changing energy mix and its impact on grid stability
TRANSCRIPT
2â CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH ZurichââChangingâenergyâmixâandâitsâimpactâonâgridâstability
Content
Introduction 3
Challenges for grid stability from renewables integration 4Withâtheâmoveâtoârenewablesâandâretirementâofâthermalâbaseloadâgenerationâplantsâ(coal,âgas,ânuclear),âwhatâareâtheâtopâchallengesâfacingâgridâstability,âandâhowâareâtheyâbeingâaddressed?â 4
Whatâisâtheâimpactâofâinvertersâonâoverallâsystemâstrengths?ââ 5
Howâdoâtheâtopâchallengesâdifferâbyâcountry?â 5
WithâtheâmoveâtoâmoreâwindâandâPhotovoltaics,âtheâinertiaâinâtheâsystemsâwillâbeâreduced.âToâwhatâextentâisâthisâshiftâimpactingâtheâgridâstability,âandâwhatâareâtheâpossibleâmitigationâmethods?â 6
Managing the challenges 8Whoâisâresponsibleâforâmanagingâreactiveâpower,âshort-circuitâcurrent,âandâfrequencyâstabilityâonâtheâgrid?â 8
Howâareâtheyâaddressingâtheseâgrowingâissues?â 8
Canâtheâuptakeâofânuclearâenergyâsmoothenâoutâtheânegativeâeffectsâonâgridâqualityâfromâtheâdecommissioningâofâcoalâplants?ââ 9
Willâtheâriskâofâpowerâblackoutsâincrease?ââ 9
Conclusion and Future Outlook 11
Acronyms 12
Disclaimer 13
Contributors 14
References 15
CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH Zurich âChangingâenergyâmixâandâitsâimpactâonâgridâstabilityâ 3
Introduction
Theâglobalâenergyâsectorâisâtransformingârapidlyâtowardsâlessâcarbon-intensiveâenergyâsystems.âManyâdevelopedâcountriesâhaveâsetârenewableâenergyâtargetsâthatâareâbackedâbyâpolicyâdirectives.
Inâtheâearlyâstagesâofâthisâtransition,ârenewableâenergyâassetsâhadâlittleâimpactâonâgridâstability.âDueâtoâtheirâlowâpenetrationâlevel,âtheyâcouldâbeâeitherâconnectedâorâdisconnectedâasârequired.
However,âwithâaâgrowingâshareâofârenewableâsourcesâinâtheâenergyâmix,âfurtherâintegrationâofârenewablesâposesâanâincreasingâchallengeâtoâpowerâsystemâstabilityâdueâtoâitsâimpactâonâvolatilityâofâpowerâflowâpatterns,âreactiveâpowerâsufficiencyâandâsystemâinertia.
Givenâtheâincreasingâshareâofârenewableâenergyâinâtheâenergyâmix,âweâexpectâthatâmanagingâgridâstabilityâbecomesâaâchallengeâgoingâforward.âGridâstabilityâincidentsâhaveâalreadyâstartedâtoâemerge,âforâexample,âinâAustraliaâ[2],âwhereâtheâblackoutâinâSouthâAustraliaâonâ28âSeptemberâ2016âisâsometimesâreferredâtoâasâtheâfirstâknownâblackoutâlinkedâtoâhighâpenetrationâofârenewableâenergyâ[3].âEvenâthoughâitâisâimportantâtoâstressâthatâtheâblackoutâwasânotâcausedâbyârenewableâenergyâsourcesâ(RES)âonly,âbutâalsoâbyâvariousâdamagesâ(e.g.,âhigh-voltageâpylons)âdueâtoâaâone-in-fifty-yearâstorm,âtheâeventâmadeâaâcaseâforâmoreâresilientâelectricityâgridsâwithâaâhighâshareâofârenewables.âInâtheirâfinalâreport,âtheâAustralianâEnergyâMarketâOperatorâ(AEMO)âconcludedâthatâtoâavoidâsuchâeventsâinâtheâfuture,âoperatorsâneedâtoâincreaseâsystemâinertia,âtheâfrequencyâofâcontrolâservicesâandâtoâstrengthenâtheâoverallâsystemâ[4].âTheâAustralianâexampleâhighlightsâtheâchallengesâtoâovercomeâasâweâtransitionâtowardsâaâdecarbonisedâelectricityâsupply.â
Inâthisâpaper,âSwissâReâandâtheâReliabilityâandâRiskâEngineeringâLaboratoryâatâETHâZurichâdiscussedâaâseriesâofâquestionsâonâtheâgridâstabilityâtopic.âTheâdiscussionâaddressedâtheâkeyâchallengesâfromâtheâincreasingâshareâofâRESâwithinâtheâenergyâmix,âhowâtheyâcanâbeâmanaged,âandâwhatâsystem-levelâsolutionsâareâavailable.
