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TheBasicsofSolarPowerforProducingElectricityUsingsolarpowertoproduceelectricityisnotthesameasusingsolartoproduceheat.Solarthermalprinciplesareappliedtoproducehotfluidsorair.Photovoltaicprinciplesareusedtoproduceelectricity.Asolarpanelismadeofthenaturalelement,silicon,whichbecomeschargedelectricallywhensubjectedtosunlight.Solarpanelsaredirectedatsolarsouthinthenorthernhemisphereandsolarnorthinthesouthernhemispheretheseareslightlydifferentthanmagneticcompassnorthsouthdirectionsatanangledictatedbythegeographiclocationandlatitudeofwheretheyaretobeinstalled.Typically,theangleofthesolararrayissetwithinarangeofbetweensitelatitudeplus15degreesandsitelatitudeminus15degrees,dependingonwhetheraslightwinterorsummerbiasisdesirableinthesystem.Manysolararraysareplacedatanangleequaltothesitelatitudewithnobiasforseasonalperiods.TheintensityoftheSunsradiationchangeswiththehouroftheday,timeoftheyearandweatherconditions.Tobeabletomakecalculationsinplanningasystem,thetotalamountofsolarradiationenergyisexpressedinhoursoffullsunlightperm,orPeakSunHours.Thisterm,PeakSunHours,representstheaverageamountofsunavailableperdaythroughouttheyear.Itispresumedthatatpeaksun,1000W/mofpowerreachesthesurfaceoftheearth.Onehouroffullsunprovides1000Whperm1kWh/mrepresentingthesolarenergyreceivedinonehouronacloudlesssummerdayonaonesquaremetersurfacedirectedtowardsthesun.Toputthisinsomeotherperspective,theUnitedStatesDepartmentofEnergyindicatestheamountofsolarenergythathitsthesurfaceoftheearthevery/hourisgreaterthanthetotalamountofenergythattheentirehumanpopulationrequiresinayear.Anotherperspectiveisthatroughly100squaremilesofsolarpanelsplacedinthesouthwesternU.S.couldpowerthecountry.ThedailyaverageofPeakSunHours,basedoneitherfullyearstatistics,oraverageworstmonthoftheyearstatistics,forexample,isusedforcalculationpurposesinthedesignofthesystem.ToseetheaveragePeakSunHoursforyourareaintheUnitedStates,U.S.SolarInsolationChoosetheareaclosesttoyourlocationforagoodindicationofyouraveragePeakSunHours.ForaviewofglobalsolarisolationvaluespeaksunhoursusethislinkGlobalPeakSunhourMaps,then,youcanusebackorpreviousonyourbrowsertoreturnrighthereifyouwantto.Soitcanbeconcludedthatthepowerofasystemvaries,dependingontheintendedgeographicallocation.FolksinthenortheasternU.S.willneedmoresolarpanelsintheirsystemtoproducethesameoverallpowerasthoselivinginArizona.Wecanadviseyouonthisifyouhaveanydoubtsaboutyourarea.Thefourprimarycomponentsforproducingelectricityusingsolarpower,whichprovidescommon120voltACpowerfordailyuseareSolarpanels,chargecontroller,batteryandinverter.Solarpanelschargethebattery,andthechargeregulatorinsuresproperchargingofthebattery.ThebatteryprovidesDCvoltagetotheinverter,andtheinverterconvertstheDCvoltagetonormalACvoltage.If240voltsACisneeded,theneitheratransformerisaddedortwoidenticalinvertersareseriesstackedtoproducethe240volts.Theoutputofasolarpanelisusuallystatedinwatts,andthewattageisdeterminedbymultiplyingtheratedvoltagebytheratedamperage.TheformulaforwattageisVOLTStimesAMPSequalsWATTS.Soforexample,a12volt60wattsolarpanelmeasuringabout2044incheshasaratedvoltageof17.1andarated3.5amperage.VAW17.1voltstimes3.5ampsequals60wattsIfanaverageof6hoursofpeaksunperdayisavailableinanarea,thentheabovesolarpanelcanproduceanaverage360watthoursofpowerperday60wtimes6hrs360watthours.Sincetheintensityofsunlightcontactingthesolarpanelvariesthroughouttheday,weusethetermpeaksunhoursasamethodtosmoothoutthevariationsintoadailyaverage.Earlymorningandlateinthedaysunlightproduceslesspowerthanthemiddaysun.Naturally,cloudydayswillproducelesspowerthanbrightsunnydaysaswell.Whenplanningasystemyourgeographicalareaisratedinaveragepeaksunhoursperdaybasedonyearlysundata.Averagepeaksunhoursforvariousgeographicalareasislistedintheabovesection.Solarpanelscanbewiredinseriesorinparalleltoincreasevoltageoramperagerespectively,andtheycanbewiredbothinseriesandinparalleltoincreasebothvoltsandamps.Serieswiringreferstoconnectingthepositiveterminalofonepaneltothenegativeterminalofanother.Theresultingouterpositiveandnegativeterminalswillproducevoltagethesumofthetwopanels,buttheamperagestaysthesameasonepanel.Sotwo12volt/3.5amppanelswiredinseriesproduces24voltsat3.5amps.Fourofthesewiredinserieswouldproduce48voltsat3.5amps.Parallelwiringreferstoconnectingpositiveterminalstopositiveterminalsandnegativetonegative.Theresultisthatvoltagestaysthesame,butamperagebecomesthesumofthenumberofpanels.Sotwo12volt/3.5amppanelswiredinparallelwouldproduce12voltsat7amps.Fourpanelswouldproduce12voltsat14amps.Achargecontrollermonitorsthebatterysstateofchargetoinsurethatwhenthebatteryneedschargecurrentitgetsit,andalsoinsuresthebatteryisntovercharged.Connectingasolarpaneltoabatterywithoutaregulatorseriouslyrisksdamagingthebatteryandpotentiallycausingasafetyconcern.Chargecontrollersoroftencalledchargeregulatorareratedbasedontheamountofamperagetheycanprocessfromasolararray.Ifacontrollerisratedat20ampsitmeansthatyoucanconnectupto20ampsofsolarpaneloutputcurrenttothisonecontroller.ThemostadvancedchargecontrollersutilizeachargingprincipalreferredtoasPulseWidthModulationPWMwhichinsuresthemostefficientbatterychargingandextendsthelifeofthebattery.EvenmoreadvancedcontrollersalsoincludeMaximumPowerPointTrackingMPPTwhichmaximizestheamountofcurrentgoingintothebatteryfromthesolararraybyloweringthepanelsoutputvoltage,whichincreasesthechargingampstothebatterybecauseifapanelcanproduce60wattswith17.2voltsand3.5amps,thenifthevoltageisloweredtosay14voltsthentheamperageincreasesto4.2814v4.28amps60wattsresultingina19increaseinchargingampsforthisexample.ManychargecontrollersalsoofferLowVoltageDisconnectLVDandBatteryTemperatureCompensationBTCasanoptionalfeature.TheLVDfeaturepermitsconnectingloadstotheLVDterminalswhicharethenvoltagesensitive.Ifthebatteryvoltagedropstoofartheloadsaredisconnectedpreventingpotentialdamagetoboththebatteryandtheloads.BTCadjuststhechargeratebasedonthetemperatureofthebatterysincebatteriesaresensitivetotemperaturevariationsaboveandbelowabout75Fdegrees.TheDeepCyclebatteriesusedaredesignedtobedischargedandthenrechargedhundredsorthousandsoftimes.ThesebatteriesareratedinAmpHoursahusuallyat20hoursand100hours.Simplystated,amphoursreferstotheamountofcurrentinampswhichcanbesuppliedbythebatteryovertheperiodofhours.Forexample,a350ahbatterycouldsupply17.5continuousampsover20hoursor35continuousampsfor10hours.Toquicklyexpressthetotalwattspotentiallyavailableina6volt360ahbattery360ahtimesthenominal6voltsequals2160wattsor2.16kWhkilowatthours.Likesolarpanels,batteriesarewiredinseriesand/orparalleltoincreasevoltagetothedesiredlevelandincreaseamphours.Thebatteryshouldhavesufficientamphourcapacitytosupplyneededpowerduringthelongestexpectedperiodnosunorextremelycloudyconditions.Aleadacidbatteryshouldbesizedatleast20largerthanthisamount.Ifthereisasourceofbackuppower,suchasastandbygeneratoralongwithabatterycharger,thebatterybankdoesnothavetobesizedforworstcaseweatherconditions.Thesizeofthebatterybankrequiredwilldependonthestoragecapacityrequired,themaximumdischargerate,themaximumchargerate,andtheminimumtemperatureatwhichthebatterieswillbeused.Duringplanning,allofthesefactorsarelookedat,andtheonerequiringthelargestcapacitywilldictatethebatterysize.Oneofthebiggestmistakesmadebythosejuststartingoutdoesnotunderstandtherelationshipbetweenampsandamphourrequirementsof120voltACitemsversustheeffectsontheirDClowvoltagebatteries.Forexample,sayyouhavea24voltnominalsystemandaninverterpoweringaloadof3amps,120VAC,whichhasadutycycleof4hoursperday.Youwouldhavea12amphourload3A4hrs12ah.However,inordertodeterminethetruedrainonyourbatteriesyouhavetodivideyournominalbatteryvoltage24vintothevoltageoftheload120v,whichis5,andthenmultiplythistimesyour120vacamphours512ah.Sointhiscasethecalculationwouldbe60amphoursdrainedfromyourbatteriesnotthe12ah.Anothersimplewayistotakethetotalwatthoursofyour120VACdeviceanddividebynominalsystemvoltage.Usingtheaboveexample3amps120volts4hours1440watthoursdividedby24DCvolts60amphours.LeadacidbatteriesarethemostcommoninPVsystemsbecausetheirinitialcostislowerandbecausetheyarereadilyavailablenearlyeverywhereintheworld.Therearemanydifferentsizesanddesignsofleadacidbatteries,butthemostimportantdesignationisthattheyaredeepcyclebatteries.Leadacidbatteriesareavailableinbothwetcellrequiresmaintenanceandsealednomaintenanceversions.AGMandGelcelldeepcyclebatteriesarealsopopularbecausetheyaremaintenancefreeandtheylastalotlonger.
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