involved than there is forasimilarly-sizedgrid-tiesystem. It ismorecriticaltomakesureyourstand-alonesystemworks:whileagrid-tiesystemwillnot let you down if you do not generate enough energy, a stand-alone systemwill.As well as considering and planning all the physical side of fitting the solarpanels,routingthecablingandhandlingthesafetyaspects,youwillalsoneedtoconsiderthevoltagethatyoursystemwillrunatanddesignabatterysystemtostoreyourenergy.

CalculateyouroptimumvoltageSolar panels and batteries are normally both 12 volts, so logically youwouldthinkthatitwouldmakethemostsensetorunyoursystemat12volts.Forsmallsystems,youwouldberight.However, therearesomelimitationsof12-volt systems. Therefore,we now need to identify the optimum voltage foryoursystem.If you are still not comfortablewith volts,watts, currents and resistance, nowwouldbeagoodtimetore-readChapter2:ABriefIntroductiontoElectricity.

VoltagesandcurrentsCurrent iscalculatedaswattsdividedbyvolts.Whenyourunat lowvoltages,yourcurrentismuchhigherthanwhenyourunathighervoltages.Takeanormalhouseholdlow-energylightbulbasanexample.A12Wlightbulbrunningfromgrid-levelvoltagesisconsuming12wattsofpowerperhour.Thecurrentrequiredtopowerthislightbulbat230voltsis0.05amps(12W÷230V=0.05amps)andat110voltsis0.1amps(12W÷110v=0.1amps).Ifyourunthesamewattagelightbulbfroma12-voltbattery,youarestillonlyconsuming12wattsofpowerperhour,butthistimethecurrentyourequireis1amp(12W÷12V=1amp).If you run the same wattage light bulb from a 24-volt battery, you halve theamps.Younowonlyrequire½amp(12W÷24V=½amp).“Sowhat?”Ihearyousay.“Whocares?Attheendoftheday,we’reusingthesameamountofenergy,whateverthevoltage.”Theissueisresistance.Resistanceistheoppositiontoanelectricalcurrentinthematerialthecurrentisrunningthrough.Thinkofitasfrictiononthemovementofelectronsthroughawire.Ifresistanceistoohigh,theresultispowerloss.Byincreasing your voltage, you can reduce your current and thereby reduceresistance.Youcancountertheresistancebyusingthickercabling,butyousoongettothepointwherethesizeofthecablingbecomesimpractical.Atthispoint,itistimetochangetoahighervoltage.

WhatvoltagescanIrunat?Foreitherastand-aloneoragridfallbacksystem,themostcommonvoltagesto

runasolarelectricsystematare12volts,24voltsor48volts.As a rule, the most efficient way to run an electrical circuit is to keep yourvoltage high and your current low. That is why the grid runs at such highvoltages:itistheonlywaytokeeplossestoaminimumoverlongdistances.However, you also need to factor cost into the equation: 12-volt and 24-voltsystems are far cheaper to implement than higher voltage systems, as thecomponentsaremorereadilyavailable,andatalowercost.12-voltand24-voltdevices and appliances are also easily available, whereas 48-volt devices andappliancesarerarer.It isunusualtogobeyond48voltsforstand-alonesystems.Whilstyoucangohigher,invertersandcontrollersthatworkatothervoltagestendtobeextremelyexpensiveandonlysuitableforspecialistapplications.Foragrid-tiesystem,youdohavetheoptiontorunyoursolararrayatamuchhigher voltage, by connecting lots of solar panels together in series. Grid-tieinverters are available thatworkanywhere from12voltsup to1,000volts. Ingrid-tiesystems, thevoltageyourunatdependson thenumberofsolarpanelsyouuse.

HowtoworkoutwhatvoltageyoushouldberunningatYourchoiceofvoltageisdeterminedbytheamountofcurrent(amps)thatyouaregeneratingwithyoursolararrayorbytheamountofcurrent(amps)thatyouareusinginyourloadatanyonetime.Tocopewithbiggercurrents,youneedbiggercablingandamorepowerfulsolarcontroller. You will also have greater resistance in longer runs of cabling,reducing the efficiency of your system, which in turn means you need togeneratemorepower.Inoursystem,weareproposinga12m(40feet) longcablerunfromthesolararraytothehouse,pluscablingwithinthehouse.Highercurrentscanalsoreducethelifespanofyourbatteries.Thisshouldbeaconsiderationwherethecurrentdrainorchargefromabatteryislikelytoexceed/ofitsamp-hourrating.Wewilllookatbatterysizinglateron,ascurrentdrawisafactorinchoosingtherightsizeofbattery. Itmaybe thatyouneed to lookatmore thanonevoltageoptionat thisstage,suchas12-voltand24-volt,anddecidewhichoneisrightforyoulateron.Finally, ifyouareplanningtouseaninverter toconvertyourbatteryvoltagetoagrid-levelACvoltage,12-voltinverterstendtohavealower

power rating than 24-volt or 48-volt inverters. This can limit what you canachievepurelywith12volts.Tosolvetheseproblems,youcanincreasethevoltageofyoursystem:doublethevoltageandyouhalveyourcurrent.Therearenohardandfastrulesonwhatvoltagetoworkonforwhatcurrent,buttypically, if the thickness of cable required to carry your current is over 6mm(and we’ll calculate that in a minute), it is time to consider increasing thevoltage.

HowtocalculateyourcurrentAsexplained inChapter2, it isverystraightforward toworkoutyourcurrent.Current(amps)equalspower(watts)dividedbyvolts:

Power÷Volts=CurrentP÷V=I

Goback toyourpoweranalysisandaddup theamountofpower (watts)yoursystemwillconsumeifyouswitchoneveryelectricalitematthesametime.Inthecaseofourholidayhome,ifIhadeverythingswitchedonatthesametime,Iwouldbeconsuming169wattsofelectricity.Usingtheholidayhomeasanexample,letuscalculatethecurrentbasedonboth12voltsand24volts,togiveusagoodideaofwhatthedifferentcurrentslooklike.Usingtheaboveformula,169wattsdividedby12voltsequals14.08amps.169wattsdividedby24voltsequals7.04amps.Likewise,weneedtolookatthesolararrayandworkouthowmanyampsthearray is providing to the system. We need a 320-watt solar array. 320 wattsdivided by 12 volts equals 26.67 amps. 320watts divided by 24 volts equals13.33amps.

CalculatingcablethicknessesIwillgointomoredetailoncablinglater,butfornow,weneedtoascertainthethicknessofcablewewillneedforoursystem.For our holiday home, we need a 12m (40 feet) cable to run from the solarcontrollertothehouseitself.Insidethehouse,therewillbedifferentcircuitsforlighting and appliances, but the longest cable run inside thehouse is a further10m(33feet).Thatmeansthelongestcablerunis22m(72½feet)long.Youcanworkouttherequiredcablesizeusingthefollowingcalculation:

(LxIx0.04)÷(V÷20)=CTLCablelengthinmetres(onemetreis3.3feet)ICurrentinampsVSystemvoltage(e.g.12Vor24V)CTCross-sectionalareaofthecableinmm²

Socalculatingthecablethicknessfora12-voltsystem:(22mx14.08Ax0.04)÷(12V÷20)=20.65mm²

Hereisthesamecalculationfora24-voltsystem:(22mx7.04Ax0.04)÷(24V÷20)=5.15mm²

And just for sake of completeness, here is the same calculation for a 48-voltsystem:

(22mx3.52Ax0.04)÷(48V÷20)=1.63mm²

Convertingwiresizes:Toconvertcross-sectionalareatoAmericanWireGaugeortoworkoutthecablediameterininchesormillimetres,usethefollowingtable:

Cross-SectionalArea(mm²)

AmericanWireGauge

(AWG)

Diameter(inches)

Diameter(mm)

107.16

0000

0.46

11.68

84.97

000

0.4096

10.4

67.4

00

0.3648

9.27

53.46

0

0.3249

8.25

42.39

1

0.2893

7.35

33.61

2

0.2576

6.54

26.65

3

0.2294

5.83

21.14

4

0.2043

5.19

16.76

5

0.1819

4.62

13.29

6

0.162

4.11

10.55

7

0.1443

3.67

8.36

8

0.1285

3.26

6.63

9

0.1144

2.91

5.26

10

0.1019

2.59

4.17

11

0.0907

2.3

3.31

12

0.0808

2.05

2.63

13

0.072

1.83

2.08

14

0.0641

1.63

1.65

15

0.0571

1.45

1.31

16

0.0508

1.29

1.04

17

0.0453

1.15

0.82

18

0.0403

1.02

0.65

19

0.0359

0.91

0.52

20

0.032

0.81

0.41

21

0.0285

0.72

0.33

22

0.0254

0.65

0.26

23

0.0226

0.57

0.2

24

0.0201

0.51

0.16

25

0.0179

0.45

0.13

26

0.0159

0.4

Fromthesefiguresyoucanseetheanswerstraightaway.Ourcablelengthsaresogreatthatwecannotpracticallyrunoursystemat12volts.Thenearestmatchfor20.65mm²cables is21.14mm².This isAWG4cable,withacablediameterof5.19mm. Cable this size is thick, heavy, inflexible, hard to source and veryexpensive.ThismeanswewouldneedtolayextremelythickAWG4cablesfromthesolararray and around our house to overcome the resistance. This would beexpensive,inflexibleanddifficulttoinstall.Realistically,duetocablesizing,wearegoingtoneedtouseeither24voltsor48voltsforoursolarelectricsystem.

MixingandmatchingsolarpanelsWhenspecifyingyoursolararray,youshouldkeep toone typeofpanel ratherthanmixingandmatchingthem.Ifyouwanta100-wattarray,forexample,youcouldcreatethiswithone100-wattsolarpanel,two50-wattsolarpanelsorfive20-wattsolarpanels.If you do wish to use different solar panels in your array, you can do so byrunningtwosetsofpanelsinparallelwitheachotherandeitherconnectingthemintoacontrollerthatcanhandlemorethanonefeed,orbyusingmorethanonecontroller.Thiscanbeausefulwayofcreatingtherightwattagesystem,ratherthanspendingmoremoneybuyingbiggersolarpanelsthatgeneratemorepowerthanyouactuallyneed.The result is slightly more complicated wiring, but it is often a more cost-effective solution to do this than to buy a larger capacity solar array thanyouactuallyneed.Thetwodiagramsbelowshowdifferentwaysofconnectingtwosolarpanelsofdifferentsizes to thesamesystem.Both thesesystemsare runningat12volts,using two different sized panels to create a 140 watt system

Thisfirstsystemusesasinglecontroller.Thecontrollerhastwoseparateinputfeeds.Thetwosolarpanelsworkindependentlyofeachotherandthe

controllerhandlesthemismatchinpoweroutput

Thissecondsystemusestwocontrollers.Thesecondcontrollerisusedtoprovideadditionalpowertothebatteriesforthesmallersolarpanel.

Thesesolutionsareeffective ifyouareplanningtostartsmallandaddtoyoursolarenergysystemwhenneedsandbudgetallows.Itmeansthatyoucancollectanassortmentof solarpanelsover timeandput them togoodusewithinyouronesolarenergysystem.Ifyouendupwithtwodifferentmakesofsolarpanelswithidenticalratings,putthemon their own separate circuits.Solarpanels fromdifferentmanufacturersarenotall identical in theiroperatingvoltagesorperformances,soputtingtwodifferent makes and models of solar panel on the same circuit is likely tocompromisetheperformanceofbothpanels,evenifthespecificationofthetwopanelsissimilar.Ifyoubuymultiplecontrollersforyoursolarenergysystem,tohandledifferentmakes,models and sizes of solar panel, you only need onemain controller tohandlethepoweroutputfromthebatteries.Yourothercontrollerscanbemuchcheaper and simpler pieces of equipment as they are only handling the powerfeedintothebatteries.Ifyouwish,youcanevenuseasimplesolarregulatorthatsimplycutsoffchargingwhen thebatteriesare full,although theseareusuallynotasefficientasapropersolarinverter.Not all solar panels are 12-volt panels. Many solar panels are now designedpredominantly forgrid-tie installationonlyandareavailable inmanydifferentvoltageconfigurations.Solarpanelswithvoltageratingsofup to120voltsareonthemarket,althoughthemostcommonare12-volt,24-voltand48-volt.12-volt panels remain the most commonly available panels and are the most

popular for stand-alone applications. If your stand-alone solar electric systemrunsatavoltageotherthan12volts,youcaneitherinstallmultiplesolarpanelsinordertoboostthesystemvoltage,orchoosehigher-voltagesolarpanels.Forexample,ifyouwanteda200-watt24-voltsolararray,youcouldachievethisinvariousways,including:

Usingtwo12-volt,100-wattsolarpanels,connectedinseriesUsingone24-volt,200-wattsolarpanel

Whenchoosingasolararray,youneedtoconsider:Thephysicalsize:willitfitintothespaceavailable? The support structure: ready-made supports may only fit certaincombinationsofpanelsHowmuchcablingyouwillneedtoassemblethearray The systemvoltage: if you arenot running at 12volts, youwill needmultiplesolarpanelsinordertobuildthesystemtothecorrectvoltageaswellaswattage

BatteriesThereareanumberofdifferentoptionswhenitcomestobatteries,andanumberofspecialistbatterysupplierswhocanadviseyouon thebestoptions foryoursolarinstallation.Leadacidbatteriesusually comeas either6-volt or12-voltbatteries, althoughothervoltagesarealsoavailable.Batteriescanbeconnectedtogetherinseriestoincrease the voltage, or in parallel to keep the same voltage but increase thecapacity.Thecapacityofabatteryismeasuredinamp-hours.Theamp-hourratingshowshowmanyhoursthebatterywilltakeaspecificdrain:forinstance,a100-amp-hourbatteryhasatheoreticalcapacitytopowera1-ampdevicefor100hours,ora100-ampdevicefor1hour.I say theoretical, because the reality is that lead acid batteries provide moreenergywhendischargedslowly:a100-amp-hourbatterywilloftenprovide20–25% less power if discharged over a five-hour period, compared to dischargeoveratwenty-hourperiod.Secondly, a lead acid batterymust not be run completely flat.Aminimumof20% state of charge (SOC) should bemaintained in a lead acid battery at alltimes to ensure the battery is not damaged. For best overall battery life, youshoulddesignyoursystemsothatthebatterychargerarelygoesbelow50%.

TypesofbatteriesTherearethreetypesofleadacidbattery:

‘Wet’batteriesrequirecheckingandtoppingupwithdistilledwater,butperformbetterandhavealongerlifespanthanotherbatteriesAGMbatteriesrequirenomaintenancebuthaveashorteroveralllife Gel batteries are alsomaintenance-free, do not emit hydrogen duringchargingandprovideareasonableoveralllife.Theycanbeplacedontheirsideorusedonthemove

In thepast,most installershaverecommended industrialquality ‘wet’batteriesforallsolarinstallations.Theseprovidethebestlong-termperformanceandthelowestcost.Oftencalledtractionbatteries(astheyareheavy-dutybatteriesusedin electric vehicles), they can often have a lifespan of 8–10 years for a solarinstallation.

Alowercostoptiontotheindustrial-qualitytractionbatteryistheleisurebattery,asusedincaravansandboats.ThesearetypicallyeitherwetbatteriesorAGMbatteries. Their lifespan is considerably shorter than traction batteries, oftenrequiring replacement after 3–4 years and significantly less in intensiveapplications.The third option is the gel battery. These have the benefit of being entirelymaintenance-free. They are also completely sealed and do not emit hydrogengas. In the past, gel batteries have not been particularly reliable in solarinstallations, tending to require replacement after 1–2 years. However, morerecently,smallergelbatterieshaveseensignificantimprovementsinlifespanandthey now are comparable to AGM batteries. The price has also droppedsignificantly.Gel batteries are not suitable for big solar applicationswith a power drain ofmore than around 400 watt-hours, but they can provide an excellent, zero-maintenancealternativetowetbatteriesforsmallerapplications.If your solar project requires batteries of 50 amp-hour capacity or less, gelbatteriesareaverygoodalternativetotractionbatteries.Notallbatterymakesare thesame.Frommyexperience, theverybestbatterymanufacturersforsolarenergyinstallationsareCrownandTrojan,bothofwhomhaveexcellentbatteries specificallydesigned for solar installations. Ifonly theverybestwilldoandyouarepreparedtopaythepremium,theOptima‘yellowtop’batteriesprovidethebenefitsofAGMbatteriesinasmaller,lighterbatterywithsomeofthebestoverallperformancefiguresofanybatteryavailabletoday.

BatteryconfigurationsYoucanuseoneormorebatteriesforpowerstorage.Likesolarpanels,youcanwireyourbatteries inparallel inorder to increase theircapacityor inseries inordertoincreasetheirvoltage.Unlikesolarpanels,whichyoucanmixandmatchtocreateyourarray,youneedtousethesamespecificationandsizeofbatteriestomakeupyourbatterybank.Mixingbatterycapacitiesandtypeswillmeanthatsomebatterieswillnevergetfullychargedandsomebatterieswillgetdischargedmorethantheyshouldbe.As a result, mixing battery capacities and types can significantly shorten thelifespanoftheentirebatterybank.

BatterylifespanBatteriesdonotlastforever,andatsomestageinthelifeofyoursolarelectric

system, youwill need to replace them.Obviously, wewant to have a batterysystem thatwill last as long as possible and soweneed to find out about thelifespanofthebatteriesweuse.Therearetwowaysofmeasuringthelifespanofabattery,bothofwhichtellyousomethingdifferentaboutthebattery.

CycleLife isexpressedasanumberofcycles toaparticulardepthofdischarge LifeinFloatServiceshowshowmanyyearsthebatterywilllastifitisstored,chargedupregularly,butneverused

CyclelifeEverytimeyoudischargeandrechargeabattery,youcyclethatbattery.Afteranumber of cycles, the chemistry in the battery will start to break down andeventuallythebatterywillneedreplacing.Thecyclelifewillshowhowmanycyclesthebatterieswilllastbeforetheyneedto be replaced. The life is shown to a ‘depth of discharge’ (DOD), and themanufacturerswillnormallyprovideagraphoratableshowingcyclelifeversesthedepthofdischarge.Typicalfiguresthatyouwillseeforcyclelifemaylooklikethis:

CYCLELIFE20%DOD1600cycles40%DOD1200cycles50%DOD1000cycles80%DOD350cycles

As you can see, the battery will last much longer if you keep your depth ofdischargelow.For this reason, it can often be better to specify a larger battery, or bank ofbatteries,ratherthanasmallersetofbatteries.Mostexpertsrecommendthatyouinstall enough batteries to ensure that your system does not usually dischargeyourbatteriesbeyond50%oftheircapacity.The second benefit of a larger bank of batteries is that this gives you moreflexibilitywithyourpowerusage.Ifyouneedtousemoreelectricityforafewdaysthanyouoriginallyplannedfor,youknowyoucandothiswithoutrunningoutofenergy.

HoldoverWhen considering batteries, you need to consider how long you want yoursystemtoworkwhilethesolararrayisnotprovidinganychargeatall.Thistimespaniscalledholdover.Unless you live inside theArctic orAntarctic Circles (both ofwhich provideexcellentsolarenergyduringtheirrespectivesummers,incidentally),thereisnosuchthingasadaywithoutsun.Eveninthedepthsofwinter,youwillreceivesomechargefromyoursolararray.You may find there are times when the solar array does not provide all theenergy you require. It is therefore important to consider how many daysholdoveryouwantthebatteriestobeabletoprovidepowerfor,shouldthesolararraynotbegeneratingalltheenergyyouneed.Formost applications, a figureof between threedays and fivedays is usuallysufficient.Inourholidayhome,wearedeliberatelynotprovidingenoughsolarenergyforthesystemtorun24/7duringthewintermonths.Duringthewinter,wewantthebatteriestoprovideenoughpowertolastalongweekend.Thebatterieswillthenberechargedwhentheholidayhomeisnolongeroccupiedandthesolarpanelcangraduallyrechargethesystem.For thispurpose, I have erredon the sideof caution and suggested a five-dayholdoverperiodforoursystem.

CalculatinghowlongasetofbatterieswilllastCalculating how long a set of batteries will last for your application is not aprecisescience.Itisimpossibletopredictthenumberofdischarges,asthiswilldependon theconditions thebatteriesarekept inandhowyouuse thesystemoveraperiodofyears.Nevertheless,youcancomeupwithareasonablygoodpredictionforhowlongthebatteriesshouldlast.Thiscalculationwillallowyoutoidentifythetypeandsizeofbatteriesyoushouldbeusing.First, write down your daily energy requirements. In the case of our holidayhome,wearelookingatadailyenergyrequirementof695watt-hours.Then,considertheholdover.Inthiscase,wewanttoprovidefivedaysofpower.Ifwemultiply695watt-hoursadayby5days,wegetastoragerequirementof3,475watt-hoursofenergy.

Batteriesareratedinamp-hoursratherthanwatt-hours.Toconvertwatt-hourstoamp-hours,wedividethewatt-hourfigurebythebatteryvoltage.Ifweareplanningtorunoursystemat12volts,wedivide3,475by12togiveus290amp-hoursat12volts.Ifweareplanningtorunoursystemat24voltsbywiringtwobatteriesinseries,wedivide3,475by24togiveus145amp-hoursat24volts.Wedonotwanttocompletelydischargeourbatteries,asthiswilldamagethem.Soweneedtolookatourcyclelifetoseehowmanycycleswewant.Wethenusethistoworkoutthecapacityofthebatteriesweneed.Onadailybasis during the spring, summer and autumn,we are expecting thesolararraytorechargethebatteriesfullyeverysingleday:itisunlikelythatthebatterieswillbedischargedbymorethan10–20%.However, during the winter months, we could have a situation where thebatteriesgetrundownoveraperiodofseveraldaysbeforethesolarpanelsgetachancetotopthebatteriesbackupagain.Sofor fourmonthsof theyear,weneed to take theworst-casescenariowherethebatteriesmaygetdischargeddownto80%depthofdischargeoverafivedayperiodandthenrechargedbythesolararray.Thebatterieswillallowustodothis350timesbeforetheycometotheendoftheirusefullife.350cyclesmultipliedby5days=1,750days=58monthsAs this scenario will only happen during the four months fromNovember toFebruary, thesebatterieswill lastus for around14½yearsbefore reaching theendoftheircyclelife.In reality, the Life in Float Service figure (i.e. the maximum shelf-life) forbatteriesislikelytobearoundtenyears,whichmeansthat,forthisapplication,theywillfailbeforetheyreachtheircyclelife.Basedonourenergyrequirementsof145amp-hoursat24volts,andamaximumdischargeof80%,wecancalculatethatweneedabatterycapacityof145÷0.8=181.25amp-hoursat24volts.

Second-handbatteriesThere is a good supply of second-hand batteries available. These are oftenavailable as ex-UPS batteries (UPS =Uninterruptable Power Supplies) or ex-electricvehiclebatteries.

Whilst thesewillnothavethelifespanofnewbatteries, theycanbeextremelycheap to buy, often selling at their scrap value. If you areworking to a tightbudgetandyourpowerdemandsarenotgreat, this isaverygoodwaytosavemoney.Donot‘mixandmatch’differentmakesandmodelsofbatteries.Usethesamemake andmodel of battery throughout your battery bank. Iwould also adviseagainstusingamixtureofnewandusedbatteries.Thisisafalseeconomyasthelifeofyournewbatteriesmaybecompromisedbytheolderones.Ifyouareconsideringsecond-handbatteries,tryandfindouthowmanycyclestheyhavehadandhowdeeplytheyhavebeendischarged.ManyUPSbatterieshavehardlybeencycledandhaverarelybeendischargedduringtheirlives.Ifbuyingex-electricvehiclebatteries,rememberthesehavehadaveryhardlifewithheavyloads.However,ex-electricvehiclebatteriescancontinuetoprovidegoodserviceforlower-demandapplications:ifyourtotalloadislessthan1kW,thesebatteriescanprovidegoodservice.Ifpossible,tryandtestsecond-handbatteriesbeforeyoubuythem.Ensuretheyarefullychargedup,andthenuseabatteryloadtesteronthemtoseehowtheyperform.If your second-hand batteries have not been deep cycled many times, thechancesaretheywillnothaveaverylongchargelifewhenyoufirstgetthem.To‘wake themup’,connectasolarcontrolleroran inverter to themandputalow-power device onto the battery to drain it to around 20% state of charge.Thenchargethebatteryupagainusingatricklechargeandrepeat.After threedeepcycles,youwillhave recoveredmuchof thecapacityofyoursecond-handbatteries.If using second-hand batteries, expect them to provide half of their advertisedcapacity.So if theyareadvertisedas100-amp-hourbatteries,assume theywillonlygiveyou50amp-hoursofuse.In thecaseofex-electricvehiclebatteries,assumeonlyone-thirdcapacity.Thechancesare,theywillgiveyoumuchmorethanthis,butbettertobehappywith the performance of your second-hand batteries than to be disappointedbecausetheyarenotasgoodasnewones.

BuildingyourbatterybankBecause we are running our system at 24 volts, we will need two 12-voltbatteriesconnectedinseriestocreateourbatterybank.

We therefore need two12-volt batteries of 181.25 amp-hours each in order tocreatethedesiredbatterybank.Itisunlikelythatyouaregoingtofindabatteryofexactly181.25amp-hours,soweneedtofindabatterythatisatleast181.25amp-hoursinsize.Whenlookingforbatteries,youneedtoconsidertheweightofthebatteries.Asingle 12-volt battery of that sizewillweigh in the region of 50kg (over 110pounds)!Safely moving a battery of that size is not easy. You do not want to injureyourself in the process. A better solution would be to buy multiple smallerbatteriesandconnectthemtogethertoprovidetherequiredcapacity.Becausebatteriescontainacid,theyshouldbeinstalledinabatterytray,sothatanyacidleaksmaybecontained.InAustraliaandCanada,regulationsstatethatbatteriesmustbeenclosedinaventilated,lockableandvermin-proofenclosure.Asitisnotpossibletobuy181.25amp-hourbatteries,Ihavedecidedtousefour100-amp-hour12-voltbatteries,givingmeabatterybankwithatotalcapacityof200amp-hoursat24volts.12-volt,100-amp-hourbatteriesarestillnotlightweight.Theycaneasilyweigh30kg(66pounds)each,sodonotbeafraidtousemore,lighter-weightbatteries,ifyouareatallconcerned.To build this battery bank, you can use four 100-amp-hour, 12-volt batteries,with two sets of batteries connected in series, and then connect both series in

parallel,asshownbelow:Four100-amp-hour12Vbatteries.Ihavepairedupthebatteriestomaketwosetsof100-amp-hour24Vbatteries,andthenconnectedeachpairin

paralleltoprovidea200-amp-hourcapacityat24volts.If Iwereputting together a12-voltbattery system insteadof a24-voltbatterysystem, I couldwire togethermultiple 12-volt batteries in parallel in order to

provide the higher capacity without increasing the voltage:

Four100-amp-hour12Vbatteriesconnectedinparalleltoprovidea400-amp-hour12Vbatterybank.

BatterysafetyWhen choosing batteries, you need to consider the safety aspects of batteries.With the exception of gel batteries, all lead acid batteries produce hydrogen,whichneedstobeventilated.Batteriescanalsobeveryheavyandcareisneededwhenliftingormovingthem.Finally,duetothehighlyacidicnatureofbatteries,protectiveclothingshouldbewornwheneverbatteriesarebeingworkedon,andachemicalclean-upkitshouldbekeptnearby.I will go into more detail about handling batteries during the chapter oninstallation.

SolarcontrollerThe solar controller looks after the batteries and stops them either beingoverchargedbythesolararrayorover-dischargedbythedevicesrunningoffthebatteries.ManysolarcontrollersalsoincludeanLCDstatusscreensoyoucancheckthecurrentbatterychargeandseehowmuchpowerthesolararrayisgenerating.Yourchoiceofsolarcontrollerwilldependonfourthings:

SystemvoltageThecurrentofthesolararray(measuredinamps)Themaximumcurrentoftheload(measuredinamps)Thelevelofdetailyourequirefromthestatusdisplay

Somesolarexpertswillsometimesaddafifthitemtothatlist:batterytype.Tobefair,thiswasaproblemwithsomeoldersolarcontrollers,whichonlyworkedwithspecificbatterytypes.Modernsolarcontrollersworkwithalltypesofleadacid battery without a problem, although you may need to tell your solarcontroller what type of batteries you are using when you are setting up thesystem.AllbuttheverycheapestsolarcontrollersprovidebasicinformationonanLCDscreenthatallowsyoutoseehowmuchpoweryouhavegeneratedcomparedtohowmuchenergyyouareusing,andcanalsoshowthecurrentchargestoredinthebattery.Somesolarcontrollersincludemoredetailedinformationthatallowsyoutocheckonadailybasishowyourpowergenerationandusagecompares.

BalancingthebatteriesAnotherimportantfunctionofasolarcontrolleristomanagethechargeineachbatteryandtoensureeachbatteryisproperlychargedup.Asbatteriesgetolder, thechargeofeachbatterywillstart tovary.Thismeansthatsomebatterieswillchargeanddischargeatdifferent rates toothers. If leftovertime,theoveralllifeofthebatterieswilldeteriorate.Intelligent solar controllers can manage these variations by balancing, orequalizing, the batteries they are charging. On most controllers, you need tomanuallyactivateabalanceaspartofaroutineinspection.

Allowforexpansion

Whenlookingatsolarcontrollers, it isworthbuyingonewithahighercurrentratingthanyouactuallyneed.Thisallowsyouextraflexibility toaddadditional loadsoradditionalpanels toyoursolararrayinthefuturewithouthavingtheadditionalexpenseofreplacingyoursolarcontroller.

MaximumpowerpointtrackingMore expensive solar controllers incorporate a technology called maximumpower point tracking (MPPT). AnMPPT controller adjusts the voltage beingreceived from the solar array toprovide theoptimumvoltage for charging thebatterieswithoutsignificantlossofwattsfromthevoltageconversion.IfyouhaveanMPPTcontroller,youcancapturearound20%moreofthepowergeneratedbythesolararraycomparedtoamorebasiccontroller.Ifyouhavelessthan120Wofsolarpanels,itcanworkoutcheapertobuyextrasolarpanelsratherthanspendtheextramoneyonanMPPTcontroller.However,pricescontinue to falland, ifyouhave thechoice,acontrollerwithmaximumpowerpointtrackingisaworthwhileinvestment.

GroundfaultprotectionMany solar controllers include ground fault protection. In the case of a shortfromthesolararray,aResidualCurrentDevice (RCD)will cutoff thecurrentflow between the solar array and the controller, thereby averting the risk ofdamagetoeitherthecontrollerorthesolararray.In the United States and Canada, RCDs are also known as Ground FaultInterrupters(GFIs).For anything larger than 100-watt solar panel systems, and for all systemsmounted to abuilding,youneed to incorporate a separateRCD/GFI intoyoursystemifyoudonothavegroundfaultprotectionbuiltintoyourcontroller.

BackuppowerSome controllers have one extra useful feature: the facility to start up anemergency generator if the batteries run too low and the solar array is notprovidingenoughpowertocopewiththeload.Thiscanbeausefulfacilityforsiteswherethesystemmustnotfailatanytime,orforcopingwithunexpectedadditionalloads.Whilstthismaynotseemsoenvironmentallyfriendly,manygeneratorsarenow

available that run on bio-diesel or bio-ethanol. Alternatively, you can use anenvironmentally friendly fuel cell system insteadof agenerator.These tend torunonbio-methanolorzincandonlyemitwaterandoxygen.

UsingmultiplecontrollersSometimes it is desirable to have multiple controllers on your solar energysystem.Forinstance,youmaywanttoinstallsolarpanelsindifferentlocationsorfacingindifferentdirections,oryoumayhavemismatchedsolarpanelsthatyouwanttouse.Ifyouneedtohavemultiplecontrollers,onlyoneneedstohavethe expensive features such as battery balancing. The other controllers can bemuchsimplerregulatorsthatsimplyprovideanadditionalchargetothebatteriesandswitchoffwhenthebatteriesarefullycharged.

InvertersWearenotusinganinverterwithourholidayhome,butmanysolarapplicationsdorequireaninvertertoswitchupthevoltagetogrid-levelACcurrent.Aninverterforstand-alonesystemsisadifferentpieceofequipmenttoagrid-

tiesolarinverter.Withagrid-tieinverter,yourpowerisfeedingintothegridandhastoworkinconjunctionwiththegrid.Theinverterconnectsdirectlytoyoursolarpanelsand switchesoffwhen the solarpanelsno longerproduceenoughenergy.Withastand-alonesystem,yourpowerisentirelyseparatefromthegrid.The

inverterconnectstoyourbatterybankandswitchesoffwhenthebatterybankisrunninglowoncharge.Therearethreethingstoconsiderwhenpurchasinganinverter:

BatterybankvoltagePowerratingWaveform

BatterybankvoltageDifferentinvertersrequireadifferentinputvoltage.Smallerinverters,providingupto3kWofpower,areavailablefor12-voltsystems.Largerinverterstendtorequirehighervoltages.

PowerratingThepowerratingisthemaximumcontinuouspowerthattheinvertercansupplytoalltheloadsonthesystem.Youcancalculatethisbyaddingupthewattagesof all the devices that are switched on at any one time. It is worth adding amargin for error to this figure. Inverters will not run beyond their maximumcontinuouspowerratingforverylong.Most invertershaveapeakpower ratingaswellasacontinuouspower rating.Thispeakpowerratingallowsforadditionalloadsforveryshortperiodsoftime,which is useful for some electrical equipment that uses an additional burst ofpowerwhenfirstswitchedon(refrigerationequipment,forexample).Asageneralruleofthumb,goforabiggerpowerratingthanyouactuallyneed.Inverterscangetveryhotwhentheygetclosetotheirmaximumloadfor longperiods of time.Many professionals recommend that you buy an inverter that

hasacontinuouspowerratingthat isat leastonethirdhigher thanyouplantouse.

