PVT集電極技術、應用和市場的基本概念

BasicconceptsofPVTcollector

technologies,

applicationsandmarkets

IEASHCTASK60|PVTSYSTEMS

BasicconceptsofPVT

collectortechnologies,

applicationsandmarkets

SHCTask60/ReportD5

Authors:ManuelL?mmle,FraunhoferISE,Germany

MaríaHerrando,UniversityofZaragoza,SpainGlenRyan,Sunovate,Australia

Contributors:LaetitiaBrottier,DualSun,France;MatteoChiappa,Solink,Italy;CorrydeKeizer,TNO,

Netherlands;AlejandrodelAmo,Abora,Spain;AlexanderFriedrich,3FSolar,Austria;AntonioGagliano,

UniversitàdiCatania,Italy;JoaoGomes,Solarus,Sweden;AndreasH?berle,HSRHochschulefürTechnikRapperswil,Switzerland;EricHawkins,Speedflex,UK;DannyJonas,Universit?tdesSaarlandes,Germany;KorbinianKramer,FraunhoferISE,Germany;UlrichLeibfried,Consolar,Germany;AlexanderMellor,NakedEnergy,UK;IlijaNasov,CamelSolar,Macedonia;ThomasNoll,easy-tnt,Germany;MarcoPelligrini,

UniversityofBologna,Italy;FernandoPerez,Abora,Spain;MarkusPr?ll,ZAEBayerne.V.,Germany;NielsRadisch,Ramboll,Denmark;DavidSauter,ZHAW,Switzerland;IonnaisSifnaios,DTU,Denmark;DanjanaTheis,HTWSaar,Germany;DanielZenh?usern,SPF,Switzerland

Date:May1st,2020

ReportnumberD5DOI:10.18777/ieashc-task60-2020-0002

Coverphoto:PVTcollectorsattheNewTownHallFreiburg?ManuelL?mmle/FraunhoferISE

ThecontentsofthisreportdonotnecessarilyreflecttheviewpointsorpoliciesoftheInternationalEnergyAgency(IEA)oritsmembercountries,theIEASolarHeatingandCoolingTechnologyCollaboration

Programme(SHCTCP)membersortheparticipatingresearchers.

IEASolarHeatingandCoolingTechnologyCollaborationProgramme(IEASHC)

TheSolarHeatingandCoolingTechnologyCollaborationProgrammewasfoundedin1977asoneofthefirst

multilateraltechnologyinitiatives("ImplementingAgreements")oftheInternationalEnergyAgency.Itsmissionis

“Toenhancecollectiveknowledgeandapplicationofsolarheatingandcoolingthroughinternationalcollaborationtoreachthegoalsetinthevisionofsolarthermalenergymeeting50%oflowtemperatureheatingandcooling

demandby2050.”

ThemembersoftheIEASHCcollaborateonprojects(referredtoasTasks)inthefieldofresearch,development,demonstration(RD&D),andtestmethodsforsolarthermalenergyandsolarbuildings.

ResearchtopicsandtheassociatedTasksinparenthesisinclude:

□SolarSpaceHeatingandWaterHeating(Tasks14,19,26,44,54)

□SolarCooling(Tasks25,38,48,53)

□SolarHeatforIndustrialorAgriculturalProcesses(Tasks29,33,49,62,64)

□SolarDistrictHeating(Tasks7,45,55)

□SolarBuildings/Architecture/UrbanPlanning(Tasks8,11,12,13,20,22,23,28,37,40,41,47,51,52,56,59,63)

□SolarThermal&PV(Tasks16,35,60)

□Daylighting/Lighting(Tasks21,31,50,61)

□Materials/ComponentsforSolarHeatingandCooling(Tasks2,3,6,10,18,27,39)

□Standards,Certification,andTestMethods(Tasks14,24,34,43,57)

□ResourceAssessment(Tasks1,4,5,9,17,36,46)

□StorageofSolarHeat(Tasks7,32,42,58)

InadditiontoourTaskwork,otheractivitiesoftheIEASHCincludeour:

InternationalConferenceonSolarHeatingandCoolingforBuildingsandIndustry

SHCSolarAcademy

SolarHeatWorldwideannualstaticsreport

Collaborationwithsolarthermaltradeassociations

CountryMembers

Australia

France

SouthAfrica

Austria

Germany

Spain

Belgium

Italy

Sweden

Canada

Netherlands

Switzerland

China

Norway

Turkey

Denmark

Portugal

UnitedKingdom

EuropeanCommission

Slovakia

SponsorMembers

EuropeanCopperInstitute

ECREEE

InternationalSolarEnergySociety

PCREEE

CCREEE

RCREEE

EACREEE

SACREEE

FormoreinformationontheIEASHCwork,includingmanyfreepublications,pleasevisit

Preface

TheaimofthisreportistoprovideasummaryofthecurrentstateofthePVTcollectortechnologies,applications,andmarkets.

ThecontentsofthisreporthavebeenusedtoupdateandenhanceaWikipediaarticleonPVTinordertobetterinformonPVTawideaudience.Therefore,themainstructureandsomeliteralfragmentsofthecurrentWikipediaarereused.InsteadofcitingtheliteralfragmentsoftheoldWikipediaarticleinthemaintext,weincludedtheoldarticleinappendixandmarkedthefragmentsthatwerereused.

Contents

Preface iii

Contents iv

1PVTcollectorsandtheirrangeofoperation 1

1.1Introduction 1

1.2PVTmarkets 2

1.3PVTcollectortechnologies 2

1.3.1ClassificationofPVTcollectors 3

1.3.2PVTliquidcollector 4

1.3.3PVTaircollector 4

1.3.4UncoveredPVTcollector(WISC) 5

1.3.5CoveredPVTcollector 5

1.3.6ConcentratingPVTcollector(CPVT) 5

1.4PVTapplicationsbytemperaturerange 6

2AreviewofPVTapplicationsandsystems 8

2.1Solarheatingsystems 8

2.1.1Processheat 8

2.1.2Domestichotwaterheating 8

2.1.3Spaceheating 8

2.1.4Swimmingpool 9

2.1.5Heatpumpsource 9

2.2Solarcoolingandsolarcombinedcoolingheatingandpowersystems 9

2.3Solarindustrialprocesses 10

2.3.1Solarwaterdesalinationandsolarstills 10

2.3.2Agro-Industrialprocesses 10

2.4References 10

3AssessmentofthemarketpotentialofPVTcollectors 14

Appendix1-ExpertsurveyontemperaturerangesforPVTcollectortechnologiesandapplications 15

Appendix2-MarkedversionoftheoriginalWikipediaarticlefrom16.03.2019 18

3.1Introduction 18

3.2Contents 19

3.3PV/Tsystemengineering 19

3.4Systemtypes 19

3.4.1PV/Tliquidcollector 19

3.4.2PV/Taircollector 19

3.4.3PV/Tconcentrator(CPVT) 20

3.5Seealso 20

3.6References 20

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BasicconceptsofPVTcollectortechnologies,applicationsandmarkets

1PVTcollectorsandtheirrangeofoperation

1.1Introduction

Photovoltaicthermalcollectors,typicallyabbreviatedasPVTcollectorsandalsoknownashybridsolarcollectors,hybridphotovoltaicthermalsolarcollectors,PV/Tcollectorsorsolarcogenerationsystems,arepowergenerationtechnologiesthatconvertsolarradiationintousablethermalandelectricalenergy.PVTcollectorscombinephotovoltaicsolarcells,whichconvertsunlightintoelectricity,withasolarthermalcollector,whichtransferstheotherwiseunusedexcessheatfromthePVmoduletoaheattransferfluid.Bycombiningelectricityandheatgenerationwithinthesamecomponent,thesetechnologiescanreachahigheroverallefficiencythansolarphotovoltaic(PV)orsolarthermalalone.1

SignificantresearchhasgoneintodevelopingadiverserangeofPVTtechnologiessincethe1970s.2ThedifferentPVTcollectortechnologiesdiffersubstantiallyintheircollectordesignandheattransferfluidandaddressdifferentapplicationsrangingfromlowtemperatureheatingandcoolinguptohightemperatureheatabove100°C.3

Figure1.14:SchematiccrosssectionofaWISC(Windandinfraredsensitivecollector)PVTcollectorwithsheet-and-tubetypeheatexchangerandrearinsulation:

1-PVmodulecoverglass(e.g.anti-reflective)

2-Encapsulant(e.g.EVA)

3-SolarPVcells

4-Encapsulant(e.g.EVA)

5-Backsheet(e.g.PVF)

6-Heatexchanger(e.g.aluminum,copperorpolymers)

7-Thermalinsulation(e.g.mineralwool),notalwayspresentforWISCcollectors.

