My Home Photovoltaic PV Power System 光伏.docx

My Home Photovoltaic PV Power System 光伏.docx

《My Home Photovoltaic PV Power System 光伏.docx》由会员分享，可在线阅读，更多相关《My Home Photovoltaic PV Power System 光伏.docx（9页珍藏版）》请在冰豆网上搜索。

MyHomePhotovoltaicPVPowerSystem光伏

MyHomePhotovoltaic（PV）PowerSystem

Latestaddition:

AdayinthelifeofmyPVsystem

I'velongbeenfascinatedbyelectricpowersystems,especiallyonesthatindividualscanownandoperate.DuringtheannualFieldDayhamradiocontestthatstressesindependentsourcesofelectricpower,Ialwaysseemedtohavemorefunplayingwiththegeneratorsthanactuallyoperatingtheradios.

Sowhenafriendandcolleague,MikeBrock（WB6HHV）,startedaphotovoltaic（PV）powersystemonhishouse,Igotinterestedindoingoneonmine.IthelpsthatCaliforniahasabundantsunlightandsomeofthemostPV-friendlylawsandregulationsinthecountry.Theseincludeanet-meteringlawthatrequirestheelectriccompanytobuymysurpluselectricityatthefullretailprice,andastate-fundedbuy-downprogramthatsubsidizespartofthecostofsucha"gridtied"PVsystem.

A"gridtied"PVsystemoperatesinconjunctionwithaconventionalelectricutilityfeed.IfthePVsystemproducesmorepowerthanneededtooperatelocalloads,theexcessis"sold"totheutility,runningtheelectricmeterbackwardsandgeneratingabillingcredit.WhenthelocalloadsaregreaterthanthepowergeneratedbythePVsystem,e.g.,atnightorwhenlargeloadsarebeingoperated,themeterrunsforward.

PVtechnologyismaturingrapidly,thoughthecostisstillnotlowenoughtocompetedirectlywithutilityelectricrates,evenwiththegovernmentsubsidies.SoImaintainnoillusionsthatI'mdoingthistosavemoney.NoramIoneofthoseloonyY2Ksurvivalists.I'mdoingitbecauseofalong-standinginterestinthetechnology.Ialsogetsomesidebenefits,suchasaUPS（uninterruptablepowersupply）thatcanrunmycomputersforhoursintheeventofapowerfailure.

SolarPanels

HereyoucanseethetwelveAstropowerAP1206solarpanelsonmyroof.TheywereinstalledbyCarlson'sSolarofHemet,California.Theyareconfiguredasthreestringsoffourpanelseach.Eachpanelconsistsof36cellsproducinganominal12VDCunderload,soeachstringproducesanominal48V（theno-loadvoltageisconsiderablyhigher,about80V）.

Theroofonwhichthepanelsaremountedslopestothesouth-southwestatabout20degrees.Ideallytheywouldfaceduesouth,butthatwouldhaverequiredmorecomplexmountingbrackets.Besides,itisfrequentlycloudyintheearlymorningshereinSanDiego,withthecloudsburningoffbylatemorning.Amorewesterlyorientationfavorstheafternoonwhenitismorelikelytobesunny.Italsofavorsproductionwhenelectricratesareattheirhighest（moreaboutthislater）.

Thepanelcablingis10-gauge2-conductorTypeTCcable,moistureandsunlightresistant.Thecablespenetratetheroofinaconventionalweatherheadusedforutilityserviceentrances.Thecablinggoesin1"flexconduittoaTraceTCB10PVCombinerBoxintheattic.Three#6wires（DC+,DC-andground）runfromthecombinerboxin1"flextothegarage.

SystemElectronics

Thearraypowerentersthebackwallofmygarage,whereIinstalledaTraceSW4048sinewaveinverter,aTraceDCdisconnect,a48volt220amp-hourbatterybankusingTrojanT-105commoditygolfcartbatteries,andaCrusingEquipmentCompanyE-meterbatterymonitor.AconventionalACsubpanelontheinverteroutputfeedsbranchcircuitsaroundthehousewithvarious"protected"loads,suchasmycomputerandnetworkinggearandmyVCR（soIwon'tlosemyprogramsintheeventofapowerfailure!

）

Hereyoucanseethebackwallofmygarage.Theconduitfromthearraysisattherightsideofthephoto;itenterstheDCbreakerpanel（theuprightrectangularwhiteboxwithahorizontalgreenstripe）.Afterpassingthroughcircuitbreakers,thearraypowerflowstoaTracePhotovoltaicGroundFaultProtector,anoverpricedandlargelyuselessdevicethatisnonethelessrequiredbysection690-5oftheNationalElectricalCode.ThePVGFPismountedinthegreyboxatthelowerright.

AfterpassingthroughthePVGFP,thearraypowerflowsthrougharelayinthePVGFPmountingbox.Thisrelayopenswheneverthebatteryvoltageexceedsaprogrammedlevel.

Undernormaloperation,therelayisalwaysclosedasanyexcesspowerfromthearraysisautomaticallysoldbacktotheutility.Thiskeepsthebatteryvoltagefromeverreachingthepointthatwouldopentherelay.Butthisrelayisimportanttoprotectmybatteriesintheeventthegridisnotavailableasa"diversionload".E.g.,theinvertercouldfail,acircuitbreakercouldopen,orthegridcouldgodown.