Managingâsystemâreactiveâpowerâisâhowâoperatorsâensureâthatâvoltageâlevelsâinâtheâsystemâremainâwithinâaâgivenârange,âaboveâorâbelowânominalâvoltageâlevels.âSystemâinertiaârefersâtoâtheâkineticâenergyâstoredâinâlargeâgeneratorsâârotatingâmass,âsuchâasâthoseâfoundâinâfossil-fuelâbasedâpowerâplants.âSystemâinertiaâisâvitalâforâmaintainingâaâstableâfrequencyâlevel.âSteadyâandâpredictableâpowerâflowâpatternsâfacilitateâtheâsuccessfulâresponseâofâsystemâoperatorsâagainstâunanticipatedâdisturbancesâ[1]
4â CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH ZurichââChangingâenergyâmixâandâitsâimpactâonâgridâstability
Challenges for grid stability from renewables integration
Withâtheâmoveâtoârenewablesâandâretirementâofâthermalâbaseloadâge-nerationâplantsâ(coal,âgas,ânuclear),âwhatâareâtheâtopâchallengesâfacingâgridâstability,âandâhowâareâtheyâbeingâaddressed?
RESâareâexpectedâtoâaccountâforâoverâhalfâofâ2021âsânewâenergyâgenerationâportfolio.âAlmostâhalfâofâthisâuptakeâisâexpectedâtoâoccurâinâChina,âfollowedâbyâtheâUnitedâStatesâofâAmerica,âtheâEuropeanâUnion,âandâIndiaâ[5].â
WithâincreasingâpenetrationâofâRESâareâtheâretirementâofâthermalâbaseloadâgenerationâplants,âthreeânewâchallengesâariseâtoâmaintainâgridâstabilityâ[6]:â
1.â Ensuringâsufficientâflexibilityâforâpowerâsystemâoperationsâandâsupply2.â Tacklingâincreasedâoperationalâcomplexityâofâtheâpowerâsystem3.â Integratingâinverter-connectedâdevices.
Ensuring sufficient flexibility while managing increased operational complexityPower system flexibilityâisââtheâabilityâtoâadaptâtoâdynamicâandâchangingâconditions".âExamplesâofâsuchâabilityâincludeâbalancingâsupplyâandâdemandâbyâtheâhourâorâminute,âorâdeployingânewâgenerationâandâtransmissionâresourcesâoverâaâperiodâofâyearsâ[7].â
FlexibilityâisâparticularlyâdesirableâgivenâtheâpaceâwithâwhichâtheâelectricâpowerâsystemâisâchangingâandâthatâmoreâRESâandâotherâsmartâenergyâtechnologiesâ(e.g.,âelectricâvehicles,âatâdifferentâelectricityâvoltageâlevels)âareâbeingâintegrated.â
Onâaâtransmissionâlevel,âflexibilityâcanâcomeâfromâtheâdispatchableâenergyâgenerationâplants,âsuchâasâgas-firedâandâhydroelectricity,âorâitâcanâcomeâfromâtheâpowerâexchangeâwithâneighbouringâcountries.âDependingâonâtheâpotentialâofâhydropowerâandâtheâdegreeâofâconnectivityâbetweenâneighbouringâcountries,âsystemâoperatorsâcanâdecideâtheâbestâoptionâtoâpursue.
Goodâconnectivityâbetweenâneighbouringâcountriesârequiresâsmoothâcoordinationâamongâtheâtransmissionâsystemâoperatorsâ(TSOs)âandâbetterâusageâofâtheâinterconnectorsâwithâreducedâsafetyâmarginsâtoâmanageâpotentialâoverloads.âFurthermore,ânewâtransmissionâinfrastructureâwillâalsoâbeârequiredâ[6].
Atâaâdistributionâlevel,âfurtherâflexibilityâcanâbeâprovidedâbyâDemandâSideâManagementâ(DSM)âand,âpotentially,âbidirectionalâelectricityâflowsâbetweenâtheâgridâandâlocalâenergyâstorage,âsuchâasâbatteryâsystemsâandâelectricâvehicles.âInâaddition,âcouplingâtheâpowerâsectorâwithâotherâenergyâsectorsâ(e.g.,âheatâandâgasâsectors)âprovidesâflexibilityâoptionsâbothâatâtheâdistributionâlevelâ[8]âandâatâtheâtransmissionâlevelâ[9],â[10].â
Energyâtransitionâisâexpectedâtoâaffectâpower system operationsâ[6].âWithâtheâintegrationâofâlargeâshareâofâRES,âinâparticularârooftopâsolarâPhotovoltaicâ(PV)âitâcanâbeâanticipatedâlargeâpowerâinjectionâfromâdistributedâgeneratorsâduringâpeakâloadâhours.âThisâwillâleadâtoâaâfewâchallenges.âFirstly,âtheâlargeâpowerâinjectionâwillâaffectâtheânetâloadâpatternsâand,âasâaâresult,ârequiresâadjustmentâtoâtheâcurrentâpeakâloadâprovidersââoperationâ(hydroâandâgas).âSecondly,âconventionalâstorageâunitsâsuchâasâhydroâdamsâandâpumpedâstorageâmayâneedâtoâadjustâtheirâoperationalâbehaviourâsignificantly.âThirdly,âtheâincreaseâinâvariableâgenerationâwillâdemandâconventionalâunitsâ(flexibilityâproviders)âtoâreactâmoreârapidlyâtoâbalanceâenergyâgenerationâandâdemand.âLastâbutânotâleast,âincreasingâpowerâgenerationâfromâdistributedâsources,âcoupledâwithâtheâflexibilityâpotentialâfromâdistributedâbatteriesâandâDSM,âwillârequireâmoreâcoordinationâbetweenâTransmissionâSystemâOperatorsâ(TSOs).âandâDistributionâSystemâOperatorsâ(DSOs).âTheâanalysesâperformedâinâtheâNexus-eâstudyâ[6]âatâETHâ
