第 52 巻第 WindandPV 2 号 EnergyIntegrationinDistributionGridsandBidirectionalGridOperations(AsamiTAKEHAMA) RitsumeikanSocialSciencesReview 2016 年 9 月 13 WindandPVEnergyIntegrationinDistributionGrids andbidirectionalgridoperations: AComparativeAnalysisinJapanandGermany AsamiTAKEHAMA ⅰ Abstract:Gridoperationsandkeyrulesenablingintegrationofwindandphotovoltaicsystemsintothe powernetworksystem injapanandgermanywereanalyzedinthisstudy.theresearchfocuseson reversepowerflowfrom lowvoltage(lv)andmedium voltage(mv)gridstoextra-highvoltage(ehv) grids.theresultsshowedthatgermangridoperatorsflexiblytransmitanddistributeelectricityina bidirectionalway,dependingonthepoweroutputfrom renewableelectricity.germangridoperators prioritizepurchaseofrenewableelectricityandtransmitittotheupstream gridasnecessary.excess electricityfrom windandpvsystemsisphysicalytransmitedtoupstream gridsandtoneighbouring zonesasapriority.injapan,gridoperationisunidirectionalandusesadownwardpowerflowbasedon electricityfrom nuclearpowerandlarge-scalecoalpowerplants.nuclearelectricityhasthefirstpriority overalothertypesofelectricitytobetransmiteddownwardfrom 500kVgridstothelowestvoltage gridsandtointer-zonetie-lines.renewableelectricityhasnolegaldefinitionwithregardtoupstream transmission.becausetherenewableenergyactinjapandoesnotobligeutilitycompaniestoexpand theirgridcapacity,therearefew opportunitiesforrenewableenergysourcesinthegridsystem. Therefore,rulesforupstream transmissionandreinforcementofupstream gridsarerequiredforutility companiesinjapan. Keywords: windenergy,photovoltaicenergy,gridintegration,reversepowerflow,upstream transmission,bi-directionalgridoperation,verticalgridload,prioritytransmission,grid capacitydevelopment Introduction Windandphotovoltaic(PV)energysourcesareusefulwaystoreduceCO2emissionsintheelectricity sector.however,distributiongridsystemsarefacingchalengesofhow besttoaccommodatewindandpv energyonalargescalebecausemiddleandlow voltagedistributiongridswerenotoriginalydesignedfor thispurpose.inthisstudy,gridoperationsinjapanandgermanyareinvestigated,withafocusonkeyrules thatenablewindandpvsystemstobeintegratedintothepowernetworkonalargescalebycomparing energypoliciesinthetwocountries. First,bidirectionalgridoperationinthe50HertztransmissionzoneinGermanyisexamined.This researchfocusesonreversepowerflow (Rückspeisung)from low voltage(lv)andmedium voltage(mv) gridstohighvoltage(hv)grids.therelationshipbetweenreversepowerflow andfeed-infrom windand ⅰ Professor,FacultyofSocialSciences,RitsumeikanUniversity
14 RitsumeikanSocialSciencesReview(Vol52.No.2) PVenergywilbeexamined.Griddatainthe50Hertzzoneisusedinthispartofthestudy.Second,thekey rulesthatenablereversepowerflow from windandpvenergyingermanywilbediscussed,including rulesconcerninggridconnection,transmissionandupstream transmissionofrenewableelectricityunderthe ErneuerbareEnergienGesetz(EEG:RenewableEnergySourcesAct) 1,2.Finaly,rulesconcerning connection,transmission,distributionandgridexpansionunderthefeed-intariflaw injapanwilbe analyzed.thereformsnecessaryforthesuccessofthislaw wilbediscussedthroughacomparisonwith gridintegrationpoliciesingermany. 1 GridoperationwithhighpenetrationofwindandPVenergyinGermany 1.1 Negativeverticalgridloadandreversepowerflow Apositiveverticalgridload(VGL)indicatesloadflowfrom the380kvtransmissiongridtothe110kv distributiongridwithavoltagedecreasethroughtransformers,whereasanegativevglindicatesreverse powerflow from the110kvgridtothe380kvgridwithavoltageincreasethroughtransformers. 