太阳电池电性能参数的计算及表征

Lecture3:SolarCellCharacteristicsAndresCuevasENGN4524SolarEnergyTechnologiesTypicalindustrialsolarcell(fromPhotowatt,France)(upto15-20cm)Typicalefficiency:15%Howmuchpower?15%*156cm2*0.1W/cm2=2.3W://://://://sharp-world.com/solar/index.html://://(V)Currentdensity(A/cm2)051015202530Power(mW)PhotovoltaicI-VPower(mW)Current-voltagecharacteristiccurveofahighefficiencysiliconsolarcell.Jsc=37mA/cm2,Voc=684mV,FF=0.81,efficiency=20.6%.TherectangleshowsthedefinitionofFillFactorexp0⎟⎠⎞⎜⎝⎛−=mkTqVIIILIosaturationcurrentmidealityfactor,usuallym=1-2ILlightgenerated,orphotogeneratedIphcurrent,approx.equaltotheshort-circuitcurrentIsc.qchargeofanelectron=1.602×10-19J/KkBoltzmannconstant=1.38×10-23J/KToperatingtemperatureofthecell;at25oC:()mV69.25Vt==qkTmmaxscocmmIVFFIVP×==maxEAP=ηSimplestmodelforsolarcells:AistheareaofthesolarcellEisthestandardirradiance,0.1W/cm2Solarcellparameters•Inopen-circuit:I=0,V=Voc•Inshort-circuit;V=0,I=IL=Isc•SpecificationsheetsgiveVocandIsc•fromVocandIscwecandetermineI0•Thesethreeparametersdefinethecharacteristicsofthesolarcell.•The“idealityfactor”mcannotbeaccuratelyknownapriori.Avaluem=1canbeassumedforoptimisticevaluations.Example1:highefficiencycell.Jsc=37mA/cm2,Voc=684mV,FF=0.811,efficiency=20.6%weobtainJ0=1x10-13A/cm2exp0⎟⎠⎞⎜⎝⎛−=mkTqVIIILIosaturationcurrentmidealityfactor,usuallym=1-2ILlightgenerated,orphotogeneratedIphcurrent,approx.equaltotheshort-circuitcurrentIsc.qchargeofanelectron=1.602×10-19J/KkBoltzmannconstant=1.38×10-23J/KToperatingtemperatureofthecell;at25oC:()mV69.25Vt==qkTmExample2:industrialcellforJsc=0.030A/cm2andVoc=600mVweobtainJ0=2x10-12A/cm2⎟⎟⎠⎞⎜⎜⎝⎛=0oclnVIIqmkTscEquivalentcircuitandcharacteristicequationconstantcurrentgeneratorILdiode+_currentIVVd+_externalloadRLexp0⎟⎠⎞⎜⎝⎛−=mkTqVIIILUnderilluminationexp0⎟⎠⎞⎜⎝⎛−=mkTqVIIDInthedark:Thisistheequationofadiode!ThiscanberepresentedbyadiodeinparallelwithacurrentsourceSothediodecurrentisaloss,anunavoidableone,becausethedioderepresentsthecellitself.Butitcanminimised;how?TheFillFactorscocmmIVIVFF=()172.0ln0++−=ocococvvvFFToevaluatethemaximumpowerpoint:•typicallythemaximumpowercurrentis95%oftheshort-circuitcurrentIm=0.95Isc•usingtheI-Vcharacteristicequation,themax.powervoltageis77mVsmallerthanVoc•Thisexample:Im=0.95IscandVm=0.87VocresultinFFo=0.828.Siliconsolarcell,100cm2,noRs,noRshunt-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.50.00.51.0-0.2-0.10.00.10.20.30.40.50.60.7Voltage(V)Current(A)CurrentPowerη=16.6%Idealfillfactor,approximatecalculationNumericalcomputationwiththeprogramPC-1DInthisexample:FF=16.6/(33.5x0.6)=0.826Example:ForatypicalindustrialVoc=600mV,FFo=0.8283ThisisaveryhighFF!!qkTmVvococ=Devicelosses:SeriesResistanceEffectsSheetresistanceFingerresistanceContactresistanceBusbarresistancep-typen-typemetalcontactContactresistanceSolarcellsarelowvoltage,highcurrentdevices!EffectofaseriesresistanceSiliconsolarcell,100cm2,Rs=0.03Ω,noRshunt-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.50.00.51.0-0.2-0.10.00.10.20.30.40.50.60.7Voltage(V)Current(A)η=13.6%()ssrFFFF−=10Approximategraphicalevaluationoftheseriesresistance:Rs=Vmp(ideal)-Vmp(real)/ImpRs=100mV/3A=0.033ohmExample:thisRsmakesthefillfactordecreasefrom0.82to0.68exp0⎥⎥⎦⎤⎢⎢⎣⎡⎟⎟⎠⎞⎜⎜⎝⎛+−=tsscmVIRVIIIscocssIVRr=constantcurrentgeneratorILdiodeinternalseriesresistanceRs+_currentIVVd+_externaNotethatVd=V+IRsEffectofashuntingresistance()7.01⎟⎟⎠⎞⎜⎜⎝⎛+−=shocoocoshrvFFvFFFF()172.0ln0++−=ocococvvvFFSiliconsolarcell,100cm2,noRs,Rshunt=0.8Ω-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.50.00.51.0-0.2-0.10.00.10.20.30.40.50.60.7Voltage(V)Current(A)η=13.4%Approximategraphicalevaluationoftheshuntresistance:Imp(ideal)-Imp(real)=Vmp/RshuntRshunt=0.4A/0.5V=0.8ohmExample:thefillfactordecreasesfromanidealvalueof0.82to0.63shunttscRVmVVIIIexp0−⎟⎟⎠⎞⎜⎜⎝⎛−=Note:VoccandecreaseduetoRshuntCombinedeffectofseriesandshuntresistances()172.0ln0++−=ocococvvvFF()ssrFFFF−=10Sisolarcell,100cm2,Rs=0.03Ω,Rshunt=0.8Ω-4.0-3.5-3.0-2.5-2.0-1.5-1.0-0.50.00.51.0-0.2-0.10.00.10.20.30.40.50.60.7Voltage(V)Current(A)η=11.4%()7.01⎟⎟⎠⎞⎜⎜⎝⎛+−=shocseriesocseriesshrvFFvFFFFEvaluategraphicallythefillfactor:FF=11.4/(32.3x0.595)=0.59•Specificationsheetsgive:•VocandIsc•VmpandImpCompleteequivalentcircuitofasolarcellconstantcurrentgeneratorILdiodeinternalseriesresistanceRsshuntresistorRsh+_currentIVVd+_externalloadRLshuntstsscRIRVmVIRVIII+−⎥⎥⎦⎤⎢⎢⎣⎡⎟⎟⎠⎞⎜⎜⎝⎛+−=exp01SingleexponentialmodelincludingbothRsandRshunt:Exercise:determinetolerablevaluesforRsandRshunt–Takea1cm2solarcell.Forexample:Jmp=30mA/cm2,Vmp=500mV–Letusspecifythatthelossduetoseriesresistanceshouldbelessthan5%.ThevoltagedropproducedbyRsshouldbe5%ofVmpJmpRs0.05*Vmp=25mV,thenRs25mV/30(mA/cm2)=0.83Ωcm2–Consideralarger,100cm2solarcell.Then:Imp=Jmp*A=30mA/cm2*100cm2=3A,butstillVmp