WaveformWaveform relates to the quality of the alternating current (AC) signal that aninverterprovides.Lower-cost inverters often provide a modified sine wave signal (sometimesadvertisedasaquasi-sinewave).Moreexpensive invertersprovideapuresinewavesignal.Modified sinewave inverters tend tobeconsiderablycheaperandalso tend tohaveahigherpeakpowerrating.However,someequipmentmaynotoperatecorrectlywithamodifiedsinewaveinverter. Some power supplies, such as those used for laptop computers andportabletelevisions,maynotworkatall,whilesomemusicsystemsemitabuzzwhenrunfromamodifiedsinewaveinverter.Thesefaultsareeliminatedwithapuresinewaveinverter,whichproducesACelectricitywithanidenticalwaveformtothestandarddomesticelectricitysupplyprovidedbythegrid.

InstallationoptionsandoperatingenvironmentSmallinverterswithacontinuouspowerratingoflessthan3kWarelightweightunitsandareoftensimplyplacedonashelforadesk.Medium-sizedinverterstend to be heavy units that need to be mounted securely on a wall. Largerinverters,ratedat10kWorabove,mayneedtobeboltedtoafloor.All inverters generate a significant amount of heat, especially when runningclosetotheirratedoutput,andrequiregoodairflowaroundtheunit.Mostoff-gridinvertersaredesignedtobeinstalledinside.Outdoorinvertersareavailable, but they are expensive and may be difficult to source. If you arelookingatinstallinganinverteroutdoors,checkthattheinverterissealedagainstdustandwateringress,ratedtoatleastIP64.Overheatinginvertersisthenumberonereasonforanysolarsystemfailing.Asaninvertergetshotter,theyprovidelesspower,andifthetemperaturecontinuesto rise they will eventually shut down to avoid permanent damage. Whenchoosinganinverter,checkitsoperatingtemperaturesandconsiderhowyoucanensureyoursystemremainswithintheselimits.Inverters should always be installed in a well-ventilated area, away from the

ceiling and with a clearance around each side, the top and the bottom. Theycannotbe installed inasealedcupboard.Some invertershave theoptionofanexternal heat sink, or temperature-controlled cooling fans to help keep theinvertercool.Ifyourinverterisproducingmorethanaround500wattsofpower,itislikelytomake a very small amount of noise. This is typically a continuous low-levelhum.This isusuallyonlynoticeable if thesurroundingareaisquiet.However,for this reason, inverters are not usually installed inside the living space in ahomeorinanofficeenvironment.Instead,considerinstallingyourinverterinagarage,oronanoutsidewallofyourbuilding.Occasionally, with larger inverters, the sound made by the inverter has beenknown to resonate with the wall, amplifying the sound and making it quiteunpleasanttolivewith,eveniftheinverterismountedtoanoutsidewallorthewallofagarage.Thisisaveryrareoccurrence,butismostlikelytooccurifyouareplanningtomountyourinverterontoawallmadeoutofsolidconcrete.Thesolution is todampen themountingbetween the inverter and thewallor floorthattheinverterismountedonto.ThereisaveryeffectiveproductcalledGreenGlue, produced by the Green Glue Company (www.GreenGlueCompany.com)that is applied between the wall and the inverter. When it is compressed byremounting the inverter, theglue spreadsout to forma sound isolationbarrierthatisparticularlyeffectiveatblockingoutlow-resonancevibrations.

GroundfaultprotectionMostinvertersnowincludegroundfaultprotection.Allinvertersmustalwaysbegrounded. If your chosen grid-tie inverter does not incorporate ground faultprotection, you need to incorporate this into your system using a ResidualCurrentDevice(RCD).RCDsareknownasGroundFaultInterrupters(GFIs)intheUnitedStatesandCanada.

CablesIt is easy to overlook them, but cables have a vital part to play in ensuring asuccessfulsolarelectricsystem.Therearethreedifferentsetsofcablesthatyouneedtoconsider:

SolararraycablesBatterycablesAppliancecabling

Solar array cabling has already been discussed. For stand-alone systems, thebatteryandappliancecablingalsoneedstobecorrectlyspecified.For all cabling, make sure that you always use cable that can cope with themaximumamountofcurrent(amps)thatyouareplanningtoworkwith.Takeintoaccountthatyoumaywishtoexpandyoursystematsomepointinthefuture,anduseahigheramperecable thanyouactuallyneed inorder tomakefutureexpansionassimpleaspossible.

BatterycablesBattery cables are used to connect batteries to the solar controller and to theinverter.Theyarealsousedtoconnectmultiplebatteriestogether.Batteryinterconnectcableisavailableready-madeupfrombatterysuppliers,oryou can make them up yourself. You should always ensure that you use thecorrectbatteryconnectorstoconnectacabletoabattery.

AppliancecablingIfyouareusinganinvertertorunyourappliancesatgrid-levelvoltage,youcanusestandarddomesticwiring,wiredinthesamewayasyouwouldwirethemforconnectiontodomesticACpower.Ifyouare runningcabling for12-voltor24-voltoperation,youcanwireyourdevices up using the same wiring structure as you would use for grid-levelvoltage,althoughyoumayneedtouselargercablesthroughouttocopewiththehighercurrent.Inahouse,youwouldtypicallyhaveanumberofcircuitsfordifferentelectricalequipment:onefordownstairslighting,oneforupstairslightingandoneortwofor appliances, depending on how many you have. This has the benefit ofkeepingeach individualcable runas short aspossible, aswell as reducing the

amountofcurrentthateachcircuitneedstohandle.As we have already learnt, low-voltage systems lose a significant amount ofpower through cabling.The reason for this is that the current (amps) ismuchhigherandthepowerlostthroughthecableisproportionaltothesquareofthecurrent. You therefore need to keep your cable runs as short as possible,especiallythecablerunswiththehighestcurrentthroughput.Ihavealreadymentionedhowyoucancalculate suitablecable thicknesses foryour solar array earlier in this chapter. You use the same calculation forcalculatingcablethicknessesforappliancecabling.

PlugsandsocketsFor12-voltor24-voltcircuitswithacurrentoflessthan30amps,youcanusethe same standard switches and light sockets as you do for normal domesticpower.However, you must not use the standard domestic plugs and sockets forattachinglow-voltagedevicestoyourlow-voltagecircuit.Ifyoudo,youruntherisk that your low-voltage devices could accidentally be plugged into a high-voltagecircuit,whichcouldhavedisastrousconsequences.Instead,youhavethechoiceofusingnon-standardplugsandsocketsorofusingthesame12-voltplugsandsocketsasusedincaravansandboats.Theselow-voltagesocketsdonotneedtohaveaseparateearth(ground)wire,asthenegativecableshouldalwaysbeearthed(grounded)onaDCcircuitsystem.

AppliancesSofar,Ihavetalkedalotabout12-voltappliances,butyoucanbuymostlow-voltageappliancesforeither12-voltor24-voltandalotofthemareswitchablebetween12and24volts.Compared toappliances that run fromgrid-levelvoltages,youoftenpaymorefor low-voltage appliances. This is not always the case, however, and withcarefulshoppingaround,itemsliketelevisions,DVDplayers,radiosandlaptopcomputersneednotcostanymoretobuythanstandardversions.

Lighting12-volt and24-volt lighting is often chosen for off-grid solar electric systems,duetothelowerpowerconsumptionofthelower-voltagelighting.Youcanbuylow-voltage, energy-saving bulbs and strip lights, both of which provide thesame quality of light as conventional lighting. Filament light bulbs are alsoavailableinlow-voltageforms,andalthoughthesearenotveryenergy-efficient,theydoprovideanexcellentqualityoflight.You can buy a lot of 12-volt lighting from ordinary hardware stores. Manykitchenandbathroomlightsworkatlowvoltageandwillworkjustaswellfroma12-voltbatterysupplyastheywillfromthe12-voltACtransformerstypicallyusedwiththislighting.Diachronicfloodlamps,halogenspotlamps,striplampsandLED lights often run at 12 volts, giving you an excellent choice. Buyingthesefromahardwarestoreratherthanfromaspecialistsolarsuppliercanalsosaveaconsiderableamountofmoney.

RefrigerationAgoodselectionofrefrigeratorsandfreezersareavailablethatwillrunfrom12-voltand24-voltpowersupplies.Somerefrigeratorswillrunonbothlow-voltageDCandgrid-levelACvoltage,andsomecanrunfromabottledgassupplyaswell.Unlike most other devices that you will use, refrigerators need to run all thetime. Thismeans that, although the power consumption can be quite low, theoverallenergyconsumptioniscomparativelyhigh.Therearethreetypesoflow-voltagerefrigeratoravailable:

Absorptionfridgesarecommonlyfoundincaravansandcanoftenuse12-volt,grid-levelvoltageandbottledgastopowerthefridge.Thesearevery

efficient when powered by gas, but efficiency when powered on lowervoltagesvariesconsiderablyfordifferentmodels Peltiereffectcoolers arenot really fridges in theirownright; theyareportablecoolers,ofthetypeoftensoldincaraccessoryshopsandpoweredbythe12-voltin-caraccessorysocket.Whilstthesearecheap,mostofthemarenotveryefficient.AvoidusingtheseforsolarapplicationsCompressorfridgesusethesametechnologyasrefrigeratorsinthehome.They are the most efficient for low-voltage operation. They are moreexpensivethanothertypesbuttheirefficiencyissignificantlybetter:manymodelsnowconsumelessthan5wattsofelectricityperhour

Youcanchoosetouseastandarddomesticfridgeforyoursolarelectricsystem,runningatgrid-levelvoltages.However, theyare typicallynotasefficientasagood 12-volt/24-volt compressor fridge. Domestic fridges also tend to have averyhighstartingcurrent,whichcancauseproblemswithinverters.A number of manufacturers now produce refrigerators that are specificallydesigned toworkwithsolarpower.CompaniessuchasWaeco,SundanzerandShoreline produce a range of refrigerators and freezers suitable for home,medicalandbusinessuse.If you wish to use a standard domestic fridge, speak to the supplier of yourinvertertomakesuretheinverterissuitable.Manyrefrigeratorshaveaveryhighstart-upcurrentandyoumayneed tobuya larger inverter thatcanhandle thissuddendemand.

MicrowaveovensStandarddomesticmicrowaveovensconsumealotmorepowerthantheirratedpower: their rated power is output power, not input. You will find the inputpoweronthepowerlabelonthebackoftheunit,oryouwillbeabletomeasureitusingawattmeter.Typically, the input power for amicrowave oven is 50%higher than its ratedpower.Low-voltagemicrowaveovensareavailable,oftensoldforuseincaravansandrecreational vehicles (RVs). They tend to be slightly smaller than normaldomestic microwaves and have a lower power rating, so cooking times willincrease,buttheyaremuchmoreenergy-efficient.

Televisions,DVDs,computergamesconsolesandmusic

Flat screenLCD televisions andDVDplayers designed for 12-volt or 24-voltoperationareavailablefromboating,campingandleisureshops.Thesetendtobequiteexpensive,oftencostingasmuchas50%morethanequivalentdomestictelevisionsandDVDplayers.However, many domestic LCD televisions (with screens up to 24-inch) andDVDplayersoftenhaveexternalpowersuppliesandmanyofthemareratedfora12-voltinput.Someinvestigationsatyourlocalelectricalstorewillallowyoutoidentifysuitablemodels.Ifyouwanttouseoneofthese,itisworthbuyinga12-voltpowerregulator toconnect between the television and your battery. Battery voltages can varybetween11.6voltsand13.6volts,whichisfineformostequipmentdesignedfor12-voltelectrics,butcoulddamagemoresensitiveequipment.Powerregulatorsfix the voltage at exactly 12 volts, ensuring that this equipment cannot bedamagedbysmallfluctuationsinvoltage.Manypowerregulatorswillalsoallowyoutorun12-voltdevicesfroma24-voltcircuit,andaremuchmoreefficientthanmoretraditionaltransformers.Power regulators also allow you to switch from one voltage to other lowvoltages, if required.Forexample, theSonyPlayStation3gamesconsoleuses8.5volts,andwithasuitablepowerregulatoryoucanpoweroneveryeffectivelyfrom12-voltbatteries.Power regulators can stepupvoltages aswell as stepdown.A suitablepowerregulatorcanswitchthevoltagefromasolarbatterybanktoanoutputvoltageofbetween1½voltsand40volts,dependingonthespecificationoftheregulator.This means that many normal household items with external power supplies,suchassmallertelevisions,laptopcomputers,DVDplayers,musicsystemsandcomputer games, to name but a few, can be connected directly to your solarpowersystem.

MusicsystemsLiketelevisionsandDVDplayers,manymusicsystemshaveanexternalpowersupply,andapowerregulatorcanbeusedinplaceoftheexternalpowersupplytopoweramusicsystem.Alternatively, you can build your own built-in music system using in-carcomponents.Thiscanbeveryeffective,bothintermsofsoundqualityandprice,withtheaddedbenefitthatyoucanhidethespeakersintheceiling.Usingamusicsystemwithaninverterwhichhasamodifiedsinewavecanbe

problematic.Musicsystemsdesignedtorunatgrid-levelvoltagesexpecttoworkonapuresinewavesystemandmaybuzzorhumifusedwithamodifiedsinewaveinverter.

Dishwashers,washingmachinesandtumbledryersDishwashers, washing machines and tumble dryers tend to be very powerhungry.Therearesmallwashingmachines, twin tubsandcool-airdryersavailable thatrun on low voltage, but these are really only suitable for small amounts ofwashing.Theymaybefineinaholidayhomeorinasmallhouseforoneperson,butarenotsuitablefortheweeklywashingforafamilyoffour.Ifyouneedtorunawashingmachinefromasolarelectricsystem,youaregoingto need an inverter to run it. The amount of energy that washing machinesconsumereallydoesvaryfromonemodeltothenext.Anenergy-efficientmodelmayonlyuse1,100watts,whereasanoldermodelmayusealmost threetimesthisamount.The same is true for dishwashers. Energy-efficient models may only use 500watts,whereasoldermodelsmayusenearer2,500watts. If youneed to runadishwasher,youwillneedtouseaninverter.Tumble dryers are hugely energy inefficient and should be avoided if at allpossible.Mostofthemusebetween2,000and3,000wattsofelectricityandrunforatleastonehourperdryingcycle.Therearevariousalternativestotumbledryers.Theserangefromthetraditionalclotheslineorclothesairertothemorehigh-techlow-energyconvectionheatingdryersthatcandryyourclothesinaroundhalfanhourwithminimalamountsofpower.Ifyoureallymusthaveatumbledryer,youmaywishtoconsiderabottledgaspowered tumble dryer. These are more energy-efficient than electric tumbledryersandwillnotputsuchastrainonyoursolarelectricsystem.

AirconditioningsystemsOverthepastcoupleofyears,anumberofmanufacturershavebeenlaunchingsolarpoweredairconditioningandaircoolingsystems.Airconditioninghastraditionallybeenverypowerhungry.Forthisreason,solarpoweredairconditioninghasbeenunaffordable,asalargesolararrayhasbeenrequiredsimplytorunthecompressors.

In response, manufacturers have developed more efficient air conditioningsystems,designedtorunfromaDCpowersource.Companies such as Austin Solar, Solar AC, Securus, Sunsource, Sedna Aire,HitachiandLGhaveallannouncedairconditioningunitsdesignedtoworkwithsolarenergy.Othermanufacturershavedevelopedevaporativeaircoolers thatusea fractionofthepowerofanairconditioningunit.Whilsttheseaircoolersdonotprovidethe‘instantchill’factorofafullairconditioningsystem,byrunningconstantlywhenthesunisshining,theycanprovideaverycomfortablelivingandworkingenvironmentatafractionofthecostoffullairconditioning.

ReputablebrandnamesMostsolarmanufacturersarenothouseholdnames,andassuchitisdifficultforsomeoneoutsidetheindustrytoknowwhichbrandshavethebestreputation.Ofcourse, this isasubjective listandsimplybecauseamanufacturerdoesnotappearonthislist,itdoesnotmeanthebrandortheproductisnotgood.

SolarpanelmanufacturersandbrandsAtlantis Energy, BP Solar, Canadian Solar, Clear Skies, EPV, Evergreen,Conergy,G.E.Electric,Hitachi, ICP,Kaneka,Kyocera,Mitsubishi,PowerUp,RECSolar,Sanyo,Sharp,SolarWorld,Spectrolab,Suntech,Uni-solar.

SolarcontrollerandinvertermanufacturersandbrandsApolloSolar,BlueSky,Enphase,EverSolar,Exeltech,Fronius,Kaco,Magnum,Mastervolt, Morningstar, Outback, PowerFilm, PV Powered, SMA, Solectria,Sterling,Steca,SunnyBoy,Xantrex.

BatterymanufacturersandbrandsEast Penn, Chloride, Crown, EnerSys, Exide, Giant, GreenPower, Hawker,ManBatt,Newmax,Odyssey,Optima,Panasonic,PowerKing,Tanya,Trojan,USBattery,Yuasa.

ShoppinglistfortheholidayhomeBecauseoursolarelectricsystemisbeinginstalledinthegarden,10metres(33feet)awayfromthehouse,wehaveworkedoutthatweneedtorunoursystemat24voltsratherthan12volts,duetothehighlevelsoflossesinthesystem.IhavealreadycalculatedthatIneed320wattsofpowerfrommysolararrayat24volts.Toachievethis,Iwillneedtoconnect12-voltsolarpanelsinseriestomakea24-voltsystem.Therearevariousdifferentoptionsavailable tomakea320-watt,24-volt solararray. After checking with a number of suppliers, I have come up with thefollowingoptions:

Buytwo160-wattpanelsfora totalof320wattsofpower– totalcost£499($768US)Buyfour80-wattpanelsforatotalof320wattsofpower–totalcost£434($668US) Buyeight40-wattpanelsfora totalof320wattsofpower– totalcost£640($985US)Buysix60-wattpanelsforatotalof360wattsofpower)–totalcost£580($893US)

It is reallyworth shopping around and finding the best price. Prices can varydramaticallyfromonesuppliertoanotherandIhaveseenmanycaseswhereonesupplier is selling a solar panel for over twice the price it is available fromelsewhere.DependingonwhatconfigurationIbuy(andwhereIbuyit),solarpanelpricesforthedifferentcombinationsvarybetween£434($668US)and£640($985).Basedonprice and convenience, I havedecided togo for the cheapest optionandbuyfourClearSkies80-wattpolycrystallinesolarpanels.BecauseIamrunningat24voltsandatarelativelylowcurrent,Ihaveagoodchoiceofsolarcontrollerswithoutspendingafortune.IdecidedtobuyaStecaMPPTcontroller,which incorporates a built-inLCDdisplay so I can seehowmuch chargemy batteries have at any one time. The cost of this controller is£225($350).

ThisdrawingshowshowIintendtowireupmysolararray.Iwillpairtwosetsofpanelstogetherinseriestobringthevoltageupfrom12voltsperpanelto24voltsperpair.Ithenconnectthepairstogetherinparalleltomaintainthe24voltsbuttoincreasethepowerofthesystemtoatotalof

320wattsIcalculatedthatIneeded181Ahof24-voltbatterystorage.Ihavedecidedtogofor fourTrojan12V,105Ahbatteries,which Iwillconnect together inpairs toprovideme 210Ah of power at 24 volts. The cost of these batteries is £560($860).

ThisdrawingshowshowIintendtowireupmybatteries.Iwillpairtwosetsofbatteriestogetherinseriestobringthevoltageupto24voltsperpair.Ithenconnectthepairstogetherinparalleltomaintainthe24volts

buttoincreasemystoragecapacityto210amp-hoursat24voltsMyStecacontrollerincorporatesGroundFaultProtection,butIhavedecidedtoinstallaseparateRCD(GFI)unitaswell.Itisa‘beltandbraces’approach,butRCDsareextremelycheapandIfeelit isworththeextramoney.Istillneedawayofisolatingthesolararraymanually.IchoosetoinstallthreeDCisolationswitches:onebetweenmycontrollerandthesolararray,onebetweenmysolarcontrollerandmybatteriesandonebetweenmycontrollerandmydistributionbox. This allows me to isolate each part of my system separately, formaintenanceorincaseofanemergency.Forlighting,Ihavedecidedon24-voltenergysavingcompactfluorescentlightbulbs for insideuseanda24-volthalogenbulkhead light foranoutdoor light.The energy saving compact fluorescent light bulbs look identical to grid-poweredenergysavinglightbulbsandprovidethesameleveloflightingastheir

grid-poweredequivalents.Bulbscostaround£8/$13eachandIcanusethesamelightswitchesandfittingsasIwouldforlightspoweredbythegrid.IhavedecidedtouseaShorelineRR14battery-poweredfridge,whichcanrunoneither12-voltor24-voltpowersupplies.Thishasaclaimedaveragepowerconsumptionof6wattsperhourandcosts£380($610).Fortelevision,IhavechosenaMeos19-inchflatscreenTVwithbuilt-inDVDplayer.TheMeosTVcan runon12-voltor24-voltpowerandhasanaveragepower consumption of 45 watts. This is slightly higher than I was originallyplanningfor(Iwasplanningtobuyamodelwitha40wattpowerconsumption),butnotbyenoughtobeofanygreatconcern.Atthisstage,InowknowthemaincomponentsIamgoingtobeusingformyholiday home. I have not gone into all the details, such as cables andconfiguration.Weneed tocomplete thatasweplan thedetaileddesignforoursolarenergysystem.

Inconclusion When choosing solar panels, buy from a reputablemanufacturer.Theperformanceofthehigh-qualitypanels,especiallyinovercastconditions,isoftenbetterthanthecheaperpanels,andtheimprovedbuildqualityshouldensurealongerlifeLeadacidbatteriescomeinvarioustypesandsizes.YoucancalculatetheoptimumsizeofbatterybasedoncyclelifewhenoperatingonyoursystemThevoltageyourunyoursystematwilldependonthesizeofcurrentyouwant to run through it. High-current systems are less efficient than low-current systems, and low-current inverters and controllers are inevitablycheaper Allowforfutureexpansioninyoursystembybuyingabiggercontrollerandinverterthanyoucurrentlyneed,unlessyouareabsolutelycertainyourrequirementsarenotgoingtochangeinthefutureManyappliancesanddevicesareavailableinlow-voltageversionsaswellasgrid-levelvoltageversions.Generally, the low-voltageversions tend tobemoreefficient Whenwiringin12-voltor24-voltsockets,donotusestandarddomesticpowersockets. Ifyoudo,youare running theriskof low-voltagedevicesbeingpluggedintogrid-levelvoltagesockets,whichcouldhavedisastrousconsequences

Planning,regulationsandapprovals

Depending on where you live around the world, there are different planningrequirements, regulations and approvals needed for installing a solar energysystem.Somecountrieshavelittleornoregulationinplace;othercountrieshaveextremelytightregulations.Insomecountries,theregulationschangefromoneregiontoanother.Consequently,itisimpossibletoprovideeverybitofrelevantinformationhere.Instead, we provide much of this information onwww.SolarElectricityHandbook.com.Youwill also be able to find informationfromyourlocalplanningauthorityandelectricityproviders.Whereveryoulivearoundtheworld, there isasimplemantrafordealingwithauthoritywhenitcomestobuildingandelectricalregulationsandapprovals:ifindoubt,ask.Ignoranceisneveranexcuse.Inthecaseofasolarinstallation,thepeopleyouneedtospeaktoareyourlocalplanning office, your buildings insurance provider and, if you are building agrid-tiesystem,yourlocalelectricitycompany.Notonlywilltheybeabletohelpensure you do not fall foul of any regulation; you will often find they are ahelpfulandusefulsourceofinformationintheirownright.

National and international standards for solarcomponentsIn the United States, Canada, Australia and across Europe, solar panels andinvertersmust complywith specific standards inorder tobeused inagrid-tiesystem.Theunitsaretestedtoensurethattheyconformtothesestandardsbeforetheyareallowedonsale.Across Europe, solar panels have to be certified to IEC safety standard IEC61730 and performance standards IEC 61215 or IEC 61646. Solar grid-tieinverters have to conform to IEC 62109. Some European countries haveadditional certification. In Germany, grid-tie inverters must have a VDE126certification,whilstintheUnitedKingdom,gridtieinvertersthatproducefewerthan16ampsofpeakpower(3.6kW)musthaveG83/1certification,andlargerinverters require the much more complicated G59/1 certification. Also in theUnitedKingdom, solar panels and inverters have to be certified by theMicrogenerationCertificateScheme (MCS) in order to be eligible for feed-in tariffsandotherfinancialincentives.In theUnited States, solar panels, solar cables and inverters have to haveULcertification. Solar panels must conform to the UL 1703 standard. Grid-tieinvertersmustconformtoUL1741andsolarcablingmustconformtoUL4703orUL854(USE-2).Ifyouareusingbatteriesinyourdesign,thebatteriesmustconformtoeitherUL1989,UL2054,UL-SU2580orUL-SU1973.In Canada, solar panels must conform to safety standard ULC/ORD-C1703-1and design standards CAN/CSA C61215-08 or CAN/CSA C61646-2, whilstgrid-tieinvertersmustconformtoCSAC22.2No.107.1.BatteriesmustconformtoCAN/CSAF382-M89(R2004).InAustralia,solarpanelsmustconformtoAS/NZS5033,whilstgrid-tieinvertersmustconformtoAS4777.Ifyouareplanningastand-alonesysteminabuilding,yoursystemmustalsoconformtoAS4509.Ifyouareplanningamobilesystem,for instance inacaravanor recreationalvehicle,your systemmustconform toAS3001.Itisworthnotingthat,inalloftheseregions,nodifferentiationismadebetweengrid-tie solar and stand-alone systems for component selection. If you arebuildingasolarenergysystemthatistobefittedtoabuilding,yoursystemmustusecertifiedcomponentsinordertocomplywithbuildingandelectricalsafetyregulationsintheseregions.

Ifyouusenon-approvedequipmentinagrid-tiesysteminthesecountries,youwillnotbeallowedtoconnectyoursystemtothegrid.Youarealsolikelytobein contravention of building regulations and may invalidate your buildingsinsurance.

InstallationregulationsInmanycountries,includingtheUnitedStates,Canada,Australia,NewZealandand throughout most of the European Union, you cannot work on buildingelectricsunlessyouareaqualifiedelectrician.Somecountriesallowyoutoworkon electrics, but your work has to be checked and certified by a qualifiedelectricianbeforecommissioning.Inthemain,low-voltageDCcircuitsareexcludedfromthislegislation,butitisworthensuringthatthisisthecaseinyourregion.Inmanycountries, thereareadditionalqualificationsforelectriciansthatallowthemtoinstallandcertifysolarenergysystems.Inmostcountries,itisnotyetalegal requirement to have additional training in order to install photovoltaicsystems.However, if youwish to get access to government subsidies, feed-in tariffs orrenewable energy certificates, you will almost certainly need to have yoursystem installed, or at least checked, tested and certified, by qualified solarinstallation specialists. This is certainly the case in the United Kingdom andAustralia.IntheUnitedStates,subsidiesvaryfromstatetostate,andoftenfromcountytocounty.

GettingyourelectricitysupplierinvolvedIfyouareplanningagrid-tiesystem,itisworthgettingyourelectricitysupplierinvolvedinyourprojectearlierratherthanlater.Sometimestheyhavetheirownrequirementsorlistsofapprovedequipment.Theyoftenhavespecialistsyoucanspeakto,whocangiveyouextraadviceandsupport.In most parts of the world, your electricity company will usually need to beinvolvedwhileyoursystemisbeinginstalled,replacingyourcurrentelectricitymeterwithaspecific import/exportmeterandcarryingout the final inspectionbeforeapprovingyoursystem.Some electricity companies will only accept feed-in connections fromprofessional solar PV installers.Almost all electricity providers insist that theinstallationisinspectedandsignedoff,eitherbyacertifiedsolarinstallerorbyone of their own inspectors, before theywill accept your connection onto thegrid.

SolargrantsandsellingyourpowerAround the world, governments are encouraging the take-up of solar energy.Financial assistance comes through various different schemes, and researchingwhatisavailablecanbeconfusingandtime-consuming.Thedifferenttypesofschemesthatareofferedindifferentplacesaredescribedinmoredetailbelow.Thespecificschemesforgrantsandtheamountofmoneyyoucanreceiveforinstallingsolarpowerandsellingyourelectricityvaryfromcountry to country, and often from county to county. Many countries arecurrentlyreviewingtheirschemes,whichmeansthatinformationthatiscurrentonemonthwillbeoutofdatethenext.The Solar Electricity Handbook website has information on specific financialincentiveschemesforvariouscountries,asthiscanbekeptmoreup-to-datethanthebook.

Generalinformationaboutgrants,taxcreditsandfeed-intariffsWhilst some schemes are flexible over who is allowed to install your solarenergy system,most schemeswork in conjunctionwith agoverningbody thatinsiststhatyoursystemisinstalledbyoneoftheirmembers.In some cases, individuals have been able to get their system signed off by asolarenergycompanyinordertoclaimthefinancialincentives.However,thisisoftenatthediscretionofthesolarinstallers,andmanywillrefuseoutright.In general, financial incentives are being offered through four differentmechanisms:

Feed-intariffsTaxcreditsRenewableEnergyCertificates(RECs)Remoteinstallationallowances

Feed-intariffsIfyouhaveagrid-tiesolarenergysystem,youcanoftensellyourpowerbacktothe electricity companies. This is done through a feed-in tariff, where theelectricityprovidersagreetobuyyoursurpluspoweratanagreedrate.In some countries, feed-in tariffs are set by the electricity companies and canvary throughout theday,dependingonsupplyanddemand. Inothercountries,

feed-intariffsarefixedbythegovernment,oftenatapremiumrateinordertocompensatesolarownersfortheup-frontcostofinstallingtheirsystems.In many cases, the government guarantees the value of feed-in tariffs for aminimumnumberofyears, therebyguaranteeing thatownersmakeareturnontheirinvestments.Acommonthemewithgovernmentsistosetaveryhighvaluefor feed-in tariffs initially and then to reduce the feed-in tariff values for newcustomers significantly after two years. This has happened in Spain, Portugal,Germany,HongKongandnowtheUnitedKingdom.Themessageisthis:ifyouareofferedguaranteed long-term feed-in tariffs at a verygood andguaranteedrateof return, takeup theoffer: thescheme isunlikely to remainavailable formorethantwoyears.TaxcreditsA second option for compensating solar energy owners is a tax credit schemewhereallorpartoftheinstallationcostofasolarenergysystemmaybeoffsetagainsttax.Insomecountries,theseschemesareonlyavailabletobusinesses;inotherstheyareavailabletoindividualsaswell.Withataxcredit,youpayfortheinstallationupfront,butthenreceivepartorallofthemoneybackthroughtaxcreditsoverone,twoorthreeyears.The United States of America are currently offering tax credits for peopleinstalling solar energy systems through the Federal TaxCredits forConsumerEnergy Efficiency scheme. There are additional tax credits available in somestatesandcounties.RenewableEnergyCertificates(RECs)RenewableEnergyCertificatesaretradablecertificatesthatprovethatacertainamountofenergywasgeneratedfromrenewablesources.Thesecertificatescanbeboughtandsoldontheopenmarket.Whoeverownsthecertificatecanclaimtohaveboughtelectricityfromarenewableresource.Therearetwomarketsforbuyingrenewableenergycertificates:

The voluntary sector –where individuals and companies elect to buygreenelectricityandpayapremiumtodoso Theelectricityprovidersthemselves,whoaremandatedbygovernmentstoprovideacertainpercentageoftheirelectricityfromgreensources

In some countries, individuals and small businesses who install solar energysystemsareeligibletoreceiverenewableenergycertificatesfortheenergytheyproduce. In many cases, renewable energy certificates are available for both

grid-tieandstand-alonesystems.In some countries, governments have encouraged the take-up of small-scalesolarbyprovidingamultiplierforsmallsolargenerators.Undertheseschemes,solar energy owners can receive two, three or even five times the number ofrenewableenergycertificatesfortheenergytheyproduce,ensuringthatownerscanearnmoneyfromtheirsmall-scalesolarenergysystems.RenewableenergycertificatesarealsoknownasGreenTagsintheUnitedStatesandTradableRenewableCertificates(TRCs)inSouthAfricaandNewZealand.RemoteinstallationallowancesRemote installationallowancesareoffered ina fewcountries.They tend tobeavailableforindividualsandbusinesseswithpremisesinremoteareas,wherethecostofconnectingthesebuildingstothegridisveryhigh.Bytheirverynature,thesesystemsarestand-alone,off-gridapplications.Agoodexample of the sort of scheme on offer is theAustralianmodel that providescreditsforpeopleinstallingsolarwherethecostofconnectingtheirpremisestothegridisgreaterthanAUS$30,000,orthedistancebetweenthepremisesandthegridisgreaterthan1km.Howmuchmoney is available, andhow it ispaid,varies fromone scheme toanother.InAustralia,theremoteinstallationallowanceisofferedbymultiplyingthe number of renewable energy certificates that owners can receive for theirsystem.