3 The valueofvglinthisstudyisdefinedasthetotalnetsum ofelectricitythroughaltransformersandtie-lines thataredirectlyconnectedtothe380kvgridinthecontrolzoneofeachtransmissionsystem operator (TSO).Reversepowerflow can occurin sometransformersubstationswith alargecapacityof interconnectedwindandpvsystems,whilesomeurbanorindustrialareashaveapositivevglatthesame time.eveniftheaggregatedvglinatso controlzoneisnegative,thereisapossibilitythattransformer substationsinsomeareaswilstilhaveapositivevgl.vglsaregiveninunitsofmw/15min. 4 Inthispaper,VGL,tie-linetransmission,andinternationaltransmissioninthe50HertzandTenneT zoneswilbeexaminedusinggriddatainunitsof15min,withtherelationshipbetweenfeed-infrom wind andpvenergyasapriority.inthe50hertzzone,windenergycapacityisaround13,4000mw andpv capacityis7,400mw.dataforcontrolareaload,vgl,windfeed-in,pvfeed-in,internationalexchange,and feed-inmanagementareshowninunitsofmw/15min,accordingtosections13(1)-enwg and13(2)-enwg (GermanEnergyIndustryAct).Thegridloadforeachtransmissionlineinthe50Hertzzoneisshownin MW/hour.Aldataareavailableatthewebsiteof50HertzGmbH. 5 1.2 VerticalgridloadandvoltagelevelsofwindandPVenergyintegration ThemagnitudeandtimesofthenegativeVGLhaveincreasedsince2011inthe50Hertzzone(Fig.1). TheamountofnegativeVGLaccountedfor0.68%ofthetotalsum ofelectricitytransmitedbetweenthe380 kvgridand110kvgrid,andhoursofnegativevglaccountedfor3%ofannualhoursin2013.browncoal, largehydro,andhardcoalplantsareconnectedtothe380kvtransmissiongridsinthe50hertzzone. However,91%ofwindcapacityandalmostalPVcapacityinthe50Hertzzoneisinterconnectedtothe 110kVandlowervoltagegrid(Fig.2).Around76%ofPVcapacityinthe50Hertzzoneisconnectedtothe MVgrid,whichindicatesthatfeed-infrom windandpvenergysatisfiestheloaddemandinthelvandmv grids. TheEEG obligesgermangridoperatorstofeed-inandtrasnmitelectricityfrom renewableenergy sources(res)asapriority.therefore,whenfeed-infrom RESexceedstheloaddemandintheLV(0.23or 0.4kV)andMV(20or35kV)grids,theexcesselectricityistransmitedtotheHV grid(110kv)witha voltageincrease.whenfeed-infrom windandpvenergyexceedstheloadinthe110kvgrid,excess electricityistransmitedtothe380kvgridwithavoltageincrease. The380kV/110kV transformersareequippedwithon-loadtapchangersthatcancontrolvoltage
WindandPV EnergyIntegrationinDistributionGridsandBidirectionalGridOperations(AsamiTAKEHAMA) 15 Fig.1.Verticalload(50Hertzzone,Jan.2011 Oct.2014) changescausedbyreversepowerflow.inaddition,almostaltransformersat380kv/110kv,hv/mvand MV/LVareequippedwithboth-directionprotectionsystemstodealwithreversepowerflow.Both-direction protectionsystemshavebeeninstaledinthepastdecade. 6 ThisisbecausetheEEG (2004version)obliged Germangridoperatorstotransmitrenewableenergyelectricityasapriority.Reversepowerflow at 380kV/110kVtransformersoccursonlywhenwindandPVfeed-inisextremelyhighandthecontrolarea loadislow.athv/mv andmv/lv transformers,however,reversepowerflow occursquiteoftenin distributionareasinwhichalargecapacityofwindandpvsystemsareinterconnectedtothegridandthe loadinthedistributionareaislow. 7 Fig.2.Integratedvoltagelevelsofrenewables (50Hertz,Oct.2014) Source:Calculatedfrom EEG-Anlagenstammdaten 8 1.3 Correlationofwindfeed-in,PVfeed-inandreversepowerflow Feed-infrom windandpv systemscanvaryaccordingtoweatherconditions.however,theeeg requiresgridoperatorstofeed-inelectricityfrom windandpvsystemsasapriority.therefore,tsosmust
16 RitsumeikanSocialSciencesReview(Vol52.No.2) ensuresystem stabilityandreliabilityofthegrid,andmustadapttochangesofwindandpvfeed-inatthe sametime.residualload(rl)indicatesifwindandpvelectricityisfed-intothegridasapriority,andwhat amountofthecontrolarealoadmustbesatisfiedwithfeed-infrom conventionalpowerplantsandother renewablepowerplants. RL=L (W +PV) (1) TheRLisdefinedinEquation(1),whereListheloadinthecontrolzone[MW].W isthewindfeed-in, andpvisthephotovoltaicfeed-in[mw].highfeed-infrom windandpvenergyandalowloadinacontrol areacausesalowornegativeresidualloadandalowornegativevgl(figs.3,4,5).vglclearlydecreases Fig.3.Verticalgridloadandhighfeed-infrom windenergy (20 28Dec.2013,50Hertzzone) Fig.4.Verticalgridload,exportandtransmissiontotheTenneTzone (20 29Dec.2013,50Hertzzone)
