A Consumer Guide to Solar Electricity for the Home

Own Your Power!

Contents

Benefits of Solar Electricity . . . . . . . . . . . . . . . . . . . 1

Solar Electricity Basics . . . . . . . . . . . . . . . . . . . . . . . 2

Types of Solar Panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2Types of Solar Electric Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Power Produced by a Solar Electric System . . . . . . . . . . . . . . . . . . . . . .5

How To Choose a System . . . . . . . . . . . . . . . . . . . . . 6

Roof Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Installation and Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Costs and Financial Incentives . . . . . . . . . . . . . . . . . 10

Purchasing Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Financing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

About this guide: The U .S . Department of Energy (DOE) receives numerous inquiries each year from consumers interested in solar electricity . This guide answers their frequently asked questions about benefits, system basics, choosing a system, financial incentives, warranty, and insurance issues . It is not meant to be a technical guide on how to design or install a system . Homeowners will need to consult with an experienced solar contractor to determine the best system for their climate and home’s energy needs . Some resources for consumers are also provided . DOE does not endorse any products in this guide .

1

Rising energy prices and growing en-vironmental concerns are making solar electric systems more attractive to homeowners. A solar electric system re-duces high energy costs and keeps your home up and running during power out-ages. The advantages to buying a solar electric system include:

•Savingasignificantamountonyourelectric bill

•Increasingyourhome’sappraisalvalue•Enjoyingreliable,clean,freepowerfor

25 to 30 years•Helpingtoboostoureconomybycreatingjobsandnewsolarcompanies.

Solar homes in California with SunPower Suntiles® integrated into their roofs.

Most solar electric systems last 30 yearsandpayforthemselvesin4to5yearsaftertaxcreditsandrebates.Thatmeanshomeownerscanenjoyfreeelectricityforyears.Ifyouinstallbatteries to back up your solar electric system,itwillprovideemergencypowerinareaswithfrequentstorms,hurricanes,andothernaturaldisasters.Inaddition,goingsolaraddsvaluetoyour home. According to the Appraisal Journal,*asolarelectricsystemincreasesyourhome’svalueby$20forevery$1inannualutilitybillsavings,whichmeansasystemalmostpaysforitselfwiththeappraisalvalueincreaseinsomecases.SeetheCostsandFinancialIncentivessection.SolarpowerreducesAmerica’sdependenceonforeignoilandfossilfuels,makingournation more secure while reducing air pollution and greenhouse gases.

*EvidenceofRationalMarketValuationsforHomeEnergyEfficiency,TheAppraisalJournal,October1998and1999.

Benefits of Solar Electricity

Benefits of Solar ElectricitySolar electricity saves money, adds value to homes, and reduces air pollution.

Quick TipA solar electric system can save tons in greenhouse gas emissions. The U.S. Environmental Protection Agency estimates the average two-person home emits approximately 41,500 pounds of greenhouse gases during a year.

2

Solarcompaniesmakesolarpanelsbycombining many solar cells together. Severalsolarpanelscombinedmakea solar array. When solar panels are strung together in series and combined withothercomponents,theybecomea solar electric system or solar array. A solar electric system can meet part or allofahome’selectricityneeds,offset-ting25%to50%ofmosthomeowners’power with solar electricity.

Types of Solar PanelsTherearetwoconventionaltypesofsolar panels: crystalline silicon and thin film.Themostcommonsolarcellma-terialiscrystallinesilicon,butnewermaterialsformakingsolarcellsincludethin-filmmaterialssuchasamorphous

This solar home in Davis, California, uses EnergyTiles® made by BP Solar.

Solar Electricity Basics

Solar Electricity BasicsSolar electric panels capture light from the sun and convert it to clean power.

Solarelectricityisproducedbychangingsunlight to power using the photovoltaic (PV)effect.ThePVeffectcausesanelectricalcurrenttoflowthroughaso-larcellwhenexposedtosunlight.So-larcellspowereverythingfromcalcula-torsandremotehighwaysignstohomes,commercialbuildings,andlargepowerplants.Solarcellspowerallsatellitesinspace,makingthemresponsiblefortheworld’scommunicationsproducts.

Quick TipA south-facing roof is most effective, but a roof over a carport, garage, or porch that receives no shading from other buildings or trees will work well.

