hiq solar - 20 common mistakes installing pv systems...

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20CommonMistakesInstallingPVSystems21December2015,v1.1IntroductionEventhemostexperiencedprofessionalsmakemistakes,andPVsystemspresentmanyopportunitiesforerrors.Inthispaperwelistsomeofthemorecommonissueswe’veseenorheardaboutoftenenoughtobeworthmentioning.Ourintentionistobebrandagnosticbutwherewecouldn’tresisttheurgetoputinourownpropagandaitsinitalics.Enjoy!

ContentsInverterPhysicalMounting.............................................................................................................2

1. NotLeavingEnoughRoomAroundInverters......................................................................22. MountinginDirectSunlight................................................................................................2

DC-SideElectrical............................................................................................................................23. StringsAren’tConnected....................................................................................................24. StringWiresReversed.........................................................................................................35. SwappedStrings..................................................................................................................36. PoorQualityCrimping.........................................................................................................47. ConnectorsNotLatched......................................................................................................48. ConnectorsExposedtoMoistureWhileOpen....................................................................49. ExcessivelyHighResistanceonDCSide...............................................................................410. NotAccountingforDifferentialThermalExpansion..........................................................411. WiresNotLongEnough.....................................................................................................512. InsulationColdFlow..........................................................................................................5

AC-SideElectrical............................................................................................................................513. ProblemswithGrounding.................................................................................................514. PhaseWiringIssues...........................................................................................................515. PhasePowerImbalance....................................................................................................616. IssueswithExternalVoltageTranslationTransformers....................................................617. HighResistance.................................................................................................................618. BreakerIssues...................................................................................................................619. ProblemswithTerminations.............................................................................................7

Communications.............................................................................................................................720. CustomerInternetConnections........................................................................................7

Acknowledgements........................................................................................................................7

20CommonMistakesInstallingPVSystems 21December2015


InverterPhysicalMounting

1. NotLeavingEnoughRoomAroundInvertersTheenemyherecanbethedesiretohaveeverythinglookingneatinsuchawaythatthereisnotenoughroomaroundtheinvertertoallowittobeaccessedorremovedbyaservicetech.Alternativelyitcanbenotbeingawareofminimumspacingofinvertersthatneedaircirculationoraccesstochangeairfilters.Ifthereareminimumspacingsforaparticularinvertertheywillbespecifiedintheinstallationmanual.

2. MountinginDirectSunlightMostinvertersareratedforoutdooruse.However,mountingstringinvertersonasouth-facingorwestfacingwallisacommonpracticewithpossiblenegativeconsequences.Mostinvertershaveawideoperatingtemperaturerange,butwillde-rateastheyexceedaparticulartemperature–sotheimpactislikelytobeonenergyharvest.Inaddition,manyhavefans,displaysetc.thatwilldegradeovertimewithtemperatureand/orUVexposure,requiringvisitsforrepairorreplacement.Overallit’srecommendedtomountinvertersinashadedlocationifpossible.TrueString™invertersaresealed,havenodisplays,nofansorairfiltersandcanbemountedunderthearray.Otherthanthenormalpowerde-ratingathightemperatureourinverterscanbemountedanywhere.

DC-SideElectrical

3. StringsAren’tConnectedThiscanbeverydifficulttodetectanddiagnosewithlargestringandcentralinverters,butthiserrorisverycommon.EasytoseewiththeTrueStringinverters.Forexample,Figure1showsagraphcomparinginverteroutputsforanarray(a);thelowestperformer(#2766)iseasytoidentify(b).Lookingattheperformancesummaryforthatspecificinverteritisobviousthatonestring(String1)istheculprit(c).

Figure1:Identifyingthelowestperforminginverterinanarray

(a)#

(b)#

(c)#



4. StringWiresReversedVerycommonwherecustomjumpersareused,canevenhavesamegenderconnectorsoneachend.Inadditiontothestringnotproducingpower,itispossiblethatthiscandamagetheinverter.Errorslikethisarelesslikelyifwiringisclearlyidentified,suchasintheinstallationofFigure2below.

Figure2:Clearlyidentifiedstringpolaritiesmakemiswiringharder

5. SwappedStringsThisislesscommon,butwehaveseenit–plusandminuswiresofunrelatedstringsconnectedtoeachinput.Forlargestringinverterswithmanystringsbundledtogetheritcanevenbeeachsideofastringconnectedtodifferentinverters.Aswiththepreviouspoint,clearlabelingateachendofwiringrunsisusuallyworththetime.Withindividualstringmonitoringandtwoseparateinputsonly,itiseasiertoseeontheTrueStringinverterthanwithlargestringinverterswithmanystringswiredinparallel.