WindandPV EnergyIntegrationinDistributionGridsandBidirectionalGridOperations(AsamiTAKEHAMA) 17 Fig.5.GridsituationofhighwindandPVfeed-in,lowload,verticalload and curtailmentaccordingtosection 13(2)-EnWG (German EnergyIndestryAct)(22 28March,2013,50Hertzzone). Fig.6.ResidualloadandVGL (50Hertzzone,2013) Fig.7.Windfeed-inandVL (50Hertzzone,2013) atatimeoflowresidualload.thisisbecauseasfeed-infrom windandpvenergyinthedistributiongrid (LV,MV.110kV)satisfiestheloadineachgrid,feed-infrom the380kv to110kv griddecreases. Electricitysuppliedtothe380kVgridismainlyfrom browncoal,hardcoal,andlargehydropowerplantsin the50hertzzone.thereisnonuclearpowerplantinthiszone.thereisaclearcorrelationoftheresidual loadandvglinthe50hertzzone(fig.6).whenwindfeed-inishigh,vgldereases,andtheamountof windfeed-inmainlydeterminesthevglinthe50hertzzone(fig.7). 1.4 Reversepowerflow anduseofdomestictie-linetransmission AtatimeofveryhighwindandPVfeed-in,theVGLinthe50Hertzzonebecomesnegativeatalmost
18 RitsumeikanSocialSciencesReview(Vol52.No.2) al380kv/110kv transformersubstations,exceptinlargecitiessuchasberlinandhamburg.excess electricityinthe110kvgridistransmitedtotheupstream 380kVgridasreversepowerflow andtothe neighbouringtennetzoneandinternationalzones(denmark,poland,andczechrepublic).thecapacity fordomestictie-linetrasnmissionfrom the50hertzzonetothetennetzonetotalsaround5000mw under stableconditions. 9 Ontheotherhand,thecapacityalocationforcross-bordercongestionmanagementin the50hertzzoneisaround2000mw (from 50Hertz)withfourcross-borderconnectionhubs. Theamountofdomestictie-linetransmissionfrom the50hertzzonetothetennetzoneisestimated usingequation(2). Tr-TenneT=(G L) Exp (2) wheretr-tennetisthetransmissionfrom the50hertzzonetothetennetzone[mw],g isthegenerated amountinthecontrolzone,listhecontrolareaload[mw],andexpisthenetexportfrom thecontrol zone[mw]. Correlationsofwindfeed-inwithdomestictie-linetransmissionfrom the50hertzzonetothetennet zone(fig.8)andwithnetexport(fig.9)aresimilar.theamountofdomestictie-linetrasnmissionreached itsmaximum limitofcapacity(fig.8)andthenetexportreacheditsmaximum trasnmissionlimit(fig.9). Fig.8.Windfeed-inandtransmissionto TenneTzone (Oct. Dec.2013,50Hertzzone) Fig.9.Windfeed-inandnetexportinthe (50Hertzzone,2013) 1.5 Tie-linetransmissiontotheTenneTzoneandwindfeed-in Inahighwindfeed-insituation,50Hertztransmissionusesthefolowingthreeroutestotransport excesselectricityfrom windenergytothetennetzone:(a)no.413,no.414(remptendorf-redwiz),(b) No.449(Vieselbach-Mecklar),No.450(Eisenach-Mecklar),and(c)No.491,No.492(Wolmirstedt- Helmstedt).Thisisbecausealargecapacityofthewindenergysystemsislocatedinnorthernareasinthe 50Hertzzone. ThegridloadsoftransmissionlinesatNo.413,No.414,No.449,andNo.450between50Hertzand TenneTareshowninFigs.10(a)and10(b).WindandPVfeed-inandTSO interventionforsystem security
WindandPV EnergyIntegrationinDistributionGridsandBidirectionalGridOperations(AsamiTAKEHAMA) 19 undersection13(1)-enwg and13(2)-enwg (GermanEnergyIndustryAct)andSection11-EEG areshown infig.10(c).theamountofpowerregulatedundersection13(1)-enwg mainlycorrespondstoredispatch from conventionalpowerplants.theamountofpowerregulatedundersection13(2)-enwg inconjunction withsection11-eeg ismainlycurtailment(feed-inmanagement)ofreselectricity. ThesolidanddotedlinesinFig.10(a-c)show 50%and70%capacityuse,whichmeansthegridloads were50%and70%ofthetransmissioncapacityofeachline,respectively.a provisoisthatthereal transmissioncapacitycanvaryaccordingtoreal-timegridsituations.thelinesfor50%and70%capacityuse inthispaperonlyindicatetheminimum value[mw]foreachlineintheyear2012.accordingtoan explanationgivenby50hertztransmission,griduseatlessthan50%capacityhasnoproblemsinacaseof linefailure.however,acapacity 50%to 70%isclosetothelimitiflinefailureoccurs.Ifthecapacityuse is>70%,itisatthelimitinacaseoflinefailure. 10 The50HertzzoneintegratesalargecapacityofwindandPVenergy,inadditionto10GW forbrown coalplants.therefore,the50hertzzoneoftenhasexcesselectricitytransmissiontothetennetzoneandto cross-bordertransmission,exceptatatimeofverylowwindfeed-in,althoughthegridloadinfig.10does notindicatethedirectionofelectricityflowfrom ortothe50hertzzone. (a) (b) (c) Fig.10.Gridloadofdomestictie-linesbetween50HertzandTenneTinDec.2012bylineinhourly values. (a)lineno.449,no.450,(b)lineno.413,no.414,(c)windandpvfeed-inandtso interventionsforsystem security(redispatchandcurtailmentsunders.13(1)and13(2)enwg (EnergyIndustryAct).