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Solar Electricity Basics

siliconandcadmiumtelluride.Morerecently,solarcompanieshavebeguntouseplasticandaluminumfoiltoproducesolarelectricity,butitmaybeseveralyearsbe-forethesenewproductsbecomeavailabletoconsumers.

Silicon Solar Panels

Theserigidpanelscomeintwotypes:crystalline(madefromasinglelargecrystal)andpolycrystalline(madefromblocksofsiliconthatcontainmanysmallcrystals).Siliconsolarpanelsarethemostefficientonthemarket,butalsothemostexpen-sive.Theyarealsothebest-performingpanelsinlow-lightconditions.Althoughpoly-crystallinesolarcellsareslightlylessefficientthanthesingle-crystaltype,siliconsolarpanelefficienciesaverageabout33%.

Thin-Film Solar Panels

Theseflexiblesolarpanelsaremadebyspreadingsiliconandothersolar-produc-ingmaterialsinaverythinlayer(aboutthethicknessofahumanhair)directlyontoalargeplatethatisusuallymadeofglassorceramics.Lessefficientthansiliconsolarpanels,thin-filmsolarpanelsarealsolessexpensivetoproduce.Thethinmaterialofthese solar panels makes them ideal as building-integrated solar products such as solarshinglesandtiles.Themostsuccessfulthin-filmmaterialsareamorphoussili-con,cadmiumtelluride,andcopperindiumdiselenide.Efficienciesrangefrom10%to19%.

Future Solar Panels

Newsolarmaterialsthatareemergingincludelightweightfoil-basedpanels,plas-ticcollectors,andhybridsolarelectric/solarwaterheatingcollectors.Thenewhy-bridsystemscapturehotairfromthesolarelectricpanelsanduseittoheatwater.Exceptforthehybridsystems,mostofthenewmaterialsarenotavailabletohome-owners.

Types of Solar Electric SystemsAsolarelectricsystemistypicallymadeupofsolarpanels,aninverter,abattery,achargecontroller,wiring,andsupportstructure.Thethreemostcommontypesofsolarelectricsystemsaregrid-connected,grid-connectedwithbatterybackup,andoff-grid(stand-alone).Eachhasdistinctapplicationsandcomponents.

Grid-Connected

Inthissystem,thesolarpanelsareconnectedtoyourlocalutilityelectricalgridtocomplementyournormalpowersupplyfromyourutilitycompany.Grid-connectedsystemsconsistof:

•Solarpanelsmountedontheroof•Aninvertertoconvertelectricityproducedbythesystemfromdirectcurrent(DC)energyintoalternatingcurrent(AC)energy

•Ajunctionboxthatconnectsthesolarpanelwiringtothebreakerpanelonthehome•Apowermeterthatdisplayshowmuchpowerthehomeproducesanduses•Adisconnectswitchthat,forsafetyreasons,preventsthesystemfromsending

power to the grid during power outages (this is called islanding).

AC Main Panel and MeterAC Disconnect (Utility Accessible)

InverterDC Disconnect

Junction Box

Solar Array

Grid-Connected System

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Solar Electricity Basics

Grid-Connected with Battery Backup

Verysimilartothegrid-connectedsystem,thissystemaddsa“batterybank”tocol-lectthepowergeneratedfromthesolarpanels.Powerstoredinthebatteriescanbeused during power outages. The battery bank collects power produced by the so-larpanels,sendsittothebreakerbox,andthenintothehousepowersystem.Thecomponentsofthistypeofsystemconsistof:

•Solarpanelsmountedontheroof•AninvertertoconvertsolarelectricityfromDCenergyintoACenergy•Abatterybankforpowerstorage•Achargecontrollertopreventoverchargingthebattery•Ajunctionboxthatconnectsthesolarpanelwiringtothebreakerpanelonthehome•Apowermeterthatdisplaystheamountofpowerused,produced,andstoredin

the battery bank•Adisconnectswitchtopreventislandingduringpoweroutages.