1Zenh?usern,Daniel,EvelynBamberger,andAleksisBaggenstos.2017.?PVTWrap-Up:EnergySystemswithPhotovoltaic-ThermalSolarCollectors?.Rapperswil,Switzerland:publishedbyEnergieSchweiz.

http://www.spf.ch/fileadmin/daten/publ/PVT_WrapUp_Final_EN.pdf

2Chow,T.T.(2010)."Areviewonphotovoltaic/thermalhybridsolartechnology".AppliedEnergy.87(2):365-379.doi:10.1016/j.apenergy.2009.06.037.

3Zondag,H.A.;Bakker,M.;vanHelden,W.G.J.(2006):PVTRoadmap-AEuropeanguideforthedevelopmentandmarketintroductionofPV-Thermaltechnology.

4ImagebyManuelL?mmle-Ownwork,CCBY-SA4.0,

/w/index.php?curid=88267419

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1.2PVTmarkets

PVTcollectorsgeneratesolarheatandelectricitybasicallyfreeofdirectCO2emissionsandarethereforeregardedasapromisingtechnologytosupplyrenewableelectricityandheatand/orcoldtobuildingsandindustrialprocesses.

Heatisthelargestenergyend-use.In2015,theprovisionofheatingforitsuseinbuildings,industrialpurposesandotherapplicationsaccountedforaround52%(205EJ)ofthetotalenergyconsumed.5Ofthis,overhalfwasusedintheindustryandaround46%inthebuildingsector.While72%oftheheatwasprovidedbythedirectcombustionoffossilfuels,only7%ofwasfrommodernrenewablessuchassolarthermal,biofuelorgeothermal.6Thelowgradeheatmarketupto150°Cisestimatedtobe26.8%oftheworldwidefinalenergydemand,whichiscurrentlyservicedbyfossilfuels(gas,oil,andcoal),electricityandrenewableheat.Thisisthesumofindustrydemand7.1%(25.5EJ)7andbuildingdemand19.7%(49.0EJresidentialand13.6EJcommercial)8.

Theelectricitydemandinbuildingsandindustryisexpectedtogrowfurtherduetoongoingelectrificationandsectorcoupling.9Forasignificantreductionofcarbonemissions,itisessentialthatthemajorshareofelectricityissourcedfromrenewableenergysources,suchaswind,solar,biomassandwater.

Themarketforrenewableheatandelectricityisthereforevast,illustratingthemarketpotentialofPVTcollectors.

Thereport“SolarHeatWorldwide”assessedtheglobalmarketofPVTcollectorsin2018.Accordingtotheauthors,thetotalareaofinstalledcollectorsamountedto1.08millionsquaremeters.Uncoveredwatercollectorshadthelargestmarketshare(57%),followedbyaircollectors(41%)andcoveredwatercollectors(2%).ThecountrywiththelargestinstalledcapacitywasFrance(41%),followedbyKorea(26%),China(12%)andGermany(10%).10

1.3PVTcollectortechnologies

PVTcollectorscombinethegenerationofsolarelectricityandheatinasinglecomponent,andthusachieveahigheroverallefficiencyandbetterutilizationofthesolarspectrumthanconventionalPVmodules.

Photovoltaiccellstypicallyreachanelectricalefficiencybetween15%and20%,whilethelargestshareofthesolarspectrum(65%-70%)isconvertedintoheat,increasingthetemperatureofPVmodulesasillustratedinFigure2.PVTcollectors,onthecontrary,areengineeredtotransferheatfromthePVcellstoafluid.Inthisway,thisexcessheatismadeusefulandcanbeutilizedtoheatwaterorasalowtemperaturesourceforheatpumps,forexample.Thus,PVTcollectorsmakebetteruseofthesolarspectrum.1

Byco-generatingsolarelectricityandheatinasinglecomponent,PVTcollectorsincreasethecombinedefficiencyandyieldanoptimizedutilizationofavailablespace.Especiallyindenselypopulatedurbanareas,PVTcollectorsareconsideredapromisingtechnologyforincreasingtheusageofvaluableroofandfacadespace.