20 RitsumeikanSocialSciencesReview(Vol52.No.2) Fig.11.Gridloadofinter-zonetransmissionlines,No.413andNo.414,sortedin orderofgridloads(marchtodec.2012,50hertzzone). Source:Calculatedfrom datafor50hertzgridloadflowbyline ThegridloadatNo.413,No.414,No.449andNo.450oftenreached50%ofthetransmissioncapacity. ThegridloadofNo.413exceeded50%capacityusein1663hoursandNo.414in1620hoursof7336 observedhoursfrom 1 st Marchto31 st Dec.2012(Fig.11).BasedonFigs.8,10and11,50Hertz Transmissionusesdomestictie-linestothemaximum limittotransmitexcesselectricityfrom windandpv energy. 1.6 Bidirectionalgridopertationstofeed-inrenewableelectricityinGermany AlargenegativeVGLinthe50Hertzzoneiscausedbycombinedefectsoffeed-infrom windandpv energy(fig.12).highlevelcapacityuseindomestictie-linesbetween50hertzandtennetsignifiesthat 50Hertztransmissionsystem operatorsusedomestictie-linesfulytotransmitexcesselectricityfrom wind andpvenergyasapriority(fig.11).reversepowerflowoccursquiteoftenfrom LVtoMVgridsandfrom Fig.12.Negativeverticalgridload,windandPVfeed-ininthe50Hertzzone(5th 12thMay2014)
WindandPV EnergyIntegrationinDistributionGridsandBidirectionalGridOperations(AsamiTAKEHAMA) 21 Fig.13.Reverse powerflow from middle volatage to high voltagegrids(energienetzmitezone,measuredat HV/MVtransformersubstations,2013) Source:Calculatedfrom datafrom EnergieNetzMite Fig.14.Reversepowerflow from renewableenergyplantsandvoltagelevels Source:BasedoninterviewswithTSOsandDSOs
22 RitsumeikanSocialSciencesReview(Vol52.No.2) MVtoHVgrids(Fig.13).However,veryfew distributiongridoperators(dsos)disclosetheirreverse powerflow(rückspeisung)datainmvgrids(20kv)orlvgrids(230vand400v). ThesedatasuggestthatGermangridoperatorscarryoutbidirectionalandflexiblegridoperationsto feed-inandtransmitrenewableenergyelectricitytoupstream gridsasapriority,ifnecessary. 11 Asimplified structureofbidirectionalgridoperationandintegratedvoltagelevelsofrenewableenergyplantsingermany isshowninfig.14.thisfigureisbasedonseveralinterviewswithdsosandtsos. 2 GridintegrationrulestoenablebidirectionalgridoperationsinGermany Thekeyrulesforgridconnection,purchaseandtransmissionofrenewableelectricityandbidirectional gridoperationsundertheeeg (2014version)aresummarizedinthissection.TheEEG requiresgerman gridoperatorstoimmediatelyandevenphysicaly,asapriority,purchase,transmitanddistributealofthe electricityproducedfrom renewableenergysourcesorfrom minegas(section11(1)-eeg).thedutiesof prioritypurchase,transmissionanddistributionareimposedongridoperatorswhoaredirectlyconnectedto renewablepowerplantsandonupstream TSOsconnectedwithrenewableplantsindirectly(section11(5)1- EEG).Thesedefinitionsrequireupstream TSOstotransmitelectricityfrom renewableenergyphysicalyas apriority.thisenablesreversepowerflow ofexcesselectricityfrom renewableenergyfrom thelower voltagegridtothehighervoltagegrid. TheEEG requiresthatgermangridoperatorsimmediatelyoptimize,reinforceandexpandtheir networkswiththeavailabletechnologytoensurepurchase,transmissionanddistributionofelectricityfrom renewableenergy(section12(1)-eeg).thedutyofgridreinforcementisevenimposedonupstream grid operatorsuptoavoltagelevelof110kv,evenifrenewablepowerplantsarenotdirectlyconnectedwith them (section12(1)-eeg).gridoperatorsareobligedtoprovidegridconnectionstorenewablepower plants,evenwhenpurchaseofrenewableelectricityisonlypossiblebyoptimizing,reinforcingand expandingthegrid(section8(4)-eeg). Itshouldbenotedthat,accordingtotheEEG,evenupstream gridoperatorsareobligedtocarryout gridreinforcement.hostingcapacityincreaseandoptimizationofvoltagecontrolinthedistributiongrid (LV,MVand110kVgrids)areessentialtoenablereversepowerflow from windandpvfeed-ininlower voltagegrids.thisisbecausereversepowerflow from excesselectricityfrom windandpvsystemsoften causesvoltagerisesindistributiongridsandtransformers,especialyatmv/lvandhv/mvtransformers inlocaldistributiongrids. 12 Therefore,thismandatorycapacityexpansionimposedongridoperators, includingupstream grids,isimportanttoachievereversepowerflowfrom windandpvenergysystemsin distributiongrids. Theoperatorcanbringthecompensationcostforfeed-inmanagement(curtailment)intothecalculation ofgridcharges.however,thegridoperatorbearsthecompensationcostsoffeed-inmanagement,ifthe operatordidnotexhaustaloptionsforoptimizing,reinforcing,andexpandingthegrid(section15(2)-eeg). ThesestrictlegaldefinitionsmakeGermangridoperatorsreinforcethegridsystem toensurepurchaseand transmissionofrenewableelectricity.thesedefinitionsarethelegalbasisofenablingreversepowerflowof renewableelectricityandbidirectionalgridoperationsingermany. 3 GridintegrationpoliciesforwindandPVenergyinJapan Thestructureofthepowersystem injapanandgridintegrationpoliciesforwindandpvenergies
WindandPV EnergyIntegrationinDistributionGridsandBidirectionalGridOperations(AsamiTAKEHAMA) 23 undertheactonspecialmeasuresconcerningprocurementofelectricityfrom RenewableEnergySources byelectricityutilities(hereinafter,therenewableenergyact)aresummarizedinthissection. First,itshouldbenotedthatinJapanthetransmissiongridsystemshaveyettobeseparatedfrom generationbusinesses.theninemajorgenerationcompanies(generalutilitycompanies;hereinafter,the utilitycompanies)ownandoperatethegridsystemsintheircontrolzones.theseninecompaniesare verticalyintegrated powercompaniesthatoperatealaspectsfrom generation,transmissionand distributiontoretailofelectricity(fig.15).theseutilitycompaniesown90%ofthetotalgenerationcapacity injapan,includingnuclearpowerplants(fig.16). Therearenolegaldefinitionsconcerningpriorityconnectionandpurchaseofrenewableelectricity undertherenewableenergyact.thereisaprovisothatwhenthereisarisktostablesupplyandgrid reliability,theutilitycompaniescanrejectaconnectionrequestfrom renewableoperators(article5, paragraph1,(2)-renewableenergyact).sixofthenineutilitycompaniessetacapacityrestrictiononpv andwindenergyintegrationineachcontrolzone(figs.17and18).therearenolegaldefinitionsofthe priorityconnection and prioritytransmission ofrenewableelectricityundertheact.thesixutility companiesinfig.18arealowedtosetcurtailment(outputreduction) withoutcompensation topv operatorswhenintegrationofpvcapacityineachcontrolzoneexceedstherestrictionamount(article6, paragraph7.enforcementregulationsintherenewableenergyact). 13 TheRenewableEnergyActdoesnotobligateutilitycompaniestoexpandandreinforcethegridsystem toaccommodaterenewableenergyplants.toincreaseintegrationofwindandpvsystems,suitablecapacity expansionandreinforcementoflow voltagegrids(0.2kv),6.6kvgridsand66kvgridsareurgently needed,forthefolowingreasons.thevoltagelevelsinthejapanesegridsystem are500,275,154,66,22 and6.6kvand100and200v(withsomeregionalvariationsincontrolzones).theinter-zonetie-linesare mainlyat500kv grids.nuclearandlargefossilfuelplantsareconnectedto500kv grids.hardcoal generatorsandlargehydropowergeneratorsareconnectedto500kv,275kvor154kvgrids.incontrast, manywindenergysystemsareinterconnectedwith66kvor154kvgrids.manypvsystemsareconnected tolow voltage,6.6kvand66kvgrids.therefore,toaccomodatewindandpvsystems,itisnecessaryto