Off-Grid or Stand-Alone

Off-gridsystemsarenottiedtoanyutilitypowerlinesandaremostcommoninre-moteareaswhereconnectingtotheutilitygridismoreexpensivethanpurchas-inganoff-gridsystem.Inoff-gridsystems,thesolarelectricsystemrepresentsthehome’smainsourceofpower.Batteriesstoreunusedsolarenergyforuseatnight.Generators,smallwindsystems,andotherbackupfuelsourcesaresometimesusedas backup power when the solar power stored in the batteries is not enough to meet householdneeds.Thesesystemsconsistofthefollowing:

Resources•U.S.DepartmentofEnergy–ConsumerGuide: http://apps1.eere.energy.gov/consumer/

•U.S.DepartmentofEnergy–PVBasics: www.eere.energy.gov/solar/pv_basics.html

•U.S.DepartmentofEnergy–PVforConsumers: www.eere.energy.gov/solar/pv_consumers.html

•SolarEnergyIndustriesAssociation: www.seia.org/cs/about_solar_energy

•CaliforniaCenterforSustainableEnergy: www.sdenergy.org

•FloridaSolarEnergyCenter(FSEC)–SolarElectricityBasics: www.fsec.ucf.edu

•NationalRenewableEnergyLaboratory–LearningAboutRenewableEnergy: www.nrel.gov/learning/

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•Solarpanelsmountedontheroof•AninvertertoconvertelectricityproducedbythesystemfromDCintoACenergy•Arectifier(sometimesusedtochangeACtoDCandbackagaintogetthemostuseoutofasystem)

•Achargecontrollertopreventoverchargingthebattery•Ajunctionboxthatconnectsthesolarpanelwiringtothebreakerpanelonthehome•Ajunctionboxforbackuppowersupplyfromagenerator•Apowermeterthatdisplaystheamountofpowerused,produced,andstoredin

the battery bank•Adisconnectswitchtopreventislandingduringpoweroutages.

Power Produced by a Solar Electric SystemSolarpanelsareassignedaratinginwattsbasedonthemaximumpowertheycanproduce under ideal sun and temperature conditions. You can use this rated out-puttoestimatethenumberofpanelsyou’llneedtomeetsomeorallofyourelectric-ityneeds.However,theexactamountofenergyproducedbyasolarelectricsystemalsodependsonrooforientationandtilt,aswellasotherfactorssuchasshading,dust,panelconversion,andwirelosses.

InsunnyclimatessuchasCalifornia,anaverage1-kilowattsystemwithoptimalori-entationandtiltwillproducebetween1,400and1,700kilowatthoursperyear.ManybuilderswhoinstallsolarelectricsystemsintheirCaliforniahousingdevelopmentsestimatethata2.4-kilowattsystemwilloffset40%to50%oftheelectricityneedsofanenergy-efficienthome.Thatnumbercouldbelowerorhigherdependingontheamountofsunlight(regardlessofclimate)yourhomereceiveseachyearandtheenergyefficiencyofyourhome.Manysolarvendorsnowsell2-to3-kilowattpack-agesystemsforhomesandcantellyouhowmuchenergywillbeoffsetbyasystemdependingonyourhome’senergyuse,rooforientation,andotherfactors.

Solar Electricity Basics

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Producing electricity by changing the photonsinsunlighttocleanpower,so-lar electric panels work in all climates—eveninspace,whichisaverycoldcli-mate.Forsolarelectricity,theamountofsunlightyourhomereceivesismuch

more important than the temperature. Manystates,suchasColorado,receiveagreatdealofsunlightthroughouttheyear,despitethecoldertemperaturesinthewinterandspring.Infact,someven-dors claim solar panels actually work better in colder climates because they don’toverheat,whichcancauseperfor-mance issues.

When purchasing a solar electric sys-tem,therightchoicewilldependonhowmuchsunlightyourareareceives,yourbudget,howmuchconventionalpoweryouwanttooffsetwithsolarpower,howmuchroomyouhaveonyourrooforinyouryard,andwherethesolarpanelswill be mounted.

How To Choose a SystemYour home’s power requirements, roof type, and solar resource will determine system type and size.

A roof-integrated solar electric system on a home in San Jose, California.

How

To Choose a System

Quick TipQuickTip:Planningtorepairor

replace your roof? That’s the perfect

time to purchase a solar electric

system because you want your

roofing material to last as long as

your system—about 25 years.

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How

To Choose a System

Roof RequirementsBeforepurchasingasolarelectricsystem,homeownersneedtodetermineavailableroofspaceandcondition.

