太阳能路灯控制系统外文资料.doc

太阳能路灯控制系统外文资料.doc

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吉林工程技术师范学院

信息工程学院

学士学位论文

中英文资料

学生姓名：

张建木

专业：

电子信息工程

班级：

D0745

学号：

11号

论文起止日期：

2011年4月至6月

英文原文：

PHOTOVOLTAICPOWERGENERATION

ABSTRACT

Thisreportisanoverviewofphotovoltaicpowergeneration.ThepurposeofthereportistoprovidethereaderwithageneralunderstandingofphotovoltaicpowergenerationandhowPVtechnologycanbepracticallyapplied.

Thereisabriefdiscussionofearlyresearchandadescriptionofhowphotovoltaiccellsconvertsunlighttoelectricity.Thereportcoversconcentratingcollectors,flat-platecollectors,thin-filmtechnology,andbuilding-integratedsystems.Thediscussionofphotovoltaiccelltypesincludessingle-crystal,poly-crystalline,andthin-filmmaterials.Thereportcoversprogressinimprovingcellefficiencies,reducingmanufacturingcost,andfindingeconomicapplicationsofphotovoltaictechnology.Listsofmajormanufacturersandorganizationsareincluded,alongwithadiscussionofmarkettrendsandprojections.

Theconclusionisthatphotovoltaicpowergenerationisstillmorecostlythanconventionalsystemsingeneral.However,largevariationsincostofconventionalelectricalpower,andotherfactors,suchascostofdistribution,createsituationsinwhichtheuseofPVpoweriseconomicallysound.PVpowerisusedinremoteapplicationssuchascommunications,homesandvillagesindevelopingcountries,waterpumping,camping,andboating.Grid-connectedapplicationssuchaselectricutilitygeneratingfacilitiesandresidentialrooftopinstallationsmakeupasmallerbutmorerapidlyexpandingsegmentofPVuse.Furthermore,astechnologicaladvancesnarrowthecostgap,moreapplicationsarebecomingeconomicallyfeasibleatanacceleratingrate.

INTRODUCTION

ThisreportistheresultofGaleGreenleaf’sOctober19,1998requestforproposal.BillLoukandTomPenickrespondedtoherrequestwithaproposal,datedOctober30,1998,tocontinueearlierresearchonphotovoltaicpowergeneration.TheproposalwasapprovedandresultedincontinuedresearchfollowedbyapresentationonNovember30,1998andthisfinalreportonphotovoltaicpowergeneration.

PHOTOVOLTAICTECHNOLOGY

Scientistshaveknownofthephotovoltaiceffectformorethan150years.Photovoltaicpowergenerationwasnotconsideredpracticaluntilthearrivalofthespaceprogram.Earlysatellitesneededasourceofelectricalpowerandanysolutionwasexpensive.Thedevelopmentofsolarcellsforthispurposeledtotheireventualuseinotherapplications.

DISCOVERYANDDEVELOPMENTOFPHOTOVOLTAICPOWER

Thephotovoltaiceffecthasbeenknownsince1839,butcellefficienciesremainedaround1%untilthe1950swhenU.S.researcherswereessentiallygivenablankchecktodevelopameansofgeneratingelectricityonboardspacevehicles.BellLaboratoriesquicklyachieved11%efficiency,andin1958,theVanguardsatelliteemployedthefirstpracticalphotovoltaicgeneratorproducingamodestonewatt.

Inthe1960s,thespaceprogramcontinuedtodemandimprovedphotovoltaicpowergenerationtechnology.Scientistsneededtogetasmuchelectricalpoweraspossiblefromphotovoltaiccollectors,andcostwasofsecondaryimportance.Withoutthistremendousdevelopmenteffort,photovoltaicpowerwouldbeoflittleusetoday.

POWEROUTPUTANDEFFICIENCYRATINGS

Thefiguresgivenforpoweroutputandefficiencyofphotovoltaiccells,modules,andsystemscanbemisleading.Itisimportanttounderstandwhatthesefiguresmeanandhowtheyrelatetothepoweravailablefrominstalledphotovoltaicgeneratingsystems.

PowerRatings

Photovoltaicpowergenerationsystemsareratedinpeakkilowatts（kWp）.Thisistheamountofelectricalpowerthatanew,cleansystemisexpectedtodeliverwhenthesunisdirectlyoverheadonaclearday.Wecansafelyassumethattheactualoutputwillneverquitereachthisvalue.Systemoutputwillbecompromisedbytheangleofthesun,atmosphericconditions,dustonthecollectors,anddeteriorationofthecomponents.Whencomparingphotovoltaicsystemstoconventionalpowergenerationsystems,oneshouldbearinmindthatthePVsystemsareonlyproductiveduringthedaytime.Therefore,a100kWphotovoltaicsystemcanproduceonlyafractionofthedailyoutputofaconventional100kWgenerator.

EfficiencyRatings

Theefficiencyofaphotovoltaicsystemisthepercentageofsunlightenergyconvertedtoelectricalenergy.Theefficiencyfiguresmostoftenreportedarelaboratoryresultsusingsmallcells.Asmallcellhasalowerinternalresistanceandwillyieldahigherefficiencythanthelargercellsusedinpracticalapplications.Additionally,photovoltaicmodulesaremadeupofnumerouscellsconnectedinseriestodeliverausablevoltage.Duetotheinternalresistanceofeachcell,thetotalresistanceincreasesandtheefficiencydropstoabout70%ofthesingle-cellvalue.Efficiencyishigheratlowertemperatures.Temperaturesusedinlaboratorymeasurementsmaybelowerthanthoseinapracticalinstallation.