Therelaydoeslacktwofeaturesofasolidstatecontroller:

amulti-stagebatterychargingprogram,andanighttimecutout.Becausemysystemisgridtied,themultistagebatterychargerprogramisnotveryusefultome.Mybatteriesarenormallyfullycharged,andiftheyaren't（e.g.,afterapowerfailure）theTraceinverteralreadyhasamultistagebatterycharger.ThelackofanighttimedropoutmeansthatunlessIopenthearraybreakeratsundown,I'llgetabout200mA（about10watts）ofbackfeedfromthebatteryintothepanelsatnight.Icouldstopthiswithdiodesonthepanelfeeds,butthepowerlossissosmallthatIwouldprobablylosemoreduringthedayinthevoltagedropacrossthediodesthanI'dsaveatnight.Therelaycoilitselfdrawsanother2-3watts.

Thebatteriesareinthebrownboxatthebottomcenterofthephoto.Imadetheboxoutof3/4"MDF（mediumdensityfiberboard）.Thetopslopesuptowardthebacktoencouragehydrogengasproducedbythebatteriestoflowintothe3"ventlineconnectedtotheleftrearcornerofthetopofthebox.Thislinecarriesthehydrogentojustbelowaturbineventintheroofofmygarage.（Personally,Ibelievehydrogeninagarageisalotlessdangerousthanordinarygasoline;whilegasolinevaporscollectandlingernearthefloor,hydrogenrapidlydissipates.Buttheinspectormademedoitanyway.）

ThebatteryisconnectedbackthroughtheDCbreakerboxthroughabig175AcircuitbreakertotheTraceinverter,thebigwhiteboxjustabovetheDCbreakerpanel.Becausetheinvertercancarrysubstantialpower,thecablesherearequiteheavy（2/0）.

ThetwogreyboxesatthetopcenterofthepictureareconventionalACsubpanels.TheoneontheleftisanexistinggaragesubpanelIputinwhenIgotmyEV1andIinstalledtheMagnechargerEVcharger（ontheleftsideofthepicture）.Theright-handsubpanelisconnectedtotheoutputoftheinverterandsupportsthespecialbranchcircuitsforthe"protected"loads（protectedagainstpowerfailure,thatis）.

Theblackcordhangingfromtheleftsideoftheinverterisforagenerator.Intheeventofanextendedpoweroutage,Icansetupaportablegeneratoranduseittosupplementthepowerfromthesolararraystooperatetheprotectedloadsandtorechargebatteries.

Batteries

Here'saviewlookingdownintothebatterybox.

Theinterconnectsare2/0buildingwirefromHomeDepot.Itwasrelativelycheap（$0.85/foot）butarealpaintoworkwith;verystiffandunforgiving.Thecablesleadingoutoftheboxontherightsideare2/0flexible"boatcable".Itismucheasiertoworkwith,butitisveryexpensive（$7.50/footatBoat/US,alocalmarinestore）.Theyellowcableisforabatterytemperaturesensoraffixedtothebatteryontherightrear.Thebluewiretapsthebatteryatthemid-pointtosupply24VDCforthee-meter;notethein-linefuseholdernearthebatteryterminal.Althoughtappingabatterylikethiscantheoreticallycausethepacktobecomeunbalanced,inpracticethedrainlowenoughthattheimbalanceisisquicklycorrectedbyroutinebatteryequalization.

Thebottomofthebatteryboxconsistsofthree2x6swithgapsbetweentoallowairtocirculateupfromventilationholesdrilledinthesidesofthebox.Undertheboxisasheetofpolyethylenetocatchanyacidspills.BeforeputtinginthebatteriesIsprinkledaboxofbakingsodaintotheboxtohelpneutralizeanyspilledacid.

DCwiring

Here'sacloserlookattheDCbreakerpanel:

TheE-meterismountedina2"knockoutontheupperleftside.The175Ainverterbreakerisinthecenterofthebox.Thearraycomesinontherightsidethrough1"flexibleconduit,andthe2/0cablestotheinverterleavein2"PVContheupperright.Notethewhitetapearoundoneoftheinvertercablesindicatingthatitisagroundedneutral.Itisconnectedtoa500A50mVbatterycurrentshuntfortheE-meter.Totherightofthesametapedcableisanegativebusbar.Thearraynegativeleadsconnecthere.

Thethreearrayhotleads（red）goto15ADCcircuitbreakersmountedattheupperright,upperleftandlowerleft.ThecombinedoutputofthesethreebreakerspassesdowntothePVGFPmountedinthegreyboxatthelowerright.

PVGroundFaultProtector

Thisisthegroundfaultdetector.ItisnothingmorethantwomechanicallygangedDCcircuitbreakers.Theoneontherighttripsat1amp;theoneontheleftisactuallyaswitchratedat100amps.The1-ampbreakerisshuntedbya50kohmresistor.Whenclosed,the1-ampbreakerconnectsthenegativeDCbus（thewhitewire,signifyingthatitisthesystemneutral）toearthground（thegreenwirewithayellowstripe）;thisistheonlyplacewheretheDCneutralisgrounded.The100Aswitchconnectsthecombinedarrayoutputtotheinputofthechargecontroller.

Theblackdevicehangingoffoneoftheredwiresisaclamp-onDCammetermeasuringarrayoutputcurrent.

Intheeventofafaultbetweenapositivelead（batteryorarray）togroundinexcessof1amp,the1ampbreakerwilltripandopenthe100Aswitchwithit.Thiswillinterruptthegroundfaultexceptforasmallamountofcurrentthatwillcontinuet