Interconnectors areâtransmissionâlinesâconnectingâtheâpowerâsystemsâofâneighbouringâcountriesâandâserveâaâcrucialâroleâinâenablingâlong-distanceâpowerâtransfersâinâinterconnectedâpowerânetworks.â
CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH Zurich âChangingâenergyâmixâandâitsâimpactâonâgridâstabilityâ 5
Zurichâalsoâshowâanâincreaseâinâelectricâpowerâexchangeâbetweenâneighbouringâcountriesâandâthusâimpliesâaâneedâforâmoreâcoordinationâamongâpowerâsystemâoperators.âOverall,âtheâtransitionâisâexpectedâtoâincreaseâtheâchallengesâofâfutureâpowerâsystemsâoperations
Integrating inverter-connected devicesInverter-basedâtechnologies,âsuchâasâPV,âwind,âfuelâcells,âmicroturbines,âbatteries,âandâelectricâvehicles,âwillâplayâaâcrucialâroleâinâenergyâtransitionâ[11].âUnlikeâtraditionalârotatingâgenerators,âtheseâtechnologiesârelyâonâso-calledâinvertersâtoâtransformâtheâdirectâcurrentâ(DC)âelectricityâintoâalternatingâcurrentâ(AC)âelectricity.âHowever,âintegratingâinverter-connectedâdevicesâposesâaâsignificantâtechnicalâchallenge.âTheâinclusionâofâsuchâdevicesâandâtheâsimultaneousâdecommissioningâofâsynchronousârotatingâgeneratorsâhasâtwoâmainâconsequencesâforâtheâsystemâstability:âtheâdecreaseâofâsystemâinertiaâandâtheâreductionâofâshort-circuitâpower.
Lowerâsystemâinertiaâwillâreduceâaâsystemâsâabilityâtoârespondââtoâdisturbances.âAâlowerâshort-circuitâpowerâwillâincreaseâtheâimpedanceâseenâbyâgeneratorsâandâthusâreduceâsystemâstability.âAdditionally,âaâreductionâinâshort-circuitâpowerâwillâleadâtoâaâhigherâmagnitudeâofâvoltageâdips,âimpactingâtheâsystemâfurther.âForâexample,âaâlowerâshort-circuitâpowerâmightâcauseâcommutationâfailuresâonâHighâVoltageâDirectâCurrentâ(HVDC)âlinksâandâimpactâtheâoperationâofâinverter-connectedâgeneratorsâ[12].âTheâNorthâAmericanâElectricâReliabilityâCouncilâ(NERC)âhasâalsoâexpressedâconcernsâaboutâtheâunexpectedâdisconnectionâofâlargeâamountsâofâinverter-connectedâdevices.âInvertersâtypicallyâdisconnectâinâtheâeventâofâabnormalâvoltageâorâfrequencyâdeviationsâtoâprotectâtheâequipment.âHowever,âtheseâinverterâdisconnectionârulesâcanâtriggerâcascadingâfailuresâofâtheâpowerâtransmissionâassetsâandâchangeâtheâdynamicsâofâaâpowerâsystem,âthusâreducingâsystemâstabilityâ[13].âPowerâsystemâstabilityâissuesâstemmingâfromâinverter-connectedâdevicesâisâfurtherânotedâbyâtheâEuropeanâNetworkâofâTransmissionâSystemâOperatorsâ(ENTSO-E)â[12],â[14].
Whatâisâtheâimpactâofâinvertersâonâoverallâsystemâstrengths?â
Theâoutputâcurrentâofâgeneratorsâwithâpowerâelectronicâconvertersâisâmaintainedâwithinâaâconstrainedâthresholdâtoâprotectâtheâsemiconductorâswitchesâagainstâoverloading.âHowever,âthisâcurrentâlimitationâresultsâinâreducedâsystemâstrength,âwhichâisâoftenârepresentedâinâtermsâofâshort-circuitâpower.âAâweakânetworkâ(i.e.,âaânetworkâwithâaâlowâshort-circuitâpower)âfacesâseveralâchallengesâasâenumeratedâbyâInternationalâCouncilâonâLargeâElectricâSystemsâ(CIGRE)âandâNERCââ[22],â[23].âTheâsystemâisâmoreâsusceptibleâtoâvoltageâinstabilityâinâtheâfaceâofâgenerationâandâdemandâfluctuations.âInverter-basedâgeneratorsâhaveâreducedâfault-ride-throughâcapabilityâwhenâintegratedâintoâweakânetworks,âi.e.,âtheyâareâlessâresilientâtoâtheâfaultsâoccurringâinâtheâsystem.âWeakânetworksâareâoftenâmarkedâbyâremoteârenewableâgenerationâthatâmustâbeâtransmittedâoverâlongâdistances;âhence,âaâpotentialâissueâinâsuchânetworksâisâtheâoverloadingâofâtransmissionâassets.âTheâlowâlevelsâofâsystemâstrengthâmayâalsoâintroduceârisksâtoâprotectionâsystemsâ[24]âandâincreaseârelaysââtripâtimeâ[25].
