外文文献跟踪器太阳能自动.docx

外文文献跟踪器太阳能自动.docx

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外文文献跟踪器太阳能自动

SolarTracker

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