Figure3:Connectingwiresfromunrelatedstrings

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ForinvertersthatusetwoormorestringsinparallelperDCinput,itisalsopossibletoaccidentallyconnectthestringsinseriesinsteadofparallel.Thisoftendamagestheinverter.

6. PoorQualityCrimpingUseofthewrongtooltocrimpconnectorscancauseoverheatingofterminals,opencircuitsandburningofconnectors.Useofthewrongtoolisverycommon,butuseofacrimperotherthanthatspecifiedbytheconnectormanufacturerwillviolatecode.

7. ConnectorsNotLatchedAnobviousone,butdifficulttoseevisually.Iftheconnectionisnotmadeitcanbeeasytoseewithgoodmonitoring;themoredangeroussituationiswherethecenterconductorsarenotfullymatedandovertimestarttoarc.

8. ConnectorsExposedtoMoistureWhileOpenThisappliestomodules,homerunsandinverters.Theprojectispartiallyfinishedthendelayed,thenarainstormcomesthrough,itsnowsorwhatever.Homerunshavetheconnectorscrimpedbutnotmatedtogether,andmoisturewicksintothewirejacketandthiscausescorrosionandperformanceandreliabilityissueslongaftertheinstallisover.ThepictureshowsaHiQTrueStringinverterintheprocessofbeinginstalled.Theinvertershipswithcapsonallconnectorstoprotectthemfrommoistureingressduringinstallation.

9. ExcessivelyHighResistanceonDCSideDamageormanufacturingdefectsinmodulessuchasbubblinginathin-filmmodulecancausehighresistancetooccur;thevoltageseemsokuntiltheinverterthetriestodrawpowerfromthemodule,thenthevoltagecollapsesandtheinvertershutsoff.Theinvertertriestorestartandthecyclerepeats.

10. NotAccountingforDifferentialThermalExpansionInthepursuitofaprofessionalandneatlookinginstall,stringwiringispulledtightandzip-tiedtotheracking,butwithoutanythermalexpansionmargin.Hotterdaysandcoldernightscombinedwiththefactthatthethermalexpansionofcopperis2xthatofaluminumrackingcanleadto:

i) Connectorpinsbeingpulledoutofsocketsleadingtodisconnectionand/orarcing

ii) Wirecrimpsbeingpulledapartiii) Strainreliefsbeingbrokeniv) Abrasionofinsulationrepeatedlyovertimeleadingtoshortingandpossiblefire

(Bakersfieldfire,forexample)



Thelongerthewiringrun,thebiggertheeffect.

11. WiresNotLongEnoughSimilarly,cuttingwirestotheexactlengthtoreachtheinvertercanbeaproblem.Firstly,itcostsflexibilityforlaterintheinstallwhenitisdiscoveredthatanystringmiswiringissueshaveoccurred,andthereisn’tenoughsparelengthtoswapthewirestothecorrectterminals.Itcanalsobeaproblemlaterwhentheservicetechhastoswapaninverterouttoadifferentdesign.TheNECrequiresa‘ServiceLoop’ofbetweenhalfandoneturnofwireinsideajunctionboxpreciselyforserviceabilitylater.

12. InsulationColdFlowWherewiresaretightlyandneatlysecuredtoamoduleframeorrackingmemberpassoverasharpcorner,overaperiodofmonthsoryearsthepressureofthecorneragainsttheinsulationcancausetheinsulationtoflowawayfromthepressureuntiltheconductorshortsagainstthemetalframe.

AC-SideElectrical

13. ProblemswithGroundingManyissuesarepossiblehere,rangingfromcodeviolationstosignificantsafetyissues.MostinstallationsrequiretheDCsidetobeungroundednowthatnon-isolated(TL)invertersarecommon,whichsimplifiesthings.Afewlessobviousones:

• Groundingusingdissimilarmetals–canbemetalswithverydifferentgalvanicvalues1suchasbarecopperwirestouchingaluminumframes;canbemetalswithsimilar(butnotidentical)galvanicvaluessuchascopperandtinplustheadditionofcoastalmoisturewithsaltoveralongerperiod.Theresultisobviouslycorrosion.Inthecaseofcoastalconditions,coatingwithdielectricgreaseismessybuteffective

• Paintedenclosurescaneitherbegroundedtorackingetc.withfastenerslistedas‘paintcutting’,orthepaintmustbeclearedoffthegroundingpointduringinstallation

14. PhaseWiringIssues

APhaseNotConnectedUsuallyrelativelyeasytodetect.