Inconclusion There are different rules and regulations for installing solar powerdependingonwhereyoulive You have to comply with the building regulations and electricalregulationsthatareinforceinyourregion Youwillbeabletofindhelpbytalkingtoyourlocalplanningofficeandyour electricity provider. You will also need to talk to your buildinginsurancecompany There aremany national and international standards for solar energysystems,coveringboththeactualphysicalhardwareandhowitisinstalled Inmanyplacesaroundtheworldtherearefinancialincentivesavailablefor solar energy providers.These schemes vary, but tend to fall into fourcamps:feed-intariffs,taxcredits,renewableenergycertificatesandremoteinstallationallowances Whatincentivesareavailable,andtheirvalue,changesregularly.Checkthewebsiteforup-to-dateinformation

DetailedDesign

Bynow,youknowwhatcomponentsyouaregoingtouseforyoursolarproject.Thenextstepis toworkonyourdetaileddesign:effectively,apictureofwhatyouwanttobuild.Evenforsimpleprojects,itmakessensetodrawupadiagrambeforeinstallation.Thebenefitsofdrawingawiringdiagramarenumerous:

ItensuresthatnothinghasbeenoverlookedItwillassistinthecablesizingprocessIthelpsensurenothinggetsforgottenintheinstallation(especiallywherethereisagroupofpeopleworkingtogetheronsite)Itprovidesusefuldocumentationformaintainingthesysteminthefuture

The wiring diagram will be different for each installation and will varydepending onwhat components are used.Read the product documentation foreachcomponentforinformationonhowitmustbewired.Ifyouhavenotyetchosenyourexactcomponentsatthisstage,drawageneraldiagrambutmakesurethatyoufleshthisoutintoadetaileddocumentbeforetheinstallationgoesahead.

Asamplewiringdiagramforasimplestand-alonelightingsystemWhen drawing up your wiring diagrams, you will need to remember thefollowing:

SafetyisdesignedinIt is easy to forget that solar energy can be dangerous.We are working withelectricityandwhilstanyindividualcomponentmayonlybelow-voltage,someof the currents involved can be quite significant. Furthermore, connectingmultiplesolarpanelsorbatteriestogetherinseriescanveryquicklycreateahighvoltage. It is therefore important that safety be taken into account during thedetaileddesignphaseoftheproject,aswellasduringinstallation.Whendesigningthesystem,askyourselfthisquestion:

“What’stheworstthatcanhappen?”Solar energy systems are relatively straightforward and the design of all thecomponentsyouwillusewillkeepriskstoanabsoluteminimum.Nevertheless,there arepotential risks. Ifyouare awareof these risks,youcan take steps toeradicatetheminyourdesign.

Whatistheworstthatcanhappenwithasolarinstallation?Withsolarenergy,wewillbeworkinginafewriskareas:DCelectricsfromthesolararray,highcurrentsfrombatteries,ACelectricsifyouareusinganinverter,andhightemperaturesfromthesolarpanelsthemselves.Each of these risk areas can pose problems, both in isolation and whencombined.Itisworthconsideringtheseriskstoensurethatyoucandesignoutasmanyofthemaspossible.

GroundingyourelectricsExcept for a very small system, such as rigging up a light in a shed, a solarenergysystemshouldalwaysbeearthed(grounded).Thismeansrunningawirefromanegativeterminaltoanearthingrod(knownasagroundingrodinNorthAmerica)thatisrammedintotheground.Anearthingrod(groundingrod)isa1m(3foot)longmetalpole,typicallymadeof copper. They are available from all electrical wholesalers and builders’merchants.Connections to a ground prevent build-up of static electricity and can helppreventcontactwithhighvoltagesifthecircuitgetsdamaged.If you are connecting a solar array to a home, you should always include agroundconnectionfromthesolararrayitself.Whilstitisoptionalinothercases,itisalwaysagoodideatoincludeagroundfromasolararray,wherethearrayis

capableofgeneratingmorethan200watts.Youmustalsoearththebatterybank,astheyarecapableofdeliveringveryhighcurrents.If you areusingbothACelectrics andDCelectrics inyour system,youmustalwayshaveaseparategroundforeachsystem.GroundingasystemwhereyoucannotconnecttothegroundTheremaybeinstanceswhereyouarebuildingasystemwherenoconnectiontotheground ispossible.For instance, aportable solar chargingunit that canbecarriedanywhere,orasolarpoweredboat.Typically,thesedesignsareverysmall,usingonlyDCelectricsandrunningonlya fewampsof current. If your solar array is less than100watts, your systemruns at 12 volts and you are drawing less than 10 amps of current, you areunlikelytoneedacommonearthforallyourcomponents.For larger systems, a ground plane is often used. A ground plane is a high-capacity cable connected to the negative pole on the battery, to which everyother component requiring a ground is also connected. A thick, heavy-dutybatteryinterconnectioncableisoftenusedasagroundplanecable,withthinnerwires connecting to this ground plane cable from every other componentrequiringanearth.Asanalternativetoahigh-capacitycable,dependingonwhatyouareinstallingyoursolarsystemon,youcanuseametalframeasthecommongroundforyoursystem.Instandardcarelectrics,forexample,thegroundplaneisthecarbodyitself.

DCElectricsDirect current electricity typically runs at relatively low voltages: we are allfamiliarwithAA batteries and low-voltage transformers used for charging updevices such as mobile phones. We know that if we touch the positive andnegativenodesonanAAbatterywearenotgoingtoelectrocuteourselves.However, direct current electricity can be extremely dangerous, even atcomparatively low voltages. Around theworld, a small number of people arekilled every year by licking 9-volt batteries, because of the electric jolt theyreceive.Scalethatuptoanindustrialgradeheavy-duty12-volttractionbattery,capable of delivering over 1,000 amps of current, or a solar array capable ofproducinghundredsofvoltsonanopencircuit,anditiseasytoseethatthereisarealriskinvolvedwithDCelectrics.IfyouareelectrocutedwithACpower,thealternatingcurrentmeansthatwhilst

theshockcanbefatal,themostlikelyoutcomeisthatyouwillbethrownbackand let go. If you are electrocutedwithDC power, there is a constant chargerunningthroughyou.Thismeansyoucannotletgo.IfyouareelectrocutedwithveryhighcurrentDC,theinjuryismorelikelytobefatal thanasimilarshockwithACpower.Becauseofthelowcurrentfromasinglesolarpanel,youareunlikelytonoticeanyjoltifyoushort-circuitthepanelandyourfingersgetintheway.However,wireupmultiplesolarpanelstogetheranditisadifferentstory.Foursolarpanelsconnectedinseriesproduceanominal48volts.Thepeakvoltageisnearer80–100volts.Atthislevel,ashockcouldprovefatalforayoungchildoranelderlyperson.Thecurrentthinkingwithgrid-tiesolarsystemsistoconnectmanysolarpanelstogetherinseries,creatingaveryhigh-voltageDCcircuit.Whilsttherearesome(small)efficiencybenefitsofrunningthesystematveryhighvoltage,therearerisks aswell, both during the installation and the ongoingmaintenance of thesystem.There are issues with the 12-volt batteries too. Industrial grade, heavy-dutybatteriescaneasilydeliverachargeof1,000ampsforashortperiod.Shortoutabatterywithaspannerand itwillbe redhot in justa fewseconds. In fact, thecurrent delivery is so great it is possible toweldmetal using a single 12-voltbattery.Thebig riskwithDCelectrics is electrocutingyourself (or somebody else) orcausinga short circuit,which in turn could cause a fire.Solarpanelsgenerateelectricity all the time, often including a small current at night, and cannotsimplybeswitchedoff.Therefore,thereneedtobemanualDCcircuitbreakers(also called isolation switches) to isolate the solar panels from the rest of thecircuit,plusagoodgroundandagroundfaultprotectionsystemtoautomaticallyswitchoffthesystemshouldashortcircuitoccur.Ifyoursystemisrunningatahighvoltage,youmaywanttoconsidermultipleDC circuit breakers/ isolation switches between individual solar panels. Thismeansthat,aswellasshuttingofftheoverallcircuit,youcanreducethevoltageofthesolararraydowntothatofasinglepanelorasmallgroupofpanels.Thiscan be of benefit when maintaining the solar array, or in the case of anemergency.A short circuit in a solar array can happen formany reasons. Sometimes it isbecause of a mistake during installation, but it can also occur as a result ofgeneral wear and tear (especially with installations where the tilt of the solar

panelsisadjustedregularly)orasaresultofanimaldamagesuchasbirdmesscorrodingcablesorjunctionboxes,orafoxchewingthroughacable.Short circuits can also occur where you are using unsuitable cabling. Solarinterconnection cabling is resistant toUV rays andhigh temperatures, and theshieldingisusuallyreinforcedtoreducetheriskofanimaldamage.Alwaysusesolarinterconnectioncablingforwiringyourarrayandforthecablingbetweenthearrayandyoursolarcontrollerorinverter.When a short circuit does occur, there is often not a complete loss of power.Instead,powergenerationdropsas resistancebuildsup.There isabuild-upofheatatthepointoffailure.IfyouhaveagroundfaultprotectionsystemsuchasanRCDorGFIinplace,thesystemshouldswitchitselfoffautomaticallyatthispoint,beforeanyfurtherdamageiscaused.Ifyoudonothaveagroundfaultprotectionsysteminplace, theheatbuild-upcan become quite intense, in some cases as high as several hundred degrees.There have been documented instanceswhere this heat build-up has started afire.Ifafiredoesbreakout,youneedtobeabletoisolatethesystemasquicklyaspossible. Because a solar array cannot be switched off (it always generatespowerwheneverthereislight)therehavebeencaseswherethefirebrigadehavenotbeenabletoputoutafiregeneratedbyafaultinasolararraybecausetherehasbeennowayofswitchingitoff.Isolatingthesolararrayquickly,usingaDCcircuitbreaker,resolvesthisproblem.However, remember that, even if you isolate the solar array, you are stillgenerating power within the solar array. If you have many solar panels, thevoltageandthecurrentcanstillbequiteconsiderable.TheabilitytoshutdownthearraybyfittingDCcircuitbreakerswithinthearraycansignificantlyreducethispower,renderingthesystemfarsaferifthereisanemergency.

ACelectricsACelectricalsafetyisthesameashouseholdelectricalsafety.Itishigh-voltageand in many countries you are not allowed to work with it unless you aresuitablyqualified.You will need to install two AC isolation switches: one switch between theinverterandthedistributionpaneltoisolatethesolarsystemcompletely,andoneswitchbetweenyourgrid-feedandyourdistributionpaneltoisolateyoursystemfromthegridifyouarerunningagrid-tiesystem.

If you are planning a grid-tie installation, you will need to speak with yourelectricitysupplier,as therewilloftenbeadditional requirements thatyouwillneedtoincorporate.Yourinverterwillneedtobeaspecificgrid-tiesystemthatswitchesoffinthecaseofagridpowercut.Thisensuresthatpowerisnotfedbackintothegridfromyoursolarsysteminthecaseofapowerfailure,whichcouldotherwiseprovefatalforanengineerworkingonrestoringpower.

HightemperaturesWe have already touched on the risk of high temperatures with a solar array.Solar panels are black and face the sun: they can therefore get very hot on awarmday.Itmaynotbehotenoughtofryanegg,butinmanyclimatesitcancertainlybehotenoughtoburnskin.Somakesureyoursolararrayisinstalledinaplacewhereitcannotbetouchedbycuriouschildren.Ifthesolarpanelsareclosetotheground,makesurethereissomeprotectiontokeeppeopleawayfromit.Thehigh temperaturesbecomemoreofaproblemif there isa faultwithin thesolararrayorwiththewiresrunningbetweensolarpanels.Ifacableorasolarpanel becomes damaged, there can be significant heat build-up. As alreadymentioned,thisheatbuild-upcanleadtoafire.Aresidualcurrentdevice(RCD),otherwiseknownasagroundfaultinterrupter(GFI) should avert this problem, allowing you to investigate the issue beforesignificantdamageoccurs.However,manualDCcircuitbreakersshouldalsobeinstalledinordertooverridethesystemincaseofanemergency.

ThinksafetyThatistheendofthesafetylecturefornow.Iwilltouchonsafetyagainwhenwe come to installation, but for now, please remember that safety does nothappen by accident.Consider the safety aspectswhen you are designing yoursystemandyouwillendupwithasafesystem.TheadditionalcostofafewACand DC circuit breakers, an earthing rod/ grounding rod, an RCD/ GFI andgetting the rightcables isnotgoing tobreak thebank. It ismoneywellworthspending.

SolararraydesignAll solarpanels in an arraymust face in the samedirection.This ensures thateach cell receives the same amount of light, which is important for optimumpowerproduction.Sometimes,youmaywant to installsolarpanels indifferent locations,suchasontwodifferentpitchesofroof.Inthisinstance,youneedtokeepthetwobanksofsolarpanelsseparate,runningthemastwoseparatearrays,eitherbyfeedingthemintoaninverterorcontrollerthatcanhandlemorethanonesolarinput,orbyfeedingthemintotwoseparateinvertersorcontrollers.Ifyouwishtomixandmatchdifferentsizesofsolarpanel,youwillalsoneedtosettheseupinseparatearraysandwiretheseseparately,eitherusinganinverteror controller that can handlemore than one solar input, or using two separateinvertersorcontrollers.Ifyouaredesigningagrid-tiesystem,whereyouareconsideringdifferentsizesor orientations of solar panels, you should seriously consider amicro-invertersystemwhereeachsolarpanelhasitsowninverter.

Solararraydesign–stand-alonesystemsIfyouhavemore thanone solarpanel andyouare runningyour solar electricsystemat12volts,thenyouwillneedtowireyourpanelstogetherinparallelinordertoincreaseyourcapacitywithoutincreasingtheoverallvoltage.Ifyouarerunningyoursolarelectricsystemathighervoltages,youeitherneedtobuyhigher-voltagesolarpanels,oryouwillneedmorethanonesolarpanel,wiredinseriestoincreasethevoltageofthesolarpanelstothevoltageofyouroverallsystem:

Fora24-voltsystem,youhavethechoiceofusing24-voltsolarpanels,ortwo12-voltsolarpanelsconnectedinseries Fora48-voltsystem,youcanuseone48-voltsolarpanel, two24-voltsolarpanelsconnected inseries,or four12-volt solarpanelsconnected inseries

Onceyouhavereachedthevoltagethatyouwant,youcanthenrunthepanelsboth in seriesand inparallel, connectingstringsofpanels together in series toreach your desired voltage, and then connecting multiple strings together inparallel to increase your capacity:

Asamplediagramofa24-voltarraywheretwosetsoftwo12-voltsolarpanelsareconnectedinseriesinordertocreatea24-voltarrayandthetwoarraysarethenconnectedinparalleltocreateamorepowerful24-volt

array.

Solararraydesign–grid-tiesystemswithmicro-invertersIfyouaredesigningagrid-tiesystemandusingmicro-inverters,yourdesignisextremely simple. Each solar panel becomes a self-sufficient solar energysystem, each feeding power into its own micro-inverter. The micro-invertersconverttheenergytoACandfeeditintothemainACcircuit.

Solararraydesign–grid-tiesystemswithasingleinverterIfyouaredesigningagrid-tiesystemwithasingleinverter,youwilltypicallybeconnectingallyoursolarpanelsinseriesandthenfeedingthishigh-voltageDCpowerintoaninverter.

Asimplifiedblockdiagramofatypicalgrid-tiesystemusingasingleinverter.Theresidualcurrentdevice(RCD)providesgroundfaultprotection.IntheUnitedStates,anRCDisknownasagroundfault

interrupter(GFI)Because of the very high DC voltages involved, additional safeguards arenecessary.Thesolararraymustalwaysbegrounded,theremustbeaDCcircuitbreaker(alsoknownasanisolationswitch)installedbetweenthesolararrayandthe inverter and there must be a DC residual current device/ ground faultinterrupterinstalledtoshutdownthesolararrayinthecaseofashortcircuit.In the diagram below, there are sixteen solar panels connected in series.Assumingeachsolarpanelproducesa12-voltoutput, thissystemwillrunatanominal 192 volts,with a peak power in the region of 320 volts and an opencircuitvoltageof416volts.Becauseoftheveryhighvoltages,IhavedecidedtoinstalladditionalDCcircuitbreakersinthemiddleofthesolararrayinordertoreducethevoltagewithinthearrayifIswitchthemoff.Thismakesthesystemsaferduringmaintenanceandcanreducetheriskoffireorelectrocutionincaseofanemergency.ThediagramshowstwoACisolationswitches:oneswitchbetweentheinverterandthedistributionpaneltoisolatethesolarsystemcompletelyfromyourhouseandoneswitchtoisolateyourbuildingfromthegrid.

Above:Asampleblockdiagramforagrid-tiesystem

IntheUnitedStates,youarenotallowedtohaveagrid-tiesolarenergysystemwhere any part of that systemhas the potential to run at over 600 volts. Thismeansthattheopenvoltageofyoursolararraymustbelessthan600volts.Ingeneral,thismeansthatyouwillnotwanttoconnectmorethantwenty12-voltsolarpanelsorten24-voltsolarpanelsinseries,inordertoensurethatyoustaywellbelowthislevel.In Europe, it is advisable that your open circuit voltage remains under 1,000volts.Ingeneral,thismeansthatyouwillnotwanttoconnectmorethanthirty12-voltsolarpanels,orfifteen24-voltsolarpanelsinseries.Ifyouarerunningclosetothislimit,therearethreeoptions,whichIhavelistedinorderofpreference:

Installamicro-invertersystem Installamulti-stringsystem,eitherusinganinverter thathandlesmorethanonesolarfeed,orbyusingtwoseparateinvertersWireyoursolarpanelsinaparallel/serieshybrid

BatteriesBatteriesarewiredinasimilarwaytoyoursolararray.Youcanwireupmultiple12-volt batteries in parallel to build a 12-volt system with higher energycapacity, or you canwiremultiple batteries in series to build a higher-voltagesystem.Whenwiringbatteriestogetherinparallel,itisimportanttowirethemupsothatyoutakethepositiveconnectionoffthefirstbatteryinthebankandthenegativeconnectionoffthelastbatteryinthebank.Thisensuresequalenergydrainandchargingacross theentirebatterybank. Ifyouusethesamebatteryinthebankfornegativeandpositiveconnectionstothecontroller and inverter, you drain this first battery faster than the rest of thebatteries in the bank. The first battery also gets the biggest recharge from thesolararray.Thisshortensthelifeofthebatteryandmeansallthebatteriesinthebankendupoutofbalance.Otherbatteries in thebanknevergetfullychargedbythesolararray,as thefirstbatterywill reportbeingfullychargedfirstandthecontrollerwill then switch thepoweroff rather than continuing to charge the rest of thebatteries in the bank. The result is that the batteries end up with a shorterlifespan.

Howtowirebatteriesinparallel:thediagramontheleft,wherepowerfeedforbothpositiveandnegativeistakenoffthefirstbatteryinthebank,showshownottodoit–itwillleadtopoorbatteryperformanceand

prematurebatteryfailure.Thediagramontheright,wherethepositivefeedistakenoffthefirstbatteryinthebankandthenegativefeedistakenoffthelastbatteryinthebank,iscorrectandwillleadtoamorebalancedsystem

withasignificantlylongerlife.

ControllerAcontrollerwillhaveconnectionstothesolararray,tothebatterybankandtoDC loads. Although controllers tend not to have the same heat problems asinverters,theycangetwarminuse.Makesuretheyareinstalledinanareawithgood ventilation around them and in a location where they can be easilychecked.

InverterWhere an inverter is used in a stand-alone or grid fallback system, it isconnecteddirectlytothebatterybankandnotthroughthecontroller.Makesurethatyoudesignyoursystemsothattheinverterisinawell-ventilatedarea.Takeintoaccounttheweightoftheinverterandensurethatitisinstalledinalocationwhereitcaneasilybechecked.

DevicesDevicesareconnectedtotheinverteriftheyrequiregrid-levelvoltage,ortothecontrolleriftheyarelow-voltageDCdevices.Theyareneverconnecteddirectlytothesolararrayorthebatteries.

SpecificsforagridfallbacksystemBecauseagridfallbacksystemdoesnotconnectyoursolarenergysystemtothegrid,youarelessrestrictedastothecomponentsyoucanuse.You must still adhere to basic wiring legislation for your country. In somecountries(suchas theUnitedKingdom,for instance) thiscanmeanhaving thefinal connection into your building electricity supply installed by a fullyqualified electrician, but this is significantly cheaper than having a grid-tiesysteminstalledandinspected.The design for a grid fallback system is very similar to a stand-alone solarsystem, i.e. solar panels, solar controller and batteries. The only difference iswhathappensafterthebatteries.Theadvantageofagridfallbacksystemisthatitcanworkinthreeways:itcanprovidepower foranentirebuilding, itcanprovidepower forspecificcircuitswithinabuildingoritcanprovidepowerforasinglecircuitwithinabuilding.MoreinformationandasamplecircuitdiagramforgridfallbackconfigurationsareincludedinAppendixE.

CircuitprotectionCircuit protection is required in any system to ensure the system shuts downsafelyintheeventofashortcircuit.Itisasvalidonlow-voltagesystemsasitisonhigh-voltagesystems.A low-voltage system can cause major problems simply because of the hugecurrent that a 12-volt battery cangenerate: in excessof 1,000amps in a shortburstcaneasilycauseasevereshockandevendeathorseriousinjuryinsomecases.Inthecaseofashortcircuit,yourwiringwillgetextremelyhotandstartmeltingwithinsecondsunlesssuitableprotectionhasbeenfitted.Thiscancausefireorburns,andnecessaryprotectionshouldbefittedtoensurethatnodamagetothesystemoccursasaresultofanaccidentalshortcircuit.

Earthing(grounding)Inallsystems,thenegativeterminalonthebatteryshouldbeadequatelyearthed(referred to as grounded in North America). If there is no suitable earthavailable,agroundingrodorgroundplaneshouldbeinstalled.

DCcircuitprotectionForverysmall systemsgenerating less than100wattsofpower, the fusebuiltinto the controllerwill normally be sufficient for basic circuit protection. In alargersystem,wherefeedforsomeDCdevicesdoesnotgothroughacontroller,afuseshouldbeincorporatedonthebatterypositiveterminal.Where you fit a fuse to the battery, youmust ensure that all current from thebatteryhastopassthroughthatterminal.InDCsystemswithmultiplecircuits,itisadvisabletofitfusestoeachofthesecircuits. Ifyouareusing12voltsor24volts,youcanuse the same fusesandcircuit breakers as youwould for normal domestic power circuits. For higher-voltageDCsystems,youmustusespecialistDCfuses.When connecting devices to your DC circuits, you do not need to include aseparateearth(ground)foreachdevice,asthenegativeisalreadyearthedatthebatteries.Fitanisolationswitch(DCdisconnectswitch)betweenyoursolararrayandyourinverter or controller.Fit a second isolation switchbetweenyourbatteries andyourcontrollerandinverter.

Unlessyourcontrollerorinverteralreadyincorporatesone,youshouldfitaDCresidual current device/ ground fault interrupter between your solar array andyourcontrollerorinverter.

ACcircuitprotectionAC circuits should be fed through a distribution panel (otherwise known as aconsumerunit).Thisdistributionpanelshouldbeearthed(grounded)andshouldincorporateanearthleakagetripwitharesidualcurrentdevice(RCD),otherwiseknownasagroundfaultinterrupter.AsyouwillhaveearthedyourDCcomponents,youmustuseaseparateearth

(ground)forACcircuits.YoumustalsoinstallanACdisconnectswitch(isolationswitch)betweenyourinverter and your distribution panel. In the case of a grid-tie system, this isnormallyalegalrequirement,butitisgoodpracticeanyway.Thewiring in the building should follownormalwiring practices.You shoulduse a qualified electrician for installing and signing off all grid-level voltagework.

CablesizingandselectionOnceyouhaveyourwiringdiagram,it isworthmakingnotesoncablelengthsforeachpartofthediagram,andmakingnotesonwhatcablesyouwilluseforeachpartoftheinstallation.

SizingyourcablesThissectionisrepeatedfromthepreviouschapter.Imakenoapologiesforthis,ascablesizingisoneofthebiggestmistakesthatpeoplemakewheninstallingasolarelectricsystem.Low-voltagesystemsloseasignificantamountofpowerthroughcabling.Thisisbecausecurrents(amps)arehighertomakeupforthelackofvoltage.Ohmslawtellsusthatthepowerlostthroughthecableisproportionaltothesquareofthecurrent: the higher the current, the greater the resistance. To overcome thisresistance,wemustusethickercables.Wherever you are using low-voltage cabling (from the solar array to thecontroller, and to all low-voltage DC equipment) you need to ensure you areusing the correct size of cable: if the cable size is too small, you will get asignificantvoltagedropthatcancauseyoursystemtofail.Youcanworkouttherequiredcablesizeusingthefollowingcalculation:

(LengthxIx0.04)÷(V÷20)=CableThicknessLength:Cablelengthinmetres(1m=3.3feet)I:CurrentinampsV:Systemvoltage(e.g.12voltsor24volts)CableThickness:Cross-sectionalareaofthecableinmm²

Thecablethicknessyouareusingshouldbeatleastthesamesizeastheresultofthiscalculation.Neverusesmallercable,asyouwillseeagreatervoltagedropwith a smaller cable, which could cause some of your devices not to workproperly.

ProtectingcablerunsWhen planning cable layouts, you need to ensure they are protected fromunwantedattentionfromanimalsandchildrenandfrompossiblevandalism.Ratsandfoxeschewingthroughcableinsulationcanbeabigprobleminsomeinstallations. This can be resolved by using rodent protected cabling. Using

conduit isoftenagood ideaaswell,especially ifyoucanusesteelconduitorthin-wallelectricalmetallictubing(EMT)toprotectcables.

DesigningyoursystemtokeepyourcablesrunsasshortaspossibleIfyouhavemultipledevices running indifferentphysical areas,youcanhavemultiplecablerunsrunninginparallelinordertokeepthecablerunsasshortaspossible, rather than extending the length of one cable to run acrossmultipleareas.By doing this, you achieve two things: you are reducing the overall length ofeach cable and you are splitting the load betweenmore than one circuit. Thebenefitofdoingthisisthatyoucanreducethethicknessofeachcablerequired,whichcanmakeinstallationeasier.If you are doing this in a house, you can use a distribution panel (otherwiseknownasaconsumerunit)forcreatingeachcircuit.In the holiday home, for instance, it would make sense to run the upstairslightingonadifferentcircuittothedownstairslighting.Likewise,itwouldmakesensetorunseparatecircuitsforpoweringappliancesupstairsanddownstairs.Inthecaseoftheholidayhome,byincreasingthenumberofcircuitsitbecomespossible touse standard2.5mmdomestic ‘twinandearth’cable forwiring thehouse, rather than more specialist cables. Not only does this simplify theinstallation,itkeepscostsdown.

SelectingsolarcableAcommonfaultwithpoorly-designedorpoorly-installedsolarenergysystemsisunderperformancewherethereisnoclearsourcefortheproblem.Inparticular,thistendstooccuraroundtwotothreeyearsafterthesystemwasfirstinstalled.The source of the problem is often either bird droppings or UV damage oncables leading fromthesolarpanels to the inverters.This isusuallycausedbynot using solar interconnection cables, which have amuch tougher insulationthatisUVprotected,designedtowithstandhightemperaturesandcanwithstandacidicbirddroppings.Itisvitalthatyouusespecificsolarinterconnectioncabletoconnectyoursolarpanelstogetherandforlinkingyoursolarpanelstoyourinverterorcontroller.Ifyouarenotsure,lookforcablethatconformstotheUL4703orUL854(USE-2) specification for PV cabling. This is available from all solar equipmentsuppliers.

ControllercableWhen calculating the thickness of cable to go between the controller and thebattery,youneedtotakethecurrentflowintothebatteryfromthesolararrayaswell as the flowoutof it (peak flow into thebattery isnormallymuchhigherthanflowout).

BatteryinterconnectioncablesYou can buy battery interconnection cables with the correct battery terminalconnectors from your battery supplier. Because the flow of current betweenbatteriescanbeverysignificantindeed,ItendtousethethickestinterconnectioncablesIcanbuyforconnectionbetweenbatteries.

SomesamplewiringdiagramsAsever,apicturecanbeworthathousandwords,soherearesomebasicdesignsand diagrams to help give you a clearer understanding of how you connect asolarelectricsystemtogether.

Above:Asimplesolarinstallation:alightwithlightswitch,asmallradioandasimpleintruderalarm–perfectforagardenshedorasmalllock-upgarage.Becauseitisasmallsystem,youmaychoosenottofitanisolationswitch.Becausethesystemisverysmall,Ihavedecidedonlytofitafuse

betweenthecontrollerandthebattery

Thisisaninterestingproject–asolarpoweredriverboat.Electricboatsaregaininginpopularity,thankstotheirvirtuallysilentrunningandlackofvibration.Theonlydownsideisrechargingthebatteries.Here,solarpanelsareusedtorechargethebatteries,chargingthemupduringtheweektoprovideallthepowerrequiredforaweekendmessingaboutontheriver.Thetotalcostofthiscompletesystemwaslessthanthecostofatraditional

outboardengineandfueltank

Above:Anexampleofa12-voltsolarsystemrunninganACinvertertoprovideanormalbuildingelectricitysupplyinanoff-gridinstallation.

Below:thesamesystem,wiredat24volts

Theholidayhomewiringdiagram

ThenextstepOnce you have yourwiring diagram, it is time to start adding cables, batteryterminal clamps, fuses, isolation switches, earthing rods (referred to asgrounding rods in North America) and, in this case, a distribution panel(otherwiseknownasaconsumerunit) toyourshoppinglist. Itcanhelp toaddmoredetail toyourwiringdiagramaswell, noting the locationsof appliancesandsockets,andthelengthsofcablesateachpoint.

SolarframemountingThereareoff-the-shelfsolararrayframesavailable,andyoursolarpanelsupplierwillbeabletoadviseyouonyourbestsolution.Sometimes, however, these are not suitable for your project. In this case, youwilleitherhavetofabricatesomethingyourself(angle ironisausefulmaterialforthisjob)orgetabespokemountingmadespecificallyforyou.Solarpanels inthemselvesarenotheavy,butyoudoneedtotakeintoaccountthe effect ofwind loadings on yourmounting structure. If thewind can blowunderneaththesolararrayitwillgeneratea‘lift’,attemptingtopullthearrayupofftheframework.However,agapbeneaththesolararrayisusefultoensurethearrayitselfdoesnotgettoohot.Thisisespeciallyimportantinwarmclimates,wheretheefficiencyofthesolarpanelsthemselvesdropsastheygethotter.Makingsurethemountingisstrongenoughisespeciallyimportantasthesolararrayitselfisnormallymountedatanoptimalangletocapturethenoondaysun.Thisoftenmeansthat,evenifyouareinstallingyoursolararrayontoanexistingroof,youmaywanttoinstallthesolarpanelsataslightlydifferentangletotheroofitselfinordertogetthebestperformanceoutofyoursystem.Itisthereforeimperativethatyoursolararraymountingframeisstrongenoughtosurvive20yearsplusinaharshenvironmentandcanbesecurelymounted.If you aremountingyour solar arrayon a roof, youmust be certain that yourroofisstrongenoughtotakethis.Ifyouarenotcertainaboutthis,askabuilder,structuralsurveyororarchitecttoassessyourroof.Ifyouareplanningtomountyoursolararrayonapoleoronaground-mountedframe, you will need to make plans for some good strong foundations.Hammeringsometentpegsintothegroundtoholdaground-mountedframewillnotlastfiveminutesinastrongwind,andapolewillquicklyblowdownifyouonlyuseabucketofcementtoholditinplace.You shouldbuild a good foundation consistingof a strong concrete base on acompacted hardcore sub-base to hold a ground-mounted frame, and the frameitself should be anchored using suitable ground anchors, bolted using 25cm–30cm(10"–12")bolts.Forapole,followtheadvicegivenbythemanufacturers.Typically,theyneedtobesetinaconcretefoundationthatisatleast3feet(1m)deep,andquiteoftensignificantlymore.

Tomount your solar panels onto your frame, make sure you use high-tensileboltsandself-lockingnutstopreventlooseningduetowindvibration.Ifyoursolararrayisgoingtobeeasilyaccessible,youmaywishtoconsideranadjustablesolarmountingsystemsoyoucanadjusttheangleoftilt throughouttheyear.Youcanthenincreasethetiltduringthewinterinordertocapturemorewinter sun, and decrease the tilt during the spring and summer in order toimproveperformanceduringthoseseasons.For the holiday home project, the solar array is to be fitted to a speciallyconstructedgardenstorewithanangledroof.Thebenefitofthisapproachisthatwecanbuildthestoreat theoptimumpositiontocapturethesun.Wecanalsoinstall the batteries and solar controller very close to the solar array. In otherwords,wearecreatingan‘allinone’powerstation.Thereareanumberofregionalshedandgardenbuildingmanufacturerswhowillbuildagardenstorelikethistoyourspecification.Agoodqualitystore,solongasitistreatedevery2–3years,willeasilylast25–30years.Ifyougo thisroute,makesureyourchosenmanufacturerknowswhatyouareplanningtouseitfor.Youneedtospecifythefollowingthings:

TheangleoftheroofhastobeaccurateinordertohavethesolarpanelsintheiroptimumpositionTheroofitselfhastobereinforcedtobeabletotaketheadditionalweightofthesolararray The floorof thegarden store (where thebatteries are stored)mustbemadeofwood.Batteriesdonotworkwellonaconcretebaseinwinter There must be ventilation built into the store in order to allow thehydrogengasgeneratedbythebatteriestodispersesafelythroughthetopoftheroof Thedoor to the garden store itself shouldbe large enough for you toeasilyinstall,checkandmaintainthebatteries Youshouldconsiderinsulatingthefloor,wallsandceilinginthegardenstore, either using polystyrene (Styrofoam) sheets or loft insulation. Thiswill help keep the batteries from getting too cold inwinter or too hot insummer

A garden storewill still require a solid concrete foundation. Consideration ofrainwater runoff is also important, to ensure the garden store does not end upstandinginapoolofwater.