Mostphotovoltaiccells(e.g.siliconbased)sufferfromadropinefficiencywithincreasedcelltemperatures.EachKelvinofincreasedcelltemperaturereducestheefficiencyby0.2–0.5%.3RemovingheatfromthePVcellscan

5Collier,Ute(2018),IEAInsightsSeries2018:RenewableHeatPolicies,Figure1,

/download/direct/1030

6Collier,Ute(2018),IEAInsightsSeries2018:RenewableHeatPolicies,Figure2,

/download/direct/1030

7Philibert,Cedric2017,IEARenewableEnergyforIndustryFromgreenenergytogreenmaterialsandfuels,Figure3,

/download/direct/1025?fileName=Insights_series_2017_Renewable_Energy_for_Industry.pdf

8Dianaürge-Vorsatz,Heatingandcoolingenergytrendsanddriversinbuildings,Figure3,

/10.1016/j.rser.2014.08.039

9IRENA(2019):GlobalEnergyTransformation:ARoadmapto2050(2019Edition).InternationalRenewableEnergyAgency,AbuDhabi.

/-/media/Files/IRENA/Agency/Publication/2019/Apr/IRENA_Global_Energy_Transformation_2019.pdf

.

10Weiss,Werner;Sp?rk-Dür,Monika(2019):SolarHeatWorldwide-GlobalMarketDevelopmentandTrendsin2018-

DetailedmarketFigures2017,

/Data/Sites/1/publications/Solar-Heat-Worldwide-2019.pdf

.

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BasicconceptsofPVTcollectortechnologies,applicationsandmarkets

thereforelowertheirtemperatureandthusincreasethecells’efficiency.ImprovedPVcelllifetimesareanotherbenefitofloweroperationtemperatures.

ThefunctionandenergeticbenefitofaPVTcollectorcanbedescribedcomprehensivelybyindicatingthe

electricalandthermalgainsinasolarspectrum(Figure1.2).Itisalsoforthisreason,thatIEASHCTask60usesthesolarspectrumaspartofitslogo.

Figure1.2:UtilizationoftheelectromagneticsolarspectrumbyaPVTcollector.11

Figure1.2isbasedontheoriginaldiagrambyDupeyrat(2011)12,whichwasupdatedwithrecentefficiencydataanddetailedopticalmeasurements(compareL?mmle(2018)13):

?SolarirradiancerepresentstheglobalAM1.5spectrumaccordingtoASTMG173-03(2012)14withanoverallirradiancedensityofG=1000W/m2.

?TheopticallossesarecalculatedbasedonmeasuredreflectanceandtransmittancespectraofaPVmodulewithp-Sisolarcells,solarglassandwithoutanti-reflectivecoating.TheopticalmeasurementswereconductedatFraunhoferISEwithaspectrometerusinganUlbrichtsphere.

?Theelectricitygainsarecalculatedbasedonthemeasurementsofthespectralresponseofac-SisolarcellwithanelectricalefficiencyofηSTC=15%.

?Theheatgainsarecalculatedbasedontheassumptionofathermalefficiencyofηth,0=61%,astypicallyfoundinunglazedorglazedPVTcollectorswithattheoperatingconditionsofTfluid,mean=Tambient.

?Heatlossesaccountfortheremainderofthesolarspectrum,asheatlosses,anditsspectraldistribution,cannotbemeasureddirectly.

Accordingly,thesolarirradiancerepresents100%oftheAM1.5spectrum,opticallossesaccountfor9%,heatlossesfor15%,heatgainsfor61%,andelectricitygainsfor15%.

1.3.1ClassificationofPVTcollectors

11ImagebyManuelL?mmle-Ownwork,CCBY-SA4.0,

/w/index.php?curid=87526248

12Dupeyrat,Patrick(2011):ExperimentaldevelopmentandsimulationinvestigationofaPhotovoltaic-Thermalhybridsolarcollector.INSAdeLyon,France.L’InstitutNationaldesSciencesAppliquéesdeLyon.