Installationâofâsynchronousâcondensersâcanâincreaseâsystemâinertiaâandâstrength.âTheâgeneratorsâofâphased-outâconventionalâpowerâplantsâcanâbeâretrofittedâforâthisâpurpose.â
Howâdoâtheâtopâchallengesâdifferâbyâcountry?
TheâchallengeâtoâintegrateâRESâwhileâmaintainingâgridâstabilityâdiffersâsignificantlyâbyâcountryâandâregionâdueâtoâtheâcharacteristicsâofâtheirâexistingâenergyâgenerationâmix,âgeographicâvariations,âandâtheâexisting/potentialâdegreeâofâregionalâcooperationâ[44].ââTheâvariabilityâintroducedâbyâRESâcanâbeâoffsetâbyâhavingâflexible,âdispatchableâenergyâsources,âsuchâasâhydropowerâandâgas-firedâgenerationâplants.âTheâbenefitâofâhavingâtheseâplantsâisâthatâtheyâmayââbalanceââanyâdifferenceâbetweenâelectricityâsupplyâandâdemandâasâtheyâdevelop.âForâexample,âSwissâhydroelectricityâproductionâisâhighlyâvaluableâtoâtheâbroaderâEuropeanânetwork,âwhichâisâmoreâdependentâonâ
6â CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH ZurichââChangingâenergyâmixâandâitsâimpactâonâgridâstability
Challenges for grid stability from renewables integration
highlyâvariableâsolarâandâwindâproduction.âHowever,âtheâbenefitâofâtheseâdispatchableâelectricityâsourcesâdependsânotâonlyâonâtheirâshareâofâelectricityâmixâcomparedâtoâthatâofâvariableâRES,âbutâalsoâonâtheâoverallâinterconnectionâofâtheâelectricityânetwork.âAustralia,âforâexample,âhasâpreviouslyâstruggledâwithâmaintainingâstabilityâ[3],â[4]âdespiteâhavingâaâhighâshareâofânaturalâgasâinâtheirâdomesticâelectricityâproductionâportfoliosâ[15];âotherâcountries,âlikeâItalyâandâChina,âhaveâsimplyââcurtailedââ(temporarilyâhalted)âRESâproductionâ[16].âTheâageâandâcarbonâintensityâofâtheâexistingâelectricityâgenerationâfleetâwillâalsoâdetermineâtheâurgencyâwithâwhichâtheânationalâelectricityâgenerationâmixâoughtâtoâchange,âpossiblyâaddingâpressureâtoâintegrateâvariableâRES.
Theâchallengeâofâmaintainingâgridâstabilityâisâfurtherâdependentâuponâtheâgeographicâcharacteristicsâofâtheâcountryâinâquestion.âCountriesâlikeâNorway,âSwitzerland,âCanada,âandâBrazilâcanâbuildâlargeâhydropowerâfacilitiesâdueâtoâtheirâmountainousâterrainâandâtemperateâclimates.âInâcontrast,âcountriesâinâtheâMiddleâEast,âNorthâAfricaâonlyâhaveâaâlimitedâpotential,âandâprojectsâoftenâhaveâaâsignificantâimpactâonâdownstreamâcountries.
Proximityâandâconnectionâtoâotherâcountriesâcanâalsoâbeâbeneficialâforâmanagingânationalâgridâstability.âAâprimeâexampleâisâDenmark,âwhichâmeetsâmoreâthanâ45%âofâdomesticâelectricityâdemandâbyâwindâandâsolarâproduction,âandâbenefitsâfromâextensiveâcross-borderâtradingâtoâmeetâitsâneedâforâflexibilityâ[17].âIncreasingânetworkâconnections,âsuchâasâthroughâhighâvoltageâoverheadâlinesâorâsubseaâcablesâinâislands,âcanâhelpâmanageâgridâstabilityâchallenges.âCountriesâ(likeâUKâforâexample)âhaveâsignificantlyâincreasedâtheirâinterconnectionâcapacityâtoâFrance,âBelgiumâandâNorwayâoverâtheâlastâyears,âwithâmoreâinterconnectionâcapacityâstillâbeingâconstructedâ[18].