expandandreinforcelowvoltage(0.2kv),6.6kv,66kvand154kvgrids. WhenwindandPVsystemsareintegratedintothegridonalargescaleandinaperiodofhighfeed-in from windandpvenergies,excesselectricityineachtrasnformersubstationwilcausereversepowerflow. Thisflow wilcausevoltageincreasesattransformersanddistributiongrids,especialyinthelow voltage and6.6kvgrids.therefore,bothgridcapacityandtransformercapacitymustbesuficientlyexpandedand reinforced.both-directionprotectionssystemsandvoltagecontrolequipmentmustbeoptimizedtoenable reversepowerflow andupstream trasnmissionwithcontrolofvoltagelevelsinapermissiblerange.in addition,theregulatoryframeworkinjapanrequiresutilitycompaniestobeobligedtoexpandandreinforce theirgridsattheirownexpense,includingupstream voltagegridssuchasthe66kvand154kvgrids,ifit isindeednecessarytoaccomodatetherenewableenergyplants. Toenablereversepowerflow attransformersubstationsinthe6.6kvand66kvgrids,upstream transmissionisessential.however,therenewableenergyactdoesnotobligetheutilitycompaniesto prioritizetransmissionofrenewableelectricitytoupstream grids. WindandPVsystem operatorsarestrictlylimitedconcerninguseofinter-zonetie-linesundertherules ofoccto (OrganizationforCross-regionalCoordinationofTransmissionOperators,Japan).Renewable energyoperatorsarerequiredtousebateries,electricitystoragemeasuresorcombinationofother electricitysourcestostabilizefeed-infrom windandpvsystems 14.
24 RitsumeikanSocialSciencesReview(Vol52.No.2) Fig.15.Gridstructureandinter-zonetielinesinJapan Source:Sammarizedfrom theinterim ReportoftheCommiteeontheMasterPlanforReinforcementofInter- ZoneTie-Lines(PowerSystem Reform Commitee,MinistryofEconomy,TradeandIndustry),2012.Looddata basedonthefederationofelectricpowercompaniesofjapan. Fig.16.GenerationcapacityinJapanin2004and2014 Source:Calculatedfrom powergenerationstatisticsfrom METI,feed-intarif schemedatadisclosurefrom METI,andTrendsinPhotovoltaicApplicationsfrom IEA-PVPS Inatimeofcurtailment(suppressionofoutputfrom generators),renewableelectricityhasapriority onlyoverfossilfuelplants.however,nuclearelectricityalwayshasthefirstpriorityoveralotherelectricity tofeed-intotrasnmissiongridsineachzone(undertherenewableenergyact) 15 andtointer-zonetie-lines (undertheoccto NetworkCode).Thiscodestatesthat long-term costrecoverygeneration hasthefirst priorityintransmissiontointer-zonelines.thenetworkcodedefinesnuclearenergyas long-term cost recoverygeneration. 16
WindandPV EnergyIntegrationinDistributionGridsandBidirectionalGridOperations(AsamiTAKEHAMA) 25 Fig.17.Capacityrestrictionsonwindenergyintegrationbymajorutility companies Source:Datafrom METINew EnergySubcommitee,FederationofElectricPower CompaniesJapan. Fig.18.CapacityrestrictionsonPV energyintegration,requestsfor connection,andinstaledcapacity Source:Datafrom METINew EnergySubcommitee,FederationofElectricPower CompaniesJapan. AccordingtotheImplementingRegulationsintheRenewableEnergyAct(hereinafter Implementing Regulations ),whenfeed-infrom renewableenergygeneratorsexceedsdemandineachcontrolzone,utility companiescanimposecurtailments(suppression)ofoutputonrenewableelectricity.utilitycompaniescan escapefrom paymentofcompensationforcurtailmentforupto360hoursayearforpvsystemsand720 hoursayearforwindenergysystems. 17 Inaddition,theregulationexemptsthefolowing designatedutility companies from thepaymentofcompensationwithoutlimitationofhours:hokkaido,tohoku,hokuriku, Shikoku,ChugokuandKyushuutilitycompaniesforPV systems,andhokkaidoandtohokuutility
