文献翻译——光伏并网发电系统的性能参数

第1页外文文献资料PerformanceParametersforGrid-ConnectedPVSystemsTheuseofappropriateperformanceparametersfacilitatesthecomparisonofgrid-connectedphotovoltaic(PV)systemsthatmaydifferwithrespecttodesign,technology,orgeographiclocation.Fourperformanceparametersthatdefinetheoverallsystemperformancewithrespecttotheenergyproduction,solarresource,andoveralleffectofsystemlossesarethefollowing:finalPVsystemyield,referenceyield,performanceratio,andPVUSArating.TheseperformanceparametersarediscussedfortheirsuitabilityinprovidingdesiredinformationforPVsystemdesignandperformanceevaluationandaredemonstratedforavarietyoftechnologies,designs,andgeographiclocations.Alsodiscussedaremethodologiesfordeterminingsystema.c.powerratingsinthedesignphaseusingmultipliersdevelopedfrommeasuredperformanceparameters.1.INTRODUCTIONAccurateandconsistentevaluationsofphotovoltaic(PV)systemperformancearecriticalforthecontinuingdevelopmentofthePVindustry.Forcomponentmanufacturers,performanceevaluationsarebenchmarksofqualityforexistingproducts.Forresearchanddevelopmentteams,theyareakeymetricforhelpingtoidentifyfutureneeds.Forsystemsintegratorsandendcustomers,theyarevitaltoolsforevaluatingproductsandproductqualitytoguidefuturedecision-making.Astheindustryhasgrown,aclearneedhasarisenforgreateruseofandeducationaboutappropriateindustry-standardperformanceparametersforPVsystems.Theseperformanceparametersallowthedetectionofoperationalproblems;facilitatethecomparisonofsystemsthatmaydifferwithrespecttodesign,technology,orgeographiclocation;andvalidatemodelsforsystemperformanceestimationduringthedesignphase.Industry-wideuseofstandard第2页performanceparametersandsystemratingswillassistinvestorsinevaluatingdifferentproposalsandtechnologies,givingthemgreaterconfidenceintheirownabilitytoprocureandmaintainreliable,high-qualitysystems.Standardmethodsofevaluationandratingwillalsohelptosetappropriateexpectationsforperformancewitheducatedcustomers,ultimatelyleadingtoincreasedcredibilityforthePVindustryandpositioningitforfurthergrowth.ParametersdescribingenergyquantitiesforthePVsystemanditscomponentshavebeenestablishedbytheInternationalEnergyAgency(IEA)PhotovoltaicPowerSystemsProgramandaredescribedintheIECstandard61724.(IEAtaskmembershaveusedtheseperformanceparameterstodevelopadatabaseofoperationalandreliabilityperformance.ThedatabasecontainsinformationforseveralhundredPV.)ThreeoftheIECstandard61724performanceparametersmaybeusedtodefinetheoverallsystemperformancewithrespecttotheenergyproduction,solarresource,andoveralleffectofsystemlosses.TheseparametersarethefinalPVsystemyield,referenceyield,andperformanceratio.ThefinalPVsystemyieldYfisthenetenergyoutputEdividedbythenameplated.c.powerP0oftheinstalledPVarray.ItrepresentsthenumberofhoursthatthePVarraywouldneedtooperateatitsratedpowertoprovidethesameenergy.TheunitsarehoursorkWh/kW,withthelatterpreferredbytheauthorsbecauseitdescribesthequantitiesusedtoderivetheparameter.TheYfnormalizestheenergyproducedwithrespecttothesystemsize;consequently,itisaconvenientwaytocomparetheenergyproducedbyPVsystemsofdifferingsize:ThereferenceyieldYristhetotalin-planeirradianceHdividedbythePVsreferenceirradianceG.Itrepresentsanequivalentnumberofhoursatthereferenceirradiance.IfGequals1kW/m2,thenYristhenumberofpeaksun-hoursorthesolarradiationinunitsofkWh/m2.TheYrdefinesthesolarradiationresourceforthePVsystem.Itisafunctionofthelocation,第3页orientationofthePVarray,andmonth-to-monthandyear-to-yearweathervariability:TheperformanceratioPRistheYfdividedbytheYr.Bynormalizingwithrespecttoirradiance,itquantifiestheoveralleffectoflossesontheratedoutputdueto:inverterinefficiency,andwiring,mismatch,andotherlosseswhenconvertingfromd.c.toa.c.power;PVmoduletemperature;incompleteuseofirradiancebyreflectionfromthemodulefrontsurface;soilingorsnow;systemdown-time;andcomponentfailures:PRvaluesaretypicallyreportedonamonthlyoryearlybasis.Valuescalculatedforsmallerintervals,suchasweeklyordaily,maybeusefulforidentifyingoccurrencesofcomponentfailures.BecauseoflossesduetoPVmoduletemperature,PRvaluesaregreaterinthewinterthaninthesummerandnormallyfallwithintherangeof0.6to0.8.IfPVmodulesoilingisseasonal,itmayalsoimpactdifferencesinPRfromsummertowinter.Decreasingyearlyvaluesmayindicateapermanentlossinperformance.ThePVUSAratingmethodusesaregressionmodelandsystemperformanceandmeteorologicaldatatocalculatepoweratPVUSATestConditions(PTC),wherePTCaredefinedas1000W/m2plane-of-arrayirradiance,20Cambienttemperature,and1m/swindspeed.PTCdiffersfromstandardtestconditions(STC)inthatitstestconditionsofambienttemperatureandwindspeedwillresultinacelltemperatureofabout50C,insteadofthe25CforSTC.Thisisforarack-mountedPVmodulewithrelativelygoodcoolingonbothsidesofthemodule.ForPVmodulesmountedclosetotherooforintegratedintothebuildingwiththeairflowrestricted,PTCwillyieldgreatercelltemperatures.NordmannandClavadetscherreportthatPVmoduletemperaturesriseaboveambientforfieldedsystemrangingfrom20Cto52Cat1000W/m2,withthelargesttemperatureriseforanintegratedfaade.Thedifferencebetweenthenameplated.c.powerratingandthesystemPVUSAratingisanindicationofthetotalsystemlossesassociatedwithconvertingd.c.moduleenergytoa.c.energy.AswithdecreasingPRvalues,decreasingPVUSAratings第4页overtimemayindicateapermanentlossinperformance.2.D.C.ANDA.C.RATINGSTheYfiscalculatedbydividingtheenergyyieldrecordedwithautilitykWhmeterbythenameplated.c.powerrating.Thenameplated.c.powerratingisdeterminedbysummingthemodulepowerslistedonthenameplatesonthebacksidesoftheindividualPVmodulesinthePVarray.ThePVmodulepowerratingsareforSTCof1000W/m2solarirradianceand25Ccelltemperature.Besidesbeingeasilydetermined,thenameplated.c.powerratingsuseintheequationforYfofferstheadvantage,ascomparedtotheuseofana.c.powerratingorconditionsotherthanSTC,ofdifferentiatingbetweensystemswithdifferentd.c.toa.c.conversionefficienciesordifferentmounting-relatedPVmoduletemperatureenvironments.Forexample,ifperformancewaswithrespecttoana.c.powerrating,twosystemsmightreportthesameYf,buthavesignificantlydifferentinverterefficiencies,orotherlossmechanisms.Similarly,ifperformancewaswithrespecttoPTC,twosystemsmightreportthesameYf,buthavesignificantlydifferentPVmoduletemperature-relatedlossesbecauseofhowthePVmodulesaremountedorintegratedintothebuilding.Althoughanameplated.c.powerratingisusedinYftoreportthenormalizedenergyproducedbyanexistingsystem,ana.c.powerratingisessentialwhenattemptingtopredicttheenergyaPVsystemwillproduceusingmodelssuchasPVWATTS,PVDesignPro,orPVGRID.Accurateenergypredictionsarecrucialtothecontinueddevelopmentofthephotovoltaicindustrybecausetheysettheinvestorsexpectationsforsystemperformanceandtheassociatedeconomicreturn.Theremainderofthissectiondiscussesa.c.powerratingsandconsiderationsintheirdetermination.PVsystemsmaybeassigneda.c.powerratingsbyaccountingfor:(1)lossesinconvertingfromd.c.toa.c.power,and(2)operatingcelltemperaturesthatareusuallygreaterthan25C.Inthefirstcase,thenameplated.c.powerratingismultipliedbyempiricallydeterminedderatefactorstocalculateana.c.powerratingatSTC.Inthesecondcase,an第5页additionalderatecanbeappliedfortemperatureotherthanSTC.Finally,thePVUSAratingmethodmaybeusedtoassignana.c.ratingtoanexistingsystemwithhistoricaldata.Toevaluatetheaccuracyofourempiricalderatefactors,PVUSAratingsweredeterminedfor24PowerLightPVsystems(twentysingle-crystallinesilicon,twomulticrystallinesilicon,andtwoamorphoussilicon)locatedthroughouttheUnitedStates.Theseratingswerethencomparedtothea.c.ratingsforthesamesystemscalculatedbyusingthederatemethodandthederatefactorsfromTable1.AllderatefactorsinTable1wereestimatedfrommeasuredlossesandcomponentspecifications.Thetypicaloverallderatefactoratnominaloperatingcelltemperature(NOCT)is0.731,representingalossof26.9%fromthenameplated.c.rating.Fortheinitialcomparison,all“typical”deratefactorsfromTable1wereused,exceptforthetemperaturederatefactorsthatweredeterminedusingthemanufacturerspowercorrectionfactorsfortemperatureandNOCTsof45C.TheresultsofthecomparisonusingthisderatemethodareshowninFig.1.Thederatemethoda.c.ratingswereasmuchas19%greaterthanthePVUSArating,andthestandarddeviationofthedifferenceswas7%.InFig.1,themeasuredlossisthedifferencebetweenthenameplated.c.ratingandthePVUSArating.Thedesignlossisthedifferencebetweenthenameplated.c.ratingandthea.c.ratingcalculatedusingthederatemethod.Foranaccuratedesign,themeasuredlossanddesignlosswillbeveryclose.The第6页measuredanddesignlossesareexpressedaspercentagesforeaseofcomparison.Fig.1.Designandmeasuredlossesusingtypicalderatefactors,exceptforthetemperaturederatefactor,whichwasmanufacturerspecific.Current-voltage(I-V)curvetestingofPVmodulesusedinthese24systemsrevealedthattheaccuracyofthenameplateratingsvariedbymanufacturer,andforcertainmanufacturerstheaccuracyvariedbyproduct.SomePVmodulesproducedasmuchas4%morethanspecified,whereasotherswereasmuchas12%lessthanspecified.Fig.2.Designandmeasuredlossesusingtypicalderatefactors,exceptforthetemperaturederatefactorandthePVmodulenameplated.c.ratingderatefactor,whichweremanufacturerspecific.Consequently,forthesecondcomparison,resultsweresignificantlyimprovedbyusingaderatefactortoaccountfortheaccuracyofthe第7页manufacturersnameplated.c.ratings,asdetailedinthefirstrowofTable1.ComparedtothePVUSAratings,thea.cratingscalculatedusingaderatemethodincludingafactorformanufacturersnameplateratingwerewithin5%,withastandarddeviationofthedifferencesof2%.Figure2illustratestheseresults.Althoughnotevaluated,stillbetteragreementmighthavebeenachievedbyusingsystem-specificderateandNOCTvaluesinsteadoftypicalvalues.3.INFLUENCEOFWEATHERVariationsinsolarradiationandambienttemperaturefrommonth-to-monthandyear-to-yearinfluencetheperformanceparameters.Therefore,itisimportanttoidentifywhichperformanceparametersaresuitableforwhichsystemevaluationsbasedontheirweather-dependence.TheYfisinfluencedthemostbecauseofitsdependencyonsolarradiation.ThePRisinfluencedlessbecausevaluesarenormalizedwithrespecttosolarradiation,butvaluesareinfluencedbyseasonalvariationsintemperature.ThePVUSAa.cpowerratingsatPTCareinfluencedtheleastbecausethemethodperformstheregressionusingsolarradiation,ambienttemperature,andwindspeedvalues.SmallvariationsinPVUSAmethoda.cpowerratingscanbeattributedtotherangeofvaluesoverwhichtheregressionisperformed,nonlinearitiesinPVmoduleandinverterperformance,andvariationsinsolarspectrum.Toillustratetheextenttowhichtheperformanceparametersmightbeinfluencedbyweather,PVsystemperformancewasmodeledusingPVFORMfora30-yearperiod.ThehourlysolarradiationandmeteorologicaldatainputtoPVFORMwasfortheBoulder,CO,stationintheNationalSolarRadiationDataBase.PVsystemspecificationswerethesameasthePVsystemlocatedontheroofoftheSolarEnergyResearchFacility(SERF)attheNationalRenewableEnergyLaboratory(NREL):single-crystallinesiliconPVmodules,nameplated.c.powerratingof7420W,PVarraytiltangleof45,andPVarrayazimuthangleof22eastofsouth.Usingmodeled,insteadofmeasured,datapermittedtheinfluenceofweathertobeevaluatedoveralongerperiodoftimeandeliminatedtheneedtocarefullyscreenerroneousdataordata第8页collectedwhenthesystemwasinoperative,ortoaccountforanyperformancedegradationthatoccurred.Usingthemodeleddataforthe30-yearperiod,monthlyandyearlyperformanceparametersandPVUSAa.cpowerratingsatPTCwerecalculated.TheresultsareshowninFig.3.Ifweatherhadnoinfluence,thevalueswouldallresideonahorizontalline,butthatisclearlynotthecase.Asexpected,YfshowsthegreatestvariabilityandthePVUSAa.cpowerratingatPTCshowstheleast.Althoughnotshown,thevariabilityofYrissimilartoYfbecauseofYfsdependenceonsolarirradiance.PRvaluesexhibittheinfluenceoftemperature,withsmallervaluesinsummerthanwinter.Foryearlyvalues,95%confidenceintervals,determinedastwicethestandarddeviations,areshown.Theconfidenceintervalof8.4%forYfmeansthat95%oftheyearlyvaluesshouldbewithin8.4%oftheaverageyearlyvalue.Asindicatedbythescatterofdata,monthlyvaluesaremorevariable,resultingingreaterconfidenceintervalsthanfortheyearlyvalues.AlthoughPRvariesfromsummertowinter,theyearlyvaluesareconsistentwithaconfidenceintervalof1.2%,whichisonlyslightlygreaterthantheconfidenceintervalof0.7%foryearlyvaluesofPVUSAa.cpowerratingsatPTC.(BecausethePVUSAratingsaredeterminedusingamonthofdata,theyearlyvaluewasdeterminedastheaverageofthe12monthlyvalues.)Consequently,bothPVUSAa.cpowerratingsatPTCandyearlyPRvaluesshouldbeabletodetectdegradationofsystemperformanceovertime.第9页Fig.3.MonthlyandyearlyYf,PR,andPVUSAa.cpowerratingatPTCfromPVperformancedatamodeledovera30-yearperiodshowtheinfluenceofweathervariability.4.EXAMPLERESULTSFORYfArizonaPublicServiceCo.operatesnumerousgrid-connectedPVsystemswithinitsserviceterritory.Table2containsalistingofsomeofthesesystemsandtheirYfvaluesforthe12-monthperiodofSeptember2003throughAugust2004.Becausethesolarresource(Yr)isgreaterforthesingle-axistrackingsystems,theirYfvaluesarelargerthanthoseforthenon-trackingsystems.Forthesingle-axistrackingsystems,Fig.4showsmonthlyandyearlyYfvaluesforthe12-monthperiod.YfvalueswerelargestfortheAirportMTA2andtheYuccapowerplantsystems,primarilybecausetheirPVmodulesperformancemettheirnameplateexpectations.Theothersystemsperformedatalowerlevelbecauseofacombinationoffactors:PVmoduleperformance,inverterefficiency,andoperationalproblems.Specifically,fortheAirport第10页MTB1system,theinverteroperatedpoorlyuntilAugust,whenallitsperformanceissueshadbeenresolved.TheGilbertNatureCentersystemexperiencedfrequentinverterfaults,andinAugustaconductorfailed,renderingthesysteminoperableoroperatingatreducedpowerformostofthemonth.Table2.ArizonaPublicServicePVSystemsandTheirYfforSeptember2003ThroughAugust2004.TheYfnormalizesperformancewithrespecttosystemsize;consequently,itisusefulforcomparingsystemsofdifferentsizetoquantifybenefitsofdesign,components,orlocations.ButunlikethePR,theYfvaluesdonotcorrectforthevariabilityofsolarradiation,andtherefore,arenotasusefulforidentifyingoperationalproblems.Theexceptionisside-by-sideoperationofsystemsofidenticaldesign,suchastheArizonaPublicServicesingle-axistrackersatthePrescottairport.Forthissituation,wecanassumethatallsystemshaveessentiallythesamesolarresource(Yr),andthatanyoperationalproblemmaybedetectedbycomparingasystemsYfagainstthatoftheothersystems.Forasinglesystem,asimilarstrategymightbeusedbydividingitintotwoormoresubsystems,witheachhavingtheirowninverteranda.c.Metering.