13L?mmle,Manuel(2018):ThermalmanagementofPVTcollectors-developmentandmodellingofhighlyefficientPVTcollectorswithlow-emissivitycoatingsandoverheatingprotection.In:PhDthesis,FraunhoferISE,INATECHAlbert-Ludwigs-Universit?tFreiburg.DOI:10.6094/UNIFR/16446.

14ASTMG173-03(2012)-StandardTablesforReferenceSolarSpectralIrradiances:DirectNormalandHemisphericalon37°TiltedSurface.

/solar//spectra/am1.5/

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ThereareamultitudeoftechnicalpossibilitiestocombinePVcellsandsolarthermalcollectors.AnumberofPVTcollectorsareavailableascommercialproducts,whichcanbedividedintothefollowingcategoriesaccordingtotheirbasicdesignandheattransferfluid:

?PVTliquidcollector

?PVTaircollector

Inadditiontotheclassificationbyheattransferfluid,PVTcollectorscanalsobecategorizedaccordingtothepresenceofasecondaryglazingtoreduceheatlossesandthepresenceofadevicetoconcentratesolarirradiation.

?UncoveredPVTcollector(WISCPVT)

?CoveredPVTcollector

?ConcentratingPVTcollector(CPVT)

Moreover,PVTcollectorscanbeclassifiedaccordingtotheirdesign,suchascelltechnology,typeoffluid,heatexchangermaterialandgeometry,typeofcontactbetweenfluidandPVmodule,fixationofheatexchanger,orlevelofbuildingintegration(buildingintegratedPVT

(BIPVT)collectors).1,

15

ThedesignandtypeofPVTcollectorsalwaysimpliesacertainadaptiontooperatingtemperatures,applications,andgivingprioritytoeitherheatorelectricitygeneration.Forinstance,operatingthePVTcollectoratlowtemperatureleadstoacoolingeffectofPVcellscomparedtoPVmodulesandthereforeanincreaseofelectricalpower.However,theheatalsohastobeutilizedatlowtemperatures.

ThemaximumoperatingtemperaturesformostPVmodulesarelimitedtolessthanthemaximumcertifiedoperationtemperatures(typically85°C).Nevertheless,twoormoreunitsofthermalenergyaregeneratedforeachunitofelectricalenergy,dependingoncellefficiencyandsystemdesign.

1.3.2PVTliquidcollector

Thebasicwater-cooleddesignuseschannelstodirectfluidflowusingpipingattacheddirectlyorindirectlytothebackofaPVmodule.Inastandardfluid-basedsystem,aworkingfluid,typicallywater,glycolormineraloil,circulatesintheheatexchangerbehindthePVcells.TheheatfromthePVcellsisconductedthroughthemetalandistransferredtotheworkingfluid(presumingthattheworkingfluidiscoolerthantheoperatingtemperatureofthecells).

1.3.3PVTaircollector

Thebasicair-cooleddesignuseseitherahollow,conductivehousingtomountthephotovoltaicpanelsoracontrolledflowofairtotherearfaceofthePVpanel.PVTaircollectorseitherdrawinfreshoutsideairoruseairasacirculatingheattransfermediuminaclosedloop.TheheattransferpropertiesofairarelowerthanthatoftypicallyusedliquidsandthereforerequiresaproportionallyhighermassflowratethananequivalentPVTliquidcollector.Theadvantageisthattheinfrastructurerequiredhaslowercostandcomplexity.

TheheatedairiscirculatedintoabuildingHVACsystemtodeliverthermalenergy.Excessheatgeneratedcanbesimplyventedtotheatmosphere.SomeversionsofthePVTaircollectorcanbeoperatedinawaytocoolthePVpanelstogeneratemoreelectricityandassistwithreducingthermaleffectsonlifetimeperformancedegradation.

AnumberofdifferentconfigurationsofPVTaircollectorsexist,whichvaryinengineeringsophistication.PVTaircollectorconfigurationsrangefromabasicenclosedshallowmetalboxwithanintakeandexhaustuptooptimizedheattransfersurfacesthatachieveuniformpanelheattransferacrossawiderangeofprocessandambientconditions.