26 RitsumeikanSocialSciencesReview(Vol52.No.2) companiesforwindenergysystems. 18 4 Conclusions: BidirectionalgridoperationinGermany,unidirectionalgridoperationinJapan GriddatainGermanyshow thatgermangridoperatorsflexiblytransmitanddistributeelectricityina bidirectionalway,dependingonthepoweroutputfrom renewableelectricity.gridoperatorsprioritize purchaseofrenewableelectricityandtransmitittotheupstream gridasnecessary.excesselectricityfrom windandpvsystemsisevenphysicalytransmitedtotheupstream gridandtoneighboringzonesasa priority.germanrenewableenergylaw obligatesgridoperatorstoexpandanddevelopgridcapacity withoutdelay toaccommodaterenewableelectricity.thislegalframeworkhasenabledbidirectionalgrid operations. Incontrast,gridoperationinJapanisunidirectionalandhasadownwardpowerflow basedonsupply from nuclearpowerandlarge-scalecoalpowerplants.nuclearelectricityhasthefirstpriorityoveralother typesofelectricitytobetransmiteddownwardfrom 500kVgridstolowestvoltagegridsandinter-zonetie lines.theutilitycompaniesgiverenewableenergysystemsverylimitedaccesstothegrid,andrenewable electricityhasnolegaldefinitioninregardtoupstream transmission.becausetherenewableenergyactin Japandoesnotobligeutilitycompaniestoexpandtheirgridcapacity,therearefew opportunitiesfor renewableenergysourcestopenetrateintothegridsystem injapan. ThefolowingreformsarenecessaryingridintegrationpoliciesforwindandPVenergyonalarge scaleinjapan.first,generationbusinessesmustbelegalyseparatedfrom gridoperationbusinesses(not onlyoperationofinter-zonetielines,butalsotransmissionanddistributiongridsineachzone).second, utilitycompaniesmustbeobligedtoconnectrenewableenergysourcestothegridasapriorityoveral otherenergysources.aslongasnuclearpowerplantssupplybasepowerasthefirstpriority,windandpv electricitycannotpenetrateintotheelectricitysupplyonalargescale.third,utilitycompaniesmustbe obligedtoexpandandreinforcetheirgrids,includingupstream gridsystems,inareasonableperiodoftime toensurepurchaseofrenewableelectricity,evenifgridexpansionandreinforcementarenecessarytobuild anew connectionwitharenewablepowerplant.inparticular,gridexpansionandreinforcementfor6.6kv, 66kVand154kVgridsareessentialtoensurewindandPVenergyintegration.Fourth,utilitycompanies mustbeobligedtotransmitelectricityfrom renewablestoupstream gridsphysicalyasapriorityifthisis necessary.rulesforupstream transmissionandgridreinforcementofupstream gridsmustbejointly imposedonutilitycompanies.capacityexpansionofgridsisimportantforutilitycompanies,bothtoenable reversepowerflow from excesselectricityoflowervoltagegrids,andtocontrolvoltagelevelsina permissiblerangeaccordingtogridtechnicalcodes.capacityexpansionisurgentlyneededforlower voltagegridswithwhichrenewableenergiesareinterconnected,andforupstream grids.fifth,thecapacity restrictionongridintegrationofpvandwindenergymustbeabolished.sixth,compensationmustbepaid forrenewableenergyoperatorswhencurtailmentissetonrenewableelectricityineachzone. Acknowledgment ThisworkwassupportedbyJSPSKAKENHIGrantNumber26340125andbytheSocietyofRitsumeikan SocialSciences.