PositioningbatteriesYou will have already identified a suitable location for your batteries. Asdiscussedonthechapteronsitesurveys,yourlocationneedstofitthefollowingcriteria:

Water-andweatherproofNotaffectedbydirectsunlightInsulatedtoprotectagainstextremesoftemperatureFacilitiestoventilategasesProtectedfromsourcesofignitionAwayfromchildrenandpets

Lead acid batteries give off very small quantities of explosive hydrogen gaswhen charging. Youmust ensure that, wherever your batteries are stored, theareareceivesadequateexternalventilationsothatthesegasescannotbuildup.Because of the extremely high potential currents involved with lead acidbatteries,thebatteriesmustbeinasecureareaawayfromchildrenandpets.Donotinstallbatteriesdirectlyontoaconcretefloor.Inextremelycoldweather,concretecancauseanadditional temperaturedrop inside thebatteries thatwilladverselyaffectperformance.You need to ensure that your batteries are accessible for regular checks andmaintenance.Manydeep-cyclebatteriesrequirewateringseveraltimeseachyearandconnectionsmustbecheckedregularlytoensuretheyhavenotcorroded.Foralloftheabovereasons,batteriesareoftenmountedonheavy-dutyracking,whichisthenmadesecureusinganopen-meshcage.Ifyouareinstallingyourbatteriesinanareathatcangetverycoldorveryhot,you should also insulate your batteries. Extreme temperatures adversely affecttheperformanceofbatteries,soifyourbatteriesarelikelytobeinanareawherethetemperaturedropsbelow8°C(46°F)orriseabove40°C(104°F),youshouldconsiderprovidinginsulation.Ifthetemperatureislikelytodropbelowfreezing,youmustprovideit.Youcanusepolystyrene(Styrofoam)sheetsunderneathandaroundthesidesofthe batteries to keep them insulated. Alternatively, foil-backed bubble-wrapinsulation(availablefromanyDIYstoreintheinsulationsection)iseveneasiertouseandhasthebenefitthatitdoesnotdisintegrateifyouevergetbatteryacid

splashedonit.Never insulate the top of the batteries, as this will stop them from ventingproperlyandmaycauseshortsinthebatteriesiftheinsulatingmaterialyouuseisconductive.

PlanningtheinstallationBynow,youshouldhaveacompleteshopping list forall thecomponentsyouneed.Youshouldknowwhereeverythingistobepositionedandwhatyouneedtoinordertoproceed.Beforeplacinganyequipmentorders,gobacktoyoursiteandcheckeverythingone last time.Make sure thatwhereyouplanned to siteyourarray, controller,batteriesandsoonisstillsuitableandthatyouhavenotoverlookedanything.Onceyouareentirelysatisfiedthateverythingisright,placeyourordersforyourequipment.Bearinmindthatsomespecialistequipmentisoftenonlybuilttoorderandmaynot be available straight away. If you require bespoke items such as solarmountingframes,or,asinthecaseoftheholidayhome,acompletegardenstoremadeupformountingthesolarpanelsandholdingthebatteriesandcontroller,takeintoaccountthatthiscouldtakeafewweekstobebuiltforyou.

Inconclusion The detailed design ensures you have not overlooked any area of thedesignConsiderthesafetyaspectsofyoursysteminyourdesign.Ateachstage,askyourself“Whatistheworstthatcanhappen?”andthendesignaroundtheproblemsThewiringdiagramhelpsyouenvisagehowtheinstallationwillwork Youneedtokeepcablerunsasshortaspracticallypossible.Youcandothisbyrunningseveralcablesinparallel,eitherdirectlyfromthecontroller,throughajunctionboxorthroughadistributionpanelSplittingthecablesintoparallelcircuitsalsomeansyoureducethecurrentload on each circuit, thereby reducing resistance and improving theefficiencyofyoursystem If you are using an inverter to run at grid-level voltages, a qualifiedelectrician is required to handle the electrical installation.However, yourwiring diagram will help your electrician to envisage how your solarelectricsystemshouldwork Youneedtodesignyourbatterystorageareatoensureyourbatteriescanperformtothebestoftheirability

Installation

Congratulationsongettingthisfar.Ifyouaredoingthisforreal,youwillnowhaveagarageorgardenshedfullofsolarpanels,batteries,cables,controllers,isolationswitches,RCDsandwhatnots.Theplanningstageisoverandthefunisabouttobegin.Beforeyougetyourscrewdriveranddrillout,therearejustafewhousekeepingitemstogetoutofthewayfirst…

Haveyoureadtheinstructions?No, of course you haven’t. Who reads instructions anyway? Well, on thisoccasion, it isworth reading through the instructions thatcomewithyournewtoyssothatyouknowwhatyouareplayingwith.Payparticularattention to the solarcontroller and the inverter: therearemanysettingsonmostcontrollersandyouneedtomakesureyougetthemright.

SafetyThereareafewsafetynoticesweoughttogothrough.Someofthesemaynotberelevanttoyou,butreadthemallfirst,justtomakesure.

Remember,youareworkingwithelectricity,dangerouschemicalsandheavybutfragileobjects.Itisbettertobesafethansorry.

YourFirstAidkitYouwillneedagoodFirstAidkitonhand,includingsomeitemsthatyouwillnotnormallyhaveinaregularFirstAidkit.Mostspecifically,youwillneedaneye-washandawashkitorgelthatcanbeappliedtoskinincaseofcontactwithbatteryacid.

Chemicalclean-upkitYou will be working with lead acid batteries that contain chemicals that arehazardoustohealth.Youwillrequirethefollowing:

Achemicalclean-upkitsuitableforcleaningupbatteryacidsinthecaseofaspillAsupplyofstrongpolythenebagsAgoodsupplyofrags/disposablewipestomopupanybatteryspillages

Chemical clean-up kits and chemical First Aid kits are available from mostbatterywholesalersand industrial toolsuppliers.Theyonlycosta fewpounds.You probably will not need them but, if nothing else, they buy you peace ofmind.

ConsideringthegeneralpublicIfyouareworking inanareawhere thegeneralpublichasaccess,youshoulduse barriers or fencing, and signage to cordon off the area. Clear diversionsignageshouldexplainanalternativeroute.Inthisscenario,Iwouldrecommendemployingaprofessionalteamofbuilderstocarryout the installationworkonyourbehalf.TheywillalreadyunderstandtheimplicationsofworkinginapublicareaandtherelevantHealthandSafetyregulations.Evenifyoudonothavetoconsiderthegeneralpublic,youshouldstillconsiderthepeoplearoundyou.Childrenlovetogetinvolvedwiththesesortsofprojectsand there really can be some safety issues involved.Keep children out of the

way,andletanyoneinthevicinityknowthatyouareworkingwithhighvoltagesandtokeepaway.

WorkingatheightYouareverylikelytobeworkingatheightandquitepossiblycrawlingaroundonslantedrooftops.Makesureyouareusingsuitableclimbingequipment(ladders,crawlerboards,safety harnesses, scaffolding). You can hire anything that you do not have atreasonableprices.Ifyouhaveanyconcernsaboutworkingatheights,orifyouareworkingbeyondyour area of competence at any time, remember there is no shame in hiring aprofessional.Aprofessionalbuildercanfitasolararraytoaroofin2–3hours.ThisistypicallylessthanhalfthetimeittakesanamateurDIYenthusiast.

HandlingBatteries,largeinvertersandsolararrayscanbeheavy.Solarpanelsthemselvesmaynotbeheavyintheirownright,butwhenseveralofthemaremountedonaframeandthenliftedtheyareheavy,bulkyandfragile.Moving and installing much of this equipment is a two-person job as aminimum.Morepeoplecanbeusefulwhenliftingasolararrayintoposition.

WorkingwithbatteriesLeadacidbatteriesareextremelyheavy,insomecasesweighingasmuchasanadult.Useproperliftinggeartomovethem,andlookafteryourback.Heavierbatteriesquiteoftenhavehoopsinthetopcase.Toliftabattery,Itendtouseapieceofropethreadedthroughthesehoopstocreateacarryinghandle.ThismeansIcancarryabatteryclosetothegroundandreducetheneedtobendovertoliftit.Lead acid batteries contain acid. Unless they are gel batteries, the acid is inliquid form. It is extremely corrosive and extremely dangerous to health.Splashesofliquidfromthebatteriescancauseseverechemicalburnsandmustbedealtwithimmediately.Whenworkingwithleadacidbatteries,staysafe:

ALWAYSwear protective clothing, including overalls, eye protection(either protective glasses or a full-face shield) and protective gloves. Iwouldalsoadviseyoutowearsteeltoe-cappedshoes

KeepbatteriesuprightatalltimesDonotdropabattery.Ifyoudo,thelikelihoodisthatthebatteryhasbeendamaged.Intheworst-casescenario,thecasingcouldbecrackedorbroken Ifyoudropabattery,placeit immediatelyinaspill tray(aheavy-dutydeep greenhouse watering tray can be used if necessary) and check fordamageandleaksIfyouhaveadamagedbattery,boththebatteryandthespilltraymustbedouble-baggedinsealedpolythenebagsandmarkedashazardouswaste Ifyouhaveaspillagefromabattery,mopupthespillageimmediatelyusingragsordisposablewipes.Placetheseragsinapolythenebag,sealitandmarkitashazardouswaste Ifanyspillagefromabatterycomesintocontactwithclothing,removeclothingimmediatelyanddisposeofitinpolythenebags If any spillage fromabattery comes into contactwith the eyes,washrepeatedlywitheye-washandseekurgentmedicalhelp Ifanyspillagefromabatterycomesintocontactwiththeskin,washoffimmediately with water, apply an anti-acid wash, cream or gel to stopburningandthenseekurgentmedicalhelpIfyouendupwithbatteryacidinyourmouth,washyourmouthoutwithmilk.DONOTswallowthemilk.Spititout.Thenseekurgentmedicalhelp Do not smoke near batteries, and ensure that the areawhere you arestoringthebatteriesisventilatedPreventarcingorshortcircuitsonbatteryterminals.Batteriescanprovidea huge current very quickly. Should you short-circuit a battery with aspanner,thespannerislikelytoberedhotwithinafewsecondsandcouldeasilyleadtofireorexplosion.Removeanyrings,braceletsorwatchesyoumaybewearingandkeeptoolsasafedistanceawayfrombatteries

GlovesYou need two different sets of gloves for installing your solar array: a set ofchemicalglovesformovingbatteriesandasetofelectricalprotectionglovesforwiringupyoursolarsystem.Whenchoosingsuitablechemicalglovesforworkingwithbatteries,consider

thefollowing:

Theglovesneedtobequitestrong,asliftingandmovingbatteriesishardonglovesAgoodgripisimportant Buyaglovewithamediumorlongcufflength,inordertoprotectboththehandsandforearmsTheglovesshouldbemadeofasuitablematerialtoprotectagainstbatteryacid

The Health and Safety Executive website suggest that 0.4mm-thick neoprenegloveswill give suitable protection through a full shift. If you do splash yourgloveswhileworkingwithbatteries,makesureyouwashthemorreplacethemimmediately,inordertoavoidtransferringacidtootherpartsofyourbody.Electrically-insulatedprotectionglovesgiveprotectionwhenworkingwithhighvoltages. These are vitally important when working with high-voltage solararraysandarerecommendedforallinstallations.Electrically-insulatedglovescomewithdifferentratingstoprovideprotectionatdifferentvoltages:

Class00glovesprovideprotectionforupto500voltsClass0glovesprovideprotectionforupto1,000voltsClass1glovesprovideprotectionforupto7,500voltsClass2glovesprovideprotectionforupto17,000voltsClass3glovesprovideprotectionforupto26,500volts

Formostsolarinstallations,Class00orClass0glovesarethemostappropriate.Rememberthattheopencircuitvoltageofasolararraycanbemorethandoublethenominalvoltageof the solar array: twenty solarpanels connected in seriesmayonlyhaveanominalvoltageof240volts,buttheopencircuitvoltagecouldbeover500volts.Like chemical gloves, choose gloves with a medium or long cuff length toprotectbothyourhandsandforearms.Ifyourelectrically-insulatedglovesaresplashedwithbatteryacid,removeandreplacetheglovesimmediately.All electrically-insulated gloves should be visually inspected and checked fortearsandholesbeforeuse.Class1–3glovesrequirefullelectricaltestingeverysixmonths.

ElectricalsafetyImakenoapologies for repeatingmymantraaboutelectrical safety.Electricalsafetyisextremelyimportantwheninstallingasolarelectricsystem.Solar panels generate electricity whenever they are exposed to sunlight. Thevoltage of a solar panel on an ‘open’ circuit is significantly higher than thesystemvoltage.A12-voltsolarpanelcangeneratea22–26voltcurrentwhennotconnected.Connectseveralsolarpanelsinseriesandthevoltagecangettodangerouslevelsveryquickly:a24-voltsolararraycangenerate45–55volts,whichcanprovideanastyshockin thewrongcircumstances,whilsta48-voltsolararraycaneasilygenerate voltages of 90–110 voltswhen not connected.These voltages can belethaltoanyonewithaheartcondition,ortochildren,theelderlyorpets.SolarsystemsproduceDCvoltage.UnlikeACvoltage, ifyouareelectrocutedfromadirectcurrent,youwillnotbeabletoletgo.Batteriescanproducecurrentsmeasuringthousandsofamps.Ashortcircuitwillgeneratehugeamountsofheatveryquicklyandcouldresultinfireorexplosion.Remove any rings, bracelets or watches you may be wearing and keep toolsawayfrombatteries.TheoutputfromaninverterisACgrid-levelvoltageandcanbelethal.Treatitwiththesamerespectasyouwouldanyothergrid-levelelectricitysupply.In many countries, it is law that if you are connecting an inverter into ahouseholdelectricalsystem,youmustuseaqualifiedelectriciantocertifyyourinstallation.

AssemblingyourtoolkitAswellasyourtrustysetofDIYtools,youwillneedanelectricalmulti-meterorvoltmeter inorder to test your installation at different stages.You shoulduseelectrically-insulated screwdrivers whilst wiring up the solar array, and a testlightcircuittestercanbeuseful.Thereareafewsundriesthatyououghttohaveaswell:

Cabletiesareveryusefulforholdingcablesinplace.TheycankeepcablerunstidyandareoftengoodfortemporaryaswellaspermanentuseAwater-anddirt-repellentglasspolishorwax,forcleaningsolarpanels Petroleum jelly is used on electrical connections on solar panels andbatteries in order to seal them from moisture and to ensure a goodconnection

PreparingyoursiteAsmentionedinthepreviouschapter,youmayneedtoconsiderfoundationsforground-or pole-mounting a solar array, or strengthening an existing roofstructureifyouareinstallingyoursolararrayonaroof.If you are installing your batteries in an areawhere there is no suitable earth(ground), you should install an earthing rod (grounding rod) as close to thebatteriesasispractical.

TestingyoursolarpanelsNow the funbegins.Start byunpackingyour solarPVpanels and carryout avisualinspectiontomakesuretheyarenotdamagedinanyway.Chippedorcrackedglasscansignificantly reduce theperformanceof thesolarpanels, so they shouldbe replaced if there is anyvisibledamage to thepanel.Damagetotheframeisnotsuchaproblem,solongasthedamagewillnotallowwateringresstothepanelanddoesnotstopthesolarpanelfrombeingsecurelymountedinposition.Next, check the voltage on the panel using your multi-meter, set to anappropriateDCvoltagerange.SolarPVpanelsgenerateamuchhighervoltageonan‘open’circuit(i.e.whenthe panel is not connected to anything) than they do when connected to a‘closed’ circuit. So do not be surprised if your multi-meter records an openvoltageof20–26voltsforasinglepanel.

InstallingthesolararrayCleaningthepanelsItisagoodideatocleantheglassonthefrontofthepanelsfirst,usingawater-anddirt-repellentglasspolishorwax.Theseglasspolishesensurethatrainanddirt do not stick to the glass, thereby reducing the performance of your solararray. They are available from anyDIY store andmany supermarkets and caraccessoriesstores.

AssemblyandconnectionsSome roof-mounted solarmounting kits are designed to be fitted to your roofbefore fitting the solar panels. Others are designed to have the solar panelsmountedtothefixingkitsbeforebeingmountedtotheroof.Withapole-mountedsystem,youtypicallyerectyourpolefirstandthenfitthesolarpanelsoncethepoleisinposition.Aground-basedmounting system is the easiest to install, as there is noheavylifting.Typically, you mount and wire the solar panels at the same time. If you aresteppingupthevoltageofyoursystembywiringthepanelsinseries,wireuptherequirednumberofpanelsinseriesfirst(i.e.setsoftwopanelsfor24volts,setsoffourfor48volts).Onceyouhavewiredup a set of panels in series, test themusingyourmulti-meter, set toavoltagesetting tocheck thatyouhave theexpectedvoltage (20voltsplusfora12-voltsystem,40voltsplusfora24-voltsystemand80voltsplusfora48-voltsystem).Take carewhen taking thesemeasurements, as 40 volts and above can give anastyshockinthewrongcircumstances.Onceyouhavewiredeachseriescorrectly,makeuptheparallelconnectionsandthen test theentirearrayusingyourmulti-meter, set to theappropriatevoltagesetting.If you have panels of different capacities, treat the different sets of panels asseparate arrays. Do not wire panels of different capacities together, either inseriesorparallel.Instead,connectthearraystogetheratthecontroller.Onceyouhavecompletedtesting,makethearraysafesothatnoonecangetan

electricshockbyaccidentfromthesystem.Todothis,connectthepositiveandnegativecablesfromthesolararraytogethertoshort-circuitthearray.Thiswillnotdamagethearrayandcouldpreventanastyshock.

Roof-mountingasolararrayIf you are roof-mounting a solar array, youwill normally have to fit a rail ormountingtotheroofbeforeattachingthesolararray.Oncethisisinplace,itistimetofitthearrayitself.Makesureyouhaveenoughpeople on hand to be able to lift the array onto the roof without twisting orbendingit.Personally,Iwouldalwaysleavethisjobtoprofessionalbuilders,butthebestwayseemstobetohavetwoladdersandtwopeopleliftingthearrayupbetweenthem,oneoneachladder,orusingscaffolding.

FinalwiringOnce your solar array is in position, route the cable down towhere the solarcontroller is to be installed. For safety purposes, ensure that the cables to thesolararrayremainshortedwhilstyoudothis.IfyouareinstallingaDCisolationswitchandaresidualcurrentdevice(knownasagroundfault interrupter inNorthAmerica), install thembetween thesolararrayandthecontroller.Onceyouhavethecablesinposition,un-shortthepositiveandnegativecablesandcheckwithametertoensureyouhavetheexpectedvoltagereadings.Thenshortthecablesagainuntilyouarereadytoinstallthesolarcontroller.

InstallingthebatteriesPre-installationBefore installing the batteries, youmay need to give them a refresher chargebeforeusingthemforthefirsttime.Youcandothisinoneoftwoways.Youcanuseabatterychargertochargeupthebatteries,oryoucaninstallthesystemandthenleavethesolarpanelstofullycharge up the batteries for a day or so before commissioning the rest of thesystem.Putastickeroneachbatterywithaninstallationdate.Thiswillbeusefulinyearstocomeformaintenanceandtroubleshooting.

PositioningthebatteriesThebatteriesneedtobepositionedsotheyareupright,cannotfalloverandareawayfrommembersofthepublic,childrenandanysourcesofignition.Forinsulationandheatingpurposes,batteriesshouldnotbestooddirectlyonaconcrete floor:during thewintermonths, a slabof concrete canget extremelycoldanditscoolingeffectscanhavedetrimentaleffectsonbatteries.Iprefertomountbatteriesonawoodenfloororshelf.

VentilationIfthereislittleornoventilationintheareawherethebatteriesaresituated,thismustbeimplementedbeforethebatteriesaresited.Asbatteriesventhydrogen,which is lighter thanair, thegaswill riseup.Theventilationshouldbedesignedsothatthehydrogenisventedoutofthebatteryareaasitrises.

AccessItisimportantthatthebatteryareaiseasilyaccessible,notjustforinstallingthebatteries (remembering that the batteries themselves are heavy), but also forroutinelycheckingthebatteries.

InsulationAsmentionedearlier,ifyouareinstallingyourbatteriesinanareathatcangetverycoldorveryhot,youshouldinsulateyourbatteries.

Polystyrene (Styrofoam) sheets or foil-backed bubble-wrap can be usedunderneath and around the sides of the batteries to keep them insulated. DONOTINSULATETHETOPOFTHEBATTERIESasthiswillstopthemfromventingproperlyandmaycauseshortsinthebatteriesiftheinsulatingmaterialyouuseisconductive.

ConnectionsOnce the batteries are in place,wire up the interconnection leads between thebatteriestoformacompletebatterybank.Alwaysusethecorrect terminalsfor thebatteriesyouareusingandmakesurethe cables provide a good connection.You should use battery interconnectioncablesprofessionallymanufacturedforthebatteriesyouareusing.Usepetroleumjellyaroundthemountingstosealitfrommoistureandensureagoodconnection.Next,addanearth(ground)tothenegativeterminal.Ifthereisnoearthalreadyavailable, install an earthing rod (grounding rod) as close as possible to thebatteries.Now check the outputs at either end of the batteries using a multi-meter toensure you are getting the correct voltage. A fully-charged battery should beshowingachargeofaround13–14voltsperbattery.

InstallingthecontrolequipmentThenextstepis toinstall thesolarcontrollerandthepowerinverterifyouareusingone.Mount these close to the batteries. Ideally they should be mounted within ametre(3feet),inordertokeepcablerunsasshortaspossible.MostsolarcontrollersincludeasmallLCDdisplayandanumberofbuttonstoconfigure thecontroller.Makesure thesolarcontroller iseasilyaccessibleandthatyoucanreadthedisplay.Some solar controllers thatwork atmultiple voltages have a switch to set thevoltage you are working at. Others are auto-sensing. Either way, check yourdocumentation tomakesureyou install thesolarcontroller inaccordancewiththemanufacturer’s instructions. If youhave to set the voltagemanually,makesureyoudothisnow,ratherthanwhenyouhavewiredupyoursystem.Inverters canget veryhot inuse and adequateventilation shouldbeprovided.They are normally mounted vertically on a wall, in order to provide naturalventilation. The installation guide that comes with your particular make ofinverterwilltellyouwhatisrequired.Someinvertersrequireanearth(ground)inadditiontotheearthonthenegativeterminalonthebattery.Ifthisisthecase,connecta2.5mm²green-yellowearthcablefromtheinvertertoyourearthrod(groundrod).If you are installing aDC isolation switch between the solar panels and yourcontrolequipment,connectthatupfirstandmakesureitisswitchedoff.Onceyouhavemountedthecontrollerandinverter,connectthenegativecablesto the battery, taking care that you are connecting the cables to the correctpolarity.Thenun-shortthepositiveandnegativecablesfromthesolararrayandconnect the negative cable from the solar array to the solar controller, againtakingcaretoensurethecableisconnectedtothecorrectpolarity.Nowdouble-checkthewiring.Makesureyouhaveconnectedthecablestotheright places.Double-check that you have connected your negative cable fromyoursolararraytothenegativesolarinputconnectiononyoursolarcontroller.Then double-check that you have connected your negative cable from yourbattery to thenegativebattery inputonyoursolarcontrollerandyour inverter.Onlythenshouldyoustartwiringupyourpositiveconnections.Startwith thebattery connection. Ifyouareplanning to install a fuse andDC

isolation switch into this cable,make sure that your fuse and switchwork forboth the solar controller and the inverter (if you are using one). Connect theinverter and the solar controller ends first anddouble-check that youhavegotyourwiringcorrect, bothvisually andbycheckingvoltageswithavoltmeter,beforeyouconnectupthebatterybank.Finally, connect up the positive connection from your solar array to the solarcontroller.At thispoint,yoursolarcontrollershouldpowerupandyoushouldstartreadingcharginginformationfromthescreen.Congratulations.Youhaveaworkingsolarpowerstation!

Installingagrid-tiesystemBefore starting to install your grid-tie system, you must have already madearrangements with your electricity provider for them to set you up as arenewableenergygenerator.Regulations and agreements vary from region to region and from electricityprovidertoelectricityprovider,butattheveryleasttheywillneedtoinstallanexportmetertoyourbuildinginordertoaccuratelymeterhowmuchenergyyouareproviding.Theywill alsoask for an inspectioncertificate fromaqualifiedelectrician,toconfirmthattheworkhasbeendonetoanacceptablestandard.Physically,installingagrid-tiesystemisverysimilartoinstallinganyothersolarenergysystem,except,ofcourse,youdonothaveanybatteriestoworkwith.However,youdohavetobecarefulwhilewiringupthehigh-voltagesolararray.Whenthesolararrayisbeingconnectedupyoucanhaveavoltagebuild-upofseveral hundred volts, which can quite easily prove fatal. If building a high-voltagearray, cover the solarpanelswhileyouareworkingon themandwearelectrically-insulatedglovesatalltimes.

CommissioningthesystemOnceyouhave stoppeddancingaround thegarden in excitement, it is time totestwhatyouhavedonesofarandconfigureyoursolarcontroller.

ProgrammingyoursolarcontrollerThe typeofsolarcontrolleryouhavewilldetermineexactlywhatyouneed toconfigure.Itmaybethatyoudonotneedtoconfigureanythingatall,buteitherwayyoushouldcheckthedocumentationthatcamewiththesolarcontrollertoseewhatyouneedtodo.Typically,youwillneed to tellyoursolarcontrollerwhat typeofbatteriesyouare using. You may also need to tell your solar controller the maximum andminimumvoltage levels to showwhen the batteries are fully charged or fullydischarged.Youshouldhavethisinformationfromyourbatterysupplier,oryoucannormallydownloadfullbatteryspecificationsheetsfromtheinternet.

TestingyoursystemYou can test your solar controller by checking the positive and negativeterminals on the output connectors on the controller using your multi-meter.Switch the multi-meter to DC voltage and ensure you are getting the correctvoltageoutofthesolarcontroller.Ifyouhaveaninverter,plugasimpledevicesuchasa table lampintotheACsocketandcheckthatitworks.Ifyourinverterdoesnotwork,switchitoffandcheckyourconnectionstothebattery.Iftheyareallinorder,checkagainwithadifferentdevice.

ChargingupyourbatteriesIfyouhavenotcarriedoutarefresherchargeonyourbatteriesbeforeinstallingthem, switch off your inverter and leave your system for at least 24 hours inordertogivethebatteriesagoodcharge.

ConnectingyourdevicesOnceyouhaveyoursolarpowerstationupandrunningandyourbatteriesarefullycharged,itistimetoconnectyourdevices.Ifyouarewiringahouseusinglow-voltageequipment,itisworthfollowingthesameguidelinesasyouwouldforinstallinggrid-voltagecircuits.Forlow-voltageapplications,youdonotneedtohaveyourinstallationtestedbyaqualifiedelectrician,butmanypeoplechoose todoso inorder tomakesuretherearenomishaps.The biggest difference betweenACwiring andDCwiring is that you do notneed to have a separate earth (ground) with DC electrics, as the negativeconnection is earthed both at the battery and, if you are using one, at thedistributionpanel.If you areusing12-volt or 24-volt low-voltage circuits, you canuse the samedistributionpanels, switches and light fittings asyouwould in a grid-poweredhome.Asalreadysuggested,donotusethesamepowersocketsforlow-voltageappliancesasyouuse forgrid-poweredappliances. Ifyoudo,yourun the riskthatlow-voltageappliancescouldbepluggeddirectlyintoahigh-voltagesocket,withdisastrousconsequences.

Inconclusion Once you have done all your preparation, the installation should bestraightforwardHeedthesafetywarningsandmakesureyouarepreparedwiththecorrectsafety clothing and access to chemical clean-up and suitable FirstAid incaseofacidspillsSolararraysarebothfragileandexpensive.LookafterthemThemostlikelythingthatcangowrongiswiringupsomethingwrongly.Double-checkeachconnection Checkeachstagebymeasuringthevoltagewithamulti-metertomakesure you are getting the voltage you expect. If you are not, inspect thewiringandcheckeachconnectioninturn

Troubleshooting

Once your solar electric system is in place, it should give youmany years ofuntroubled service. If it does not, youwill need to troubleshoot the system tofindoutwhatisgoingwrongandwhy.

KeepsafeAll the safetywarnings that gowith installation also relate to troubleshooting.Rememberthatsolararrayswillgenerateelectricityalmostallthetime(exceptincompletedarkness),andbatteriesdonothavean‘off’switch.

CommonfaultsUnless you keep an eye on your solar energy system, problems can often goundetected formonths.Only if you have a stand-alone system and the powerswitchesoffwillyoufindoutthatyouhaveaproblem.Thefaultsaretypicallytobefoundinoneofthefollowingareas:

Excessive power usage – i.e. you are using more power than youanticipatedInsufficientpowergeneration–i.e.youarenotgeneratingasmuchpowerasyouexpectedDamagedwiring/poorconnectionsWeakbatteriesObstructions(shading)Faultyearth(ground)Inverterfaults

Obstructions are a big subject by themselves, and I cover this in muchmoredetailinAppendixA.Otherfaultsarecoveredbelow.

ExcessivepowerusageThis is themostcommon reason for solarelectric systems failing: theoriginalinvestigationsunderestimatedtheamountofpowerthatwasrequired.Almost all solar controllers provide basic information on an LCD screen thatallowsyoutoseehowmuchpoweryouhavegeneratedcomparedtohowmuchenergy you are using, and shows the amount of charge currently stored in thebattery bank. Some solar controllers include more detailed information thatallows you to check on a daily basis how your power generation and powerusagecompares.Usingthisinformation,youcancheckyourpowerdraintoseeifitishigherthanyouoriginallyexpected.If you have an inverter in your system, you will also need to measure thisinformation from your inverter. Some inverters have an LCD display and canprovidethisinformation,butifyoursystemdoesnotprovidethis,youcanuseaplug-inwattmetertomeasureyourpowerconsumptionoveraperiodoftime.Ifyour solarcontrolleroryour inverterdoesnotprovide this information,youcan buy amulti-meterwith data logging capabilities. Thesewill allow you tomeasure thecurrentdrain from the solarcontroller and/oryour inverteroveraperiodoftime(youwouldtypicallywanttomeasurethisoveraperiodofaday).Attach the multi-meter across the leads from your batteries to your solarcontrollerandinverter.Logtheinformationforatleast24hours.Thiswillallowyouidentifyhowmuchpowerisactuallybeingused.Some data logging multi-meters will plot a chart showing current drain atdifferent times of the day,which can also help you identifywhen the drain ishighest.

SolutionsIfyouhave identified thatyouareusingmorepower thanyouwereoriginallyanticipating,youhavethreechoices:

ReduceyourpowerloadIncreasethesizeofyoursolararrayAddanotherpowersource(suchasafuelcell,windturbineorgenerator)totopupyoursolarelectricsystemwhennecessary

InsufficientpowergenerationIfyouhavedoneyourhomeworkcorrectly,youshouldnothaveaproblemwithinsufficientpowergenerationwhenthesystemisrelativelynew.However, over a period of a few years, the solar panels and batteries willdegrade in their performance (batteriesmore so than the solar panels), whilstnewobstructionsthatcutoutsunlightmaynowbecausingproblems.Youmay also be sufferingwith excessive dirt on the solar panels themselves,whichcansignificantlyreducetheamountofenergythesolararraycangenerate.Pigeonsandcatsaretheworstculpritsforthis!Yoursitemayhaveanewobstructionthatisblockingsunlightatacertaintimeofday:atreethathasgrownsubstantiallysinceyoucarriedouttheoriginalsitesurvey,forinstance.Alternatively,youmayhavemadeamistakewiththeoriginalsitesurveyandnotidentifiedanobstruction.Unfortunately,thisisthemostcommonmistakemadeby inexperienced solar installers. It is also themost expensive problem to fix.Thisiswhycarryingoutthesitesurveyissoimportant.To identify if your system is not generating as much power as originallyexpected, check the input readings on your solar controller to see howmuchpower has been generated by your solar panels on a daily basis. If your solarcontrollercannotprovidethisinformation,useamulti-meterwithdataloggertorecordtheamountofenergycapturedbythesolarpanelsoverathree-to-fivedayperiod.

SolutionsIfyouhaveidentifiedthatyouarenotgeneratingasmuchpowerasyoushouldbe,startbycheckingyoursolararray.Checkfordamageonthesolararrayandthen give the array a good wash with warm, soapy water and polish using awater-anddirt-repellentglasspolishorwax.Checkall thewiring.Makesurethatthereisnounexplainedhighresistanceinanyofthesolarpanelsoronanyrunofwiring.Itcouldbeafaultyconnectionoradamagedcablethatiscausingtheproblems.Carryoutanothersitesurveyandensure therearenoobstructionsbetweenthesolararrayandthesun.Double-checkthatthearrayitselfisintherightpositiontocapturethesunatsolarnoon.Finally,checkthatthearrayisattheoptimumangletocollectsunlight.