PVTaircollectorscanbecarriedoutasuncoveredorcovereddesigns

.1

15L.Brottier(2018).Optimisationbiénergied’unpanneausolairemultifonctionnel:ducapteurauxinstallationsinsitu.Mécanique[physics.med-ph].UniversitéParis-Saclay,2019

.https://tel.archives-ouvertes.fr/tel-02133891

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BasicconceptsofPVTcollectortechnologies,applicationsandmarkets

1.3.4UncoveredPVTcollector(WISC)

UncoveredPVTcollectors,alsodenotedasunglazedorwindand/orinfraredsensitivePVTcollectors(WISC),typicallycompriseofaPVmodulewithaheatexchangerstructureattachedtothebackofthePVmodule.WhilemostPVTcollectorsareprefabricatedunits,someproductsareofferedasheatexchangerstoberetrofittedtooff-the-shelfPVmodules.Inbothcases,agoodandlongtimedurablethermalcontactwithahighheattransfercoefficientbetweenthePVcellsandthefluidisessential.16

TherearsideoftheuncoveredPVTcollectorcanbeequippedwiththermalinsulation(e.g.mineralwoolorfoam)toreduceheatlossesoftheheatedfluid.UninsulatedPVTcollectorsarebeneficialforoperationnearandbelowambienttemperatures.ParticularlyuncoveredPVTcollectorswithincreasedheattransfertoambientairareasuitableheatsourceforheatpumpsystems.Whenthetemperatureintheheatpump’ssourceislowerthantheambient,thefluidcanbeheateduptoambienttemperatureeveninperiodswithoutsunshine.

Accordingly,uncoveredPVTcollectorscanbecategorizedinto:

?UncoveredPVTcollectorwithincreasedheattransfertoambientair

?UncoveredPVTcollectorwithoutrearinsulation

?UncoveredPVTcollectorwithrearinsulation

UncoveredPVTcollectorsarealsousedtoproviderenewablecoolingbydissipatingheatviathePVTcollectortotheambientairorbyutilizingtheradiativecoolingeffect.Indoingso,coldairorwaterisharnessed,whichcanbeutilizedforHVACapplications.

1.3.5CoveredPVTcollector

Covered,orglazedPVTcollectors,featureanadditionalglazing,whichenclosesaninsulatingairlayerbetweenthePVmoduleandthesecondaryglazing.Thisreducesheatlossesandincreasesthethermalefficiency.Moreover,coveredPVTcollectorscanreachsignificantlyhighertemperaturesthanPVmodulesoruncoveredPVTcollectors.Theoperatingtemperaturesmostlydependonthetemperatureoftheworkingfluid.Theaveragefluidtemperaturecanbebetween25°Cinswimmingpoolapplicationsto90°Cinsolarcoolingsystems(Figure3).

CoveredPVTcollectorsresembletheformanddesignofconventionalflatplatecollectorsorevacuatedvacuumtubes.Yet,PVcellsinsteadofspectrally-selectiveabsorbercoatingsabsorbtheincidentsolarirradianceandgenerateanelectricalcurrentinadditiontosolarheat.

Theinsulatingcharacteristicsofthefrontcoverincreasethethermalefficiencyandallowforhigheroperatingtemperatures.However,theadditionalopticalinterfacesincreaseopticalreflectionsandthusreducethegeneratedelectricalpower.Anti-reflectivecoatingsonthefrontglazingcanreducetheadditionalopticallosses.17

1.3.6ConcentratingPVTcollector(CPVT)

Aconcentratorsystemhastheadvantagetoreducethephotovoltaic(PV)cellareaneeded.ThereforeitispossibletousemoreexpensiveandefficientPVcells,e.g.multi-junctionphotovoltaiccells.TheconcentrationofsunlightalsoreducestheamountofhotPV-absorberareaandthereforereducesheatlossestotheambient,whichimprovessignificantlytheefficiencyforhigherapplicationtemperatures.

