Outback UL 1741 SA Grid Support Summary

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GridSupportingFunctions/UL1741SA
NewInverterRequirementstoSupportaHighPercentageSolarGrid
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BACKGROUND
Whenthesolarindustryfirstfoughtthebattletoconnecttothegridandstandardizeinterconnection
requirementsinthefirsteditionofIEEE1547,theutilitiesmandatedthatalldistributedgeneration,
includingsolar,complywithextremelynarrowwindowsofoperation–ifthevoltageorfrequency
strayedoutsidenarrowbounds,inverterswereforcedtotripoffline.Ineffect,theutility’spositionwas
intheeventofagriddisturbanceforanyreasonitwas“everybodyoutofthepool.”Fiveminutesafter
thingswerebackundercontrolandstabilized,inverterscouldreconnectandgetbacktobusiness.
Thesenarrowwindowsforcedinverterstobe“twitchy”andsomeinstallationshadtroublewith
nuisancetrips,buttherewaslittlethatinstallerscoulddootherthanattempttocompensateby
oversizingfeederconductors.
Perhapsevenmoreimportantly,theoriginalIEEE1547standardprohibitedinvertersfromhelping
regulatevoltage;invertersweremandatedtooperateatunitypowerfactor–nomattertheneedsof
thegrid,andtheywerenotallowedtomodifytheiroutputtohelpstabilizeandsupportthegrid.This
wasn’taproblemintheearlydays,butassolarandwindhaveexplodedinpopularitythisbecomesa
limitingfactorasutilitiesinsuccessfulsolarregionssaytheirfeedersandcircuitsarereachinglimitsdue
tovoltagerise.Tomitigatethis,theiroptionsareoftenlimitedtoimposinginterconnectionrestrictions
orincreasedcostsondeveloperstoaddresshostingcapacityconstraints.
CURRENTSITUATION
Today,distributedresourceslikesolarandwindareasubstantialpartoftheenergymixinagrowing
portionoftheUS.StateslikeCaliforniaandHawaiiroutinelysetnewrecordsforthepercentageof
renewableenergyprovidedacrossthegrid.Utilitiescannolongeraffordtohavesolartripofflineinthe
eventofagriddisturbance–theyneedallgenerationtostayonlineasmuchaspossible,toridethrough
thedisturbanceandhelpclearthefault.Inaddition,theinvertersconnectedtothatsolarcanprovide
additionalgridsupportingfunctionstohelpfurtherincreasethehostingcapacityinaregion,toenable
evenmoresolartobeinterconnectedonagivenfeederorcircuit.
UL1741SA
Toaddressthesecriticalneeds,utilitieshavebeenchangingtheirgridinterconnectionstandardsto
allowandevenrequiregrid‐supportingfunctions.Asafirststep,IEEE1547wasamendedin2014to
removerestrictionsagainstinvertersactivelyparticipatinginvoltageregulationandtoallowvoltage
controlanddisturbanceride‐through.Atthesametimeutilities,developers,manufacturersandother
industrystakeholdersworkedcollaborativelytodefinearangeofnew“SmartInverter”functionswhich
inverterscanprovidetosupportthegridandallowincreasedpercentagesofsolar,followedbyanew
expansionofUL1741totestandcertifythesenewfunctions.ThisnewcertificationisknownasUL1741
SA,orSupplementalAnnex.