WindandPV EnergyIntegrationinDistributionGridsandBidirectionalGridOperations(AsamiTAKEHAMA) 27 Notes 1 GesetzfürdenAusbauerneuerbarerEnergien(Erneuerbare-Energien-Gesetz-EEG,2014). 2 GesetzfürdenVorrangErneuerbarerEnergien(Erneuerbare-Energien-Gesetz-EEG,2012). 3 ThevoltagelevelsintheGermanpowersystem aresuperhighvoltage(shv)fortransmissiongridsat380kv or220kv,highvoltage(hv)fordistributiongridsat110kv,medium voltage(mv)forlocaldistributiongrids at20kv(and35kvinsomeregions,sincethereareregionaldiferencesinmvlevels),andlowvoltage(lv) forlocaldistributiongridsat400vand230v,mainlyforsmal-scaleconsumers. 4 50Hertz:Verticalgridload.availablefrom htp://www.50hertz.com/de/kennzahlen/vertikale-netzlast 5 Datausedinthisstudy:(a)50Hertzzonein2013:Generationouput,Verticalgridload,Controlareaload, Windfeed-in,PVfeed-in,Maßnahmennach 13.1EnWG, 13.2EnWG,Loadflowscross-border,inMW/15 min.(b)50hertzzone:gridloadbyline,hourlydatainmw. 6 BasedoninterviewswithFraunfoherIWES(inAug.2015),HanseWerke(inMay.2014),StromnetzHamburg (insep.2015),50hertz,andamprion(insep.2014). 7 Stetz,T.,Kraiczy,M.,et.al.Technicalandeconomicalassessmentofvoltagecontrolstrategiesindistribution grids.prog.photovolt.res.appl.(2013),doi:10.1002/pip.2331 8 50HertzGmbH:availablefrom htp://www.50hertz.com/de/eeg/veroefentlichung-eeg-daten. 9 Informationfrom 50HertzGmbH.Actualtransmissioncapacitycanchangeaccordingtogridconditions. 10 50Hertz:Explanationongridloadandcapacityusage:htp://www.50hertz.com/en/Grid-Data/Grid-load 11 Stetz,T.,Kraiczy,M.Diwold,K.etal.Transitionfrom unidirectionaltobidirectionaldistributiongrids.iea- PVPS,task14(2014). 12 ConcerningthevoltagerisecausedbyhighPVpenetrationinthelocaldistributiongrid,thenecessarygrid expansionmeasuresareexplainedinthefolowingpapers:stetz,t.,kraiczy,m.diwold,k.country-specific analysis,germany.iea-pvpstask14,subtask2:highpenetrationsofphotovoltaicsystemsindistribution Grids(2014).Stetz,T.,KraiczyM.,et.al.,Technicalandeconomicalassessmentofvoltagecontrolstrategiesin distributiongrids.prog.photovolt.res.appl.(2013),doi:10.1002/pip.2331. 13 Concerning thedesignated UtilityCompaniesshown in Fig.18and theokinawapowercompany. ImplementingRegulationsfortheActonSpecialMeasuresConcerningProcurementofElectricityfrom RenewableEnergySourcesbyElectnicityUtilities. 14 OCCTO:NetworkCodesoftheOrganizationforCross-regionalCoordinationofTransmissionOperators, Japan.Article202,Paragraph3-(i),(amendedApril2016). 15 ImplementingRegulationsfortheActonSpecialMeasuresConcerningProcurementofElectricityfrom RenewableEnergySourcesbyElectricityUtilities.Article6,Paragraph1,Point3-(1). 16 OCCTO,NetworkCodesoftheOrganizationforCross-RegionalCoordinationofTransmissionOperators, Japan.Article202,Paragraph1-(vi),(vi),Article210,Paragraph1(amendedApril2016). 17 ImplementingRegulationsfortheActonSpecialMeasuresConcerningProcurementofElectricityfrom RenewableEnergySourcesbyElectricityUtilities.Article6,Paragraph1,Point3-(1). 18 ImplementingRegulations.Article6,Paragraph1,Point7.
28 RitsumeikanSocialSciencesReview(Vol52.No.2) 風力 太陽光発電の配電網への系統連系, 双方向潮流対応の系統運用について 日本とドイツの比較分析 竹濱朝美 ⅰ 本稿は, 風力 太陽光発電システムを配電網に大量連系するための規則と系統運用について, 日本とドイツを比較した 特に, 配電網から送電網への逆潮流に焦点を当てて分析した ドイツでは, 系統運用者 ( 送電会社および配電会社 ) は, 風力 太陽光発電からの電力を, 出力状況に応じて柔軟に, 低圧および中圧系統から高圧系統へ, さらには, 特別高圧系統に逆潮流させる双方向潮流対応の系統運用を行っている ドイツの系統運用者は, 再生可能エネルギー電力を最優先で給電し, かつ, 上位電圧系統に優先送電する義務を負う 系統運用者は, 風力 太陽光発電からの給電が配電網内の需要を上回る場合, 上位電圧系統 ( 送電網 ) に, 物理的にも電力を上流送電し, 他の送電区域に地域間送電する これに対して日本では, 長期固定電源 ( 原子力, 大型水力, 地熱発電 ) の電力を500kV 送電系統から低圧系統に, 下方一方向潮流で配電する系統運用である 日本では, 原子力発電からの電力を他の全ての電源に優先して, 給電 配電する 地域間送電線の使用においても, 日本では, 原子力発電の電力を最優先で送電する規則となっている 日本では, 再生可能エネルギーからの電力を, 下位電圧系統から上位電圧系統へ優先的に上流送電 ( 逆潮流 ) させる規則は整備されてない 日本の再エネ特措法は, 一般電気事業者に電力網の系統容量の拡張を義務付けていないため, 系統容量の拡張が不十分なままで, 再生可能エネルギー電源の連系を制約している 再生可能エネルギー電源を大量に電力網に連系させるには, 一般電気事業者に対して, 再生可能エネルギー電力の上流送電と電力網の系統増強を義務付ける必要がある キーワード : 風力発電, 太陽光発電, 系統連系, 逆潮流, 上流送電, 双方向潮流対応, 垂直負荷, 優先送電, 系統増強 ⅰ 立命館大学産業社会学部教授