how does solar energy work - fefpa
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FLORIDA SOLAR ENERGY CENTERA Research Institute of the University of Central Florida
How does Solar Energy Work
Florida Solar Energy Center1679 Clearlake Road
Cocoa, Florida , USA, 32922
October 3, 1998 2
Objectives
Understand the variables affecting the amount of solar energy received on a given surface Differentiate between solar irradiance (power) and solar insolation (energy)Demonstrate how solar radiation and weather data are used in sizing photovoltaic systemsAssess site specific issues such as array location, orientation and shading, roof condition, safety hazards, and other requirements for PV installations.
October 3, 1998 3
Solar Spectral Data and PV Device Response
0
400
800
1200
1600
2000
0 0.5 1 1.5 2 2.5 3
Wavelength (micron)
Irrad
ianc
e (W
/m2)
0
0.2
0.4
0.6
0.8
1
Qua
ntum
Effi
cien
cy (%
)
ASTM892 ASTM891 Cz-Si
October 3, 1998 4
Factors Affecting the Solar Radiation Received on a Surface
Geometric effects:rotation of the earth about a tilted axis and earth’s orbit around the sunOrientation of the surface with respect to the sun’s rays
Atmospheric effects:scattering and absorption by atmospheric constituentseffects vary significantly with altitude, latitude, time of day and year, and local weather conditions
Shading effects:Objects shading the sun from the array
October 3, 1998 5
Earth’s Rotation and Declination
Sun
Earth’s Rotational AxisArctic Circle 66.55 oN
Tropic of Cancer 23.45 oN
Equator
Tropic of Capricorn 23.45 oS
Antarctic Circle 66.55 oS
EquatorialPlane
Solar Declination (*)
Ecliptic Plane
October 3, 1998 6
Earth’s Orbit Around the Sun
1
2
3
4
Earth’s Orbit Around the Sun(counter- clockwise)
Sun
Earth’s axis ofrotation
EclipticPlane
Vernal Equinox: March 21Declination = 0o
Autumnal Equinox: September 23Declination = 0o
Perhelion -January 2
Aphelion - July 296 million miles
(1.017 AU)90 million miles
(0.983 AU)
Winter Solstice: December 22Declination = - 23.45o
Summer Solstice: June 22Declination = +23.45o
October 3, 1998 7
Sun Paths for 30o N Latitude
1
2 4
3
NorthPointO
East
West
Zenith
June 22: 12 noon
September 23 and March 21: 12 noon
December 21: 12 noon
10 am
8 am2 pm
4 pm
4 pm
4 pm
8 am
8 am2 pm
2 pm
10 am
10 am
South
October 3, 1998 8
Atmospheric Effects
Results in the scattering, attenuation and absorption of direct solar radiation received outside the earth’s atmosphereEffects vary significantly with altitude, latitude, time of day and year, and local weather conditions.
October 3, 1998 9
Effect of Air Mass
Sun at noon
Atmosphere
Sun at mid-morning ormid-afternoon
1.5 Air Mass( AM 1.5 )
One Air Mass(AM 1 )
Earth
Atmospheric path length affects the amount and spectral content of solar radiation.PV module performance is rated under AM 1.5 spectral distribution
October 3, 1998 10
Sun Position - Definitions
NorthPoint O
East
West
Zenith90 deg altitude
South0 deg azimuth
Altitude Angle (")
Azimuth Angle (R)
October 3, 1998 11
Solar Irradiance (Power)
Solar irradiance is the radiant power per unit area, commonly expressed in units of kW/m2, or W/m2
Outside the earth’s atmosphere, the sun’s power is relatively constant, equal to 1.36 kW/m2 and is referred to as the Solar Constant.Typical peak terrestrial irradiance values are approximately 1 kW/m2 (1000 watts/m2) for surfaces normal to the sun’s rays under clear sky conditions.1 kW/m2 is also used as the peak rating condition for PV module performance.