Country-levelâchallengesâmayâalsoâbeâmitigatedâdependingâonâtheâdegreeâofâregionalâcooperation,âbothâinâtermsâofâregulationâandâintegrationâofâtheâpowerâsystems.âTheâlevelâofâcooperationâvariesâenormouslyâbetweenâdifferentâregionsâinâtheâworld.âAnâexampleâofâaâtrendâtowardsâstrongâcooperationâandâmarketâintegrationâisâtheâEuropeanâUnion,âwhichâbeganâwithâtheâDirectiveâonâcommonârulesâforâtheâinternalâmarketâinâelectricityâinâ1996.âByâestablishingâtheâAgencyâforâtheâCooperationâofâEnergyâRegulatorsâ(ACER)âthroughâtheâThirdâEnergyâPackageâinâ2009,âtheâEUâhasâestablishedâtheâbasisâforâmarketâintegrationâofâtheâEuropeanâcountries.âSinceâthen,âseveralânetworkâcodesâandâguidelinesâhaveâbeenâdeveloped,âshapingâtheâtransitionâtowardsâanâintegratedâelectricityâmarketâ[19].âEvenâthoughâthereâareâstillâobstaclesâthatâneedâtoâbeâovercome,âtheâEuropeanânationsâalreadyâbenefitâfromâtheirâgeographicâproximityâdueâtoâaâregulatoryâframeworkâforâtechnicalâcooperationâ[20].âByâcontrast,âtheâUSâTexanâelectricityâgridâisâpoorlyâconnectedâtoâotherâregionsâforâhistoricalâreasons,âmakingâitâmoreâdifficultâtoâmaintainâfunctionalityâwhenâlocalâdisruptionsâoccurâ[21].â
WithâtheâmoveâtoâmoreâwindâandâPhotovoltaics,âtheâinertiaâinâtheâsystemsâwillâbeâreduced.âToâwhatâextentâisâthisâshiftâimpactingâtheâgridâstability,âandâwhatâareâtheâpossibleâmitigationâmethods?
Reducingâinertiaâthreatensâpowerâsystemâstability.âSystemâinertiaârespondsâimmediatelyâtoâsuddenâchangesâinâtheâfrequencyâlevel,âforâexample,âdueâtoâanâunforeseenâoutageâofâaâgenerator.âTherefore,âsystemâinertiaâhelpsâbridgeâtheâtimeâuntilâtheâsystemârespondsâtoâtheâunforeseenâchangeâ[1].
Evenâthoughâinverter-connectedâgenerationâcanâtheoreticallyâprovideâvirtualâinertia,âsuchâapproachesâhaveâyetâtoâbeâtestedâandâimplementedâ[26].âOneâofâtheâpossibleâmitigationâactionsâconsistsâofâdeployingâdifferentâformsâofânon-synchronousârenewableâgenerationâandâenergyâstorageâsuchâasâhydropowerâorâpumpâstorageâcapacityâorâflywheels,âwhichâprovideârotaryâturbineâmassâandâfastâreactionsâtoâpowerâimbalancesâ[27].âTheâoptimalâpercentageâofâdispatchableâgenerationâthatâneedsâtoâbeâreadilyâavailableâasâaâbackupâtoâensureâgridâstabilityâandâsupplyâadequacyâdependsâonâtheâentireâgenerationâmix,âi.e.,âtheâavailabilityâofâhydropowerâgenerationâ
CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH Zurich âChangingâenergyâmixâandâitsâimpactâonâgridâstabilityâ 7
andâdistributedâflexibilityâproviders.âFurthermore,âitâdependsâonâtheâgridâconfiguration,âtheâinterconnectionsâandâtheâtradeâwithâtheâneighbouringâcountries.âThisâoptimalâpercentageâisâidentifiedâbyâtheâtransmissionâsystemâoperator,âwhoâhasâtheâmandateâtoâensureâelectricityâsupplyâatâtheânationalâlevel.
WithâincreasingâPVâandâwindâintegration,âreducedâinertiaâisâbecomingâanâimportantâissueâinâmanyâpowerâsystemsâworldwide.âTheâsituationâcanâbeâcriticalâinâcountriesâwithâlowerâtransmissionâcapacitiesâ(longâtransmissionâdistances,âlittleâmeshing,âlimitedâcapacity),âsuchâasâAustraliaâ[28].âInâsuchâcases,âimprovingâtheâinterconnectionâcanâalsoâmitigateâtheâeffectsâofâreducedâinertia.âFinally,âimprovingâtheâfaultâride-throughâofâwindâgenerationâ(whichâdoesâprovideâsomeâinertiaâbutâneedsâtoâstayâconnectedâifâtheâgridâfrequencyâisâdisturbedâbyâaâfault)âcouldâbeâanâadditionalâpuzzleâpieceâtoâmitigateâinertiaâreductionâ[28].
8â CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH ZurichââChangingâenergyâmixâandâitsâimpactâonâgridâstability
Managing the challenges
Whoâisâresponsibleâforâmanagingâreactiveâpower,âshort-circuitâcurrent,âandâfrequencyâstabilityâonâtheâgrid?
Theâresponsibilityâforâmanagingâtheâreactiveâpower,âshort-circuitâcurrent,âandâfrequencyâstabilityâresidesâwithâtheâsystemâoperatorâofâtheâtransmissionâgrid.âInâEurope,âthisâisâtheâtaskâofâTSOs,âwhoâbuildâandâmaintainâtheâhighâvoltageânetworkâandâareâresponsibleâforâitsâoperation,âprocuringâancillaryâservicesâandâensuringâgridâstability.âTypically,âTSOsâoperateâonâaânationalâorâregionalâbasis,âwithâmostâEuropeanâcountriesâhavingâoneâTSOâmanagingâtheâentireâcountryâsâgrid.âByâcontrast,âtheâUnitedâStatesâofâAmericaâhasâseveralâentitiesâmanagingâtheâhigh-voltageâelectricityâgridâonâaâsub-nationalâbasis.âDependingâonâtheirâsize,âtheyâareâreferredâtoâasâindependentâsystemâoperatorsâ(ISOs),âorâregionalâtransmissionâoperatorsâ(RTOs).âUnlikeâtheirâEuropeanâcounterparts,âtheseâentitiesâdoânotâown,âbutâmerelyâmanageâtheâelectricityâgrid,âandâoperateâenergyâasâwellâasâancillaryâservicesâmarketsâ[29].â
Howâareâtheyâaddressingâtheseâgrowingâissues?
