外文文献跟踪器太阳能自动文档格式.docx
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外文文献跟踪器太阳能自动文档格式.docx
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December15,2005
DukeUniversitySmartHousePrattSchoolofEngineering
TheSolarTrackerteamwasformedinthefallof2005fromfivestudentsinanMEdesignteam,andaSmartHouseliaison.Wecontinuedtheworkofaprevioussolartrackergroup.Thetaskwastodesignaprototypetrackingdevicetoalignsolarpanelsoptimallytothesunasitmovesoverthecourseoftheday.TheimplementationofsuchasystemdramaticallyincreasestheefficiencyofsolarpanelsusedtopowertheSmartHouse.Thisreportexaminestheprocessofdesigningandconstructingtheprototype,theexperiencesandproblemsencountered,andsuggestionsforcontinuingtheproject
1.Introduction
Solartrackingistheprocessofvaryingtheangleofsolarpanelsandcollectorstotakeadvantageofthefullamountofthesun’senergy.Thisisdonebyrotatingpanelstobeperpendiculartothesun’sangleofincidence.Initialtestsinindustrysuggestthatthisprocesscanincreasetheefficiencyofasolarpowersystembyupto50%.Giventhosegains,itisanattractivewaytoenhanceanexistingsolarpowersystem.Thegoalistobuildarigthatwillaccomplishthesolartrackingandrealizethemaximumincreaseinefficiency.Theultimategoalisthattheprojectwillbecosteffective–thatis,thegainsreceivedbyincreasedefficiencywillmorethanoffsettheonetimecostofdevelopingtherigovertime.Inadditiontothefunctionalgoals,theSmartHousesetforththeotherfollowinggoalsforourproject:
itmustnotdrawexternalpower(self-sustaining),itmustbeaestheticallypleasing,anditmustbeweatherproof.
Thedesignofoursolartrackerconsistsofthreecomponents:
theframe,thesensor,andthedrivesystem.Eachwascarefullyreviewedandtested,institutingchangesandimprovementsalongthedesignprocess.Theframeforthetrackerisanaluminumprismaticframesuppliedbytheprevioussolartrackinggroup.Itutilizesan‘A-frame’designwiththerotatingaxleinthemiddle.Attachedtothebottomofthissquarechannelaxleistheplatformwhichwillhousethemainsolarcollectingpanels.Theframeitselfisatanangletodirectthepanelstowardthesun(alongwiththeinclinationoftheroof).Itsrotationtracksthesunfromeasttowestduringtheday.
Thesensordesignforthesystemusestwosmallsolarpanelsthatlieonthesameplaneasthecollectingpanels.Thesesensorpanelshavemirrorsverticallyattachedbetweenthemsothat,unlessthemirrorfacesdonotreceiveanysun,theyareshadingoneofthepanels,whiletheotherisreceivingfullsunlight.Oursensorreliesonthisdifferenceinlight,whichresultsinalargeimpedancedifferenceacrossthepanels,todrivethemotorintheproperdirectionuntilagain,themirrorsarenotseeinganysunlight,atwhichpointbothsolarpanelsonthesensorreceiveequalsunlightandnopowerdifferenceisseen.
Afterevaluationofthepreviousdirectdrivesystemforthetracker,wedesignedabeltsystemthatwouldbeeasiertomaintaininthecaseofafailure.Ononeendoftheframeisamotorthathasthedrivepulleyattachedtoitsoutputshaft.Themotorrotatesthedrivebeltwhichthenrotatesthepulleyontheaxle.Thissystemissimpleandeasilydisassembled.Itiseasyto
interchangemotorsasneededforfurthertestingandalsoallowsforoptimizationofthefinalgearratioforresponseofthetracker.
Aswithanydesignprocesstherewereseveralsetbackstoourprogress.Thefirstandforemostwasinclementweatherwhichdeniedusofvaluabletestingtime.Despitethesetbacks,webelievethisdesignandprototypetobeaveryvaluableproof-of-principle.Duringourtestingwehaveeliminatedmanyoftherepetitiveproblemswiththemotorandwiringsothatfutureworkontheprojectwillgomoresmoothly.Wealsohaveachievedourgoaloftrackingthesunina‘hands-off’demo.Wewereabletohavethetrackerrotateunderitsownpowertotheangleofthesunandstopwithoutanyassistance.ThiswasthemaingoalsetforthtousbytheSmartHousesowebelieveoursensedmotionprototypeforsolartrackingwillbethefoundationastheymoveforwardinthefuturedevelopmentandimplementationofthistechnologytothehouse.
