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外文原文SolarTrackingSystem:MoreEfficientUseofSolarPanelsAbstract—Thispapershowsthepotentialsystembenefitsofsimpletrackingsolarsystemusingasteppermotorandlightsensor.Thismethodisincreasingpowercollectionefficiencybydevelopingadevicethattracksthesuntokeepthepanelatarightangletoitsrays.Asolartrackingsystemisdesigned,implementedandexperimentallytested.Thedesigndetailsandtheexperimentalresultsareshown.Keywords—RenewableEnergy,PowerOptimization.I.INTRODUCTIONExtrectinguseableelectricityfromthesunwasmadepossiblebythediscoveryofthephotoelectricmechanismandsubsequentdevelopmentofthesolarcell–asemi-conductivematerialthatconvertsvisiblelightintoadirectcurrent.Byusingsolararrays,aseriesofsolarcellselectricallyconnected,aDCvoltageisgeneratedwhichcanbephysicallyusedonaload.Solararraysorpanelsarebeingusedincreasinglyasefficienciesreachhigherlevels,andareespeciallypopularinremoteareaswhereplacementofelectricitylinesisnoteconomicallyviable.Thisalternativepowersourceiscontinuouslyachievinggreaterpopularityespeciallysincetherealisationoffossilfuel’sshortcomings.Renewableenergyintheformofelectricityhasbeeninusetosomedegreeaslongas75or100yearsago.SourcessuchasSolar,Wind,HydroandGeo-thermalhaveallbeenutilisedwithvaryinglevelsofsuccess.Themostwidelyusedarehydroandwindpower,withsolarpowerbeingmoderatelyusedworldwide.Thiscanbeattributedtotherelativelyhighcostofsolarcellsandtheirlowconversionefficiency.Solarpowerisbeingheavilyresearched,andsolarenergycostshavenowreachedwithinafewcentsperkW/hofotherformsofelectricitygeneration,andwilldropfurtherwithnewtechnologiessuchastitanium-oxidecells.Withapeaklaboratoryefficiencyof32%andaverageefficiencyof15-20%,itisnecessarytorecoverasmuchenergyaspossiblefromasolarpowersystem.Thisincludesreducinginverterlosses,storagelosses,andlightgatheringlosses.Lightgatheringisdependentontheangleofincidenceofthelightsourceprovidingpower(i.e.thesun)tothesolarcell’ssurface,andtheclosertoperpendicular,thegreaterthepower[1-7].Ifaflatsolarpanelismountedonlevelground,itisobviousthatoverthecourseofthedaythesunlightwillhaveanangleofincidencecloseto90°inthemorningandtheevening.Atsuchanangle,thelightgatheringabilityofthecellisessentiallyzero,resultinginnooutput.Asthedayprogressestomidday,theangleofincidenceapproaches0°,causingansteadyincreaseinpoweruntilatthepointwherethelightincidentonthepaneliscompletelyperpendicular,andmaximumpowerisachieved.Asthedaycontinuestowarddusk,thereversehappens,andtheincreasinganglecausesthepowertodecreaseagaintowardminimumagain.Fromthisbackground,weseetheneedtomaintainthemaximumpoweroutputfromthepanelbymaintaininganangleofincidenceascloseto0°aspossible.Bytiltingthesolarpaneltocontinuouslyfacethesun,thiscanbeachieved.ThisprocessofsensingandfollowingthepositionofthesunisknownasSolarTracking.Itwasresolvedthatreal-timetrackingwouldbenecessarytofollowthesuneffectively,sothatnoexternaldatawouldberequiredinoperation.II.THESENSINGELEMENTANDSIGNALPROCESSINGManydifferentmethodshavebeenproposedandusedtotrackthepositionofthesun.ThesimplestofallusesanLDR–aLightDependentResistortodetectlightintensitychangesonthesurfaceoftheresistor.Othermethods,suchasthatpublishedbyJeffDammin‘HomePower’[8],usetwophototransistorscoveredwithasmallplatetoactasashieldtosunlight,asshowninFig.1.Fig.1AlternativesolartrackingmethodWhenmorningarrives,thetrackerisinstateAfromthepreviousday.Theleftphototransistoristurnedon,causingasignaltoturnthemotorcontinuouslyuntiltheshadowfromtheplatereturnsthetrackertostateB.Asthedayslowlyprogresses,stateCisreachedshortly,turningontherightphototransistor.ThemotorturnsuntilstateBisreachedagain,andthecyclecontinuesuntiltheendoftheday,oruntiltheminimumdetectablelightlevelisreached.Theproblemwithadesignlikethisisthatphototransistorshaveanarrowrangeofsensitivity,oncetheyhavebeensetupinacircuitundersetbiasconditions.Itwasbecauseofthisfactthatsolarcellsthemselveswerechosentobethesensingdevices.Theyprovideanexcellentmechanisminlightintensitydetection–becausetheyaresensitivetovaryinglightandprovideanear-linearvoltagerangethatcanbeusedtoanadvantageindeterminingthepresentdeclinationorangletothesun.Asaresult,asimpletriangularset-upwasproposed,withthetwosolarcellsfacingoppositedirections,asshowninFig.2.Initsrestposition,thesolarcellsbothreceiveanequalamountofsunlight,astheangleofincidence,althoughnot90°,isequalinbothcasesasseeninFig.3.Fig.2Set-upofsolarreferencecellsFig.3SolarreferencecellsatrestpositionFig.4SolarreferencecellsatasignificantangletothesunItcanbeseeninFig.4thatasthesunmovesinthesky,assumingthatthesolartrackerhasnotyetmoved,theangleofincidenceoflighttothereferencepanelswillcausemorelighttofallononecellthantheother.Thiswillobviouslycauseavoltagedifference,wherethecellthatisfacingthesunwillhavehigherpotentialthantheother.Thisphenomenonwillresultinadetectablesignalateachcell,whichcanbeprocessedbyasuitablecircuit.III.APROTOTYPESOLARTRACKERThefinalstageinvolvedcouplingthecircuitrytothemotorandmountingitontothebracket.ThefinalproductisseencompleteinFig.5.IthasaSolarex9Wsolararraymadeofpolycrystallin