Ensuringâsufficientâreactiveâpower,âfrequencyâstability,âandâavoidingâshort-circuitâcurrentsâareâallâkeyâcomponentsâofâaâwell-managedâgrid.âTheseâtechnicalâissuesâareâtoâsomeâextentâaffectedâbyâtheâintegrationâofâRES,âandâareâaddressedâonâdifferentâtimeâscalesâ[6].
Reactiveâpowerâmanagementâisâusedâtoâcontrolâtheâvoltageâlevelâofâtheâgridâandâisâthereforeâaâcrucialâelementâforâmaintainingâgridâstability.âCurrently,âreactiveâpowerâisâsuppliedâmainlyâbyâsynchronousâgenerators,ânamelyâtraditionalârotaryâgeneratorsâlikeâcoal,âgas,âandânuclearâpowerâplants.âWithâtheâphase-outâofâtheseâlargeâsynchronousâgenerators,âotherâsourcesâareâneededâtoâsupplyâtheâreactiveâpowerâdemandâandâmaintainâvoltageâstability.âWindâandâsolarâplantsâhaveâtheâtechnicalâpotentialâtoâprovideâreactiveâpowerâmanagementâandâcanâfillâthisâneed.âTherefore,âTSOsâshouldâincludeâtheseâsourcesâinâtheâprovisionâofâreactiveâpowerâtoâensureâvoltageâstability,âasâisâcurrentlyâdoneâinâGermanyâ[30].âTheâGermanâgridâcodeârequiresâthatâtheâRESâunitsâoperateâupâtoâaâpowerâfactorâofâ0.95âandâ0.90âforâunder-âandâover-excitedâoperation,ârespectivelyâ[31].âAâpowerâfactorâofâ1âmeansânoâproductionâofâreactiveâpower,âwhileâaâpowerâfactorâofâ0âindicatesâ100%âreactiveâpower,âandânoâactiveâpowerâisâproduced.âAlternatively,âreactiveâpowerâcanâbeâprocuredâfromânon-powerâgeneratingâunitsâwithâaâconstantâpowerâfactorâofâ0â[32],â[33],âe.g.,âsynchronousâcondensers,âpassiveâshuntâcompensatorsâ(i.e.,âfixedâorâswitchableâcapacitors,âfilters,âandâreactors),âstaticâshuntâcompensators,âandâseriesâlineâcompensatorsâ(e.g.,âseriesâcapacitors).âSomeâofâtheseâlatterâmeasuresâareâalreadyâcommonplaceâbutâmayâneedâtoâbeâexpandedâtoâmeetâtheâgrowingâneedâforâreactiveâpower.â
TSOsâmustâalsoâmaintainâaâstableâgridâfrequencyâbyâbalancingâgenerationâandâloadâatâallâtimes.âTheâTSOââmaintainsâaâstableâfrequencyâbyâactivatingâpowerâreservesâinâcaseâofâaâdeviationâfromâtheâtargetâfrequencyâofâ50Hzâ[34].âItâisâexpectedâthatâtheârequiredâamountâofâreservesâwillâincreaseâwithâtheâintegrationâofâRESâ[6],âbutâitâalsoâdependsâonâtheâremainderâofâtheâgenerationâmix
Theâreasonsâforâshort-circuitsâareâinternalâ(failureâofâinsulation)âandâexternalâinitiatorsâ(suchâasâinclementâweatherâevents,âforeignâbodies,âlikeâbranches,âmakingâcontactâwithâtheâelectricityâline).âTheâTSOsâregularlyâmaintainâtheirâassetsâ(transformers,âoverheadâlines,âcables,âswitchgear)âtoâavoidâequipmentâfailures.âFurthermore,âtheyâalsoâmaintainâtheâvegetationâcorridorsâaroundâtheâpowerâlinesâtoâavoidâbranchesâcomingâintoâcontactâwithâtheâconductors.âRecently,âTSOsâhaveâbeenâexploringâmachineâlearningâmethodsâtoâdetectâanomaliesâinâpowerâgridâassetsâthatâwillâeventuallyâleadâtoâfailures.