Ifyouare experiencing theseproblemsonlyat a certain timeof theyear, it isworthadjusting theangleof the solarpanel toprovide themaximumpotentialpower generation during this time, even if this means compromising poweroutputatothertimesofyear.Checkthevoltageatthesolararrayusingamulti-meter.Thencheckagainatthesolar controller. If there is a significant voltage drop between the two, theresistanceinyourcableistoohighandyouarelosingsignificantefficiencyasaresult.This could be due to an inadequate cable installed in the first place, ordamage in thecable. Ifpossible, reduce the lengthof thecableand test again.Alternatively,replacethecablewithalargerandbetterqualitycable.Ifnoneofthatworks,youhavethreechoices:

ReduceyourpowerloadIncreasethesizeofyoursolararrayAddanotherpowersource(suchasafuelcell,windturbineorgenerator)totopupyoursolarelectricsystemwhennecessary

Damagedwiring/poorconnectionsIf you have damaged wiring or a poor connection, this can have some verystrangeeffectsonyoursystem.Ifyouhaveoddsymptomsthatdonotseemtoaddup toanything inparticular, thenwiringproblemsorpoorconnectionsareyourmostlikelyculprit.Examples of some of the symptoms of a loose connection or damagedwiringare:

Asuddendropinsolarenergyinverywarmorverycoldweather.Thisisoften due to a loose connection or damaged wiring in the solar array orbetweenthesolararrayandthesolarcontroller Suddenorintermittentlossofpowerwhenyouarerunninghighloads.Thissuggestsalooseconnectionbetweenbatteries,orbetweenthebatteriesandsolarcontrollerorinverter Suddenorintermittentlossofpoweronparticularlywarmdaysafterthesolararrayhasbeenin thesunforaperiodof time.Thissuggestsa looseconnectionsomewhereinthearray,adamagedpanelorhighresistanceinacable Significantly lower levels of power generation from the solar arraysuggest a loose wire connection or a short circuit between solar panelswithinthearray Asignificantvoltagedroponthecablebetweenthesolararrayandthesolarcontrollersuggestseitheraninadequatecableordamagetothecableitself Likewise, a significant voltage drop on the cable between the solarcontroller and your low-voltage devices suggests an inadequate cable ordamagetothecableitself Ifyoufindacablethatisverywarmtothetouch,itsuggeststheinternalresistanceinthatcableishigh.Thecableshouldbereplacedimmediately

Unfortunately,diagnosingexactlywherethefaultiscanbetime-consuming.Youwillrequireamulti-meter,atestlightandplentyoftime.Yourfirsttaskistoidentifywhichpartofthesystemisfailing.Asolarcontrollerthatcantellyouinputsandoutputsisusefulhere.Theinformationfromthiswilltellyouwhetheryoursolararrayisunderperformingorthedevicesarejustnotgettingthepowertheyneed.

Once you know which part of the system to concentrate on, measure theresistanceofeachcableusingtheohmsettingonyourmulti-meter.Iftheinternalresistanceishigherthanyouwouldexpect,replaceit.Ifanycableisexcessivelyhot, replace it. The problem could be caused either by having an inadequatecableinthefirstplace(i.e.toosmall)orbyinternaldamagetothecable.Next, check all the connections in the part of the system you are looking at.Makesurethequalityoftheconnectionsisgood.Makesurethatallcablesareterminated with proper terminators or soldered. Make sure there is no wateringress.

WeakbatteryThesymptomsofaweakbatteryarethateitherthesystemdoesnotgiveyouasmuchpowerasyouneed,oryougetintermittentpowerfailureswhenyouswitchonadevice.Inextremecases,afaultybatterycanactuallyreverseitspolarityandpulldowntheefficiencyoftheentirebank.Weak battery problems first show themselves in cold weather and when thebatteriesaredischarged tobelow50–60%capacity. Inwarmweather,orwhenthebatteriesarechargedup,weakbatteriescanquiteoftencontinuetogivegoodserviceformanymonthsoryears.Ifyour solarcontroller shows thatyouaregettingenoughpower in fromyoursolar array to cope with your loads, then your most likely suspect is a weakbatterywithinyourbatterybank,orabadconnectionbetweentwobatteries.Startwiththecheapandeasystuff.Cleanallyourbatteryterminals,checkyourbatteryinterconnectioncables,makesurethecableterminatorsarefittingtightlyonthebatteriesandcoateachterminalwithalayerofpetroleumjellyinordertoensuregoodconnectivityandprotectionfromwateringress.Thencheckthewaterlevelsinyourbatteries(iftheyare‘wet’batteries).Topupasnecessary.Checktomakesurethateachbatteryinyourbatterybankisshowingasimilarvoltage. If there isadisparityofmore than0.7volts, it suggests thatyoumayneedtobalanceyourbatteries.If, however, you are seeing a disparity on one battery of 2 volts or over, it islikelythatyouhaveafailedcellwithinthatbattery.Youwillprobablyfindthatthisbatteryisalsoabnormallyhot.Replacethatbatteryimmediately.Ifyoursolarcontrollerhasthefacilitytobalancebatteries,thenusethis.Ifnot,topupthechargeontheweakerbatteries,usinganappropriatebatterycharger,untilallbatteriesarereadingasimilarvoltage.Ifyouarestillexperiencingproblemsaftercarryingoutthesetests,youwillneedto run a load test on all your batteries in turn.To do this,make sure all yourbatteriesarefullychargedup,disconnectthebatteriesfromeachotheranduseabattery load tester (youcanhire thesecheaplyfromtoolhirecompanies).Thisloadtesterwillidentifyanyweakbatterieswithinyourbank.

ChangingbatteriesIfallyourbatteriesareseveralyearsoldandyoubelievetheyaregettingtotheendoftheirusefullives,itisprobablyworthreplacingthewholebatterybankinone go. Badly worn batteries and new batteries do not necessarily mix well,becauseofthevoltagedifference.Ifyoumixnewandused,youcaneasilyendupwithabankwheresomeofthebatteriesneverfullychargeup.Ifyouhaveabankofpart-wornbatteriesandonebatteryhasfailedprematurely,itmaybeworthfindingasecond-handbatteryofthesamemakeandmodelasyours.Many battery suppliers can supply youwith second-hand batteries: notonlyaretheymuchcheaperthannew,butbecausethesecond-handbatterywillalso be worn, it will have similar charging and discharging characteristics toyourexistingbank,whichcanhelpitbeddownintoyoursystem.Ifyoucannotfindapart-wornbattery,youcanuseanewone,butmakesureyouusethesamemakeandmodelastheotherbatteriesinyourbank.Nevermixandmatch different models of batteries, as they all have slightly differentcharacteristics.Ifyouaddanewbatterytoapart-wornbank,youmayfindthelifeofthenewbattery is less than you would expect if you replaced all them. Over a fewmonthsofuse,theperformanceofthenewbatteryislikelytodegradetosimilarlevelstotheotherbatteriesinthebank.Beforechangingyourbattery,makesurethatallofyourbatteries(bothnewandold)arefullycharged.Putalabelonthenewbattery,notingthedateitwaschanged.Thiswillcomeinusefulinfutureyearswhentestingandreplacingbatteries.Once you have replaced your battery, take your old one to your local scrapmerchants.Leadacidbatterieshaveagoodscrapvalueand theycanbe100%recycledtomakenewbatteries.

InverterissuesThesymptomsofinverterissuescaninclude:

Buzzing or humming sounds from some electronic equipment whenpoweredfromtheinverterFailureofsomeequipmenttorunfromtheinverterRegulartrippingofcircuitsSuddenlossofpower

Ifyouareexperiencingbuzzingorhummingsoundsfromelectronicequipmentwhenpowered from the inverter,or if someequipment isnot runningat all, itsuggests that the inverter isnotproducingapureACsinewave. Ifyouhaveagrid-tiesystem,theACpuresinewaveformgeneratedbytheinvertermaynotbeperfectlycoordinatedwiththewaveformfromthegrid.Thiswouldsuggestpoorqualitypowerfromthegrid,agroundingissueorafaultyinverter.If you have a stand-alone system and have purchased a modified sine waveinverter (or quasi-sine wave), it may be that you cannot resolve these issueswithout replacing the inverter. Some electronic equipment, such as laptopcomputers andportable televisions,maynotwork at all using amodified sinewave inverter, whilst other equipment will emit a buzz when run from theseinverters.Ifyouhavesuddenandunexplained trippingofcircuitswhenrunningfromaninverter, or experience sudden loss of power, there are a number of things tocheck:

Does the trippingoccurwhenaheavy-loadappliance suchasa fridgeswitchesitselfonoroff?Doesthetrippingoccurwhentheinvertercutsinatthestartofthedayorwhenitcutsoutattheendoftheday? Does the trippingoccurmoreoftenonverywarmdaysorafterheavyrain?

Unfortunately,circuittrippingandsuddenpowerlossoftenonlyoccurswhenacombination of events occur, which can make diagnosis time-consuming anddifficulttogetright.The most common reasons for circuit tripping or sudden power loss aretemperature-related issues. Inverters can generate a huge amount of heat. The

hottertheyget,thelesspowertheyproduce.Iftheinverterisrunningtoohot,asuddenpeakdemandcanbeenough to shut the inverterdownmomentarily. Ifthe inverter runs toohot for too long, itwill shutdown for a longerperiodoftimeinordertocool.If this is the case, you are going to have to provide your inverter with moreventilation.Ifyoucannotkeepitcool,itmayalsomeanthatyourequireamorepowerfulinverterinordertocopewiththeload.Iftheissueoccursduringsuddenrainoronveryhotdays,youmayalsohaveagroundingproblem.ChecktheinverterwithaPATtestertoensurethatyouarenot getting a ground leakage from the inverter itself. If you are, check all theconnectionsfromtheDCinputofyourinverter.

MaintainingYourSystem

There is very little maintenance to be carried out on a solar electric system.There are some basic checks that should be carried out on a regular basis.Typicallytheseshouldtakenomorethanafewminutestocarryout.

AsrequiredCleanthesolararray.Thisactuallytakesverylittleeffort:unlessyoulivein averydry anddustypart of theworld, the rainwill usuallydoaverygoodjobofwashingyoursolarpanelscleanonaregularbasis Telescopic window cleaner kits are available to clean solar arraysmountedonlowersectionsofaroof.Ifyoucaneasilyaccessthepanels,adirt-and rain-repellent glass polish can help keep your solar array cleanerforlongerIfyouhaveathicklayerofsnowonyoursolararray,brushitoff!Athickblanket of snow very quickly stops your solar array from producing anyenergyatall

Everymonth Ifyoursolarcontrolleror inverter includesadisplaythatshowspowerinputandpoweroutput,checktheperformanceofyoursolararray.Checkthat it is in line with your expectations for the time of year. It is worthkeepinga logof theperformancesoyoucancompare it fromoneyear tothenext If there is an unexplained drop in performance, clean the solar array,visuallycheck theconditionof thecablesandbalance thebatteries. If theperformancedoesnotimprove,followthetroubleshootingguideforfurtherassistance

EverythreemonthsChecktheventilationinthebatterybox Checkthebatteryareaisstillweatherproofandtherearenoleaksfromthebatteries

Cleandirtanddustoffthetopofbatteries Visually check all the battery connectors.Make sure they are tightly-fitting.Cleanandprotectthemwithpetroleumjellywhererequired Check theelectrolyte level inbatteriesand topupwithdistilledwaterwhererequired

Everysixmonths If you have amulti-battery system and your solar controller has thefacilitiestodoso,balancethebatterybank Oncethebatteriesarebalanced,useavoltmeterormulti-metertocheckthevoltageon each individual battery.Ensure thevoltages arewithin0.7voltsofeachother If one or more battery has a big difference in voltage, follow theinstructionsonweakbatteriesinthetroubleshootingsectionofthisbook

EveryyearIfyouhaveabatterybankwithmorethantwobatteries,swaptheorderofthe batteries in your bank. Place the batteries that were in themiddle ofyour bank at either end and the batteries that were at either end of yourbankinthemiddle.Thenbalancethem Thiswill ensure that all the batteries get evenwear throughout theirlifetimeandtherebyincreasetheoveralllifespanofthebatteries

AtthestartofeachwinterChecktheinsulationaroundthebatteries Checkthattheareaaroundthebatteriesisfreeofrodents.Miceandratslike tokeepwarm,and insulationaroundbatteries is a tempting target. Iftheyhavefoundyourbatteries,theyarelikelytognawthecablingaswell Cleanthesolararraytoensureyougetthebestpossibleperformanceattheworsttimeoftheyear

InternetSupport

Afreewebsitesupportsthisbook.Itprovidesup-to-the-minuteinformationandonlinesolarenergycalculators tohelpsimplify thecostanalysisanddesignofyoursolarelectricsystem.Tovisitthissite,gotothefollowingaddress:

www.SolarElectricityHandbook.com

ToolsavailableonthewebsiteOnlineprojectanalysisTheonlineprojectanalysistoolonthissitetakesawayalotofthecalculationsthat are involved with designing a new solar electric system, includingestimating the size and type of solar panel, the size and type of battery, thethickness of low-voltage cable required and providing cost and timescaleestimates.Tousetheonlineprojectanalysis,youwillneedtohavecompletedyourpoweranalysis(seethechapteronProjectScoping),andideallycompletedyourwholeproject scope.The solar calculatorwill factor in the system inefficiencies andproduceathirteen-pageanalysisforyourproject.

MonthlyinsolationfiguresMonthlysolarinsolationfiguresforeverycountryintheworldareincludedonthewebsite.Thesecanbeaccessedbyselectingyourcountryand thenameofyournearesttownorcityfromalist.Everycountryintheworldisincluded.The solar insolation figures used aremonthly averages based on three-hourlysamplestakenovera22-yearperiod.

SolaranglecalculatorThe solar angle calculator shows theoptimumangle for your solar panel on amonth-by-month basis, and showswhere the sunwill rise and set at differenttimesoftheyear.

SolarresourcesAdirectory of solar suppliers is included on thewebsite, alongwith links forfindingouttheverylatestaboutgrantschemesandsellingyourelectricitybacktotheelectricitycompanies.

QuestionsandanswersThesite includesanextensive listofquestionspostedon thesitebyother sitevisitors, along with my answers. These questions and answers cover almosteveryconceivableareaofsolardesignandinstallationandareworthabrowse.Ifyouhaveaquestionofyourown,postitonthesite.

Authoronline!

Ifyouhavenoticedamistakeinthebook,orfeelatopichasnotbeencoveredinenoughdetail,Iwouldwelcomeyourfeedback.Thishandbookisupdatedonayearlybasisandanysuggestionsyouhaveforthenexteditionwouldbegratefullyreceived.Thewebsitealsoincludesan‘askmeaquestion’facility,soyoucangetintouchwithanyotherquestionsyoumayhave,orsimplybrowsethroughthequestionsandanswersintheFrequentlyAskedQuestionssection.

SolararticlesNewarticlesaboutsolarpowerareregularlyaddedtoourarticlessection.

AFinalWord

Solarelectricpower isanexcellentandpractical resource. It canbeharnessedrelativelyeasilyandeffectively.Itisnotwithoutitsdrawbacksanditisnotsuitableforeveryapplication.Togetthebestoutofa solarelectric system, it is important todoyourplanning firstand to bemeticulous with detail. Only thenwill you have a system that willperformproperly.Fromanenthusiast’sperspective,designingandbuildingasolarelectricsystemfromscratchisinteresting,educationalandfun.Ifyouaretemptedtohaveago,start with something small like a shed light, and feel free to experimentwithdifferentideas.Ifyouareaprofessionalarchitectorbuilder,youshouldnowhaveaclearideaofhowsolarenergycanbeusedinyourprojects:itsbenefitsanditsdrawbacks.It isquiteamazing, the first timeyouconnecta solarpanelup toanelectricalitemsuchasalightbulbandwatchitpowerupstraightaway.Eventhoughyouknow it is going towork, there is somethingalmostmagical aboutwatchingasystemthatgenerateselectricityseeminglyfromthinair!Teaching children about solar electricity is also fun. There are small solarpoweredkitssuitableforchildren.Thesecanbeassembledbylittlefingersandthey teach the fundamentals of electricity and solar power in a fun andinterestingway.Ifthisbookhasinspiredyoutoinstallasolarelectricsystemyourself,thenithasserveditspurpose.Iwishyoutheverybestforyourproject.

Allthebest

MichaelBoxwellJanuary,2012

AppendixA–CrystallineSolarPanelsandShading

Asmentioneda few times in thisbook, shading is abig issuewith crystallinephotovoltaicpanels.Asmallamountofshadinghasabigimpactontheamountofelectricalpowergeneratedbyyoursolarsystem.Unlikesolar thermal (hotwater)systems, the lossofpower throughshading ismuchgreater than theamountof thepanel that is inshade.Withsolar thermalsystems,ifonly5%ofthepanelisinshade,youloselessthan5%ofthepowerproduction.Withamorphous(thin-film)PVpanels,youwouldusuallylose15–20%ofthepowerproductioninasimilarscenario.With crystalline solar panels, the difference is significantlymore and in someinstances canbringpowergenerationdown to zero, even if the amount of thepanelinshadeissmall.Thereasonfor this is in theconstructionof thesolarpanel itself.Acrystallinesolarpanelismadeupofanumberofindividualsolarcells.Typically,eachofthese cells generates ½ volt of potential energy. These cells are connectedtogetherinseriestoincreasethevoltagetoamoreusefullevelinsidethesolarpanel.Eachindividualsolarpanelhasoneormorestringsofsolarcells.Because these strings of cells are connected in series, a solar panel is only asgoodas itsweakestcell. Ifonecellproducesaweakoutput,all theothercellswithin thestringarecompromisedaswell.Thismeans that ifyouhavea‘softshade’suchasadistanttreebranch,creatingasoftdappledshadeacrossjustoneortwocellsonasolarpanel,theeffectcanbetoreducetheoutputofthewholestringtoasimilarleveltoadull,overcastday.Worsehappenswhenyouhaveamoredirectshadow,creatingabiggercontrastbetween light and shade. When even one cell is in complete shade and theremainder are in bright sunlight, the shaded cell short-circuits as the flow ofelectronswithinthecellgoesintoreverse.However,becausethecellisconnectedinserieswiththeothercellsinthepanel,current is forced through the reversed cell. In this scenario, the reversed cellabsorbsthepowerproducedbytheothercellsinthepanel,generatingheatand

creatingahotspotwithinthesolarpanel.The amount of power that is absorbed by a single reversed cell isdisproportionatetotheamountofpowerasinglecellcangenerate.Asinglecellmayonlyproduce½voltofpotentialenergy,butcanabsorb6–8voltswhenithasgoneintoreversal.Ifunchecked,asolarcellleftinthisstatecaneasilybedestroyed.Thehotspotgenerated by the blocked cell can very quickly reach dangerous temperaturelevels too,andamateurhome-built solarpanelshavebeenknown toburst intoflamespreciselyforthisreason.Thankfully,solarpanelmanufacturershaveasolutiontothisprobleminordertoavoid the panel itself becoming damaged. All professionally manufacturedcrystallinesolarpanelshavein-builtprotectiontoroutepoweraroundastringofcellswhereoneormoreofthecellsareinreversal.Ifyoursolarpanelhasonlyasinglestringofsolarcellswithinit,thiseffectivelymeans theentiresolarpanel isbypassedandproducesnopoweratall. Ifyoursolarpanelhastwostringsofsolarcells,itmeansthepoweroutputofthepanelishalved.Becauseasolararrayistypicallyputtogetherbyinstallingmultiplesolarpanelsinseries,theeffectsofshadingonjustpartofonepanelimpactstheperformanceoftheentiresolararray.

TypesofobstructionShadecanbebrokendownintotwocategories:softshadeandhardshade.Asoftshadeisadistantobstructionwheretheshadowisdispersedordiffused,which significantly reduces the amount of light reaching the solar cells. Ashadowfromatreewouldbeclassedasasoftshade.Hard shade is an obstruction that blocks out light from reaching the solar cellcompletely.Birddroppings, fallen leavesor a treebranch sittingon topof theglasswouldbeclassedasahardshade.Where cells are soft shaded, you will see a significant drop off in energyproduction.Effectively, theproductionof the entire arraywill dropdown to asimilarleveltoadullday.Wherecellsarehardshaded,theproductionoftheentirearraywilldropdowntothesamelevelastheaffectedcells:ifthecellsarecoveredcompletely,youmaysee a complete power shutdown (depending on how shade-tolerant your solarpanelsare).Ifthecellsareonlypartiallycovered,youwillseeasignificantdropinenergyproduction.

Designingshade-tolerantsolarsystemsIfyoucannotavoidshadeinyoursolarenergysystem,thesolutionistodesignashade-tolerantsystem.Inotherwords,youhavetodesignyoursysteminsuchawaythattheeffectofshadeonanyonepartofyoursystemhasassmallaneffectontheoverallarrayaspossible.Designingshade-tolerantsolararraysisacomplexsubjectandaspecialistareaevenamongstsolardesignexperts.Thereareentirebookswrittenonthissubjectalone.Consequently,itisnotpossibletocoverthewholesubjecthere.However,it is possible to design a basic solar energy systemwith a reasonable level ofshadetolerancewithoutahugeamountofspecialistknowledge.If you need to design a system thatwill continue to performwell in partiallyshadedconditions,thereareoptionsavailabletoyou:

TracktheshadeFirst,youshouldneverdesignasystemthatwillhavetocopewithhardshading.Solar panels should bemounted so that they are not covered in leaves and sotheycanbeinspectedandcleanedofanyhardobstructionsifnecessary.Ifthereisapermanentobstructionthatwillbecreatingahardshade,youshouldnotbeinstallingsolarpanelsinthatparticularlocation.If you have a soft shade, for how much of the day does this shade your

panels?Remember,evenasoftshadeoverasmallareacanhaveabigimpact.Typical core power generation times for solar energy during the summer arethree hours either side of solar noon (i.e. between9amand3pm, if your timezoneequatestosolartime).Ifyouhaveshadingeitherbeforethisperiodorafterit,youwill losearound20%ofyourcapabilityinthesummer,or40%ofyourcapabilityifyouhaveshadinginboththeearlymorningandlateafternoon.Duringthewinter,thedifferenceisnotsogreat.Becausethesunislowerin

theskyandtheintensityofthesunlightissignificantlylower,almostallofyourpowerisgeneratedduringthecorepowergenerationtimes.Ifyouhaveshadingbefore 9am or after 3pm during the winter, you will probably be losing onlyaround5–10%ofyourgeneratingcapabilities.However, if you are suffering from shadewithin the core power generation

times,youaregoing to severely compromise theperformanceofyour system.Theexactimpactontheperformanceofyoursystemwillvaryaccordingtoyourlocation,theseverityofshadingandthetypeofsolarpanelsyouareusing,butin

generalterms,thisishowmuchofyoursolarenergyproductionyoucanexpecttolosefromonehourofshadingduringcorepowergenerationtimes:

PeriodofShading

Winterloss

(%)

Summerloss

(%)

9am–10am(2–3hoursbeforesolarnoon)

3%

6%

10am–11am(1–2hoursbeforesolar

noon)

15%

10%

11am–solarnoon

27%

14%

Solarnoon–1pm

27%

14%

1pm–2pm(1–2hoursaftersolar

noon)

15%

10%

2pm–3pm(2–3hoursaftersolar

noon)

3%

6%

Thistableshowstheapproximateperformancelossfromyoursystemifitisshadedforonehourduringcoreproductiontimes

As you see, you can lose a significant amount of energy production due toshadingduringthemiddleoftheday.Thisiswhyshadingduringthemiddleofthe day is the number one reason for solar arrays failing to live up toexpectations.However,becauseyoucannowquantifytheimpactoftheshading,itispossibletodosomethingtocountertheeffects.

IncreasingthenumberofsolarpanelsThefirstoptionisthemostobvious:ifyouhavethespace,youcanincreasethenumberofsolarpanelsyouinstallinordertocountertheperiodsofshade.Thisisnotalwayspossible,eitherbecauseofspaceorcostrestrictions.Also,itisnotalwaysthemostefficientwayofgettingaroundtheproblem.

PanelorientationIfshadeaffectsyouataparticular timeoftheday,consideranglingyoursolarpanels away from theobstruction.Thiswill increase their effectivenessduringthe unobstructed parts of the day and reduce or remove the impact of theobstructioninthefirstplace.Thereductioninpowergenerationfromanglingthepanelsawayfromduesouthisoftenlessthantheimpactonshadingifyoucaneliminatetheshadeproblemaltogether.

ChoiceofsolarpanelAnother option is to choose amorphous (thin-film) solar panels. Amorphoussolarpanelsdonotsufferfromcellreversalinthesamewaythatcrystallinesolarpanelsdo,andconsequentlyprovidefarbettershadetolerance.Becauseoftheirlowerefficiencylevels,youwillneedtotakeintoaccountthatyouwillrequirearoundtwiceasmuchphysicalspacetoinstallamorphoussolarpanels.Ifspaceisnotanissue,usingamorphoussolarpanelsislikelytobethesimplestandmostcost-effectivesolutionforstand-alonesolarinstallations.Sharp,Mitsubishi,Uni-Solar,SolarFrontierandSanyonowmanufacturehigh-qualityamorphoussolarpanelsthatofferexcellentperformanceandreliability.

Usemicro-invertersIfyouarebuildingagrid-tiesystem,possiblythebestsolutionistousemicro-inverters,whereeachpanelhasitsownpowerinverterandisafullsolarenergysysteminitsownright.With amicro-inverter system, each solar panel runs entirely independently ofeveryother solarpanel. If shadeaffectsonepanel, noneof theotherpanels isaffectedinanyway.Using micro-inverters also means that you can have solar panels facing indifferent directions from each other. For instance, if you are installing solarpanelsonaroofandyourroofhasmultiplepitchesandangles,youcanchooseto install your solar array on more than one part of the roof using a micro-invertersystem.Thisapproachgivesyougreaterflexibilityastowhereyoumountsolarpanels:itmayevenbepossibletoavoidyourshadingissuesaltogether.

DesignaparallelsolararrayByconnectingsolarpanels inparallel rather than inseries,youcanreduce the

overall effect of shading on just one or two parts of the array. In a parallelsystem,whenonesolarpanel is inshade, thepoweroutputsofotherpanels inthearrayarenotaffected.If you are designing a grid-tie solar energy system and want a high-voltagesystem,itispossibletoachievethiswithaparallelarraybyusinghigh-voltagegrid-tiespecificsolarpanels.Anumberofmanufacturersnowofferthesepanels,oftenproducingover100volts fromasinglepanel.Otherpanelsareavailablethatprovideeither24-voltor48-voltoutput,andthesecanbesuitableforlargerstand-alonesolarenergysystemsthatrequiremorethan12volts.

Designamulti-stringsolararrayInsteadofdesigningyoursystemtohavejustonesetofsolarpanelsconnectedin series, you can design your system to havemultiple series of solar panels.Controllersandinvertersareavailablethatallowyoutohavemultiplestringsofsolarpanels,oryoucanhaveacontrollerorinverterforeachindividualstring.In effect, thismeansyouendupwith two smaller solarpower systems, ratherthanone.Thismaymeanyoucanfaceyourtwodifferentsetsofsolararraysatdifferentangles,givingyoutheopportunity tomount theminentirelydifferentlocationsifyousowish.In this scenario, you can design your system so that partial shadingwill onlyaffectoneofyourstringsratherthanyourentirearray.Aswithmicro-inverters,suchanapproachmayevenallowyoutoavoidtheshadingissuealtogether.

OtheroptionsThereareotheroptions,butthedesignscanbecomeextremelycomplicatedandarereallyinthedomainofhighlyspecialistsolardesigners.Ifyouaredesigninga shade-tolerant solar energy system and the above optionswill not work foryou,itistimetocallinasolarshadingspecialist.Unlessyouhave significant shading issues,youcanusuallydesignaround theproblems using one of the options I have suggested here, or by using acombinationofoptionstocomeupwithaworkablesolution.Overthepastfewyears, I have designed a number of shade-tolerant systems, including systemsthataredesignedtoworkinanentirelyshadedenvironmentallyearround.Withcarefulplanning,itisoftenpossibletoovercometheissues.

Ifallelsefails...Sometimesitisnotpossibletodesignaroundshadingproblems.Inthisscenario,itrequiresarethinkofwhatyoucanachieveusingsolar.This is an issue that I havewithmy own home.My house is on the edge ofancientwoodland.Formostof theyear,myhomeisalmostentirelyshadedbythe tall trees that surround it.Even in the height of summer, the sun does notreachmygardenuntilmid-afternoon.This shading means I could never run my own home completely from solarpower.However,Ihavedesignedasmallersolarenergysystemthatprovidesmewithenoughenergy to runmylightingandprovidebackuppower incaseofapowercut.Ihaveachieved thisby installingamorphoussolarpanelsonto thebackofmyhome, facing south-west to catch the afternoon and evening sun. Despitereceivingverylittlesunlight,thissystemprovidesenoughelectricitytoprovidemewithmylightingandbackuppowerrequirementsthroughouttheyear,eveninthedepthsofwinter.

Inconclusion Shadeisabigproblemforsolarenergy–especiallyifusingcrystallinesolarpanelsEvenaverysmallamountofshadecanhaveabigimpactonyoursystemAmorphoussolarpanelsalsosufferinshade,butnottothesameextentascrystallinepanels If youhave shade during core power generating periods of the day –typically the three hours either side of solar noon – youwill lose a verysignificantamountofyourpotentialpowergeneration There are things you can do to reduce the impact of shading, eitherthroughyourchoiceofmaterialsoryoursystemdesign Insomecaseswhereyouhaveverysignificantshadingissues,youmayneedtoreconsiderwhatyoucanrealisticallyachievewithsolar

AppendixB–SolarInsolation

Solarinsolationshowsthedailyamountofenergyfromthesunyoucanexpectpersquaremetreatyourlocation,averagedoutovertheperiodofamonth.Thefiguresarepresentedasanaverage irradiance,measured inkilowatt-hourspersquaremetrespreadovertheperiodofaday(kWh/m²/day).Averages have been collated over a 22-year period between 1983 and 2005,basedonathree-hoursamplerate.The book only shows solar insolation figures for the United States, Canada,Australia, New Zealand, UK and Ireland. Whilst I have tried to show thisinformationasclearlyaspossible,theinformationisintabularformwhichdoesnotdisplaywellonsomesmallereBookreaders.Moredetailedinformationcanbeaccessedatwww.SolarElectricityHandbook.com,withfiguresforeverymajortown and city in every country in the world, thereby allowing you to accessinformationthatisspecifictoyourarea.

UnderstandingthisinformationTheamountofenergyyoucapturefromthesundiffers,dependingonthetiltofthe solarpanels. Ifyoumountyour solarpanelshorizontallyorvertically,youwill capture less energy than if you face them due south (due north in theSouthernHemisphere)andtiltthemtowardsthesun.Thetablesonthefollowingpagesshowtheirradiancefiguresbasedonmountingyoursolarpanelsatthefollowingangles:

Flat(horizontal)UprightTiltedtowardstheequatorforbestyear-roundperformanceTiltedforbestperformanceduringthewintermonthsTiltedforbestperformanceduringthesummermonthsTiltedwiththeangleadjustedeachmonththroughouttheyear

Wherethefiguresshowthepanelstiltedatafixedangle,Ishowthisangleinthelefthandcolumnastheangleadjustmentfromanupright(vertical)position.Onthebottomrow,wheretheoptimumtiltchangeseachmonth,Ishowthisangleunderneath each month’s irradiance figures. Please note: all angles are indegreesfromvertical.For a more detailed explanation of these figures, refer to the chapter onCalculatingSolarEnergy.