October 3, 1998 12
Peak Solar Irradiance on a Surface
Sunlight intensity measured in watts per square meter
With sun directly over head and PV flat on the ground
1 mOne
SquareMeter = 1000 watts = 1 kilowatt
1 m
October 3, 1998 13
Solar Insolation (Energy)
Solar irradiance (power) summed over time equals solar insolation (energy)Solar Insolation is the radiant energy per unit area, and is expressed in units of kWh/(m2-day)Peak Sun Hours (PSH) is the amount of solar energy received on a surface, and is equivalent to the number of hours that the solar irradiance would be at a peak level of 1 kW/m2, or the equivalent number of hours per day that a PV array will operate at peak output levels.
October 3, 1998 14
Solar Insolation(Peak Sun Hours)
Sola
r Irr
adia
nce
(W/m
2 )
Time of Day (hrs)
1000 W/m2
Sunrise Noon Sunset
peak sun hours
Solar insolation
Solar irradianceArea of box equalsarea under curve
500 W/m2
October 3, 1998 15
Array Orientation
North
East
West
Zenith
Array azimuthangle (R)
Array tilt angle (")
Array surface
South
Surfacenormal
Solar incidenceangle (()
October 3, 1998 16
Array Orientation – Tilt Angle
Optimal performance of PV arrays is achieved by facing the array south (north in the southern hemisphere), and at a tilt angle from horizontal using the guidelines below:
Application Best Array Tilt AngleMaximum Annual Energy 90% of LatitudeProductionWinter Peak Load Latitude plus 15 degreesSummer Peak Load Latitude minus 15 degrees
October 3, 1998 17
Array Orientation – Azimuth
Optimal energy performance of PV arrays is achieved by facing the array due south. In most cases, latitude-tilt surfaces with azimuth orientations of +/- 45 degrees from due south will receive 75-80 percent of solar energy on south-facing surfaces.Where magnetic declination is significant,adjust compass readings for due north south by adding magnetic declination:
See: http://geomag.usgs.gov/For example, a magnetic compass needle in central California will point 15 degrees east of true north, and a compass in New York will point 15 degrees west of true north.
October 3, 1998 18
U.S. Magnetic Declination
October 3, 1998 19
U.S. Solar Radiation DataJune
October 3, 1998 20
U.S. Solar Radiation DataDecember
October 3, 1998 21
Peak Sun-Hour Data
Minimum daily Peak Sun-hours during hurricane season.
October 3, 1998 22
U.S. Solar Radiation Data Availability
National Renewable Energy Laboratory - Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors:
http://rredc.nrel.gov/solar/pubs/redbook/Other solar resource data is available from:
http://rredc.nrel.gov/solar/pubs/
October 3, 1998 23
Solar Radiation Measurement
PSP
PV - PSP
October 3, 1998 24
Solar Radiation Measurement
Solar Meter: See: http://www.solaqua.com/daysolmet.html
October 3, 1998 25
What is Required for Energy Estimation
While there are several methods to determine PV system performance, the following parameters are required
Nominal Array SizePeak Sun-hours - Sunlight Energy incident on the PV arrayArray TiltArray Azimuth Angle
October 3, 1998 26
The PV Installation Process
Conducting a Site Survey
Installing the System
Selecting a System
System Checkout & Inspection
October 3, 1998 27
Solar Photovoltaic System (SPS)
Solar Photovoltaic System (690.2)The total components and subsystems that, in combination, convert solar energy into electrical energy suitable for connection to autilization load.
loadutilization
energysource power
conditioning
energyconversion
InverterCharger
Controller
PV Arrayenergydistribution
loadcenter
batteryenergystorage
electricutilitynetwork
October 3, 1998 28
Solar Photovoltaic System (SPS) Components
PV Array: An electrical assembly of photovoltaic modules that convert sunlight to DC electricity.Inverter: A device that converts DC power from batteries or PV arrays into utility-grade AC power.Energy Storage: Electrical or other storage devices sometimes used to store energy produced by PV arrays for later consumption.System Charge Control: A device used to protect batteries from overcharge and overdischarge, sometimes provide load control functions.Load: Energy consuming electrical appliances served by the system.Balance of System (BOS) Components: Other equipment required to control, conduct, protect and distribute power in the system.