Onâaâfinalânote,âthereâisâwidespreadâunderstandingâthatâsomeâofâtheâresponsibilitiesâofâtheâTSOâmayâbeâshiftedâorâcomplementedâbyâservicesâofferedâbyâtheirâlocal,âlowerâvoltageâlevelâcounterparts,âtheâDistributionâSystemâOperatorsâ(DSOs)â[45],â[46].âTheâinterestâinâhavingâDSOsâtakeâonâgreaterâresponsibilityâinâmanagingâtheâelectricityâsystemâstemsâfromâtheâfactâthatâmanyâchangesâtoâtheâsystemâareâoccurringâatâaâ
CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH Zurich âChangingâenergyâmixâandâitsâimpactâonâgridâstabilityâ 9
consumerâlevelâ[35],â[36].ââResidentialâsolarâPV,âadoptionâofâsmartâappliances,âandâincreasingâsalesâofâelectricâvehiclesâareâallâgoodâexamples.âIncorporatingâtheseâconsumerâtechnologiesâhasâaâdistinctlyâlocalâimpact,âhenceâtheâsuggestionâtowardsâmanagingâthemâonâtheâsameâscale.âThus,âtheâroleâofâDSOsâwillâhaveâtoâchange,ârequiringâthemâtoâtakeâaâmoreâactiveâroleâinâtheâmanagementâofâtheâelectricityâsystem.âThisâchangeâcanâalreadyâbeâobservedâinâGermany,âwhereâtheââRedispatchâ2.0ââregulationârequiresâtheâDSOsâtoâparticipateâactivelyâinâtheâredispatchâprocessâfromâOctoberâ2021.âThisâisâaâsignificantâchangeâfromâformerâtimes,âwhereâorganisingâredispatchâmeasuresâwasâtheâsoleâresponsibilityâofâtheâfourâGermanâTSOsâ[37].â
Canâtheâuptakeâofânuclearâenergyâsmoothenâoutâtheânegativeâeffectsâonâgridâqualityâfromâtheâdecommissioningâofâcoalâplants?â
Theâroleâofânuclearâpowerâinâtheâdecarbonisationâofâtheâelectricityâgridâisâhighlyâdebated.âHowever,ânuclearâpowerâcanâcontributeâtoâaâdecarbonisedâelectricityâsupply,âandâitâisâcurrentlyâtheâworldâsâsecond-largestâlow-carbonâelectricityâsourceâafterâhydropowerâ[38].âWhetherânuclearâpowerâcanâhelpâmanageâtheânegativeâeffectsâofâcoalâphase-outâisârelevantâinâcountriesâlikeâtheâUK,âFrance,âFinland,âRussia,âIndia,âChina,âandâSouthâKorea,âwhereâaboutâ40ânuclearâreactorsâareâunderâconstruction.
Generally,ânuclearâplantsâareâbaseâloaders,âi.e.âtheyâtypicallyârunâatâfullâcapacityâmostâofâtheâtime.âHence,âtheyâareâlikelyâtoâreduceâtheâresidualâdemandâthatârenewableâelectricityâsatisfiesâwhenâonlineâandâprovideâsomeâweather-independentâelectricityâsupply.âAlthoughânuclearâpowerâplantsâareâbaseloadâunits,âtheyâcanâchangeâtheirâpowerâoutputâtoâadaptâtoâchangesâinâdemandâ[39].âTheârateâofâchangeâinâtheâoutputâofânuclearâplantsârangesâfromâ1%âtoâ5%âperâminuteâ[40].âThisâallowsânuclearâpowerâplantsâtoâprovideâfrequencyâcontrolâservices,âincludingâprimary,âsecondary,âandâtertiaryâreservesâ[41].âGoodâexamplesâofâthisâmodeâofâusageâareâtheânuclearâpowerâplantsâinâFranceâ[42].âThus,âitâcanâbeâassumedâthatânuclearâpowerâplantsâcanâpartlyâcompensateâforâRESâvariabilityâandâthusâsmoothenâtheâdecommissioningâeffectsâofâcoal-firedâpowerâplants.âHowever,âtheâcostâatâwhichânuclearâpowerâplantsâcanâsupplyâreservesâmayâbeâhigherâthanâtheâtypicalâprovidersâ(coal,âhydro,âgas).â
Theâhighâavailabilityâofânuclearâpower,âirrespectiveâofâmostâweatherâconditions,âcanâbeâvaluableâduringâlowâsolarâandâwindâavailabilityâtimes.âTheâmainâweather-inducedâunavailabilityâofânuclearâpowerâplantsâisâexpectedâtoâoccurâwhenâhighâatmosphericâtemperaturesâandâdroughtsâareâpresent,âsuchâasâinâaâheatwave.âInâthisâcase,âtheâcoolingâofânuclearâplantsâcanâbeâaffected,âleadingâtoâaâreductionâinâpowerâoutputâorâevenâaâcompleteâshut-downâ[43].