2.ConceptsandResearch
2.1TrackingType
Ourgroupusedabrainstormingapproachtoconceptgeneration.Wethoughtofideasfordifferentsolartrackingdevices,whichproveddifficultattimesduetotheexistingframeandconceptpresentedtousbySmartHouse.Otherconceptsweregeneratedthroughresearchofpre-existingsolartrackingdevices.OriginallyourconceptgenerationwasgearedtowardscreatingacompletelynewsolartrackeroutsideoftheconstraintsofthepreviousstructuregiventousbySmartHouse.Thisinitialbrainstorminggeneratedmanyconcepts.Thefirstonewasauni-axialtrackingsystemthatwouldtrackthesuneasttowestacrosstheskyduringthecourseofadayandreturnattheendoftheday.Thisconceptpresentedtheadvantageofsimplicityandpresenteduswiththeoptiontousematerialsfromthepreviousstructure(whichwasalsointendedtobeauni-axialtracker)inconstruction.Anothermorecomplexconceptwastotrackthesunbi-axiallywhichwouldinvolvetrackingthesunbotheasttowestandthroughouttheseasons.Theadvantageofthisconceptwasamoreefficientharvestingofsolarenergy.Thethirdconceptwastoonlytrackthroughouttheseasons.Thiswouldprovidesmallefficiencygainsbutnowherenearthegainprovidedbytrackingeasttowest.
Thedifferentstructureswecameupwithtoaccomplishtrackingmotionincludedarotatingcenteraxlewithattachedpanels,hydraulicormotorizedliftswhichwouldmovethemainpanelinthedirectionofthesun,andaroboticarmwhichwouldturntofacethesun.Theclearefficiencygainscoupledwiththesimplicityofdesignoftheuni-axialtrackingsystemandtheexistenceofusableparts(i.e.motorandaxle)fortherotatingcenteraxlestructure,ledustothechoiceoftheEasttoWesttracking,rotatingcenteraxleconcept.
2.2Structure
Oncethemethodofmotionwaschosen,itwasnecessarytogenerateconceptsforthestructuralsupportoftheaxle.SupportcouldbeprovidedbythetriangularprismaticstructurewhichwasattemptedbythepreviousSmartHousesolartrackergrouporthroughtheuseofcolumnswhichwouldsupporttheaxisoneitherside.Whiletheprismaticstructurepresentedtheadvantageofmobilityandanexistingframe,thecolumnswouldhaveprovideduswitheaseofconstruction,simplegeometricconsiderations,andeaseofprospectivemountingontheroof.Duetotheheightenedintensityoftimeconsiderations,thepreviousfinancialcommitmenttotheprismaticstructurebySmartHouse,andourlimitedbudget,thepresenceofthepre-existingframeprovedtobethemostimportantfactorindecidingonastructure.DuetothesefactorswedecidedtoworkwithintheframewhichwasprovidedtousfromthepreviousSolarTrackergroup.
2.2TrackingMotion
Oncethestructuralsupportwasfinalizedweneededtodecideonameanstoactualizethismotion.Wedecidedbetweensensedmotion,whichwouldsensethesun’spositionandmovetofollowit,andcontinuousclocktypemotion,whichwouldtrackthesunbasedonitspre-determinedpositioninthesky.Wechosetheconceptofcontinuousmotionbasedonitsperceivedaccuracyandtheexistenceofknowntimingtechnology.Duringtheevaluationstage,however,werealizedthatcontinuousmotionwouldprovedifficult.Onereasonwastheinabilitytodrawconstantvoltageandcurrentfromthesolarpanelsnecessarytosustainconsistentmotion,resultinginthenecessityforsensingtherotationpositiontocompensate.Continuousmotionalsorequirednearlyconstantpowerthroughouttheday,whichwouldrequireamechanismtostorepower.Asidefromtheseconsiderations,theimplementationofatimingcircuitandlocationsensingdeviceseemeddaunting.AfterconsultingDr.RhettGeorge,wedecidedonadeviceusingtwopanelsandshadingforsensedmotion.
3.DetailedDesign
3.1Frame
Theframewasdesignedfromoneinchsquarealuminumtubing,andafivefootlong,twoinchsquaretubefortheaxle.Itisconstructedwitharigidbaseandtriangularprismaticframewithsidesupportingbarsthatprovidestability.Theendoftheaxleisattachedtoasystemofpulleyswhicharedrivenbythemotor.Itiseasilytransportedbyremovingthesidesofthebaseandfoldingthestructure.
3.2Sensor
OursensingpanelsareboltedtothebottomofthemainsolarpanelframeandbracedunderneathwithhalfinchL-brackets.ThemirrorsareattachedtotheinsideofthesensingpanelsandbracedbyL-bracketsaswell.Thewholestructureattacheseasilytothemainpanelframewhichisattachedtothemainaxleusingfour2-inchU-bolts.Athirdpanelisboltedtothestructuretoreturnthemainpanelsdirectiontowardsthehorizonofsunrise.
3.3HowtheSensorWorks
Oursensorcreatesmovementofthemotorbyshadingoneofthepanelsandamplifyingtheotherwhenthesystemisnotdirectlyfacingthesun.Thetwosensingpanelsaremountedparalleltothemainpanelssymmetricallyaboutthecenteraxlewithtwomirrorsinbetweenthem.Theshadingononeofthepanelscreateshighimpedance,whiletheamplifiedpanelpowersthemotor.Thishappensuntilthepanelsreceivethesameamountofsunlightandbalanceeachotherout(i.e.whenthesensingpanelsandmainpanelsarefacingthesun.).Weinitiallyattemptedusingaseriesconfigurationtotakeadvantageofthevoltagedifferencewhenoneofthepanelswasshaded(AppendixC).Thisdifference,however,wasnotlargeenoughtodrivethemotor.Wesubsequentlyattemptedaparallelconfigurationwhichwou
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