外文翻译--太阳能发电的基础.doc

TheBasicsofSolarPowerforProducingElectricityUsingsolarpowertoproduceelectricityisnotthesameasusingsolartoproduceheat.Solarthermalprinciplesareappliedtoproducehotfluidsorair.Photovoltaicprinciplesareusedtoproduceelectricity.Asolarpanelismadeofthenaturalelement,silicon,whichbecomeschargedelectricallywhensubjectedtosunlight.Solarpanelsaredirectedatsolarsouthinthenorthernhemisphereandsolarnorthinthesouthernhemisphere(theseareslightlydifferentthanmagneticcompassnorth-southdirections)atanangledictatedbythegeographiclocationandlatitudeofwheretheyaretobeinstalled.Typically,theangleofthesolararrayissetwithinarangeofbetweensite-latitude-plus15degreesandsite-latitude-minus15degrees,dependingonwhetheraslightwinterorsummerbiasisdesirableinthesystem.Manysolararraysareplacedatanangleequaltothesitelatitudewithnobiasforseasonalperiods.TheintensityoftheSunsradiationchangeswiththehouroftheday,timeoftheyearandweatherconditions.Tobeabletomakecalculationsinplanningasystem,thetotalamountofsolarradiationenergyisexpressedinhoursoffullsunlightperm,orPeakSunHours.Thisterm,PeakSunHours,representstheaverageamountofsunavailableperdaythroughouttheyear.Itispresumedthatatpeaksun,1000W/mofpowerreachesthesurfaceoftheearth.Onehouroffullsunprovides1000Whperm=1kWh/m-representingthesolarenergyreceivedinonehouronacloudlesssummerdayonaone-squaremetersurfacedirectedtowardsthesun.Toputthisinsomeotherperspective,theUnitedStatesDepartmentofEnergyindicatestheamountofsolarenergythathitsthesurfaceoftheearthevery+/-hourisgreaterthanthetotalamountofenergythattheentirehumanpopulationrequiresinayear.Anotherperspectiveisthatroughly100squaremilesofsolarpanelsplacedinthesouthwesternU.S.couldpowerthecountry.ThedailyaverageofPeakSunHours,basedoneitherfullyearstatistics,oraverageworstmonthoftheyearstatistics,forexample,isusedforcalculationpurposesinthedesignofthesystem.ToseetheaveragePeakSunHoursforyourareaintheUnitedStates,U.S.-SolarInsolationChoosetheareaclosesttoyourlocationforagoodindicationofyouraveragePeakSunHours.Foraviewofglobalsolarisolationvalues(peaksun-hours)usethislink:GlobalPeakSun-hourMaps,then,youcanusebackorpreviousonyourbrowsertoreturnrighthereifyouwantto.Soitcanbeconcludedthatthepowerofasystemvaries,dependingontheintendedgeographicallocation.FolksinthenortheasternU.S.willneedmoresolarpanelsintheirsystemtoproducethesameoverallpowerasthoselivinginArizona.Wecanadviseyouonthisifyouhaveanydoubtsaboutyourarea.Thefourprimarycomponentsforproducingelectricityusingsolarpower,whichprovidescommon120voltACpowerfordailyuseare:Solarpanels,chargecontroller,batteryandinverter.Solarpanelschargethebattery,andthechargeregulatorinsuresproperchargingofthebattery.ThebatteryprovidesDCvoltagetotheinverter,andtheinverterconvertstheDCvoltagetonormalACvoltage.If240voltsACisneeded,theneitheratransformerisaddedortwoidenticalinvertersareseries-stackedtoproducethe240volts.Theoutputofasolarpanelisusuallystatedinwatts,andthewattageisdeterminedbymultiplyingtheratedvoltagebytheratedamperage.TheformulaforwattageisVOLTStimesAMPSequalsWATTS.Soforexample,a12volt60wattsolarpanelmeasuringabout2044incheshasaratedvoltageof17.1andarated3.5amperage.VA=W17.1voltstimes3.5ampsequals60wattsIfanaverageof6hoursofpeaksunperdayisavailableinanarea,thentheabovesolarpanelcanproduceanaverage360watthoursofpowerperday；60wtimes6hrs=360watt-hours.Sincetheintensityofsunlightcontactingthesolarpanelvariesthroughouttheday,weusethetermpeaksunhoursasamethodtosmoothoutthevariationsintoadailyaverage.Earlymorningandlate-in-the-daysunlightproduceslesspowerthanthemid-daysun.Naturally,cloudydayswillproducelesspowerthanbrightsunnydaysaswell.Whenplanningasystemyourgeographicalareaisratedinaveragepeaksunhoursperdaybasedonyearlysundata.Averagepeaksunhoursforvariousgeographicalareasislistedintheabovesection.Solarpanelscanbewiredinseriesorinparalleltoincreasevoltageoramperagerespectively,andtheycanbewiredbothinseriesandinparalleltoincreasebothvoltsandamps.Serieswiringreferstoconnectingthepositiveterminalofonepaneltothenegativeterminalofanother.Theresultingouterpositiveandnegativeterminalswillproducevoltagethesumofthetwopanels,buttheamperagestaysthesameasonepanel.Sotwo12volt/3.5amppanelswiredinseriesproduces24voltsat3.5amps.Fourofthesewiredinserieswouldproduce48voltsat3.5amps.Parallelwiringreferstoconnectingpositiveterminalstopositiveterminalsandnegativetonegative.Theresultisthatvoltagestaysthesame,butamperagebecomesthesumofthenumberofpanels.Sotwo12volt/3.5amppanelswiredinparallelwouldproduce12voltsat7amps.Fourpanelswouldproduce12voltsat14amps.Achargecontrollermonitorsthebatterysstate-of-chargetoinsurethatwhenthebatteryneedscharge-currentitgetsit,andalsoinsuresthebatteryisntover-charged.Connectingasolarpaneltoabatterywithoutaregulatorseriouslyrisksdamagingthebatteryandpotentiallycausingasafetyconcern.Chargecontrollers(oroftencalledchargeregulator)areratedbasedontheamountofamperagetheycanprocessfromasolararray.Ifacontrollerisratedat20ampsitmeansthatyoucanconnectupto20ampsofsolarpaneloutputcurrenttothisonecontroller.ThemostadvancedchargecontrollersutilizeachargingprincipalreferredtoasPulse-Width-Modulation(PWM)-whichinsuresthemostefficientbatterychargingandextendsthelifeofthebattery.EvenmoreadvancedcontrollersalsoincludeMaximumPowerPointTracking(MPPT)whichmaximizestheamountofcurrentgoingintothebatteryfromthesolararraybyloweringthepanelsoutputvoltage,whichincreasesthechargingampstothebattery-becauseifapanelcanproduce60wattswith17.2voltsand3.5amps,thenifthevoltageisloweredtosay14voltsthentheamperageincreasesto4.28(14v4.28amps=60watts)resultingina19%increaseinchargingampsforthisexample.ManychargecontrollersalsoofferLowVoltageDisconnect(LVD)andBatteryTemperatureCompensation(BTC)asanoptionalfeature.TheLVDfeaturepermitsconnectingloadstotheLVDterminalswhicharethenvoltagesensitive.Ifthebatteryvoltagedropstoofartheloadsaredisconnected-preventingpotentialdamagetoboththebatteryandtheloads.BTCadjuststhechargeratebasedonthetemperatureofthebatterysincebatteriesaresensitivetotemperaturevariationsaboveandbelowabout75Fdegrees.TheDeepCyclebatteriesusedaredesignedtobedischargedandthenre-chargedhundredsorthousandsoftimes.ThesebatteriesareratedinAmpHours(ah)-usuallyat20hoursand100hours.Simplystated,amphoursreferstotheamountofcurrent-inamps-whichcanbesuppliedbythebatteryovertheperiodofhours.Forexample,a350ahbatterycouldsupply17.5continuousampsover20hoursor35continuousampsfor10hours.Toquicklyexpressthetotalwattspotentiallyavailableina6volt360ahbattery；360ahtimesthenominal6voltsequals2160wattsor2.16kWh(kilowatt-hours).Likesolarpanels,batteriesarewiredinseriesand/orparalleltoincreasevoltagetothedesiredlevelandincreaseamphours.Thebatteryshouldhavesufficientamphourcapacitytosupplyneededpowerduringthelongestexpectedperiodnosunorextremelycloudyconditions.Alead-acidbatteryshouldbesizedatleast20%largerthanthisamount.Ifthereisasourceofback-uppower,suchasastandbygeneratoralongwithabatterycharger,thebatterybankdoesnothavetobesizedforworstcaseweatherconditions.Thesizeofthebatterybankrequiredwilldependonthestoragecapacityrequired,themaximumdischargerate,themaximumchargerate,andtheminimumtemperatureatwhichthebatterieswillbeused.Duringplanning,allofthesefactorsarelookedat,andtheonerequiringthelargestcapacitywilldictatethebatterysize.Oneofthebiggestmistakesmadebythosejuststartingoutdoesnotunderstandtherelationshipbetweenampsandamp-hourrequirementsof120voltACitemsversustheeffectsontheirDClowvoltagebatteries.Forexample,sayyouhavea24voltnominalsystemandaninverterpoweringaloadof3amps,120VAC,whichhasadutycycleof4hoursperday.Youwouldhavea12amphourload(3A4hrs=12ah).However,inordertodeterminethetruedrainonyourbatteriesyouhavetodivideyournominalbatteryvoltage(24v)intothevoltageoftheload(120v),whichis5,andthenmultiplythistimesyour120vacamphours(512ah).Sointhiscasethecalculationwouldbe60amphoursdrainedfromyourbatteries-notthe12ah.Anothersimplewayistotakethetotalwatt-hoursofyour120VACdeviceanddividebynominalsystemvoltage.Usingtheaboveexample；3amps120volts4hours=1440watt-hoursdividedby24DCvolts=60amphours.Lead-acidbatteriesarethemostcommoninPVsystemsbecausetheirinitialcostislowerandbecausetheyarereadilyavailablenearlyeverywhereintheworld.Therearemanydifferentsizesanddesignsoflead-acidbatteries,butthemostimportantdesignationisthattheyaredeepcyclebatteries.Lead-acidbatteriesareavailableinbothwet-cell(requiresmaintenance)andsealedno-maintenanceversions.AGMandGel-celldeep-cyclebatteriesarealsopopularbecausetheyaremaintenancefreeandtheylastalotlonger.