October 3, 1998 29
Solar Cell
Solar Cell (690.2)The basic photovoltaic device that generates dc electricity when exposed to light. A typical silicon solar cell produces about 0.5 volt and up to 6 amps and 3 watts for larger area cells.
electrical load
typical crystalline silicon photovoltaic cell
(-)
(+)
phosphorous-doped (N-type) silicon layer ~ 0.3 x 10-6 mboron-doped (P-type)
silicon layer ~ 250 x 10-6 m
dc current flow
sun
October 3, 1998 30
Photovoltaic Modules
Module (690.2)A complete, environmentally protected unit consisting of solar cells, optics, and other components, exclusive of tracker, designed to generate dc power when expose to sunlight.
60 watt polycrystallinemodule
75 watt crystallinemodule
12 watt thin filmmodule
October 3, 1998 31
Photovoltaic Modules and Arrays
Typical PV modules range in size from around 0.5 m2 to over 3 m2 surface area, with peak power output of 50 to 300 watts dc. Area power densities range from 80-120 W/m2. Most commercially available crystalline and multi-crystalline PV modules have 36 cells in series, and have open-circuit voltages of 20-22 volts dc, and designed for battery charging applications. Most listed modules can be connected in series up to 600 volts DC.Some thin-film modules have open circuit voltages as high as 100 volts dc, and may use multiple parallel module connections per source circuit.
October 3, 1998 32
Definitions: Photovoltaic Cells, Modules, Panels and Arrays
cell module
panelarray
October 3, 1998 33
Typical Module Label Required by National Electrical Code
Siemens Solar IndustriesCamarillo, CA 93011
MODEL M55PHOTOVOLTAIC MODULEAT 1000 W/M2 SOLAR IRRADIANCEAND 25oC CELL TEMPERATURE 30B9 LISTED
MAX. POWER SHORT CKT. RATED 53 WATTS 3.35 A 3.05 A
MAX. SYST. OPEN CKT. V. OPEN CKT. RATED 600 VOLTS 21.7 V 17.4 V
FIRE RATING SERIES FUSE CLASS C 5 A
FIELD WIRING BYPASS DIODECOPPER ONLY, 14 AWG MIN. INSTALLATION GUIDEINSULATED FOR 75 C MIN. 233-701500-20 MADE IN U.S.A.
October 3, 1998 34
Identification of Photovoltaic System Components
Photovoltaic source circuits
Solar cells
Blocking diodes
Module
Panel
Array
Fuses
Photovoltaicoutput circuits
Adapted from NEC 2002Figure 690.1(A)
October 3, 1998 35
PV System Charge Controllers
October 3, 1998 36
Battery Charging
Battery charging modes:Bulk or normal chargingFinishing chargeEqualizing charge
Temperature compensationminimizes excessive charge and electrolyte when hot,improves capacity when cold.
October 3, 1998 37
Inverters for PV Systems
Inverter (690.2)Equipment that is used to
change dc input to ac output, and may also function as a battery charger for systems using storage.Inverters for PV systems in
sizes from 100 watts to custom designs of up to 1 MW or moreDC operating voltages of 12
volts up to 600 volts, with AC outputs from 120 V single phase to 480 V three phase.
October 3, 1998 38
PV Inverter Classifications
Stand-Alone InvertersInverter in solar PV systems that operate and supply power independent of the electrical production and distribution network, typically operate from storage batteries.
Utility-Interactive or Grid-Connected InvertersInverters in solar PV system that operate in parallel with and may deliver power to an electrical production and distribution network, may be connected to PV arrays or batteries.
Bi-Modal InvertersCan operate either in interactive or stand-alone mode, but not simultaneously, typically use batteries.
October 3, 1998 39
Alternating Current Waveforms
square wavesine wave
quasi-sine wave
Time
Am
plitu
de
One Cycle
October 3, 1998 40
Inverter Efficiency vs. Load
Output Power Level
Effic
ienc
y
October 3, 1998 41
Batteries for PV Systems
Storage Batteries (690.71, 480)Batteries are used in some PV systems to store energy produced by the PV array and supply it to electrical loads as needed.Charge control is required in most cases to protect batteries from overcharge by PV array, and overdischarge from loads.