ConcentratorsystemsoftenrequirereliablecontrolsystemstoaccuratelytrackthesunandtoprotectthePVcellsfromdamagingover-temperatureconditions.However,therearealsostationeryPVTcollectortypesthatusenon-imagingreflectors,suchastheCompoundParabolicConcentrator(CPC),anddonothavetotrackthesun.

16Adam,Mario;Kramer,Korbinian;Fritzsche,Ulrich;Hamberger,Stephan(2014):AbschlussberichtPVT-Norm.F?rderkennzeichen01FS12035-?Verbundprojekt:StandardisierungundNormungvonmultifunktionalenPVTSolarkollektoren(PVT-Norm)“.

17Zondag,H.A.(2008):Flat-platePV-Thermalcollectorsandsystems:Areview.In:RenewableandSustainableEnergyReviews12(4),S.891–959.

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Underidealconditions,about75%ofthesun'spowerdirectlyincidentuponsuchsystemscanbegatheredaselectricityandheat.Formoredetails,seethediscussionofCPVTwithinthearticleforconcentratedphotovoltaics.

Alimitationofhigh-concentrator(i.e.HCPVandHCPVT)systemsisthattheymaintaintheirlong-termadvantagesoverconventionalc-Si/mc-Sicollectorsonlyinregionsthatremainconsistentlyfreeofatmosphericaerosolcontaminants(e.g.lightclouds,smog,etc.).Powerproductionisrapidlydegradedbecause1)radiationisreflectedandscatteredoutsideofthesmall(oftenlessthan1°-2°)acceptanceangleofthecollectionoptics,and2)absorptionofspecificcomponentsofthesolarspectrumcausesoneormoreseriesjunctionswithintheMJcellstounderperform.Theshort-termimpactsofsuchpowergenerationirregularitiescanbereducedtosomedegreebyincludingelectricalandthermalstorageinthesystem.

1.4PVTapplicationsbytemperaturerange

TherangeofapplicationsofPVTcollectors,andingeneralsolarthermalcollectors,canbedividedaccordingtotheirtemperaturelevels:18

?lowtemperatureapplicationsupto50°C

?mediumtemperatureapplicationsupto80°C

?hightemperatureapplicationsabove80°C

Lowtemperatureapplicationsincludeheatpumpsystemsandheatingswimmingpoolsorspasupto50°C.PVTcollectorsinheatpumpsystemsacteitheraslowtemperaturesourcefortheheatpumpevaporatororontheloadsidetosupplymediumtemperatureheattoastoragetank.Moreover,regenerationofboreholesandgroundsourceheatexchangersispossible.1UncoveredPVTcollectorswithenhancedair-to-waterheatexchangecanevencomprisetheonlysourceofaheatpumpsystem.IncombinationwithasystemarchitectureallowingtostorecoldproducedwithWISCoraircollectors,alsoairconditioningispossible.

Lowandmediumtemperatureapplicationsforspaceheatinganddomestichotwaterprovisionarefoundinbuildings,withtemperaturesfrom20°Cto80°C.Thetemperaturesofthespecificsystemdependontherequirementsoftheheatsupplysystemfordomestichotwater(e.g.freshwaterstation,temperaturerequirementsforlegionellaprevention)andforspaceheating(e.g.underfloorheating,radiators).Moreover,thePVTcollectorarraycanbedimensionedtocoveronlysmallerfractionsoftheheatdemand(e.g.hotwaterpre-heating),thusreducingoperatingtemperaturesofthePVTcollector.

Processheatincludesadiverserangeofindustrialapplicationswithlowtohightemperaturerequirements(e.g.solarwaterdesalination,solarcooling,orpowergenerationwithconcentratingPVTcollectors).19PVTcollectortechnologiescanbeclusteredaccordingtotheirtemperaturelevelinthesameway:thesuitabilitypertemperaturerangedependsonthePVTcollectordesignandtechnology.Therefore,eachPVTcollectortechnologyfeaturesdifferentoptimaltemperatureranges.

Figure3showstypicaltemperaturerangesofbothPVTapplicationsandcollectortechnologies.20TheoperatingtemperatureofthePVTapplicationsultimatelydefinesthesuitabilityofeachtypeofPVTcollectortechnology.

18KalogirouSA(2014).Solarenergyengineering:processesandsystems.SecondEdition.AcademicPres