CONVERTINGSUNLIGHTTOELECTRICITY

Atypicalphotovoltaiccellconsistsofsemiconductormaterial（usuallysilicon）havingap-njunctionasshowninFigure1.Sunlightstrikingthecellraisestheenergylevelofelectronsandfreesthemfromtheiratomicshells.Theelectricfieldatthep-njunctiondrivestheelectronsintothenregionwhilepositivechargesaredriventothepregion.Ametalgridonthesurfaceofthecellcollectstheelectronswhileametalback-platecollectsthepositivecharges.

Figure1.Howsolarcellswork

ThinFilmTechnology

Thin-filmsolarcellsaremanufacturedbyapplyingthinlayersofsemiconductormaterialstoasolidbackingmaterial.Thecompositionofatypicalthin-filmcellisshowninFigure2.Sunlightenteringtheintrinsiclayergeneratesfreeelectrons.Thep-typeandn-typelayerscreateanelectricfieldacrosstheintrinsiclayer.Theelectricfielddrivesthefreeelectronsintothen-typelayerwhilepositivechargescollectinthep-typelayer.Thetotalthicknessofthep-type,intrinsic,andn-typelayersisaboutonemicron.Althoughlessefficientthansingle-andpoly-crystalsilicon,thin-filmsolarcellsoffergreaterpromiseforlarge-scalepowergenerationbecauseofeaseofmass-productionandlowermaterialscost.Thin-filmisalsosuitableforbuilding-integratedsystemsbecausethesemiconductorfilmsmaybeappliedtobuildingmaterialssuchasglass,roofing,andsiding.

Figure2Typicalthin-filmamorphoussiliconconstructions

Usingthinfilmsinsteadofsiliconwafersgreatlyreducestheamountofsemiconductormaterialrequiredforeachcellandthereforelowersthecostofproducingphotovoltaiccells.Galliumarsenide（GaAs）,copperindiumdiselenide（CuInSe2）,cadmiumtelluride（CdTe）andtitaniumdioxide（TiO2）arematerialsthathavebeenusedforthinfilmPVcells.Titaniumdioxidethinfilmshavebeenrecentlydevelopedandareinterestingbecausethematerialistransparentandcanbeusedforwindows.

TinOxide

Tinoxideisaconductivematerialthatistransparentwheninathinlayer.Tinoxideisusedinplaceofametallicgridforthetoplayerofthinfilmphotovoltaicsheets.

AmorphousSilicon（a-Si）

Amorphous（uncrystallized）siliconisthemostpopularthin-filmtechnology.Itispronetodegradationandproducescellefficienciesof5-7%.Double-andtriple-junctiondesignsraiseefficiencyto8-10%.Theextralayerscapturedifferentwavelengthsoflight.Thetopcellcapturesbluelight,themiddlecellcapturesgreenlight,andthebottomcellcapturesredlight.Variationsincludeamorphoussiliconcarbide（a-SiC）,amorphoussilicongermanium（a-SiGe）,microcrystallinesilicon（mc-Si）,andamorphoussilicon-nitride（a-SiN）.

CadmiumTelluride（CdTe）andCadmiumSulphide（CdS）

PhotovoltaiccellsusingthesematerialsareunderdevelopmentbyBPSolarandSolarCellsInc.

Poly-crystallineSilicon

Poly-crystallinesiliconoffersanefficiencyimprovementoveramorphoussiliconwhilestillusingonlyasmallamountofmaterial.

CopperIndiumDiselenideandCopperIndiumGalliumDiselenide

Thesematerialsarecurrentlybeinginvestigated,andhavenotbeenusedcommerciallyforphotovoltaics.

ConcentratingCollectors

Byusingalensormirrortoconcentratethesun’sraysonasmallarea,itispossibletoreducetheamountofphotovoltaicmaterialrequired.Asecondadvantageisthatgreatercellefficiencycanbeachievedathigherlightconcentrations.Toaccommodatethehighercurrentsinthephotocells,alargermetallicgridisused.Forexample,inasystemwitha22Xconcentrationratio,thegridcoversabout20%ofthesurfaceofthesolarcell.Topreventthisfromblocking20%ofthesunlight,aprismisusedtoredirectsunlightontothephotovoltaicmaterial,asshowninFigure3.Asecondproblemisthehighertemperaturesofaconcentratingsystem.Thecellsmaybecooledwithaheatsinkortheheatcanbeusedtoheatwater.

Figure3.Prismcoverforhigh-currentsolarcell

Onlydirectsunlight,notscatteredbycloudsorhaze,canbeconcentrated.Therefore,theconcentratingcollectorsarelesseffectiveinlocationsthatarefrequentlycloudyorhazy,suchascoastalareas.

CONCLUSION

Photovoltaicefficiencyandmanufacturingcostshavenotreachedthepointthatphotovoltaicpowergenerationcanreplaceconventionalcoal-,gas-,andnuclear-poweredgeneratingfacilities.Forpeakloaduse（nobatterystorage）,thecostofphotovoltaicpowerisaroundtwotofourtimesasmuchasconventionalpower.（Costcomparisonsbetweenphotovoltaicpowerandconventionallygeneratedpoweraredifficultduetowidevariationsinutilitypowercost,sunlightavailability,andnumerousothervariables.）

REFERENCE