Solarinsolationvalues–AustraliaNewSouthWales

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

5.91

5.25

4.48

3.56

2.73

2.49

2.68

3.49

4.6

5.41

5.88

6.24

Upright-0°

2.34

2.56

2.93

3.36

3.43

3.77

3.78

3.83

3.54

2.83

2.40

2.31

56°

5.38

5.11

4.84

4.42

3.87

3.90

4.04

4.68

5.33

5.50

5.43

5.57

angleYear-roundtilt40°angleBestwintertilt

4.74

4.66

4.62

4.45

4.07

4.20

4.32

4.82

5.22

5.11

4.82

4.85

72°angleBestsummertilt

5.78

5.32

4.82

4.16

3.46

3.37

3.54

4.28

5.16

5.63

5.80

6.04

Tiltadjustedeachmonth

5.7872°

5.3464°

4.8456°

4.4748°

4.0740°

4.2732°

4.3240°

4.8248°

5.3356°

5.6364°

5.8072°

6.2480°

NorthernTerritory

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

5.83

5.18

5.07

4.81

4.35

4.24

4.47

5.07

5.98

6.59

6.5

6.27

Upright-0°

2.43

1.81

2.28

3.09

3.73

4.24

4.23

3.75

2.99

2.02

2.32

2.79

73°angleYear-roundtilt

5.85

5.04

5.13

5.15

4.94

4.99

5.20

5.62

6.23

6.48

6.48

6.36

57°angle

5.58

4.68

4.94

5.21

5.23

5.43

5.61

5.83

6.13

6.04

6.12

6.13

Bestwintertilt89°angleBestsummertilt

5.84

5.18

5.08

4.84

4.40

4.29

4.52

5.12

6.00

6.59

6.51

6.28

Tiltadjustedeachmonth

5.8489°

5.1881°

5.1373°

5.2265°

5.2357°

5.5650°

5.6157°

5.8365°

6.2373°

6.6081°

6.5189°

6.3796°

Queensland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

6.19

5.39

4.95

3.98

3.23

3.02

3.22

4.04

5.12

5.52

6.07

6.35

Upright-0°

2.09

2.28

2.81

3.22

3.41

3.75

3.76

3.85

3.39

2.49

2.13

2.04

62°angleYear-roundtilt

5.65

5.22

5.19

4.61

4.12

4.13

4.29

4.99

5.65

5.50

5.61

5.71

46°angleBestwintertilt

4.98

4.78

4.96

4.63

4.32

4.44

4.57

5.15

5.54

5.11

4.99

4.98

78°angleBest

6.06

5.41

5.15

4.34

3.71

3.59

3.78

4.56

5.47

5.62

5.98

6.18

summertiltTiltadjustedeachmonth

6.0678°

5.4270°

5.1962°

4.6554°

4.3246°

4.5038°

4.5746°

5.1554°

5.6562°

5.6270°

5.9878°

6.3586°

SouthAustralia

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

6.81

6.18

4.91

3.75

2.71

2.29

2.53

3.21

4.32

5.34

6.29

6.67

Upright-0°

2.54

2.94

3.32

3.72

3.54

3.48

3.63

3.52

3.37

2.87

2.54

2.42

55°angleYear-roundtilt

6.15

6.05

5.42

4.80

3.94

3.60

3.86

4.29

5.01

5.45

5.80

5.93

39°angleBestwintertilt

5.36

5.49

5.19

4.86

4.15

3.87

4.12

4.41

4.89

5.05

5.12

5.13

71°angleBestsummertilt

6.65

6.31

5.37

4.49

3.51

3.13

3.39

3.95

4.86

5.58

6.21

6.45

Tiltadjustedeach

6.6571°

6.3263°

5.4255°

4.8747°

4.1539°

3.9332°

4.1239°

4.4147°

5.0155°

5.5863°

6.2171°

6.6878°

monthVictoria

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

6.36

5.83

4.51

3.23

2.23

1.78

1.94

2.59

3.55

4.72

5.74

6.22

Upright-0°

2.62

3.00

3.24

3.35

3.02

2.77

2.81

2.89

2.85

2.72

2.56

2.49

52°angleYear-roundtilt

5.75

5.74

5.04

4.22

3.33

2.87

3.00

3.48

4.10

4.80

5.30

5.53

36°angleBestwintertilt

5.02

5.20

4.81

4.25

3.48

3.06

3.17

3.55

3.98

4.43

4.69

4.79

68°angleBestsummertilt

6.22

6.00

5.01

3.97

3.00

2.52

2.67

3.24

4.02

4.94

5.67

6.01

Tiltadjustedeachmonth

6.2268°

6.0260°

5.0452°

4.2744°

3.4836°

3.0928°

3.1736°

3.5544°

4.1052°

4.9460°

5.6768°

6.2376°

WesternAustralia

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-

8.41

7.49

5.93

4.34

3.09

2.62

2.82

3.62

5.04

6.41

7.71

8.45

90°Upright-0°

2.46

3.08

3.76

4.12

3.77

3.68

3.71

3.74

3.74

3.09

2.55

2.3

58°angleYear-roundtilt

7.51

7.31

6.53

5.46

4.29

3.89

4.05

4.69

5.80

6.54

7.06

7.39

42°angleBestwintertilt

6.47

6.61

6.28

5.55

4.53

4.18

4.32

4.83

5.69

6.07

6.16

6.28

74°angleBestsummertilt

8.18

7.62

6.43

5.07

3.82

3.37

3.56

4.3

5.59

6.67

7.59

8.14

Tiltadjustedeachmonth

8.1874°

7.6366°

6.5358°

5.5650°

4.5342°

4.2534°

4.3242°

4.8350°

5.8058°

6.6766°

7.5974°

8.4582°

Solarinsolationvalues–CanadaAlberta

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.79

1.70

3.15

4.56

5.32

5.66

5.56

4.76

3.14

1.85

0.99

0.48

Upright-0°

1.58

2.60

3.52

3.63

3.24

3.11

3.19

3.36

3.03

2.51

1.81

0.95

36°angleYear-roundtilt

1.61

2.84

4.26

5.00

4.87

4.82

4.89

4.84

3.86

2.84

1.89

0.97

20°angleBestwintertilt

1.66

2.85

4.09

4.55

4.30

4.21

4.30

4.33

3.63

2.80

1.93

1.00

52°angleBestsummertilt

1.47

2.69

4.21

5.20

5.29

5.33

5.39

5.14

3.90

2.74

1.75

0.89

Tiltadjustedeachmonth

1.6620°

2.8628°

4.2636°

5.2144°

5.2952°

5.7260°

5.3952°

5.2044°

3.8636°

2.8528°

1.9320°

1.0012°

BritishColumbia

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.00

1.88

2.9

4.18

5.18

5.7

6.11

5.37

4.00

2.19

1.18

0.84

Upright-0°

1.52

2.44

2.73

2.93

2.89

2.86

3.15

3.43

3.54

2.62

1.73

1.37

42°angleYear-roundtilt

1.63

2.78

3.52

4.34

4.75

4.92

5.42

5.40

4.78

3.09

1.87

1.43

26°angleBestwintertilt

1.67 2.78 3.37 3.97 4.17 4.24 4.69 4.85 4.53 3.06 1.91 1.48

58°angleBestsummertilt

1.51

2.63

3.50

4.52

5.12

5.42

5.91

5.70

4.79

2.96

1.74

1.31

Tiltadjustedeachmonth

1.6726°

2.8034°

3.5242°

4.5350°

5.1258°

5.7566°

5.9158°

5.7450°

4.7842°

3.1034°

1.9126°

1.4818°

Manitoba

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.24

2.17

3.43

4.74

5.57

5.84

5.92

5.00

3.45

2.25

1.42

0.99

Upright-0°

2.15

3.01

3.50

3.48

3.16

3.00

3.15

3.28

3.07

2.81

2.34

1.84

40°angleYear-roundtilt

2.24

3.37

4.41

5.08

5.13

5.05

5.27

5.04

4.09

3.26

2.47

1.87

24°angleBestwintertilt

2.31

3.39

4.24

4.65

4.51

4.42

4.57

4.53

3.87

3.24

2.54

1.95

56°

2.04

3.18

4.34

5.26

5.53

5.57

5.74

5.31

4.12

3.12

2.27

1.69

angleBestsummertiltTiltadjustedeachmonth

2.3124°

3.4132°

4.4140°

5.2648°

5.5356°

5.9064°

5.7456°

5.3648°

4.0940°

3.2732°

2.5424°

1.9516°

NewBrunswick

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.61

2.46

3.68

4.46

4.91

5.45

5.25

4.78

3.75

2.45

1.53

1.28

Upright-0°

2.53

3.11

3.45

3.03

2.64

2.64

2.66

2.90

3.10

2.81

2.19

2.06

45°angleYear-roundtilt

2.67

3.59

4.52

4.69

4.56

4.75

4.68

4.73

4.32

3.37

2.39

2.15

29°angleBestwintertilt

2.77

3.61

4.37

4.30

4.03

4.11

4.09

4.27

4.1

3.35

2.45

2.24

61°angleBestsummertilt

2.43

3.37

4.45

4.84

4.90

5.21

5.08

4.98

4.34

3.22

2.20

1.95

Tilt

2.77

3.62

4.52

4.85

4.90

5.48

5.08

5.02

4.32

3.38

2.45

2.24

adjustedeachmonth

29° 37° 45° 53° 61° 68° 61° 53° 45° 37° 29° 22°

NewfoundlandandLabrador

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.23

2.07

3.27

4.16

4.75

5.16

4.90

4.36

3.25

2.09

1.26

0.99

Upright-0°

1.91

2.68

3.12

2.87

2.64

2.62

2.59

2.73

2.72

2.43

1.83

1.63

43°angleYear-roundtilt

2.03

3.06

4.03

4.30

4.34

4.48

4.35

4.29

3.73

2.89

1.99

1.7

27°angleBestwintertilt

2.09

3.07

3.88

3.94

3.83

3.88

3.80

3.87

3.53

2.86

2.03

1.77

59°angleBestsummertilt

1.87

2.89

3.99

4.47

4.68

4.93

4.74

4.53

3.77

2.77

1.85

1.55

Tiltadjustedeachmonth

2.0927°

3.0835°

4.0343°

4.4851°

4.6859°

5.2066°

4.7459°

4.5851°

3.7343°

2.9035°

2.0327°

1.7720°

NovaScotia

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.54

2.39

3.47

4.29

4.98

5.57

5.49

4.85

3.91

2.66

1.57

1.21

Upright-0°

2.85

3.27

3.34

2.84

2.59

2.59

2.66

2.87

3.28

3.23

2.49

2.25

45°angleYear-roundtilt

2.89

3.70

4.39

4.45

4.62

4.85

4.90

4.82

4.62

3.82

2.64

2.27

29°angleBestwintertilt

3.06

3.77

4.26

4.09

4.07

4.18

4.26

4.34

4.40

3.84

2.74

2.4

61°angleBestsummertilt

2.56

3.42

4.28

4.61

4.96

5.31

5.32

5.06

4.60

3.60

2.39

2.01

Tiltadjustedeachmonth

3.0629°

3.7837°

4.3945°

4.6153°

4.9661°

5.6068°

5.3261°

5.1053°

4.6245°

3.8637°

2.7429°

2.4222°

Ontario

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.53

2.35

3.29

4.35

5.12

5.88

5.87

5.02

3.92

2.64

1.55

1.24

Upright-0°

2.63

3.04

3.02

2.83

2.61

2.64

2.74

2.91

3.21

3.07

2.29

2.21

46°angleYear-roundtilt

2.71

3.50

4.04

4.50

4.75

5.12

5.24

4.98

4.58

3.68

2.47

2.24

30°angleBestwintertilt

2.85

3.55

3.91

4.13

4.19

4.41

4.55

4.49

4.36

3.69

2.56

2.37

62°angleBestsummertilt

2.41

3.25

3.96

4.65

5.10

5.6

5.69

5.23

4.56

3.48

2.25

1.99

Tiltadjustedeachmonth

2.8530°

3.5638°

4.0446°

4.6654°

5.1062°

5.9070°

5.6962°

5.2754°

4.5846°

3.7138°

2.5630°

2.3922°

PrinceEdwardIsland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.35

2.10

3.22

4.28

5.40

6.05

6.04

5.22

3.91

2.34

1.29

0.98

Upright-0°

2.09

2.63

2.98

2.9

2.89

2.88

3.00

3.20

3.30

2.70

1.81

1.51

44°angleYear-roundtilt

2.21

3.04

3.90

4.42

5.01

5.23

5.37

5.20

4.57

3.23

1.98

1.6

28°angleBestwintertilt

2.29 3.05 3.75 4.05 4.40 4.50 4.65 4.68 4.33 3.20 2.02 1.65

60°angleBestsummertilt

2.03

2.87

3.87

4.59

5.40

5.75

5.85

5.48

4.58

3.09

1.84

1.47

Tiltadjustedeachmonth

2.2928°

3.0636°

3.9044°

4.6052°

5.4060°

6.0968°

5.8560°

5.5252°

4.5744°

3.2436°

2.0228°

1.6520°

Quebec

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.51

2.44

3.60

4.51

4.97

5.48

5.21

4.70

3.49

2.15

1.40

1.18

Upright-0°

2.42

3.16

3.44

3.10

2.71

2.7

2.69

2.91

2.91

2.47

2.03

1.97

43°angleYear-roundtilt

2.55

3.61

4.46

4.7

4.59

4.76

4.64

4.66

4.02

2.95

2.21

2.04

27°angleBestwintertilt

2.64

3.64

4.31

4.31

4.05

4.12

4.05

4.20

3.81

2.93

2.26

2.12

59°

2.33

3.40

4.40

4.87

4.93

5.23

5.04

4.91

4.04

2.83

2.04

1.85

angleBestsummertiltTiltadjustedeachmonth

2.6427°

3.6535°

4.4643°

4.8851°

4.9359°

5.5266°

5.0459°

4.9551°

4.0243°

2.9635°

2.2627°

2.1320°

Saskatchewan

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.11

1.98

3.25

4.79

5.60

5.78

6.23

5.06

3.65

2.28

1.36

0.91

Upright-0°

1.94

2.77

3.32

3.57

3.21

3.00

3.33

3.36

3.33

2.90

2.30

1.74

40°angleYear-roundtilt

2.02

3.10

4.16

5.15

5.15

4.99

5.54

5.11

4.40

3.36

2.41

1.76

24°angleBestwintertilt

2.08

3.11

4.00

4.71

4.51

4.36

4.78

4.58

4.16

3.33

2.48

1.83

56°angleBestsummertilt

1.85

2.92

4.11

5.34

5.56

5.51

6.04

5.39

4.42

3.21

2.22

1.59

Tilt

2.08

3.12

4.16

5.35

5.56

5.85

6.04

5.44

4.44

3.37

2.48

1.84

adjustedeachmonth

24° 32° 40° 48° 56° 64° 56° 48° 40° 32° 24° 16°

Solarinsolationvalues–IrelandBordersRegion

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.57

1.25

2.34

3.96

5.34

5.41

4.92

4.10

2.87

1.53

0.71

0.4

Upright-0°

1.06

1.85

2.44

3.13

3.31

3.04

2.89

2.90

2.77

2.05

1.23

0.81

35°angleYear-roundtilt

1.10

2.03

2.98

4.25

4.89

4.61

4.31

4.10

3.50

2.32

1.29

0.82

19°angleBestwintertilt

1.12

2.02

2.83

3.87

4.33

4.03

3.79

3.66

3.29

2.28

1.31

0.84

51°angleBestsummertilt

1.01

1.94

2.98

4.44

5.32

5.09

4.75

4.36

3.55

2.25

1.21

0.75

Tiltadjustedeachmonth

1.1219°

2.0427°

2.9835°

4.4643°

5.3251°

5.4758°

4.7551°

4.4343°

3.5035°

2.3227°

1.3119°

0.8412°

Dublin,TheMidlandsandMidlands-EastRegions

Flat-90° 0.62 1.19 2.09 3.34 4.32 4.36 4.21 3.52 2.53 1.44 0.82 0.5Upright-0°

1.03

1.59

1.97

2.45

2.61

2.46

2.44

2.37

2.25

1.78

1.33

0.92

37°angleYear-roundtilt

1.08

1.78

2.48

3.42

3.90

3.76

3.70

3.42

2.93

2.05

1.41

0.94

21°angleBestwintertilt

1.10

1.77

2.34

3.10

3.47

3.3

3.26

3.06

2.74

2.01

1.43

0.97

53°angleBestsummertilt

1.01

1.71

2.50

3.59

4.25

4.14

4.05

3.64

2.98

1.99

1.32

0.87

Tiltadjustedeachmonth

1.1021°

1.7929°

2.4837°

3.6245°

4.2553°

4.4260°

4.0553°

3.7145°

2.9337°

2.0529°

1.4321°

0.9714°

South-East,WestandSouthWestRegions

Flat-90°

0.67

1.26

2.15

3.46

4.46

4.53

4.41

3.72

2.66

1.52

0.87

0.56

Upright-0°

1.06

1.65

2.00

2.52

2.66

2.51

2.52

2.48

2.35

1.86

1.37

0.99

38°angleYear-roundtilt

1.13

1.86

2.53

3.54

4.04

3.90

3.88

3.63

3.08

2.16

1.47

1.02

22°angleBestwintertilt

1.15

1.84

2.40

3.22

3.59

3.43

3.43

3.25

2.88

2.12

1.49

1.05

54°angleBestsummertilt

1.05

1.79

2.55

3.72

4.39

4.30

4.25

3.86

3.13

2.10

1.37

0.94

Tiltadjustedeachmonth

1.1522°

1.8730°

2.5338°

3.7446°

4.3954°

4.5862°

4.2554°

3.9246°

3.0838°

2.1630°

1.4922°

1.0514°

Solarinsolationvalues–NewZealandNorthIsland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

6.41

5.65

4.59

3.31

2.35

1.96

2.18

2.83

3.96

4.82

5.86

6.26

Upright-0°

2.58

2.87

3.23

3.36

3.14

3.05

3.20

3.17

3.20

2.73

2.55

2.46

53°angleYear-roundtilt

5.80

5.54

5.10

4.27

3.47

3.14

3.39

3.82

4.63

4.92

5.41

5.57

37°angleBestwintertilt

5.07

5.03

4.87

4.3

3.64

3.36

3.60

3.91

4.52

4.56

4.79

4.83

69°angleBestsummertilt

6.27

5.79

5.06

4.02

3.12

2.75

2.99

3.53

4.51

5.05

5.79

6.06

Tiltadjustedeachmonth

6.2769°

5.8161°

5.1053°

4.3245°

3.6437°

3.4130°

3.6037°

3.9145°

4.6353°

5.0561°

5.7969°

6.2776°

SouthIsland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

5.75

5.01

3.92

2.67

1.82

1.36

1.60

2.28

3.39

4.50

5.49

5.82

Upright-0°

2.75

2.94

3.18

3.14

3.05

2.64

3.01

3.08

3.17

2.90

2.76

2.67

46°angleYear-roundtilt

5.21

4.98

4.56

3.77

3.19

2.63

3.03

3.49

4.23

4.66

5.09

5.07

30°angleBestwintertilt

4.54

4.50

4.34

3.78

3.35

2.81

3.23

3.57

4.10

4.28

4.47

4.39

62°angleBestsummertilt

5.64

5.23

4.55

3.56

2.85

2.30

2.67

3.23

4.13

4.82

5.47

5.55

Tiltadjustedeachmonth

5.6462°

5.2654°

4.5646°

3.8038°

3.3530°

2.8422°

3.2330°

3.5738°

4.2346°

4.8254°

5.4762°

5.8470°

Solarinsolationvalues–UnitedKingdomLondon

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.75

1.37

2.31

3.57

4.59

4.86

4.82

4.20

2.81

1.69

0.92

0.60

Upright-0°

1.20

1.80

2.18

2.58

2.7

2.64

2.71

2.80

2.47

2.07

1.43

1.01

38°angleYear-roundtilt

1.27

2.04

2.76

3.67

4.17

4.2

4.25

4.16

3.26

2.41

1.53

1.05

22°angleBestwintertilt

1.30

2.03

2.62

3.34

3.66

3.69

3.76

3.73

3.06

2.37

1.56

1.08

54°angleBestsummertilt

1.19

1.95

2.77

3.84

4.52

4.63

4.66

4.41

3.31

2.33

1.43

0.97

Tiltadjustedeachmonth

1.3022°

2.0530°

2.7638°

3.8646°

4.5254°

4.9162°

4.6654°

4.4646°

3.2638°

2.4130°

1.5622°

1.0814°

SouthEast

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-

0.80

1.44

2.42

3.70

4.73

4.99

5.00

4.31

2.88

1.75

0.95

0.62

90°Upright-0°

1.34

1.94

2.33

2.71

2.8

2.72

2.81

2.9

2.57

2.18

1.51

1.09

38°angleYear-roundtilt

1.41

2.18

2.94

3.84

4.31

4.32

4.42

4.3

3.37

2.53

1.61

1.12

22°angleBestwintertilt

1.44

2.18

2.81

3.5

3.79

3.80

3.92

3.86

3.17

2.49

1.64

1.16

54°angleBestsummertilt

1.30

2.08

2.94

4.01

4.68

4.76

4.85

4.55

3.41

2.43

1.50

1.03

Tiltadjustedeachmonth

1.4422°

2.2030°

2.9438°

4.0346°

4.6854°

5.0562°

4.8554°

4.6046°

3.3738°

2.5330°

1.6422°

1.1614°

SouthWest

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.81

1.51

2.49

3.91

5.13

5.37

5.28

4.37

3.07

1.74

1.01

0.65

Upright-0°

1.26

1.98

2.36

2.83

2.97

2.84

2.9

2.88

2.72

2.09

1.54

1.08

39°

1.34

2.25

3.00

4.07

4.7

4.64

4.68

4.34

3.60

2.45

1.65

1.13

angleYear-roundtilt23°angleBestwintertilt

1.37

2.24

2.86

3.72

4.13

4.08

4.07

3.90

3.40

2.41

1.68

1.16

55°angleBestsummertilt

1.25

2.14

3.00

4.24

5.08

5.12

5.12

4.59

3.64

2.36

1.54

1.04

Tiltadjustedeachmonth

1.3723°

2.2631°

3.0039°

4.2647°

5.0855°

5.4362°

5.1255°

4.6547°

3.6039°

2.4531°

1.6823°

1.1616°

EastofEngland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.72

1.34

2.37

3.60

4.68

4.90

4.86

4.20

2.82

1.64

0.91

0.57

Upright-0°

1.18

1.80

2.30

2.63

2.78

2.68

2.75

2.83

2.52

2.04

1.45

1.01

38°angleYear-roundtilt

1.25

2.03

2.89

3.71

4.24

4.21

4.27

4.16

3.30

2.36

1.55

1.04

22°angle

1.27

2.02

2.74

3.38

3.77

3.69

3.77

3.73

3.10

2.32

1.57

1.07

Bestwintertilt54°angleBestsummertilt

1.16

1.94

2.90

3.89

4.61

4.65

4.69

4.41

3.35

2.29

1.45

0.96

Tiltadjustedeachmonth

1.2722°

2.0430°

2.8938°

3.9146°

4.6154°

4.9662°

4.6954°

4.4846°

3.3038°

2.3730°

1.5722°

1.0714°

EastMidlands

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.64

1.31

2.20

3.37

4.44

4.51

4.50

3.82

2.59

1.54

0.8

0.51

Upright-0°

1.07

1.80

2.11

2.47

2.67

2.53

2.59

2.59

2.31

1.93

1.27

0.94

37°angleYear-roundtilt

1.13

2.01

2.64

3.45

4.01

3.88

3.95

3.74

3.01

2.22

1.36

0.96

21°angleBestwintertilt

1.15

2.00

2.51

3.13

3.56

3.40

3.48

3.35

2.81

2.18

1.37

0.99

53°angleBest

1.05

1.92

2.66

3.62

4.37

4.28

4.33

3.98

3.06

2.15

1.27

0.89

summertiltTiltadjustedeachmonth

1.1521°

2.0229°

2.6437°

3.6545°

4.3753°

4.5760°

4.3353°

4.0545°

3.0137°

2.2229°

1.3721°

0.9914°

WestMidlands

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.71

1.35

2.28

3.47

4.51

4.69

4.69

4.04

2.70

1.65

0.90

0.57

Upright-0°

1.18

1.84

2.18

2.54

2.70

2.59

2.68

2.73

2.41

2.08

1.45

1.03

38°angleYear-roundtilt

1.24

2.06

2.74

3.56

4.09

4.05

4.14

3.99

3.14

2.4

1.55

1.06

22°angleBestwintertilt

1.26

2.05

2.60

3.25

3.64

3.55

3.65

3.58

2.95

2.36

1.57

1.09

54°angleBestsummertilt

1.15

1.97

2.75

3.73

4.45

4.46

4.53

4.23

3.19

2.31

1.44

0.97

Tiltadjustedeach

1.2622°

2.0730°

2.7438°

3.7646°

4.4554°

4.7462°

4.5354°

4.3046°

3.1438°

2.4030°

1.5722°

1.0914°

monthNorth-EastEngland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.61

1.35

2.45

3.88

5.35

5.47

5.13

4.29

2.91

1.66

0.77

0.44

Upright-0°

1.17

2.03

2.61

3.04

3.31

3.06

3.01

3.05

2.81

2.27

1.38

0.94

35°angleYear-roundtilt

1.21

2.23

3.17

4.14

4.9

4.65

4.49

4.32

3.56

2.56

1.44

0.95

19°angleBestwintertilt

1.24

2.22

3.03

3.76

4.33

4.07

3.95

3.85

3.34

2.52

1.46

0.98

51°angleBestsummertilt

1.11

2.12

3.17

4.33

5.33

5.15

4.96

4.59

3.60

2.46

1.34

0.86

Tiltadjustedeachmonth

1.2419°

2.2427°

3.1735°

4.3643°

5.3351°

5.5358°

4.9651°

4.6643°

3.5635°

2.5627°

1.4619°

0.9812°

North-WestEngland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-

0.66

1.32

2.30

3.63

4.92

5.00

4.88

3.98

2.73

1.53

0.79

0.50

90°Upright-0°

1.16

1.85

2.28

2.74

2.99

2.79

2.82

2.74

2.51

1.95

1.29

0.95

36°angleYear-roundtilt

1.21

2.06

2.83

3.79

4.49

4.31

4.31

3.94

3.23

2.23

1.37

0.96

20°angleBestwintertilt

1.24

2.05

2.69

3.46

4.00

3.78

3.8

3.54

3.04

2.19

1.39

0.99

52°angleBestsummertilt

1.12

1.96

2.83

3.97

4.89

4.77

4.73

4.18

3.28

2.16

1.28

0.88

Tiltadjustedeachmonth

1.2420°

2.0728°

2.8336°

3.9944°

4.8952°

5.0860°

4.7352°

4.2544°

3.2336°

2.2328°

1.3920°

1.0012°

YorkshireandtheHumber

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.62

1.30

2.30

3.51

4.69

4.78

4.64

3.89

2.67

1.54

0.75

0.47

Upright-0°

1.12

1.86

2.31

2.64

2.86

2.68

2.7

2.68

2.46

1.99

1.25

0.92

36°

1.16

2.06

2.85

3.64

4.24

4.09

4.07

3.83

3.16

2.28

1.32

0.94

angleYear-roundtilt20°angleBestwintertilt

1.19

2.04

2.71

3.31

3.77

3.58

3.58

3.42

2.96

2.24

1.34

0.97

52°angleBestsummertilt

1.08

1.96

2.86

3.82

4.63

4.50

4.47

4.08

3.21

2.2

1.24

0.86

Tiltadjustedeachmonth

1.1920°

2.0628°

2.8536°

3.8544°

4.6352°

4.8360°

4.4752°

4.1544°

3.1636°

2.2828°

1.3420°

0.9712°

CentralandSouthernScotland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.51