第11页Fig.4.MonthlyandyearlyYfforArizonaPublicServicesingle-axistrackersforSeptember2003throughAugust2004.5.EXAMPLERESULTSFORPRThePRisadimensionlessquantitythatindicatestheoveralleffectoflossesontheratedoutput.Byitself,itdoesnotrepresenttheamountofenergyproduced,becauseasystemwithalowPRinahighsolarresourcelocationmightproducemoreenergythanasystemwithahighPRinalowsolarresourcelocation.However,foranygivensystem,location,andtime;ifachangeincomponentordesignincreasesthePR,theYfincreasesaccordingly.PRvaluesareusefulfordeterminingifthesystemisoperatingasexpectedandforidentifyingtheoccurrenceofproblemsduetoinverteroperation(faults/failures,peak-powertracking,software/control),circuit-breakertrips,solder-bondfailuresinsidePVmodulejunctionboxes,diodefailures,inoperativetrackers,shading,snow,soiling,long-termPVsystemdegradation,orotherfailures.LargedecreasesinPRindicateeventsthatsignificantlyimpactperformance,suchasinvertersnotoperatingorcircuit-breakertrips.SmallormoderatedecreasesinPRindicatethatalesssevereproblemexists.ThePRcanidentifytheexistenceofaproblem,butnotthecause.Thecauseoftheproblemrequiresfurther第12页investigation,whichmayincludeasitevisitbymaintenancepersonnel.DecreasesinPRfromsoilingorlong-termPVsystemdegradationmaynotbereadilyevidentunlessviewedovermonths,oryearsinthecaseofthelatter.Decreasesfromsoilingaresite-andweather-dependent,withgreatersoiling(upto25%forsomeCalifornialocations)forhigh-traffic,high-pollutionareaswithinfrequentrain.For2001,Fig.5presentsdaily,weekly,andmonthlyPRvaluesfortheNRELSERFPVsystemdescribedinaprevioussection.Formostoftheyear,thePRvaluesareconsistentwiththosemodeledforthesamesystemandshowninFig.1.Butforwinterandspringmonths,PRvaluesarelowerfordayscoincidingwithlogbookentriesreportingsnowfallandforthreedaysinFebruarywhenthesystemwasoff.Dependingontheamountofsnow,dailyPRvaluesaslowaszerooccurred.TheinfluenceofsnowisalsoevidentintheweeklyandmonthlyPRvalues,buttoalesserextent.Fig.5.Daily,weekly,andmonthlyPRvaluesfortheNRELSERFPVsystemfor2001.AsanexampleofusingPRtomeasurelong-termchangesinperformance,Fig.6presentsforthreePVsystemsthelinearleast-squarefitsofmonthlyPRvaluesoveraperiodofseveralyears.Forcomparison,resultsusingthePVUSAmethodarealsoshown.Bothmethodsshowsimilardegradationrates,eventhoughtheyuse第13页somewhatdifferentinputdata.WhereasthecalculationofPRusesallvaluesofirradiance,thePVUSAmethodrestrictsirradiancevaluesto800W/m2orabove.Toexamineonlytheeffectsoflong-termperformancechanges,bothmethodsexcludeddatawhenthea.c.powervalueindicatedthesystemwasnotoperating.Ifinsteadtheintenthadbeentoevaluateoverallsystemperformance,datawouldnothavebeenexcludedandvalueswouldhavebeenless.TheresultsdepictedinFig.6areanexampleofusingPRtomeasureperformancechangesovertime,andarenotmeantasadefinitiveanalysisofaPVtechnologyslong-termperformanceforDenveroranyotherlocation.Therelativeperformanceofthethreesystemswasinfluencedbyusinginverterswithdifferentconversionefficienciesandoperatingcharacteristics.Also,thereliabilityofthesesmallsystemsmaynotberepresentativeofthatoflargersystems,andperformancechangesmayhavebeendifferentiftestedinadifferentclimateorlocation.Forthesystemusingthea-Si/a-Si/a-Si:GePVmodules,datacollectionbeganafterbeingdeployedforseveralmonthsandtheirinitialperformancedegradationhadoccurred.第14页Fig.6.Long-termdegradationratesforthreePVsystemsatNRELfrommonthlyvaluesofPRandPVUSAratings.UpperregressionlinesfrommonthlyPRvaluesshownby+symbols.LowerregressionlinesfrommonthlyPVUSAvaluesshownbysymbols.第15页中文翻译稿光伏并网发电系统的性能参数使用适当的性能参数，有利于比较不同设计、技术、地理位置时光伏并网发电系统的不同。从生产能源、太阳能资源、和整个系统的损失效应角度看，系统的整体性能由四个性能参数决定：光伏系统的最终产量、参考收益率、性能比和美国的光伏评级。这些性能参数表明，它们的适用性在于提供光伏系统在设计、性能评级方面所需的信息和展现系统使用的各种技术、设计和地理位置。再者在测定性能参数时还发现，系统在开发设计阶段使用乘法器时系统交流额定功率的