NeutralConnectedtoHotPhaseAgain,usuallyrelativelyeasytodetect.

TwoHotPhasesConnectedtoOneSeepicture,twophasesoftheinverteroutputmightaccidentallyconnecttothesamegridphase.Commonlyleadstoaninverterfault.

1http://inspectapedia.com/BestPractices/Galvanic_Scale_Corrosion.php

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15. PhasePowerImbalanceCanbeadesignissue,oranelectricianissue.Withamaximumimbalanceallowedof6kW,thiscanbeanissueincommercialinstallsparticularlywithsingle-phaseinverters.Obviouslyaninherently3-phaseinvertersuchasourTrueStringdoesnothavethisissue.

16. IssueswithExternalVoltageTranslationTransformersThelackofcost-effective208Vinvertersuntilrecentlyhasmeanttheuseoftransformers.Somepossibleissues:

• Neutralnotcarriedthroughthetransformer.Ifcommunicationsbetweeninverterandgatewayisoverpowerline,thiscaninhibitthemtalkingifthegatewayisontheothersideofthetransformer

• Transformershaveparasiticlosses24hoursaday,soitiscommontodisconnectthemovernight,controlledbyatimer.Ifpowertothetimerisinterruptedthearraycanhaveproductivehourswastedformonthsoryearsifnobodynoticesthatthetimeisoffset.

17. HighResistanceGridvoltagemeasuresokuntilpowerisexportedfromtheinverter–becauseofthehighresistancethevoltagethenrises,andcancauseovervoltagetrippingoftheinverter.Thepictureshowsonephaseofa3-phasebreakernottorqueddownproperly,whichresultedinahighresistanceandovervoltagetrippingoftheinverter.

18. BreakerIssuesInadditiontotheexampleabove,breakerscanfailinalotofwaysontheirown,althoughthisismorecommoninoldersystems–theycanfailopenorclosed,orjustonephasecanfailopenorclosedwhenthehandleindicatesallthreephasesareclosedorviceversa.Verydangerous,alwaysde-energizeandtest,testagainbeforetouching–don’ttrustthelabelonthehandle.Ofcoursethereisalsoselectingtherightbreakerinthefirstplace–sizingit,physicalformfactorforthepanelboard,havingtherightinterruptionratingwhichissomethingthatdoesn’t

Shutdown)

(a)) (b))



comeupuntilit’scalledupontostopthebuildingcatchingonfire.TheOCPDInterruptRatingmustbesizedtobethesameorgreaterthantheshortcircuitcurrentcapabilityoftheutilityconnection.Thencoordinatingwiththeotherovercurrentprotectiondevices.

19. ProblemswithTerminationsWhenyouhavealotofthemorthey’rebig,there’salottogetright.Thesecanbeterminals,inverters,spliceboxes,otherconductors.Aretheconnectionstight,letalonetorquedproperly,atleasttight?Forstrandedconductors,arethereanywaywardstrandsthatcouldoccasionallyarcovertothenextconductor?Forbreakersarethewiresterminatingproperly,andthenisthebreakerterminatingproperlyonthebusbars?Andtherecanbeanissuewithcoldflow.Afteraconnectionistorqued,andovertime,thesoftcopperoraluminumconductor“givesway”andcausestheconnectiontoloosen.Itisalwaysadvisabletodoafollow-upretorqueingofmajorconnectionssomemonthsafterinstallation.

Communications

20. CustomerInternetConnectionsUsingthecustomer’sinternetconnectiontokeeptrackofthesystemperformanceisalowcostapproach,butcanbefraughtwithissueslater.ThesecanincludedelaysgettingthesystemconnectedatthebeginningwhilethelocalITdepartmentdragsitsfeetopeningtherightportsontherouter.ItcancatchyoulaterwhentheytakeonanewITguy,orchangesecuritypolicyandclosealltheportsthatdon’tdirectlyaffectthem.Fromthispointofviewcellularmodemsthatareentirelyindependentofthecustomerseemexpensivebutareprobablyworththecost.ForcellularmodemsinfarawayareasitcanbeagoodideatohavethemonanACtimertoautomaticallyandregularlypowercyclethemincaseoflock-up.

AcknowledgementsThankstoBlakeGleasonofSunLightandPower(http://sunlightandpower.com)forhelpwiththisarticle.CopyrightHiQSolar,Inc.,2015www.hiqsolar.com

hiq solar - 20 common mistakes installing pv systems...

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