Space and Orientation

NorthAmerica’ssunfollowsasouthernpath.Formaximumperformance,yoursolarelectricsystemneedsabout100squarefeetofunshadedsouth-facingrooforyardspaceforeverykilowattofelectricityproduced.Thin-filmsystemsmayrequire175squarefeetofspaceperkilowatt.Ifyourroofdoesnotfacesouth,youcanstilluseasolarelectricsystem,buttheperformancewillbeabout5%lesswithasoutheast-orsouthwest-facingsystem.Eastern,western,andnorthernexposuresarenotrec-ommendedforsolarelectricsystems.

Rooftiltisalsoimportanttocapturethepathofthesun,buttherequirementsvarywith location. Your solar vendor and installer should be able to calculate the proper tiltbasedonthesolarresourceforyourarea(theamountofsunlightyourareare-ceives).Whenasouth-facingroofisnotavailable,somepeopleinstallsolarelectricsystemsongarageroofsorusethemaswindowawningsandporchcoverings.

Solarpanelsareusuallyroofmounted,butifyouhaveashortageofroofspace,theycanbemountedonapoleorinyouryard.Solarpanelscanalsobeintegratedintoroofshinglesandtiles.Someevencomeas“peel-and-stick”laminatesformetalstanding-seamroofs.

Condition

Ifyourroofismorethan15yearsold,youmaywanttoconsiderreplacingitwhenyoupurchaseyoursolarelectricsystem.Mostsolarvendorsrecommendusingroof-ingmaterialthatwilllastaslongasthesystem,whichisabout25to30years.

North

Solar panel(module)

June 21

East

December 21

Sun’s Path During Summer and Winter

Makesuretheroofcanholdtheweightofthesystem,whichisestimatedat3to5poundspersquarefoot,dependingonthetypeoftechnologyusedandinstallationmethods.

Shading

Shadingapanelreducesitsperformancebecauseitblockssunlight.Themostcommonitemsthatshadesolarpanelsaretrees,chimneys,nearbybuildings,andelectricalcables,aswellasheatingandcoolingequipment.Alsocheckshadingfrompipes,skylights,andvents.Todeterminepossibleshadingproblems,consultasolarprofessionalwhousesasoftwareprogramthatcanestimatesiteshading.Somepeoplewillexamineaproposedlocationthroughoutthedayandyeartoseehowtheareashadingchanges.Forexample,shadinginanareacanchangefromsummertowinterbecausethesun’spathchanges.

Ground-Mounted Systems

Ifyoudon’thaveasouth-facingrooforenoughroofspace,consideraground-orpole-mountedsolarsystem,whichcanbeinstalledwiththesameorientationandtiltasaroof-mountedsystem.Ground-mountedsystemsaregreatforhomeswithlargeyards.Somesystemscomemountedonatrackerthatfollowsthesun’smovement.

Installation and MaintenanceBeforepurchasingasolarelectricsystem,homeownersneedtobeawareofissuesthataffectsysteminstallationandmaintenance.

WarrantiesandInsurance

Mostsolarelectricsystemscomewitha25-yearwarranty,butmaintenancemayberequiredtocomplywithamanufacturer’swarranty.Inverterwarrantiesareusually10years,andyoucanreasonablyexpecttohavetoreplacetheinverterduringthelifeofthesystem.Mosthomeownerinsurancepolicieswillcoverthesystems,butcheckwithyourinsuranceagenttobesure.Also,besuretoaskyourinsuranceagentifyouneedtobeawareofanyinstallationissuesthatcouldaffectcoveragefortheroof,suchasroofpenetrationsduringsysteminstallation.

Zoning and Permits

Localzoninglawsmayrestrictwhereyoucanplacecollectorsonyourhome.Checkwithyourcity,county,orhomeownerassociationtofindoutaboutanyrestrictions.Somestateshavesolaraccesslawsthatmayrequireahomeownerassociationtoapproveinstallation.Homeownerswillneedtoobtainanylocalpermitsrequiredbeforeinstallation.Typically,yourinstallerwillassistyouinobtainingpermitsandclearancefromthecity.