1.16

2.03

3.22

4.55

4.66

4.31

3.63

2.42

1.33

0.64

0.38

Upright-0°

0.99

1.75

2.05

2.46

2.85

2.68

2.58

2.55

2.28

1.76

1.14

0.86

34°angleYear-roundtilt

1.02

1.91

2.51

3.32

4.11

3.97

3.77

3.52

2.87

1.99

1.20

0.86

18°angle

1.04

1.90

2.37

3.00

3.64

3.47

3.31

3.17

2.68

1.95

1.21

0.89

Bestwintertilt50°angleBestsummertilt

0.94

1.83

2.53

3.49

4.49

4.37

4.15

3.77

2.93

1.93

1.12

0.78

Tiltadjustedeachmonth

1.0418°

1.9226°

2.5134°

3.5342°

4.4950°

4.7258°

4.1550°

3.8642°

2.8734°

1.9926°

1.2118°

0.8910°

NorthScotland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.47

1.11

2.05

3.30

4.52

4.63

4.31

3.61

2.45

1.31

0.59

0.32

Upright-0°

0.99

1.74

2.16

2.59

2.88

2.7

2.61

2.57

2.38

1.80

1.12

0.77

33°angleYear-roundtilt

1.00

1.88

2.62

3.44

4.08

3.93

3.75

3.50

2.96

2.01

1.16

0.76

17°angleBestwintertilt

1.03

1.87

2.46

3.12

3.62

3.43

3.30

3.15

2.77

1.97

1.18

0.79

49°angleBest

0.92

1.80

2.61

3.62

4.46

4.32

4.11

3.75

3.02

1.95

1.08

0.69

summertiltTiltadjustedeachmonth

1.0317°

1.8925°

2.6233°

3.6641°

4.4649°

4.6956°

4.1149°

3.8441°

2.9633°

2.0125°

1.1817°

0.7910°

SouthWales

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.72

1.33

2.21

3.52

4.57

4.75

4.71

3.97

2.71

1.55

0.89

0.59

Upright-0°

1.14

1.74

2.04

2.54

2.7

2.59

2.66

2.64

2.37

1.87

1.35

0.99

38°angleYear-roundtilt

1.21

1.97

2.59

3.61

4.15

4.11

4.16

3.91

3.12

2.18

1.45

1.03

22°angleBestwintertilt

1.23

1.96

2.46

3.29

3.65

3.61

3.68

3.51

2.93

2.14

1.47

1.06

54°angleBestsummertilt

1.13

1.89

2.61

3.78

4.51

4.52

4.56

4.14

3.17

2.11

1.36

0.95

Tiltadjustedeach

1.2322°

1.9830°

2.5938°

3.8046°

4.5154°

4.8062°

4.5654°

4.2046°

3.1238°

2.1830°

1.4722°

1.0614°

monthNorthWales

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.66

1.32

2.30

3.63

4.92

5.00

4.88

3.98

2.73

1.53

0.79

0.50

Upright-0°

1.14

1.83

2.26

2.72

2.97

2.77

2.81

2.72

2.49

1.93

1.27

0.92

37°angleYear-roundtilt

1.19

2.04

2.81

3.78

4.48

4.30

4.29

3.93

3.22

2.22

1.35

0.95

21°angleBestwintertilt

1.22

2.03

2.68

3.44

3.98

3.77

3.79

3.52

3.02

2.18

1.37

0.98

53°angleBestsummertilt

1.11

1.95

2.82

3.96

4.88

4.76

4.72

4.18

3.27

2.15

1.26

0.87

Tiltadjustedeachmonth

1.2221°

2.0529°

2.8137°

3.9845°

4.8853°

5.0860°

4.7253°

4.2445°

3.2237°

2.2229°

1.3721°

0.9814°

NorthernIreland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-

0.61

1.25

2.15

3.39

4.54

4.54

4.30

3.64

2.56

1.42

0.74

0.43

90°Upright-0°

1.09

1.79

2.12

2.55

2.79

2.58

2.54

2.51

2.36

1.82

1.25

0.82

35°angleYear-roundtilt

1.13

1.98

2.62

3.51

4.12

3.9

3.79

3.56

3.02

2.08

1.32

0.83

19°angleBestwintertilt

1.16

1.97

2.49

3.19

3.66

3.42

3.34

3.19

2.83

2.04

1.34

0.86

51°angleBestsummertilt

1.05

1.89

2.64

3.68

4.49

4.27

4.15

3.79

3.07

2.02

1.24

0.77

Tiltadjustedeachmonth

1.1619°

1.9927°

2.6235°

3.7143°

4.4951°

4.5958°

4.1551°

3.8643°

3.0235°

2.0827°

1.3419°

0.8612°

Solarinsolationvalues–UnitedStatesofAmericaAlabama

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.32

2.9

4.06

5.01

5.54

5.64

5.7

5.14

4.58

3.84

2.68

2.17

Upright-0°

2.94

2.85

3.06

2.67

2.30

2.15

2.22

2.46

3.03

3.72

3.29

3.00

58°angleYear-roundtilt

3.29

3.64

4.60

5.04

5.10

5.02

5.14

4.96

4.98

4.86

3.76

3.22

42°angleBestwintertilt

3.45

3.68

4.46

4.65

4.52

4.36

4.49

4.50

4.75

4.90

3.92

3.42

74°angleBestsummertilt

2.96

3.42

4.5

5.18

5.46

5.45

5.55

5.20

4.96

4.56

3.39

2.85

Tiltadjustedeachmonth

3.4542°

3.6950°

4.6058°

5.1866°

5.4674°

5.6482°

5.5574°

5.2266°

4.9858°

4.9250°

3.9242°

3.4534°

Alaska

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

0.40

1.07

2.22

3.73

4.95

5.26

4.86

3.86

2.46

1.37

0.58

0.00

Upright-0°

0.88

1.75

2.51

3.09

3.22

3.08

2.98

2.83

2.47

2.00

1.20

0.00

32°angleYear-roundtilt

0.89

1.89

2.97

4.06

4.50

4.47

4.24

3.81

3.03

2.21

1.23

0.00

16°angleBestwintertilt

0.92 1.88 2.83 3.68 3.99 3.90 3.73 3.43 2.84 2.17 1.25 0.00

48°angleBestsummertilt

0.82

1.80

2.97

4.25

4.93

4.93

4.66

4.07

3.09

2.13

1.14

0.00

Tiltadjustedeachmonth

0.9216°

1.9024°

2.9732°

4.2740°

4.9348°

5.3556°

4.6648°

4.1640°

3.0332°

2.2124°

1.2516°

0.008°

Arizona

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

3.20

4.07

5.45

6.62

7.37

7.52

6.78

5.97

5.45

4.48

3.50

2.95

Upright-0°

4.63

4.59

4.29

3.33

2.57

2.28

2.34

2.70

3.60

4.51

4.76

4.63

57°angleYear-roundtilt

4.92

5.55

6.45

6.83

6.74

6.57

6.08

5.78

6.03

5.82

5.24

4.74

41°angleBestwintertilt

5.28

5.74

6.34

6.33

5.87

5.58

5.26

5.22

5.78

5.93

5.57

5.14

73°

4.28

5.04

6.20

6.96

7.26

7.23

6.60

6.05

5.95

5.39

4.60

4.06

angleBestsummertiltTiltadjustedeachmonth

5.2841°

5.7449°

6.4557°

6.9765°

7.2673°

7.5280°

6.6073°

6.0765°

6.0357°

5.9449°

5.5741°

5.2434°

Arkansas

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.39

3.03

4.01

5.19

5.51

5.91

6.02

5.52

4.74

3.71

2.60

2.15

Upright-0°

3.14

3.09

3.07

2.80

2.33

2.22

2.31

2.64

3.20

3.62

3.23

3.02

55°angleYear-roundtilt

3.45

3.88

4.56

5.24

5.10

5.26

5.44

5.36

5.20

4.70

3.66

3.21

39°angleBestwintertilt

3.64

3.94

4.44

4.84

4.52

4.57

4.76

4.86

4.98

4.74

3.82

3.42

71°angleBestsummertilt

3.08

3.62

4.46

5.38

5.44

5.72

5.88

5.61

5.16

4.41

3.30

2.83

Tilt

3.64

3.94

4.56

5.38

5.44

5.91

5.88

5.63

5.20

4.75

3.82

3.45

adjustedeachmonth

39° 47° 55° 63° 71° 78° 71° 63° 55° 47° 39° 32°

California

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.18

3.09

4.65

6.08

7.21

7.93

7.79

7.02

5.64

4.12

2.63

1.99

Upright-0°

3.35

3.68

4.09

3.53

2.96

2.69

2.82

3.46

4.34

4.83

3.96

3.37

51°angleYear-roundtilt

3.52

4.36

5.72

6.32

6.64

6.91

6.95

6.95

6.64

5.86

4.23

3.41

35°angleBestwintertilt

3.73

4.46

5.61

5.83

5.79

5.84

5.95

6.25

6.39

5.98

4.47

3.66

67°angleBestsummertilt

3.12

4.02

5.52

6.49

7.16

7.63

7.60

7.29

6.52

5.40

3.75

2.97

Tiltadjustedeachmonth

3.7335°

4.4643°

5.7251°

6.4959°

7.1667°

7.9574°

7.6067°

7.3159°

6.6451°

5.9843°

4.4735°

3.7128°

Colorado

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.41

3.27

4.49

5.42

6.28

6.70

6.35

5.68

5.03

3.90

2.67

2.18

Upright-0°

4.20

4.18

4.05

3.25

2.80

2.60

2.64

2.99

3.90

4.66

4.30

4.21

50°angleYear-roundtilt

4.27

4.85

5.58

5.62

5.81

5.90

5.72

5.60

5.87

5.60

4.52

4.12

34°angleBestwintertilt

4.58

4.99

5.47

5.17

5.10

5.05

4.96

5.05

5.63

5.71

4.79

4.47

66°angleBestsummertilt

3.72

4.43

5.39

5.78

6.24

6.47

6.21

5.87

5.79

5.17

3.98

3.53

Tiltadjustedeachmonth

4.5834°

4.9942°

5.5850°

5.7858°

6.2466°

6.7374°

6.2166°

5.8958°

5.8750°

5.7142°

4.7934°

4.5626°

Connecticut

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.88

2.73

3.76

4.52

5.23

5.80

5.54

5.00

4.11

3.01

1.97

1.63

Upright-0°

3.20

3.50

3.41

2.83

2.57

2.52

2.54

2.79

3.23

3.45

3.00

3.01

48°angleYear-roundtilt

3.29

4.05

4.62

4.65

4.85

5.07

5.01

4.92

4.73

4.17

3.21

3.00

32°angleBestwintertilt

3.49

4.14

4.50

4.28

4.28

4.38

4.37

4.45

4.51

4.20

3.35

3.21

64°angleBestsummertilt

2.91

3.73

4.50

4.80

5.20

5.53

5.42

5.16

4.71

3.92

2.88

2.61

Tiltadjustedeachmonth

3.4932°

4.1440°

4.6248°

4.8056°

5.2064°

5.8172°

5.4264°

5.1956°

4.7348°

4.2140°

3.3532°

3.2524°

Delaware

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.97

2.73

3.69

4.65

5.27

5.67

5.50

5.05

4.25

3.33

2.24

1.77

Upright-0°

2.99

3.16

3.10

2.77

2.46

2.36

2.40

2.68

3.15

3.65

3.21

2.93

51°angleYear-roundtilt

3.17

3.78

4.35

4.73

4.86

5.01

4.95

4.92

4.78

4.51

3.50

3.00

35°angleBestwintertilt

3.34 3.84 4.22 4.36 4.29 4.34 4.32 4.44 4.56 4.54 3.66 3.20

67°angleBestsummertilt

2.82

3.52

4.26

4.89

5.21

5.47

5.36

5.17

4.77

4.23

3.14

2.64

Tiltadjustedeachmonth

3.3435°

3.8543°

4.3551°

4.8959°

5.2167°

5.6874°

5.3667°

5.2059°

4.7851°

4.5643°

3.6635°

3.2328°

Florida

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

3.56

4.44

5.29

6.11

6.49

5.97

5.55

5.26

4.76

4.52

3.78

3.35

Upright-0°

4.03

4.07

3.44

2.62

2.06

1.88

1.91

2.15

2.68

3.68

4.04

4.07

63°angleYear-roundtilt

4.66

5.39

5.80

6.11

5.98

5.38

5.08

5.06

4.96

5.27

4.85

4.51

47°angleBestwintertilt

4.96

5.56

5.69

5.68

5.28

4.69

4.50

4.62

4.75

5.33

5.11

4.85

79°

4.11

4.94

5.61

6.23

6.39

5.82

5.45

5.26

4.93

4.93

4.32

3.92

angleBestsummertiltTiltadjustedeachmonth

4.9647°

5.5655°

5.8063°

6.2371°

6.3979°

5.9786°

5.4579°

5.2871°

4.9663°

5.3455°

5.1147°

4.9240°

Georgia

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.50

3.12

4.28

5.19

5.80

5.59

5.72

5.17

4.46

3.91

2.82

2.36

Upright-0°

3.21

3.14

3.23

2.74

2.34

2.13

2.21

2.46

2.92

3.76

3.48

3.32

56°angleYear-roundtilt

3.55

3.96

4.86

5.24

5.36

5.00

5.18

5.01

4.82

4.92

3.96

3.52

40°angleBestwintertilt

3.74

4.02

4.74

4.86

4.74

4.37

4.55

4.55

4.60

4.97

4.15

3.76

72°angleBestsummertilt

3.17

3.69

4.74

5.38

5.72

5.42

5.58

5.23

4.80

4.60

3.55

3.09

Tilt

3.74

4.03

4.86

5.38

5.72

5.59

5.58

5.25

4.82

4.98

4.15

3.80

adjustedeachmonth

40° 48° 56° 64° 72° 80° 72° 64° 56° 48° 40° 32°

Hawaii

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

4.09

5.06

5.85

6.58

6.97

7.35

7.21

6.88

6.36

5.41

4.34

3.90

Upright-0°

4.06

4.12

3.33

2.33

1.77

2.80

1.69

2.01

3.00

3.96

4.22

4.12

69°angleYear-roundtilt

4.98

5.84

6.24

6.50

6.43

7.37

6.52

6.63

6.60

6.10

5.24

4.83

53°angleBestwintertilt

5.29

6.03

6.13

6.04

5.65

6.92

5.65

6.03

6.34

6.20

5.56

5.19

85°angleBestsummertilt

4.40

5.34

6.03

6.62

6.89

7.43

7.08

6.88

6.50

5.67

4.65

4.21

Tiltadjustedeachmonth

5.2953°

6.0361°

6.2469°

6.6377°

6.8985°

7.4692°

7.0885°

6.8977°

6.6069°

6.2161°

5.5653°

5.2746°

Idaho

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.72

2.66

4.07

5.38

6.36

7.24

7.37

6.44

4.99

3.43

1.97

1.49

Upright-0°

3.17

3.67

4.01

3.53

3.08

2.98

3.18

3.66

4.33

4.56

3.35

3.00

47°angleYear-roundtilt

3.21

4.15

5.28

5.72

5.92

6.26

6.56

6.51

6.14

5.28

3.49

2.96

31°angleBestwintertilt

3.41

4.25

5.16

5.26

5.17

5.31

5.61

5.85

5.89

5.38

3.67

3.17

63°angleBestsummertilt

2.83

3.82

5.10

5.88

6.38

6.89

7.16

6.83

6.04

4.88

3.11

2.57

Tiltadjustedeachmonth

3.4131°

4.2539°

5.2847°

5.8855°

6.3863°

7.2670°

7.1663°

6.8555°

6.1447°

5.3839°

3.6731°

3.2124°

Illinois

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.92

2.55

3.62

4.69

5.40

5.90

6.12

5.38

4.57

3.32

2.10

1.71

Upright-0°

2.91

2.91

3.06

2.83

2.54

2.44

2.59

2.86

3.48

3.70

2.95

2.84

50°angleYear-roundtilt

3.08

3.48

4.28

4.80

5.01

5.23

5.52

5.29

5.24

4.53

3.22

2.90

34°angleBestwintertilt

3.24

3.53

4.15

4.42

4.42

4.52

4.80

4.78

5.01

4.58

3.36

3.09

66°angleBestsummertilt

2.74

3.25

4.19

4.95

5.36

5.71

5.99

5.54

5.19

4.24

2.90

2.55

Tiltadjustedeachmonth

3.2434°

3.5442°

4.2850°

4.9558°

5.3666°

5.9274°

5.9966°

5.5758°

5.2450°

4.5942°

3.3634°

3.1226°

Indiana

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.83

2.54

3.55

4.49

5.19

5.91

5.98

5.24

4.55

3.26

2.02

1.57

Upright-0°

2.70

2.89

2.99

2.70

2.46

2.44

2.56

2.80

3.46

3.60

2.78

2.47

50°angleYear-roundtilt

2.87

3.46

4.18

4.57

4.80

5.24

5.40

5.15

5.21

4.42

3.05

2.56

34°angleBestwintertilt

3.02 3.51 4.05 4.21 4.25 4.53 4.70 4.65 4.98 4.46 3.17 2.72

66°angleBestsummertilt

2.57

3.24

4.10

4.71

5.14

5.72

5.85

5.39

5.17

4.15

2.76

2.27

Tiltadjustedeachmonth

3.0234°

3.5242°

4.1850°

4.7258°

5.1466°

5.9374°

5.8566°

5.4258°

5.2150°

4.4842°

3.1734°

2.7426°

Iowa

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.91

2.56

3.62

4.56

5.39

6.12

6.02

5.32

4.41

3.14

2.02

1.64

Upright-0°

3.26

3.15

3.23

2.84

2.62

2.59

2.67

2.94

3.50

3.67

3.10

3.04

48°angleYear-roundtilt

3.35

3.68

4.40

4.68

4.99

5.33

5.43

5.26

5.13

4.42

3.31

3.04

32°angleBestwintertilt

3.55

3.74

4.27

4.31

4.40

4.59

4.71

4.74

4.90

4.46

3.46

3.25

64°

2.96

3.42

4.30

4.84

5.36

5.83

5.90

5.52

5.09

4.14

2.97

2.65

angleBestsummertiltTiltadjustedeachmonth

3.5532°

3.7540°

4.4048°

4.8456°

5.3664°

6.1372°

5.9064°

5.5556°

5.1348°

4.4740°

3.4632°

3.2924°

Kansas

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.15

2.72

3.91

4.80

5.61

6.15

6.37

5.48

4.67

3.41

2.30

1.92

Upright-0°

3.40

3.13

3.32

2.84

2.56

2.46

2.60

2.86

3.50

3.76

3.32

3.32

51°angleYear-roundtilt

3.57

3.75

4.66

4.89

5.16

5.41

5.70

5.36

5.33

4.64

3.61

3.36

35°angleBestwintertilt

3.78

3.81

4.53

4.50

4.54

4.65

4.93

4.83

5.09

4.68

3.78

3.60

67°angleBestsummertilt

3.16

3.50

4.55

5.05

5.54

5.93

6.21

5.63

5.29

4.35

3.24

2.93

Tilt

3.78

3.81

4.66

5.06

5.54

6.17

6.21

5.66

5.33

4.69

3.78

3.64

adjustedeachmonth

35° 43° 51° 59° 67° 74° 67° 59° 51° 43° 35° 28°

Louisiana

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.59

3.25

4.31

5.21

5.79

5.65

5.66

5.30

4.72

4.03

3.04

2.56

Upright-0°

2.95

3.02

3.01

2.57

2.19

2.00

2.07

2.34

2.89

3.55

3.42

3.22

60°angleYear-roundtilt

3.41

3.95

4.76

5.23

5.35

5.07

5.14

5.11

5.02

4.85

4.03

3.54

44°angleBestwintertilt

3.57

4.00

4.63

4.86

4.75

4.43

4.53

4.65

4.80

4.89

4.21

3.77

76°angleBestsummertilt

3.08

3.69

4.65

5.35

5.71

5.48

5.53

5.33

4.99

4.55

3.63

3.13

Tiltadjustedeachmonth

3.5744°

4.0152°

4.7660°

5.3568°

5.7176°

5.6584°

5.5376°

5.3568°

5.0260°

4.9052°

4.2144°

3.8036°

Maine

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.69

2.57

3.64

4.43

4.87

5.35

5.28

4.85

3.78

2.56

1.60

1.33

Upright-0°

3.25

3.61

3.52

2.91

2.52

2.50

2.56

2.84

3.10

3.01

2.51

2.57

46°angleYear-roundtilt

3.28

4.07

4.63

4.59

4.50

4.64

4.69

4.80

4.39

3.60

2.68

2.58

30°angleBestwintertilt

3.48

4.16

4.50

4.21

3.96

4.01

4.09

4.32

4.17

3.60

2.78

2.74

62°angleBestsummertilt

2.88

3.75

4.52

4.76

4.84

5.09

5.10

5.05

4.39

3.41

2.43

2.27

Tiltadjustedeachmonth

3.4830°

4.1638°

4.6346°

4.7654°

4.8462°

5.3770°

5.1062°

5.0954°

4.3946°

3.6238°

2.7830°

2.7622°

Maryland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.94

2.68

3.67

4.63

5.31

5.58

5.53

4.94

4.19

3.33

2.19

1.71

Upright-0°

2.89

3.06

3.06

2.75

2.47

2.33

2.40

2.62

3.09

3.63

3.08

2.75

51°angleYear-roundtilt

3.09

3.68

4.31

4.70

4.89

4.93

4.97

4.80

4.70

4.50

3.37

2.84

35°angleBestwintertilt

3.24

3.73

4.18

4.33

4.31

4.27

4.34

4.34

4.47

4.53

3.52

3.02

67°angleBestsummertilt

2.76

3.44

4.23

4.86

5.24

5.38

5.39

5.04

4.69

4.22

3.04

2.51

Tiltadjustedeachmonth

3.2435°

3.7443°

4.3151°

4.8759°

5.2467°

5.5974°

5.3967°

5.0859°

4.7051°

4.5543°

3.5235°

3.0428°

Massachusetts

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.80

2.62

3.61

4.46

5.13

5.50

5.60

4.99

4.04

2.93

1.89

1.54

Upright-0°

3.15

3.40

3.30

2.83

2.56

2.47

2.59

2.81

3.22

3.41

2.94

2.91

48°angleYear-roundtilt

3.22

3.91

4.44

4.59

4.75

4.79

5.05

4.91

4.67

4.10

3.13

2.90

32°angleBestwintertilt

3.42 3.99 4.32 4.22 4.19 4.15 4.40 4.43 4.45 4.12 3.27 3.10

64°angleBestsummertilt

2.85

3.62

4.34

4.74

5.10

5.24

5.49

5.16

4.66

3.86

2.82

2.53

Tiltadjustedeachmonth

3.4232°

3.9940°

4.4448°

4.7556°

5.1064°

5.5172°

5.4964°

5.1956°

4.6748°

4.1440°

3.2732°

3.1424°

Michigan

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.78

2.51

3.44

4.45

5.24

6.07

5.93

5.03

4.13

2.79

1.69

1.41

Upright-0°

3.13

3.22

3.11

2.84

2.61

2.64

2.70

2.86

3.33

3.20

2.47

2.55

47°angleYear-roundtilt

3.20

3.71

4.20

4.59

4.86

5.29

5.36

4.97

4.81

3.86

2.67

2.56

31°angleBestwintertilt

3.39

3.78

4.07

4.22

4.29

4.55

4.65

4.49

4.59

3.87

2.77

2.73

63°

2.83

3.44

4.11

4.74

5.21

5.78

5.82

5.22

4.78

3.64

2.43

2.25

angleBestsummertiltTiltadjustedeachmonth

3.3931°

3.7839°

4.2047°

4.7455°

5.2163°

6.0970°

5.8263°

5.2555°

4.8147°

3.8939°

2.7731°

2.7524°

Minnesota

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.71

2.55

3.44

4.54

5.32

5.96

6.05

5.19

4.00

2.78

1.76

1.37

Upright-0°

3.41

3.65

3.33

3.03

2.75

2.73

2.87

3.08

3.39

3.49

3.03

2.81

45°angleYear-roundtilt

3.39

4.08

4.36

4.76

4.96

5.19

5.40

5.20

4.76

4.08

3.15

2.77

29°angleBestwintertilt

3.62

4.18

4.24

4.37

4.36

4.47

4.68

4.68

4.54

4.12

3.30

2.97

61°angleBestsummertilt

2.97

3.74

4.25

4.91

5.33

5.68

5.87

5.46

4.73

3.83

2.82

2.42

Tilt

3.62

4.18

4.36

4.92

5.33

5.99

5.87

5.48

4.76

4.13

3.30

3.00

adjustedeachmonth

29° 37° 45° 53° 61° 68° 61° 53° 45° 37° 29° 22°

Mississippi

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.52

3.24

4.24

5.34

5.89

5.98

5.80

5.36

4.75

3.99

2.94

2.39

Upright-0°

3.08

3.20

3.09

2.72

2.30

2.12

2.17

2.46

3.04

3.71

3.53

3.17

58°angleYear-roundtilt

3.48

4.07

4.75

5.39

5.43

5.33

5.25

5.17

5.12

4.94

4.05

3.44

42°angleBestwintertilt

3.66

4.14

4.62

5.00

4.80

4.62

4.60

4.70

4.90

4.99

4.24

3.65

74°angleBestsummertilt

3.12

3.79

4.64

5.52

5.80

5.79

5.66

5.41

5.09

4.63

3.64

3.03

Tiltadjustedeachmonth

3.6642°

4.1450°

4.7558°

5.5266°

5.8074°

5.9882°

5.6674°

5.4366°

5.1258°

5.0050°

4.2442°

3.6934°

Missouri

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.09

2.71

3.85

4.94

5.53

5.95

6.18

5.52

4.62

3.42

2.23

1.89

Upright-0°

3.13

3.04

3.21

2.90

2.52

2.40

2.54

2.85

3.42

3.70

3.07

3.10

51°angleYear-roundtilt

3.32

3.67

4.54

5.05

5.11

5.27

5.57

5.41

5.24

4.59

3.37

3.17

35°angleBestwintertilt

3.51

3.72

4.41

4.65

4.51

4.55

4.84

4.89

5.01

4.63

3.52

3.38

67°angleBestsummertilt

2.95

3.42

4.43

5.20

5.47

5.74

6.04

5.67

5.20

4.30

3.04

2.77

Tiltadjustedeachmonth

3.5135°

3.7343°

4.5451°

5.2059°

5.4767°

5.9674°

6.0467°

5.7059°

5.2451°

4.6543°

3.5235°

3.4228°

Montana

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.64

2.51

3.65

4.72

5.60

6.31

6.58

5.70

4.30

2.83

1.83

1.37

Upright-0°

2.59

3.19

3.41

3.22

2.95

2.94

3.18

3.45

3.62

3.31

2.73

2.25

43°angleYear-roundtilt

2.73

3.67

4.48

4.98

5.21

5.48

5.87

5.71

5.04

3.95

2.94

2.34

27°angleBestwintertilt

2.83

3.69

4.33

4.58

4.59

4.71

5.08

5.14

4.79

3.94

3.03

2.44

59°angleBestsummertilt

2.48

3.45

4.41

5.14

5.61

6.00

6.39

6.00

5.04

3.76

2.70

2.12

Tiltadjustedeachmonth

2.8327°

3.7135°

4.4843°

5.1551°

5.6159°

6.3466°

6.3959°

6.0451°

5.0443°

3.9735°

3.0327°

2.4520°

Nebraska

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.09

2.68

3.83

4.78

5.57

6.35

6.35

5.48

4.63

3.35

2.26

1.86

Upright-0°

3.55

3.26

3.39

2.93

2.64

2.60

2.71

2.97

3.63

3.90

3.51

3.50

49°angleYear-roundtilt

3.65

3.82

4.65

4.91

5.16

5.54

5.73

5.41

5.38

4.70

3.72

3.47

33°angleBestwintertilt

3.88 3.90 4.53 4.53 4.55 4.77 4.96 4.89 5.15 4.76 3.92 3.74

65°angleBestsummertilt

3.20

3.55

4.53

5.07

5.54

6.06

6.22

5.67

5.33

4.39

3.32

3.00

Tiltadjustedeachmonth

3.8833°

3.9041°

4.6549°

5.0757°

5.5465°

6.3672°

6.2265°

5.7057°

5.3849°

4.7741°

3.9233°

3.7926°

Nevada

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.29

3.15

4.61

5.85

7.01

7.77

7.76

6.89

5.60

4.06

2.60

2.11

Upright-0°

3.84

3.94

4.16

3.48

2.98

2.74

2.90

3.49

4.42

4.91

4.10

3.95

51°angleYear-roundtilt

3.95

4.60

5.75

6.10

6.47

6.77

6.93

6.85

6.67

5.89

4.33

3.91

35°angleBestwintertilt

4.21

4.72

5.64

5.61

5.64

5.72

5.93

6.15

6.41

6.01

4.58

4.22

67°

3.46

4.22

5.55

6.26

6.97

7.47

7.58

7.17

6.55

5.42

3.83

3.36

angleBestsummertiltTiltadjustedeachmonth

4.2135°

4.7243°

5.7551°

6.2659°

6.9767°

7.7974°

7.5867°

7.2059°

6.6751°

6.0143°

4.5835°

4.3028°

NewHampshire

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.74

2.62

3.61

4.43

4.92

5.42

5.47

4.91

3.92

2.72

1.71

1.46

Upright-0°

3.17

3.54

3.38

2.85

2.51

2.48

2.58

2.82

3.16

3.17

2.63

2.86

47°angleYear-roundtilt

3.23

4.03

4.51

4.57

4.55

4.71

4.90

4.85

4.54

3.80

2.81

2.84

31°angleBestwintertilt

3.42

4.12

4.38

4.20

4.01

4.08

4.26

4.36

4.31

3.81

2.92

3.03

63°angleBestsummertilt

2.85

3.72

4.40

4.73

4.89

5.16

5.32

5.10

4.53

3.59

2.54

2.47

Tilt

3.42

4.12

4.51

4.74

4.89

5.43

5.32

5.13

4.54

3.83

2.92

3.07

adjustedeachmonth

31° 39° 47° 55° 63° 70° 63° 55° 47° 39° 31° 24°

NewJersey

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.92

2.71

3.69

4.57

5.21

5.61

5.51

4.97

4.15

3.13

2.07

1.66

Upright-0°

3.03

3.25

3.18

2.77

2.49

2.39

2.45

2.69

3.15

3.47

2.99

2.83

50°angleYear-roundtilt

3.18

3.84

4.41

4.66

4.81

4.96

4.97

4.85

4.70

4.26

3.24

2.88

34°angleBestwintertilt

3.35

3.91

4.28

4.28

4.25

4.29

4.33

4.38

4.48

4.28

3.38

3.07

66°angleBestsummertilt

2.82

3.57

4.32

4.81

5.16

5.42

5.38

5.10

4.69

4.01

2.93

2.53

Tiltadjustedeachmonth

3.3534°

3.9142°

4.4150°

4.8258°

5.1666°

5.6374°

5.3866°

5.1358°

4.7050°

4.3042°

3.3834°

3.1026°

NewMexico

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

3.04

3.85

5.14

6.32

7.04

7.22

6.51

5.81

5.41

4.39

3.29

2.81

Upright-0°

4.80

4.49

4.27

3.39

2.70

2.42

2.44

2.79

3.80

4.73

4.83

4.87

54°angleYear-roundtilt

4.98

5.39

6.20

6.48

6.47

6.33

5.85

5.66

6.11

5.93

5.18

4.85

38°angleBestwintertilt

5.36

5.56

6.10

5.98

5.66

5.40

5.08

5.12

5.87

6.05

5.52

5.28

70°angleBestsummertilt

4.31

4.91

5.96

6.65

6.96

6.95

6.34

5.92

6.02

5.47

4.54

4.13

Tiltadjustedeachmonth

5.3638°

5.5646°

6.2054°

6.6562°

6.9670°

7.2278°

6.3470°

5.9562°

6.1154°

6.0546°

5.5238°

5.4030°

NewYork

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.74

2.60

3.57

4.34

5.04

5.64

5.55

4.97

3.95

2.80

1.76

1.47

Upright-0°

3.02

3.39

3.27

2.76

2.54

2.52

2.58

2.82

3.15

3.22

2.63

2.73

47°angleYear-roundtilt

3.09

3.89

4.40

4.46

4.67

4.92

5.02

4.91

4.56

3.88

2.83

2.73

31°angleBestwintertilt

3.28

3.97

4.27

4.10

4.13

4.26

4.37

4.43

4.35

3.89

2.94

2.91

63°angleBestsummertilt

2.74

3.60

4.29

4.61

5.01

5.37

5.44

5.16

4.55

3.66

2.56

2.39

Tiltadjustedeachmonth

3.2831°

3.9739°

4.4047°

4.6255°

5.0163°

5.6570°

5.4463°

5.1955°

4.5647°

3.9139°

2.9431°

2.9424°

NorthCarolina

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.43

3.05

4.20

5.22

5.73

5.80

5.68

5.08

4.43

3.76

2.73

2.30

Upright-0°

3.39

3.24

3.33

2.87

2.43

2.25

2.30

2.52

3.05

3.82

3.64

3.56

54°angleYear-roundtilt

3.66

4.00

4.87

5.29

5.29

5.16

5.15

4.93

4.86

4.87

4.03

3.67

38°angleBestwintertilt

3.87 4.07 4.75 4.89 4.69 4.49 4.51 4.47 4.64 4.93 4.24 3.94

70°angleBestsummertilt

3.24

3.72

4.74

5.44

5.66

5.61

5.55

5.15

4.84

4.55

3.60

3.20

Tiltadjustedeachmonth

3.8738°

4.0746°

4.8754°

5.4462°

5.6670°

5.8078°

5.5570°

5.1862°

4.8654°

4.9446°

4.2438°

430°

NorthDakota

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.48

2.35

3.47

4.77

5.72

6.26

6.49

5.48

4.06

2.73

1.71

1.27

Upright-0°

2.36

3.02

3.29

3.29

3.06

2.98

3.22

3.39

3.47

3.25

2.61

2.15

43°angleYear-roundtilt

2.49

3.46

4.28

5.01

5.27

5.43

5.79

5.50

4.78

3.85

2.80

2.22

27°angleBestwintertilt

2.58

3.48

4.13

4.60

4.63

4.67

5.01

4.95

4.54

3.83

2.88

2.32

59°

2.28

3.26

4.22

5.19

5.68

5.96

6.30

5.78

4.78

3.67

2.57

2.01

angleBestsummertiltTiltadjustedeachmonth

2.5827°

3.5035°

4.2843°

5.1951°

5.6859°

6.3066°

6.3059°

5.8251°

4.7843°

3.8735°

2.8827°

2.3220°

Ohio

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.77

2.49

3.31

4.47

5.18

5.64

5.76

5.11

4.26

3.08

1.86

1.46

Upright-0°

2.64

2.86

2.76

2.70

2.47

2.39

2.51

2.74

3.23

3.37

2.51

2.28

50°angleYear-roundtilt

2.81

3.43

3.86

4.54

4.77

4.98

5.18

4.99

4.84

4.16

2.78

2.38

34°angleBestwintertilt

2.95

3.47

3.73

4.17

4.21

4.31

4.50

4.50

4.61

4.18

2.88

2.51

66°angleBestsummertilt

2.53

3.21

3.80

4.69

5.12

5.44

5.62

5.24

4.82

3.92

2.54

2.12

Tilt

2.95

3.47

3.86

4.70

5.12

5.66

5.62

5.28

4.84

4.20

2.88

2.52

adjustedeachmonth

34° 42° 50° 58° 66° 74° 66° 58° 50° 42° 34° 26°

Oklahoma

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.59

3.20

4.29

5.40

5.84

6.32

6.73

5.86

4.81

3.72

2.75

2.33

Upright-0°

3.70

3.43

3.39

2.94

2.44

2.31

2.46

2.79

3.31

3.73

3.64

3.59

54°angleYear-roundtilt

3.97

4.23

4.98

5.47

5.38

5.59

6.03

5.70

5.32

4.79

4.05

3.71

38°angleBestwintertilt

4.21

4.31

4.86

5.05

4.75

4.82

5.22

5.15

5.09

4.83

4.25

3.98

70°angleBestsummertilt

3.50

3.92

4.85

5.63

5.76

6.10

6.55

5.97

5.28

4.49

3.62

3.23

Tiltadjustedeachmonth

4.2138°

4.3146°

4.9854°

5.6362°

5.7670°

6.3378°

6.5570°

5.9962°

5.3254°

4.8546°

4.2538°

4.0430°

Oregon

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.41

2.24

3.26

4.33

5.26

6.19

6.85

6.04

4.55

2.82

1.49

1.16

Upright-0°

2.40

2.91

3.03

2.83

2.68

2.74

3.06

3.48

3.91

3.47

2.23

2.04

46°angleYear-roundtilt

2.49

3.35

4.02

4.47

4.86

5.35

6.07

6.07

5.53

4.10

2.41

2.09

30°angleBestwintertilt

2.61

3.39

3.89

4.10

4.27

4.58

5.20

5.44

5.28

4.12

2.49

2.20

62°angleBestsummertilt

2.23

3.12

3.95

4.64

5.23

5.88

6.63

6.39

5.47

3.85

2.20

1.86

Tiltadjustedeachmonth

2.6130°

3.4038°

4.0246°

4.6454°

5.2362°

6.2270°

6.6362°

6.4254°

5.5346°

4.1438°

2.4930°

2.2122°

Pennsylvania

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.87

2.65

3.52

4.32

5.11

5.44

5.50

4.86

4.03

3.07

1.97

1.58

Upright-0°

2.91

3.16

3.00

2.63

2.46

2.35

2.45

2.64

3.05

3.39

2.78

2.62

50°angleYear-roundtilt

3.07

3.74

4.17

4.38

4.71

4.82

4.96

4.74

4.55

4.16

3.03

2.69

34°angleBestwintertilt

3.23

3.80

4.04

4.03

4.17

4.18

4.33

4.28

4.33

4.18

3.16

2.86

66°angleBestsummertilt

2.73

3.48

4.09

4.53

5.05

5.26

5.37

4.98

4.54

3.92

2.75

2.38

Tiltadjustedeachmonth

3.2334°

3.8042°

4.1750°

4.5458°

5.0566°

5.4674°

5.3766°

5.0158°

4.5550°

4.2042°

3.1634°

2.8826°

RhodeIsland

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.89

2.69

3.75

4.54

5.31

5.76

5.57

5.07

4.13

3.07

1.98

1.62

Upright-0°

3.25

3.44

3.40

2.85

2.60

2.52

2.55

2.83

3.26

3.58

3.04

2.99

48°angleYear-roundtilt

3.33

3.97

4.61

4.67

4.93

5.04

5.04

5.01

4.76

4.31

3.24

2.98

32°angleBestwintertilt

3.53 4.06 4.49 4.30 4.35 4.36 4.40 4.52 4.55 4.34 3.39 3.19

64°angleBestsummertilt

2.93

3.67

4.49

4.82

5.28

5.49

5.45

5.25

4.74

4.03

2.91

2.60

Tiltadjustedeachmonth

3.5332°

4.0640°

4.6148°

4.8256°

5.2864°

5.7772°

5.4564°

5.2856°

4.7648°

4.3640°

3.3932°

3.2324°

SouthCarolina

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.52

3.14

4.28

5.41

5.88

5.90

5.75

5.13

4.44

3.80

2.83

2.39

Upright-0°

3.33

3.19

3.26

2.85

2.37

2.18

2.23

2.46

2.93

3.67

3.59

3.49

56°angleYear-roundtilt

3.67

4.03

4.89

5.47

5.40

5.23

5.18

4.95

4.81

4.80

4.05

3.67

40°angleBestwintertilt

3.87

4.09

4.76

5.05

4.77

4.53

4.53

4.49

4.58

4.83

4.25

3.93

72°

3.27

3.76

4.77

5.62

5.79

5.70

5.60

5.19

4.79

4.50

3.64

3.22

angleBestsummertiltTiltadjustedeachmonth

3.8740°

4.0948°

4.8956°

5.6264°

5.7972°

5.9080°

5.6072°

5.2164°

4.8156°

4.8548°

4.2540°

3.9732°

SouthDakota

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.75

2.54

3.61

4.79

5.83

6.51

6.60

5.75

4.42

3.04

1.93

1.47

Upright-0°

3.44

3.52

3.48

3.16

2.91

2.84

2.99

3.33

3.77

3.91

3.40

3.04

46°angleYear-roundtilt

3.45

3.98

4.58

5.02

5.41

5.62

5.85

5.76

5.33

4.57

3.53

3.01

30°angleBestwintertilt

3.68

4.07

4.45

4.60

4.73

4.80

5.03

5.17

5.08

4.62

3.71

3.21

62°angleBestsummertilt

3.03

3.67

4.47

5.19

5.83

6.19

6.39

6.06

5.28

4.27

3.14

2.62

Tilt

3.68

4.07

4.58

5.19

5.83

6.54

6.39

6.09

5.33

4.63

3.71

3.25

adjustedeachmonth

30° 38° 46° 54° 62° 70° 62° 54° 46° 38° 30° 22°

Tennessee

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.06

2.72

3.83

4.97

5.47

5.79

5.79

5.30

4.63

3.62

2.43

1.88

Upright-0°

2.72

2.81

3.00

2.77

2.38

2.26

2.33

2.63

3.23

3.69

3.13

2.69

54°angleYear-roundtilt

3.00

3.51

4.38

5.02

5.04

5.13

5.22

5.14

5.13

4.70

3.52

2.87

38°angleBestwintertilt

3.14

3.54

4.25

4.63

4.46

4.45

4.55

4.65

4.90

4.74

3.67

3.03

70°angleBestsummertilt

2.71

3.29

4.30

5.17

5.40

5.58

5.64

5.39

5.10

4.41

3.18

2.55

Tiltadjustedeachmonth

3.1438°

3.5546°

4.3854°

5.1862°

5.4070°

5.7978°