October 3, 1998 42
Secondary Battery Types and Characteristics
BATTERY TYPE Cost Deep CyclePerformance
Maintenance
FLOODED LEAD-ACIDLead-Antimony low good highLead-Calcium Open Vent low poor mediumLead-Calcium Sealed Vent low poor lowLead Antimony/Calcium Hybrid medium good medium
CAPTIVE ELECTROLYTE LEAD-ACID(VRLA)
Gelled medium fair lowAbsorbed Glass Mat medium fair low
October 3, 1998 43
Rack-Mounted PV Arrays
October 3, 1998 44
Tracking Array Configurations
October 3, 1998 45
Standoff-Mounted Arrays
Above and parallel to roof slopePromotes array coolingCan Reduce heat gain into buildings
October 3, 1998 46
Commercial BIPV System
Image courtesy of PowerLight Corp
October 3, 1998 47
Direct-Coupled Stand-Alone Systems
Simplest type of stand-alone PV system, common applications include water pumps and fans.DC load is directly connected to a PV array, no energy storage.No overcurrent device typically required.
PV Array DC Load
October 3, 1998 48
Stand-Alone PV System with Battery Storage
PV array charges battery which supplies power to DC electrical loads as needed.Without charge control, battery is susceptible to overcharge and overdischarge.Charge control may only be eliminated under special circumstances the load is well defined and the battery is oversized.
PV Array Battery DC Load
October 3, 1998 49
Stand-Alone PV System with Batteries and Charge Control
Charge control is required whenever the load is variable and the battery is not oversized.Protects the battery from overcharge and overdischarge, and may provide load control functions.
DC LoadPV Array
Battery
ChargeController
October 3, 1998 50
Stand-Alone PV System with AC and DC Loads
DC LoadPV Array
Battery
ChargeController
Inverter/Charger
AC Load AC Source(Charger Only)
October 3, 1998 51
Stand-Alone PV Hybrid System
DC LoadPV Array
Battery
ChargeController
Inverter
AC LoadEngine-generator, wind turbine or grid backup
Rectifier
ChargerDC Bus
AC Bus
October 3, 1998 52
Basic Utility-Interactive or Grid-Connected PV System
DistributionPanel
PV Array Inverter/PowerConditioner
AC Loads
ElectricUtility
October 3, 1998 53
Utility-Interactive PV SystemNo Battery Storage – Dual Metering
PV Array
InverterCustomerElectrical
Panel
CustomerElectrical Loads
Customer-supplied meter for PV generation(recommended)
OutdoorDisconnect
Customer-supplied visible break, lockable PV disconnect
(utility may require)
PV kWh
To UtilitykWh
Electric UtilityNetwork
Customer
Utility
From UtilitykWh
* Arrows indicate directions of power flows Two, unidirectional revenue meters, or single bi-directional recording meter (utility-supplied)
October 3, 1998 54
Utility-Interactive PV System with Energy Storage
PV Array
Inverter/Charger
BatteryStorage
Critical LoadSub Panel
BackupAC Loads
Main Panel
PrimaryAC Loads
ElectricUtility
Bypass circuit
* Arrows indicate directions of power flows
October 3, 1998 55
Utility-Interactive PV System with Battery Storage – Net Metering
PV Array
Battery Storage
CustomerMain Electrical
Panel
Customer PrimaryElectrical Loads
Customer-supplied sub metering(recommended)
OutdoorDisconnect
Customer-supplied visible break, lockable PV disconnect
(utility may require)
To MainkWh
ElectricUtility
Network
Utility
Inverter Bypass CircuitTransfer Switch
Utility NetkWh