Maintenance

Propermaintenanceofyoursystemwillkeepitrunningsmoothly.Mostvendorsrec-ommendayearlymaintenancecheckbyyourinstaller,butyoushouldcarefullyre-view the maintenance instructions shown in the system manual with your system

8

How

To Choose a System

Resources• U.S.DepartmentofEnergy–MakingYourOwnCleanElectricity: www.eere.energy.gov/consumer/your_home/electricity/index.cfm/mytopic=10510

• U.S.DepartmentofEnergy–ConsideringaSmallSolarElectricSystem: www.eere.energy.gov/consumer/your_home/electricity/index.cfm/mytopic=10730

• FSEC–CertifiedPVModules: www.fsec.ucf.edu/en/industry/testing/PVmodules/pv_flashtest_list.htm

• FSEC–CertifiedSystems: www.fsec.ucf.edu/en/industry/testing/PVsystems/certified_systems/index.htm

• FindaSolarInstaller: www.find-solar.org

• NABCEP: www.nabcep.org

• EnergyCalculatorsandSoftware: www.eere.energy.gov/consumer/calculators/homes.html

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provider.Systemswithelectricalcomponentsusuallyrequirereplacementpartsafter10years.Solarpanelsmayneedtobecleanedinclimateswithinfrequentrainfall.

Installation

Usingaprofessional,licensedcontractortoinstallyoursolarelectricsystemcanprevent problems with the system caused by improper installation and maintenance. Professionalinstallerscanalsohelpwithpaperworkfortaxcreditsandrebates.TheNorthAmericanBoardofCertifiedEnergyPractitioners(NABCEP)maintainsalistofcertifiedsysteminstallers.TheU.S.DepartmentofEnergysponsorsaWebsitecalledFind-Solar.orgthatprovidesalistoflocalcertifiedinstallersbyzipcodeandcompanyname.BotharelistedintheResourcessection.

Questionstoaskanysolarenergydealerandinstallerinclude:

•Whatexperienceandcertificationdoyouhave?•Howlonghaveyoubeeninbusiness?•Whatdoyouknowaboutzoning,electricalrequirements,andcodes?•AreyourinstallersNABCEPcertified?•Doyouhandlepaperworkforfederalandstateincentives?•Doyouoffermaintenanceservice?•Areyouamemberofanysolartradeorganization,suchastheSolarEnergyIndustriesAssociation?

•Whatwarrantiesdoyouoffer?•Whatpaymentoptionsdoyouoffer?•Doyouofferpackagedsystems?

How

To Choose a System

Purchasing ConsiderationsPurchasingasolarelectricsystemrepresentsaninvestmentwithmanybenefits.Be-sidesraisingthepropertyvalueofyourhome($20forevery$1inutilitybillsavings),asolar electric system provides savings on your monthly utility bill. As energy bills con-tinuetorise,andinsomestatesdouble,financingasolarelectricsystemcangivehomeownerssecurityinknowingtheirenergybillswillremainvirtuallythesameforyears—it’sthemonthlypaymentonthesystem.Mostsystemspayforthemselveswithin5yearsafterrebatesandtaxcredits,sohomeownersenjoyfreeenergyforyears to come.

ExampleSavingsandPropertyValueIncreaseforaSolarElectricSystem

Average monthly utility bill $100 per month

Estimated system size required 4 .48 kW

System cost (at $9 per watt national average) $40,320

Estimated system cost after tax credits and rebates (Colorado) $12,544

Estimated first year utility bill savings $518 to $988

Estimated increase in property value $10,360*

Estimated monthly payment on system (6 .5% Annual Percentage Rate, 30 years) $79

*Ifbasedonaverageannualutilitysavingsover25yearsof$869to$1,658,propertyvalueincreaseis$17,380.

10

Costs and Financial Incentives

A 1-kilowatt solar electric system was integrated into the roof of each of the 77 units in this housing development in San Diego, California.

Costs and Financial IncentivesMany financial incentives are available to homeowners to offset system cost.

Energy Efficiency Can Help

Beforepurchasingasolarelectricsystem,trysomeenergy-savingstrategiestohelploweryourelectricitybillstogetthemostoutofyourexistingsystem.TheU.S.De-partmentofEnergyprovidesanonlineconsumerguide,listedintheResourcessec-tion,thatincludesenergyefficiencyandcost-savingmeasuresforhomes.