5.6470°

5.4262°

5.1354°

4.7646°

3.6738°

3.0530°

Texas

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.83

3.41

4.40

5.25

5.62

6.36

6.56

5.94

4.97

4.05

3.07

2.63

Upright-0°

3.35

3.21

3.07

2.57

2.16

2.05

2.14

2.50

3.03

3.55

3.45

3.35

60°angleYear-roundtilt

3.82

4.18

4.86

5.27

5.19

5.65

5.90

5.72

5.31

4.87

4.07

3.67

44°angleBestwintertilt

4.03

4.25

4.74

4.89

4.61

4.88

5.12

5.18

5.08

4.90

4.25

3.91

76°angleBestsummertilt

3.41

3.89

4.75

5.39

5.54

6.15

6.38

5.98

5.27

4.57

3.66

3.24

Tiltadjustedeachmonth

4.0344°

4.2552°

4.8660°

5.3968°

5.5476°

6.3684°

6.3876°

6.0068°

5.3160°

4.9252°

4.2544°

3.9536°

Utah

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.31

3.11

4.47

5.54

6.55

7.31

7.08

6.11

5.10

3.76

2.45

2.07

Upright-0°

4.10

3.99

4.10

3.36

2.91

2.73

2.83

3.21

4.03

4.53

3.92

4.07

50°angleYear-roundtilt

4.17

4.62

5.61

5.76

6.04

6.38

6.33

6.04

6.01

5.43

4.14

3.99

34°angleBestwintertilt

4.46

4.74

5.49

5.30

5.27

5.41

5.43

5.43

5.76

5.52

4.37

4.32

66°angleBestsummertilt

3.64

4.24

5.42

5.93

6.51

7.03

6.91

6.34

5.93

5.03

3.67

3.43

Tiltadjustedeachmonth

4.4634°

4.7442°

5.6150°

5.9358°

6.5166°

7.3474°

6.9166°

6.3758°

6.0150°

5.5342°

4.3734°

4.3926°

Vermont

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.61

2.53

3.54

4.34

4.86

5.43

5.49

4.81

3.72

2.45

1.50

1.26

Upright-0°

3.06

3.55

3.42

2.87

2.53

2.54

2.65

2.84

3.06

2.85

2.30

2.38

46°angleYear-roundtilt

3.08

4.00

4.49

4.51

4.50

4.72

4.89

4.77

4.33

3.41

2.46

2.40

30°angleBestwintertilt

3.27 4.09 4.37 4.14 3.97 4.08 4.26 4.30 4.11 3.41 2.55 2.54

62°angleBestsummertilt

2.72

3.68

4.38

4.66

4.84

5.17

5.31

5.02

4.32

3.24

2.24

2.11

Tiltadjustedeachmonth

3.2730°

4.0938°

4.4946°

4.6754°

4.8462°

5.4570°

5.3162°

5.0554°

4.3346°

3.4338°

2.5530°

2.5622°

Virginia

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.17

2.83

3.89

4.76

5.38

5.63

5.56

4.98

4.28

3.58

2.43

1.94

Upright-0°

3.11

3.10

3.15

2.73

2.42

2.28

2.34

2.56

3.04

3.79

3.32

3.00

53°angleYear-roundtilt

3.34

3.79

4.53

4.82

4.97

5.00

5.02

4.83

4.74

4.75

3.65

3.12

37°angleBestwintertilt

3.52

3.84

4.40

4.44

4.39

4.34

4.39

4.38

4.52

4.79

3.82

3.32

69°

2.98

3.53

4.43

4.97

5.31

5.44

5.42

5.07

4.72

4.44

3.28

2.74

angleBestsummertiltTiltadjustedeachmonth

3.5237°

3.8545°

4.5353°

4.9761°

5.3169°

5.6476°

5.4269°

5.0961°

4.7453°

4.8145°

3.8237°

3.3530°

Washington

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.06

1.93

2.94

4.05

4.99

5.51

5.88

5.20

3.98

2.25

1.25

0.91

Upright-0°

1.55

2.42

2.69

2.76

2.73

2.72

2.97

3.23

3.42

2.62

1.79

1.43

43°angleYear-roundtilt

1.68

2.79

3.52

4.15

4.55

4.76

5.21

5.18

4.68

3.13

1.95

1.51

27°angleBestwintertilt

1.72

2.79

3.37

3.80

4.01

4.10

4.51

4.65

4.43

3.10

1.99

1.56

59°angleBestsummertilt

1.56

2.65

3.50

4.33

4.91

5.24

5.68

5.47

4.70

3.00

1.82

1.39

Tiltadjustedeachmonth

1.7227°

2.8135°

3.53243°

4.3451°

4.9159°

5.5566°

5.6859°

5.5151°

4.6843°

3.1435°

1.9927°

1.5620°

WestVirginia

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.85

2.49

3.51

4.58

5.09

5.82

5.63

4.99

4.31

3.33

2.12

1.65

Upright-0°

2.56

2.66

2.84

2.68

2.37

2.36

2.39

2.61

3.14

3.53

2.81

2.46

52°angleYear-roundtilt

2.79

3.27

4.05

4.64

4.70

5.15

5.07

4.85

4.82

4.42

3.13

2.59

36°angleBestwintertilt

2.91

3.29

3.92

4.27

4.16

4.45

4.43

4.39

4.59

4.44

3.25

2.74

68°angleBestsummertilt

2.51

3.07

3.98

4.79

5.03

5.62

5.49

5.09

4.80

4.15

2.84

2.31

Tiltadjustedeachmonth

2.9136°

3.3044°

4.0552°

4.7960°

5.0368°

5.8376°

5.4968°

5.1260°

4.8252°

4.4644°

3.2536°

2.7528°

Wisconsin

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

1.80

2.67

3.58

4.49

5.33

5.97

5.87

5.05

4.01

2.76

1.79

1.52

Upright-0°

3.34

3.63

3.34

2.89

2.67

2.63

2.71

2.89

3.25

3.23

2.82

3.05

47°angleYear-roundtilt

3.39

4.13

4.45

4.64

4.92

5.18

5.24

4.99

4.67

3.87

3.00

3.01

31°angleBestwintertilt

3.60

4.22

4.32

4.25

4.33

4.45

4.54

4.49

4.44

3.88

3.12

3.22

63°angleBestsummertilt

2.98

3.81

4.35

4.80

5.30

5.67

5.71

5.25

4.66

3.65

2.70

2.61

Tiltadjustedeachmonth

3.6031°

4.2239°

4.4547°

4.8055°

5.3063°

5.9970°

5.7163°

5.2955°

4.6747°

3.9039°

3.1231°

3.2624°

Wyoming

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Flat-90°

2.13

2.92

4.10

5.13

6.14

6.92

6.65

5.82

4.79

3.52

2.34

1.89

Upright-0°

3.81 3.78 3.76 3.18 2.84 2.73 2.80 3.15 3.83 4.28 3.83 3.76

49°angleYear-roundtilt

3.88

4.37

5.12

5.32

5.66

5.98

5.96

5.76

5.65

5.11

4.03

3.69

33°angleBestwintertilt

4.13

4.47

4.99

4.89

4.96

5.09

5.13

5.18

5.40

5.18

4.25

3.99

65°angleBestsummertilt

3.39

4.02

4.97

5.49

6.10

6.58

6.50

6.05

5.59

4.75

3.58

3.18

Tiltadjustedeachmonth

4.1333°

4.4741°

5.1249°

5.4957°

6.1065°

6.9372°

6.5065°

6.0857°

5.6549°

5.1941°

4.2533°

4.0526°

AppendixC–TypicalPowerRequirements

When creating your power analysis, you need to establish the powerrequirements for your system. The best way is to measure the actual powerconsumptionusingawattmeter.Findingaballparkfigureforsimilardevicesistheleastaccuratewayoffindingoutyourtruepowerrequirements.However,foraninitialprojectanalysisitcanbeausefulwayofgettingsomeinformationquickly:

Householdandoffice

Airconditioning–2500wAircooling–700wCellphonecharger–10wCentralheatingpump–800wCentralheatingcontroller–20wClothesdryer–2750wCoffeemaker–espresso–1200wCoffeepercolator–600wComputersystems:–Broadbandmodem–25w–Broadbandandwireless–50w–DesktopPC–240w–Documentscanner–40w–Laptop–45w–Monitor–17"flatscreen–70w

–Monitor–19"flatscreen–85w–Monitor–22"flatscreen–120w–Netbook–15w–Networkhub–large–100w–Networkhub–small–20w–Inkjetprinter–250w–Laserprinter–350w–Server–large–2200w–Server–small–1200wDeepfatfryer–1450wDishwasher–1200wElectricblanket–double–100wElectricblanket–single–50wElectriccooker–10000wElectrictoothbrush–1wFan–ceiling–80wFan–desk–60wFishtank–5wFoodmixer–130wFridge–12cu.ft.–280wFridge–caravanfridge–110wFridge–solarenergysaving–5wFridge-freezer–16cu.ft.–350wFridge-freezer–20cu.ft.–420wHairdryer–1000wHeater–fan–2000wHeater–halogenspotheater–1000wHeater–oilfilledradiator–1000wHeater–underfloor(perm²)–80w

Iron–1000wIron–steam–1500wIron–travel–600wKettle–2000wKettle–travel–700wLightbulb–energysaving–11wLightbulb–fluorescent–60wLightbulb–halogen–50wLightbulb–incandescent–60wMicrowaveoven–large–1400wMicrowaveoven–small–900wMusicsystem–large–250wMusicsystem–small–80wPhotocopier–1600wPowershower–240wRadio–15wSewingmachine–75wShaver–15wSlowcooker–200wTelevision:–LCD15"–50w–LCD20"–80w–LCD24"–120w–LCD32"–200w–DVDplayer–80w–Settopbox–25w–Videogamesconsole–45wToaster–1200wUprightfreezer–250w

Vacuumcleaner-700wWashingmachine–550wWaterheater–immersion–1000w

GardenandDIY

Concretemixer–1400wDrill:–Benchdrill–1500w–Hammerdrill–1150w–Handhelddrill–700w–Cordlessdrillcharger–100wElectricbikecharger–100wFloodlight:–Halogen–large–500w–Halogen–small–150w–Fluorescent–36w–LED–5wHedgetrimmer–500wLathe–small–650wLathe–large–900wLawnmower:–Cylindermower–small–400w–Cylindermower–large–700w–Hovermower–small–900w–Hovermower–large–1400wLawnraker–400wPond:–Smallfilter–20w–Largefilter–80w–Smallfountainpump–50w

–Largefountainpump–200wRotavator–750wSaw:–Chainsaw–1150w–Jigsaw–550w–Anglegrinder–small–1050w–Anglegrinder–large–2000wShedlight:–Largeenergysaving–11w–Smallenergysaving–5wStrimmer–small–250wStrimmer–large–500w

Caravans,boatsandrecreationalvehicles

Aircooling–400wAirheating–750wCoffeepercolator–400wFridge:–Coolbox–small–50w–Coolbox–large–120w–Electric/gasfridge–110w–Lowenergysolarfridge–5wKettle–700wFluorescentlight–10wHalogenlighting–10wLEDlighting–5w

AppendixD–LivingOff-Grid

Livingoff-grid isanaspiration formanypeople.Youmaywant to ‘growyourown’electricityandnotbereliantonelectricitycompanies.Youmayliveinthemiddleofnowhereandbeunabletogetanoutsideelectricitysupply.Whateveryourmotive,therearemanyattractionsforusingsolarpowertocreatecompleteself-sufficiency.Donotconfuselivingoff-gridwithagrid-tieinstallationandachievingabalancewhereenergyexportedtothegridminusenergyimportedfromthegridequalsazerooverallimportofelectricity.Agenuinelyoff-gridsystemmeansyouusetheelectricityyougenerateeverytimeyouswitchonalightbulborturnontheTV.Ifyoudonothaveenoughelectricity,nothinghappens.Beforeyoustart,beundernoillusions.Thisisgoingtobeanexpensiveprojectand formost people it will involvemaking some significant compromises onpowerusageinordertomakelivingoff-gridareality.Inthisbook,Ihavebeenusingtheexampleofaholidayhome.Thedifferencebetweenaholidayhomeandamainhomeissignificant:ifyouareplanningtolive off-grid all the time, you may not be so willing to give up some of thecreature comforts that this entails. Compromises that youmay be prepared toacceptforafewdaysorweeksmaynotbesodesirableforahomeyouarelivinginforfifty-twoweeksayear.Rememberthatasolarelectricsystemisalong-terminvestment,butwillrequirelong-termcompromisesaswell.Youwillnothavelimitlesselectricityavailablewhenyouhaveasolarelectricsystem,andthiscanmeanlimitingyourchoiceslater on. If you have children at home, consider their needs aswell: theywillincreaseastheybecometeenagersandtheymaynotbesohappyaboutmakingthesamecompromisesthatyouare.Youneedtobeabletoprovideenoughpowertolivethroughthewinteraswellasthesummer.Youwillprobablyusemoreelectricityduringthewinterthanthesummer:morelightingandmoretimespentinsidethehousemeanhigherpowerrequirements.Most off-grid installations involve a variety of power sources: a solar electricsystem, awind turbine and possibly a hydro-generation system if you have a

fast-flowingstreamwithasteepenoughdrop.Ofthesetechnologies,onlyhydroonasuitablestreamhastheabilitytogenerateelectricity24hoursaday,sevendaysaweek.Inadditiontousingsolar,windandhydroforelectricalgeneration,asolarwatersystemwillhelpheatupwaterandagroundsourceheatpumpmaybeusedtohelpheatthehome.When installing these systems in a home, it is important to have a failoversystem in place. A failover is simply a power backup so that if the powergenerationisinsufficienttocopewithyourneeds,abackupsystemcutsin.Dieselgeneratorsareoftenused for thispurpose.Someof themoreexpensivesolarcontrollershavethefacilitytoworkwithadieselgenerator,automaticallystartingupthegeneratorinordertochargeupyourbatteriesifthebatterybankrunstoolowonpower.Advancedsolarcontrollerswiththisfacilitycanlinkthisinwithatimertomakesurethegeneratordoesnotstartrunningatnightwhenthenoisemaybeinappropriate.

AsolarelectricsysteminconjunctionwithgridelectricityTraditionally,ithasrarelymadeeconomicsensetoinstallasolarelectricsystemforthispurpose.Thishaschangedoverthepastthreeyears,withtheavailabilityoffinancialassistanceinmanypartsoftheworld.If youare considering installing a systempurelyon environmental grounds,

make sure thatwhat you are installing actually doesmake a difference to theenvironment.Ifyouareplanningtosellbackelectricitytotheutilitygridsduringtheday,thenunlesspeakdemandforelectricityinyourareacoincideswiththetimesyoursolarsystemisgeneratingelectricity,youareactuallyunlikelytobemakinganyrealdifferencewhatsoever.AsolarenergysysteminthesouthernstatesofAmericacanmakeadifference

to theenvironment,aspeakdemandforelectricity tends tobewhenthesun isshining and everyone is running air conditioningunits.Agrid-tie solar energysystem in the United Kingdom is unlikely to make a real difference to theenvironment unless you are using the electricity yourself or you live in anindustrialareawherethereishighdemandforelectricityduringtheday.IfyouareintheUnitedKingdomorCanadaandareinstallingasolarenergy

systemfor theprimarymotiveof reducingyourcarbon impact,agrid fallbacksystemisthemostenvironmentallyfriendlysolution.Inthisscenario,youdonotexportenergybacktothegrid,butstoreitanduseityourself.Whenthebatterieshave run down, your power supply switches back to the grid. There is moreinformationongridfallbackinAppendixE.There may be other factors that make solar energy useful. For example,

ensuringanelectricalsupplyinanareawithfrequentpowercuts,usingthesolarsysteminconjunctionwithanelectriccar,or forenvironmental reasonswheretheenvironmentalbenefitsofthesystemhavebeenproperlyassessed.One of the benefits of building a system to work in conjunction with aconventionalpowersupplyis thatyoucantakeitstepbystep, implementingasmallersystemandgrowingitasandwhenfinancesallow.As outlined in Chapter Three, there are three ways to build a solar electricsysteminconjunctionwiththegrid:agrid-tiesystem,agridinteractivesystemandgridfallback.Youcanchoosetolinkyoursolararrayintothegridasagrid-tiedsystemifyou

wish, so that you supply electricity to the grid when your solar array isgeneratingthemajorityofitselectricityandyouusethegridasyourbattery.Itisworthnotingthatifthereisapowercutinyourarea,yoursolarelectricsystemwillbeswitchedoffasasafetyprecaution,whichmeansyouwillnotbeabletousethepowerfromyoursolarelectricsystemtorunyourhome,shouldtherebeapowercut.Alternatively,youcandesignastand-alonesolarelectricsystemtorunsomeofyour circuits in your house, either at grid-level AC voltage or on a DC low-voltagesystem.Lightingisapopularcircuit tochoose,as it isarelativelylowdemandcircuittostartwith.Asathirdalternative,youcanwireyoursolarelectricsystemtorunsomeorallofthecircuitsinyourhouse,butuseanACrelaytoswitchbetweenyoursolarelectricsystemwhenpowerisavailable,andelectricityfromthegridwhenyourbattery levelsdrop too low. Inotherwords,youareusing thegrid as apowerbackup,shouldyoursolarelectricsystemnotprovideenoughpower.Thissetupis known as a grid fallback system. A diagram showing this configuration isshowninthenextAppendixunderthesectionongridfallback.

AppendixE–OtherSolarProjects

Gridfallbacksystem/gridfailoversystemGridfallbackandgridfailoverarebothoftenoverlookedasaconfigurationforsolarpower.Both thesesystemsprovideACpower toabuildingalongside thenormalelectricitysupplyandprovidethebenefitofcontinuedpoweravailabilityinthecaseofapowercut.For smaller systems, a solar electric emergency power system can be cost-competitivewith installing an emergency power generator and uninterruptablepowersupplies.Asolarelectricemergencypowersystemalsohasthebenefitofproviding power all of the time, thereby reducing ongoing electricity bills aswellasprovidingpowerbackup.Thedifferencebetweenagrid fallbacksystemandagrid failover system is intheconfigurationofthesystem.Agridfallbacksystemprovidessolarpowerforas much of the time as possible, only switching back to the grid when thebatteriesareflat.Agridfailoversystemcutsinwhenthereisapowercut.Mostbackuppowersystemsprovidelimitedpowertohelptidepremisesoverashort-term power cut of 24 hours or less. Typically, a backup power systemwouldprovide lighting,enoughelectricity to runaheatingsystemandenoughelectricityforafewessentialdevices.Aswithallothersolarprojects,youmuststartwithaprojectscope.Anexamplescope for a backup power project in a small business could be to provideelectricityforlightingandforfourPCsandtorunthegascentralheatingforamaximumofonedayintheeventofapowerfailure.Ifyourpremiseshaveanumberofappliancesthathaveahigh-energyuse,suchasopenfridgesandfreezerunits,forexample,itisprobablynotcost-effectivetousesolarpowerforabackuppowersource.Installing anybackuppower systemwill require a certain amountof rewiring.Typically, you will install a secondary distribution panel (also known as aconsumerunit)containingtheessentialcircuits,andconnectthisafteryourmaindistributionpanel.YoutheninstallanACrelayoratransferswitchbetweenyourmain distribution panel and the secondary distribution panel, allowing you to

switch between your main power source and your backup source:

Inthisabovediagram,asecondconsumerboxhasbeenwiredintotheelectricalsystem, with power feeds from both the main consumer box and an inverterconnectedtoasolarsystem.Switchingbetweenthetwopowerfeedsisanautomatictransferbox.Ifyouareconfiguring this system to be a grid fallback system, this transfer box isconfigured to take power from the solar systemwhen it is available, but thenswitchesbacktogrid-sourcedelectricityifthebatteriesonthesolarsystemhaverundown.Thisprovidesabackupforcriticalpowerwhenthenormalelectricitysupplyisnotavailable,butalsousesthepowerfromthesolarsystemtorunyourdeviceswhenthisisavailable.Ifyouareconfiguringthissystemtobeagridfailoversystem,thetransferboxisconfiguredtotakepowerfromthenormalelectricitysupplywhenitisavailable,butthenswitchestopowerfromthesolarsystemifitisnot.Oneissuewith thissystemis thatwhenthe transferboxswitchesbetweenonepowersourceandtheother,theremaybeaveryshortlossofpowerofaround/ofasecond.Thiswillcauselightstoflickermomentarily,andinsomecasesmayresetelectronicequipmentsuchascomputers,TVsandDVDplayers.Manymoderntransferboxestransferpowersoquicklythatthisisnotaproblem.However, if you do experience this problem it can be resolved by installing asmall uninterruptable power supply (UPS) on any equipment affected in thisway.Youcanbuyfullybuilt-upautomatictransferboxes,oryoucanbuildyourownrelatively easily and cheaply using a high-voltage AC Double-Pole/ Double-

Throw(DPDT)PowerRelay,wiredsothatwhentheinverterisprovidingpower,therelaytakespowerfromthesolarsystem,andwhentheinverterswitchesoff,therelayswitchesthepowersupplybacktothenormalelectricitysupply.

PortablesolarpowerunitApopularandsimpleproject,abriefcase-sizedportablepowerunitallowsyoutotakeelectricitywithyouwhereveryougo.Theyarepopularwithpeoplewhogo camping, or with repair people who need to take small power tools tolocationswheretheycannotalwaysgetaccesstoelectricalpower.In essence, a portable power unit comprises four components: a small solarpanel,asolarcontroller,asealedleadacidgelbatteryandaninverter,allbuiltintoabriefcase.Manypeoplewhobuildthemaddextrabitsaswell.Acoupleoflightbulbsareapopularaddition,asisacigarettelighteradaptertorun12-voltcaraccessories.Forsafetypurposes,itisimportanttouseasealedleadacidgelbatteryforthisapplication, so that you can place the unit on its side, if necessary,without itleaking.For occasional use, a portable solar power unit can be a good alternative to apetrol generator: they are silent in operation and extremely easy to use. Theirdisadvantage is that, once the battery is flat, you cannot use it until it is fullychargedupagainandonsolarpoweralonethiscantakeseveraldays.For this reason, solar powered generators often include an external charger sotheycanbechargedupquicklywhennecessary.

SolarboatBoating on inland waterways has been undergoing a revival in recent years,especiallywithsmallcraftpoweredwithoutboardmotors.Electricoutboardmotorsarealsobecomingextremelypopular:theyarelighter,more compact, easier to use and cheaper to buy than the equivalent petroloutboardmotor.Bestofall,theirsilentrunningandlackofvibrationmakethemideallysuitedtoexploringinlandwaterwayswithoutdisturbingthewildlife.Forasmallopenboat,a100-wattelectricmotorwillpowertheboateffectively.Depending on what they are made from, small, lightweight boats can beexceptionally light – a 5m (15 foot) boat may weigh as little as 20kg (44pounds),whilst a simple ‘cabin cruiser’ constructed from alloymayweigh aslittleas80kg(175pounds).Consequently,theydonotrequirealotofpowertoprovideampleperformance.An 80 amp-hour leisure battery will provide around eight hours of constantmotorusebeforerunningflat.Thisismorethanenoughformostleisureactivity.Becausemostboats are typicallyonlyusedatweekendsduring the summer, asolar panel can be a good alternative to lugging around a heavy battery (thebatterycanquiteeasilyweighmorethantherestoftheboat!).Provided theboat ismoored in anareawhere itwill capturedirect sunlight, a50–60wattpanelisnormallysufficienttochargeupthebatteriesoveraperiodofaweek,withoutanyexternalpowersource.

SolarshedlightThereareseveraloff-the-shelfpackagesavailableforinstallingsolarshedlightsandtheseoftenofferexcellentvalueformoneywhenboughtasakitratherthanbuyingtheindividualcomponentsseparately.However, the manufacturers of these kits tend to state the best possibleperformanceoftheirsystemsbasedonoptimumconditions.Consequently,manypeoplearedisappointedwhenthe‘fourhoursdailyusage’turnsouttobeclosertotwentyminutesinthemiddleofwinter.Of course, if you have done a proper site survey and design, you will haveidentifiedthisproblembeforeyouboughtthesystem.Ifyouneedlongerusage,youcanthenbuyasecondsolarpanelwhenyoubuythekitinordertoprovideenoughsolarenergy.

SolarelectricbikesElectricbikesandmotorbikesaregaininginpopularityandareanexcellentwayofgettingaroundonshorterjourneys.Electric bikeswith pedals and a top power-assisted speed of 15mph are road-legal acrossEurope,Australia,Canada and theUnitedStates.Youcan ride anelectricbikefromtheageoffourteen.Legally, they are regarded as normal bicycles and do not require tax orinsurance. They typically have 200-watt or 250-watt motors (up to 750-wattmotorsarelegalinNorthAmerica).Mostelectricbikeshaveremovablebatterypackssotheycanbechargedupoffthebikeandusuallyhaveatotalcapacityof330–400watt-hoursandarangeof12–24miles(20–40km).Thankstotheirrelativelysmallbatterypacks,anumberofownershavebuiltasolararraythatfitsontoagarageorshedrooftochargeuptheirbikebatteries.This isespeciallyusefulwhenyouhave twobatterypacks.Onecanbe leftonchargewhilethesecondisinuseonthebike.Anumberofpeoplehavealsofittedsolarpanelsontoelectrictrikesinordertopowerthetrikewhileitisonthemove.Dependingonthesizeoftrikeandthespaceavailable,itisusuallypossibletofituptoaround100wattsofsolarpanelsto a trike,whilst some of the load-carrying trikes and rickshaws have enoughspaceforaround200wattsofsolarpanels.Suchasystemwouldprovideenoughpower to drive 15–20 miles during the winter, and potentially an almostunlimited range during the summer, making them a very practical andenvironmentallyfriendlyformofpersonaltransport.Whilstthesolar-onlyrangemaynotseemthatgreat,therearemanydriverswholive in a sunny climate and only use their cars for short journeys a few timeseachweek.Forthesepeople,itcouldmeanthatalmostalltheirdrivingcouldbepoweredfromthesun.EvenincolderclimatessuchastheUnitedKingdomandNorthernCanada,solarpowerhas itsuses inextendingtherangeof thesecars:bytrickle-chargingthebatteriesduring thedaytime, thebatteriesmaintain theiroptimumtemperature,therebyensuringagoodrangeevenincoldconditions.Meanwhile,anumberofelectriccarownershavealreadymadetheircarssolarpowered by charging up their cars from a larger home-based solar array,providing trulygreenmotoring formuchgreaterdistances.Severalelectriccarclubs have built very small and lightweight solar powered electric cars and

tricyclesandatleastoneelectriccarowners’clubisplanningtoprovideasolarrooftofittoexistingelectriccarsinthecomingyear.

AppendixF–BuildingYourOwnSolarPanels(andWhyYouShouldn’t)

Anumberofpeoplehaveaskedmeaboutbuildingtheirownsolarpanelsfromindividual solar cells and asked formy opinion on a number ofwebsites thatmake claims that you can build enough solar panels to power your home foraround$200(£120).Ihaveahugeamountofrespectforpeoplewith theaptitudeandtheability tobuild their ownequipment.Thesepeopleoftenderive agreat deal ofpersonalsatisfaction frombeingable to say,“Ibuilt thatmyself.”Largely, thesepeopleare to be encouraged. If youwant to build your own solar panels, however, Iwouldadvisecaution.Therehavebeenmanyclaimsmadefromcertainwebsitesthatsayitispossibletobuildyourownsolarpanelsandrunyourentirehouseonsolarforanoutlayof$200orless,sellingexcesspowerbacktotheutilitygridandevengeneratinganincomefromsolar.Mostoftheclaimsmadebythesewebsitesareeitherfalseormisleading.Whenyousubscribetotheseservices,youtypicallyreceivethefollowing:

Instructionsonhowtobuildasolarpanelthatarevirtuallyidentical toinstructionsthatareavailablefreefromsiteslikeinstructables.comInformationontaxcreditsandrebatesforinstallingsolarPVintheUnitedStates.(However,thesecreditsandrebatesarenotapplicableforhome-builtequipment.Thewebsitesomittotellyouthat.) AlistofcompaniesandeBaysellerswhowillsellyouindividualsolarcells

Manyofthewebsitesclaim,oratleastimply,thatyoucanrunyourhomeonasolar panel built for around$200. In reality, this amountwill buyyou enoughsolarcellstobuildasolarpanelproducing60–120watts,whichiscertainlynotenoughtoallowyoutorunyourhomeonsolarpower.Leaving aside the obvious point that you can buy a cheap, but professionallybuilt 60–100watt solar panelwith five-yearwarranty and anticipated 25-yearlifespan for around$200 (£120) if you shop around, there are various reasons

whyitisnotagoodideatobuildyourownsolarpanelsusingthisinformation: A solar panel is a precision piece of equipment, designed to surviveoutside for decades of inclementweather and huge temperature variationincludingintenseheat Professionally manufactured solar panels use specifically designedcomponents. They are built in a clean room environment to very highstandards.Forexample,theglassisaspecialtemperedproductdesignedtowithstand huge temperatures and ensuremaximum light penetrationwithzerorefraction Thesolarcellsyoucanbuy fromsellersoneBayare factoryseconds,rejected by the factory. Many of them are blemished or chipped anddamaged. They are extremely fragile, almost as thin as paper, brittle likeglassandveryeasytobreakUnlessyouareanexpertatsolderingtechniques,youarelikelytocreateacoldsolderjointbetweenoneormoresolarcells.Coldsolderjointsinsideasolarpanelarelikelytocreateahightemperaturearc,whichcanstartafire Thereareseveraldocumentedcaseswherehome-madesolarpanelshavecaughtfireandcauseddamagetopeople’shomes.Thesefiresaretypicallycausedbypoorqualitysolderingortheuseofwrongmaterials Manyofthewebsitespromotinghome-madesolarpanelsclaimthatyoucanpoweryourhousewith them. In theUnitedStates, connectinghome-made panels to your household electrics would be in violation of theNationalElectricCodeandyouwouldthereforenotbeallowedapermittoinstallthem Manyofthesewebsitesimplythatyoucanalsosellyourpowerbacktothe utility companies. It is actually illegal to install non-approved powergenerationequipment to theutilitygrid inmanycountries, includingboththeUnitedStatesandtheUnitedKingdom ThetaxcreditsandrebatesthatareavailableforinstallingsolarPVonyourhomearenotavailableforhome-builtsolarpanels

Manypeoplewhomaketheirownsolarpanelshavefoundthattheyfailafterafewmonthsduetomoisturepenetration,orfailafteronlyafewdaysorweeksduetohightemperaturearcingandpanelfailure.MostinstructionsrecommendbuildingaframeoutofwoodandcoveringitwithPlexiglasoracrylic.Thisisextremelybadadvice:

Never build a solar panel frame and backing out of wood. This isdangerousbecauseof the intenseheatbuild-up ina solarpanel.Onahotand sunny day, the surface temperature of the panel can exceed 90°C(175°F). If there is any additional heat build-up within the panel due toshortcircuitsorpoorqualitysoldering,thesespottemperaturescouldbeashighas800°C(1,472°F).Atthesesortsoftemperatures,youcaneasilystartafire DonotusePlexiglasor acrylic tocoveryourhome-made solarpanel.Tinyimperfectionsinthematerialcanleadtolightrefractionsandintenseheatbuild-uponelementswithin thepanel.Plexiglasandacryliccanalsodistortunderhightemperatures,increasingtheselightrefractionsovertime.Theeffectcanbelikeamagnifyingglass,concentratingtheintensityofthesunlightontoasmallspotonthesolarcell,whichcouldresultinfire

Ifyouwishtobuildasmallsolarpanelforfun,asawayoflearningmoreaboutthe technology, thenyoucanget instructionsonhow todo this freeof chargefrom many websites such as instructables.com. Build a small one as a funproject if you sowish.Youwill learn a lot about the technologybydoing so.However:

Treat your project as a learning exercise, not as a serious attempt togenerateelectricityNeverbuildasolarpanelwithawoodframeTreatyourhome-madesolarpanelasafirehazard Donotmountyourcompletedhome-made solarpanel as apermanentfixture Only use your home-made solar panel under supervision, checkingregularlyforheatbuild-uponthesolarpanelorframe.Rememberthatthefront of the solar panel may get extremely hot, especially on hot, sunnydays.Donottouchthesolarpanelwithyourfingers Visuallycheckyourhome-madesolarpaneleverytimeyouplugitintoensure there is nomoisture penetration. If you spotmoisture penetration,stopusingthesolarpanelimmediatelyUsethecheapestsolarchargecontrolleryoucanfindforyourproject.Thewarrantywillbeinvalidatedonthecontrollerbyusingahome-madepanel,but at least if you damage a cheap controller you haven’t damaged anexpensiveone

Neverchargebatteriesusingyourhome-madesolarpanelwithoutusingasolarchargecontrollerNeverrunaninverterdirectlyfromyourhome-madesolarpanel

TableofContentsCopyrightIntroducingSolarEnergyABriefIntroductiontoElectricityTheFourConfigurationsforSolarPowerComponentsofaSolarElectricSystemTheDesignProcessScopingtheProjectCalculatingSolarEnergySurveyingYourSiteUnderstandingtheComponentsComponentsforGrid-TiesystemsComponentsforStand-AloneSystemsPlanning,regulationsandapprovalsDetailedDesignInstallationTroubleshootingMaintainingYourSystemInternetSupportAFinalWordAppendixA–CrystallineSolarPanelsandShadingAppendixB–SolarInsolationAppendixC–TypicalPowerRequirementsAppendixD–LivingOff-GridAppendixE–OtherSolarProjectsAppendixF–BuildingYourOwnSolarPanels(andWhyYouShouldn’t)