CustomerBackup Load
Customer Sub Panel
Inverter/Charger
Customer
FromMain kWh
FromMain kWh
* Arrows indicate directions of power flowsStandard, bi-directional revenue meter (utility-supplied)
October 3, 1998 56
Utility-Interactive PV System with Battery Storage
Source: Xantrex/Trace Engineering
October 3, 1998 57
Watts Electrical Schematic
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EXTERNAL GFDI MAY BE
REQUIRED (690.5)
15A FUSEDCOMBINERS
40A BREAKERS
PV MODULES
40A CHARGECONTROLLERS
+
-
120V OUTPUT
+ - GND
NEUTRAL BUS
+
-
+
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+
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POSITIVEBUS
120VEMERGENCY
LOADSSUBPANEL
GROUNDINGELECTRODE
[250.64]
UTILITYCONNECTION
AC LOADCENTERUTILITY
DISCONNECT
INTERCONNECTPER 690.64
2
3
BATT
ERY
BO
X
4
2
4
250A
80A4 4
56
6
3
7
7
50A
60A
1 2 #10 USE-2 W/ #10 BARE EQUIPMENT GROUND, NOT INCONDUIT (NOTE: SOME JURISDICTIONS REQUIRE A #6BARE GROUND
2 #10 USE-2 TRANSITIONS TO #8 THWN-2 IN METALJUNCTION BOX; METAL CONDUIT CONNECTSCONSECUTIVE JUNCTION BOXES
3 6 #8 THWN-2 IN METAL CONDUIT TO COMBINERS
4 2 #6 THHN IN CONDUIT
ROOFTOP MODULES & CONDUITALL OTHER EQUIPMENT
ASSUMED AMBIENTTEMPERATURES:
65˚C30˚C
ALL TERMINAL TEMPERATURERATINGS ASSUMED TO BE 75˚C,
EXCEPT FOR 90˚C MODULETERMINALS
7
5 2 #4 THHN IN CONDUIT
6 2 #4/0 THHN IN CONDUIT
#10/
#6 G
RO
UN
D
#8 THWN-2 IN METAL CONDUIT
#6 T
HH
N
#6 THHN
#4 T
HH
N
#4/0 THHN
7 2 #6 THHN IN CONDUIT
#6 THHN
#6 THHN
#10
US
E-2
INVERTER
October 3, 1998 58
October 3, 1998 59
Zero Energy Homes
October 3, 1998 60
Energy Estimation Software
Selected PV Software ProgramsMaui Solar PV Design Pro
http://www.mauisolarsoftware.comPV CAD: http://www.iset.uni-kassel.dePV F-Chart: http://www.fchart.com/pvfchart/pvfchart.htmlPV Sol: http://www.valentin.de/englisch/startseite-e.htmPVSYST 3.21: http://www.pvsyst.comKeryChip: http://www.kerychip.dk/eng.htmHOMER: http://analysis.nrel.gov/homer/PV Watts: http://www.pvwatts.org
October 3, 1998 61
Solar Hot Water Systems
Differential controller operated Direct pumped systemPhotovoltaic operated systemIndirect pumped systemDrain back systemIntegral collector storage (ICS) systemThermosiphon system
October 3, 1998 62
Types of Solar Water Heating SystemsPassive
Direct
Indirect
Active
October 3, 1998 63
Typical Thermal System Diagram
October 3, 1998 64
Solar Water Heat – Large Fields
Martin County Correctional InstituteTwo fields, each:
70 flat plate collectorsTwo 3000 gallon tanksThree pump loops
October 3, 1998 65
Large Utility Scale Power
October 3, 1998 66
Large Scale Power – CSP Dish
UNLV PilotPlanned: 1-MW, >40 units near Las Vegas
October 3, 1998 67
Audubon Society Nature Center, LA
100 % Solar Thermal ACHeat, DHW w/800 SF array25 kWp PV for pumps, fans, electrical
October 3, 1998 68
Other - Transpired Collector wall
October 3, 1998 69
Many designs and proven performancePersonal cookers to Village cookers
October 3, 1998 70
Solar Thermal Shower
October 3, 1998 71
Summary
Identified factors affecting the amount of solar energy received at a given locationDefine solar irradiance and insolationDiscussed criteria for orienting PV arraysDemonstrated use of solar radiation data in estimating the performance of PV systemsIdentified considerations for PV installation site surveys