Costs

Solarelectricsystemscostonaverage$8to$10perwattinstalled,butnewtechnol-ogies are bringing the costs down every year. Federal and state incentives give con-sumerstaxcreditsandrebatesforthepurchaseofasolarelectricsystemtoreducethecost.Somevendorsarenowsellingthesystemsat“after-rebate”pricesandcompletingallthepaperworkthemselves.Beforerebatesandtaxcredits,theaver-age2-kilowatt(2,000-watt)systemwillcostbetween$16,000and$20,000.However,thecostperwattusuallygoesdownasthesystemsizeincreases,soa5-kilowattsystemmaybeinstalledfor$35,000($7perwatt).Dependingonwhereyoulive,afterrebatesandtaxcredits,thecostfora5-kilowattsystemmaybereducedto$2.50perwattor$12,500.

FederalandStateIncentives

Thenumerousincentivesforbuyingasolarelectricsysteminclude:•Federaltaxcredit•Statetaxcredits•Utilityrebates•Propertytaxcreditsinsomestates.

InOctober2008,thefederaltaxcreditwasextendedforanother8years,nowallow-ingforataxcreditupto30%forresidentialandcommercialsolarinstallations.Taxcreditsandutilityrebatesvarybystate.ChecktheDatabaseofStateIncentivesforRenewableEnergy(DSIRE)foralistoftheseincentives.DSIREincludesinformationaboutwhichstateswon’tincreaseyourpropertytaxesforthepurchaseofasolarelectricsystem.Find-Solar.orghasacostcalculatorthatincludesfederalandstateincentivesforyourarea.BothorganizationsarelistedintheResourcessection.

NetMetering

Manystateshavenetmeteringlawsthatrequireutilitycompaniestogivehomeown-erscreditforexcesspowerproducedbytheirsolarelectricsystems.Thatmeansyourlocalutilitygivesyoucreditforeverykilowatt-hourofsolarpowernotconsumedbyyourhome,reducingyourelectricitybillbythesameamount.Yourmeteressen-tiallyspinsbackwardwhenexcesspowerisproduced.Generally,homeownersre-ceive credit at higher rates during the summer when their systems are producing the mostpowerandatlowerratesduringthewinterwhentheirsystemsaren’tproducingasmuchsolarenergy.Manystatesoffernetmetering,butNewJerseyandColoradoareratedamongthebestfornetmeteringpolicies.

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Costs and Financial Incentives

FinancingIfyoucan’tpurchaseasystemoutright,considerfinancingthesystem.Severalresourcesareavailableforfinancingasolarelectricsystem,including:

•Homerefinance•Firstmortgages•Banks(manywillfinanceforlessthanprimerate)•Constructionloans•Homeequityloans•Solarvendors(somenowfinancethesystemsthemselves).

Mortgageloansandhomeequityloansofferseveraladvantages:longerterms,lowerinterestratesthanconventionalbankloans,andtax-deductibleinterest.Inaddition,addingasolarelectricsystemtoaloanatthesametimethatyoubuild,buy,orrefi-nancewillreducepaperworkandsimplifythepurchase.Otherbenefitstofinancingthecostofasolarelectricsystemincludealowmonthlypaymentonthesystemandlocked-inelectricitycostsforthenext25years.

Resources:• U.S.DepartmentofEnergy–EnergySavers: www.energysavers.gov/

• U.S.DepartmentofEnergy–TheEconomicsofaSmallSolarElectricSystem: www.eere.energy.gov/consumer/your_home/electricity/index.cfm/mytopic=10750

• U.S.EnvironmentalProtectionAgency–FederalTaxCredits: www.energystar.gov/index.cfm?c=products.pr_tax_credits

• DSIRE: www.dsireusa.org/

• FindSolarCostEstimator: www.find-solar.org

• SolarEnergyIndustriesAssociation: www.seia.org/cs/the_investment_tax_credit_itc

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Costs and Financial Incentives

For more information contact: EERE Information Center 1-877-EERE-INF (1-877-337-3463) www.eere.energy.gov

Prepared by the National Renewable Energy Laboratory (NREL) NREL is a national laboratory of the U.S. Department of Energy Operated by the Alliance for Sustainable Energy, LLC

DOE/GO-102009-2656 • January 2009

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 10% postconsumer waste.