Willâtheâriskâofâpowerâblackoutsâincrease?â
ScenarioâanalysesâonâtheâSwissâpowerâsystemâtransitionâshowâhowâtheâriskâofâcascadingâfailuresâchangesâinâ2020â2050â[6].âCascadingâfailuresâhaveâtheâpotentialâtoâsplitâtheâpowerâtransmissionânetworkâandâleadâtoâelectricalâinstabilityâandâblackouts.âThisâstudyâconsidersâtheâphase-outâofânuclearâgenerationâandâsignificantâincreaseâofâRESâinâtheâsystem,âaffectingâtheâflexibilityâprovidersââoperations.âFurthermore,âunderâsuchâscenarios,âtheâutilisationâofâtheâpowerâgridâchanges.âAlthough,âonâaverage,âtheâloadingâofâtheâgridâdecreases,âthereâisâanâincreaseâinâextremeâassetâloadingâcasesâandâanâincreaseâinâtheâutilisationâofâtheâinterconnectors.âInâgeneral,âtheâincreaseâofâextremeâoperatingâconditionsâandâtheâdecreaseâofâsafetyâmarginsâforâpowerâoverloadsâcanâbringâunprecedentedâchallengesâforâtheâsystemâoperators,âwhichâmayârequireâtheâcontrolâroomâtoâreactâinâaâveryâshortâtimeâframe.âTheâanalysesâshowâthat,âwithâmultipleâfailureâevents,âtheâdemandânotâservedâincreasesâcomparedâtoâtheâdemandânotâservedâofâtheâ2015âreferenceâyear.âHowever,âtheâsystemâsecurityâcanâbeârestoredâtoâaâlevelâsimilarâtoâ2015âwithâtransmissionâsystemâupgrades.âFurthermore,âtheâstudyâshowsâthatâinâscenariosâwhereâtheâamountâofâbatteryâenergyâstorageâsystemsâ(BESS)âandâDSMâincrease,âi.e.,âmoreâdistributedâflexibilityâisâavailable,âtheâriskâofâcascadingâfailuresâdecreases.âAtâtheâmoment,âtheseâ
10â CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH ZurichââChangingâenergyâmixâandâitsâimpactâonâgridâstability
Managing the challenges
analysesâareâsubjectâtoâpronouncedâuncertaintiesâandâassumptions,âandâshouldâbeâconsideredâasâindicatingâgeneralâtrendsâratherâthanâprovidingâexactâquantifications.
Onâaâdifferentânote,âtheâNERCâandâtheâENTSO-Eâhaveâvoicedâconcernsâthatâlargeâamountsâofâinverter-connectedâdevicesâcanâinjectâunprecedentedâcommonâcauseâfailureâmodesâinâpowerâsystemsâ[12],â[13],â[14].âThisâisâoftenâtheâcaseâwhenânewâtechnologiesâpenetrateâmassivelyâinâtraditionallyâconservativeâbusinessesâsuchâasâtheâelectricâpowerâsector..
CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH Zurich âChangingâenergyâmixâandâitsâimpactâonâgridâstabilityâ 11
Conclusion and Future Outlook
Maintainingâgridâstabilityâisâkeyâtoâensuringâintegrityâofâtheâelectricâpowerâsystem.âAsâtheâshareâofârenewableâenergyâsourcesâinâtheâoverallâelectricityâproductionâmixâcontinuesâtoârise,âmaintainingâgridâstabilityâbecomesâmoreâchallenging.âSimplyâput,âpowerâgridsârelyingâonâhigherâcontributionsâfromâvariableârenewableâenergyâsourcesârequireâaâgreaterâdegreeâofâoperationalâflexibilityâthanâthoseârelyingâonâdispatchableâenergyâsources,âsuchâasâthermal,âhydroelectric,âandânuclearâgenerators.âFromâthisâperspective,âthreeâmainâchallengesâariseâforâintegratingârenewableâenergyâsources,ânamely:â
1.â âEnsuringâsufficientâflexibilityâforâpowerâsystemâoperationsâandâsupply2.â âTacklingâincreasedâoperationalâcomplexityâandâreducedâcentralisedâcontrolâofâtheâ
powerâsystem3.â âIntegratingâinverter-connectedâdevices.
Theâscopeâofâtheâchallengeâandâassociatedâmitigatingâstrategiesâdependâstronglyâonâcontext.ââTheâexistingâgenerationâmix,âgeography,âandâregionalâcooperationâ&âpowerâgridâinterconnectionâareâallâcontributingâfactors.âSeveralâpossibleâfutureâdevelopmentsâcanâgreatlyâinfluenceâtheâeaseâandâdegreeâtoâwhichârenewableâenergyâisâintegratedâintoâtheâelectricâpowerâsupply,âincluding:
SignificantâexpansionâofâDemandâSideâManagement Sectorâcoupling,âe.g.,âviaâelectrificationâofâheatâandâtransportâ[47]â Widespreadâadoptionâofâvehicle-to-gridâ(V2G)âchargingâandâdischargingâ
technologyâ[47] Costâandâtechnologicalâbreakthroughsâallowingâforâaâwiderâdeploymentâofâpower-
to-Xâtechnologies,âespeciallyâpower-to-hydrogenâ[47]â[49]â Reconsiderationâofânuclearâpowerâasâanâacceptableâlow-carbonâenergyâgenerationâ
sourceâ[50]
Notwithstandingâtheseâpotentialâdevelopments,âanâarrayâofâstrategiesâforâmaintainingâgridâstabilityâalreadyâexists.âTheseâstrategiesâincludeâincreasingâtheâelectricityânetworkâinterconnection,âensuringâaâwell-functioningâpowerâmarket,âensuringâsufficientâreactiveâpower,âmanagingârenewableâenergyâatâaâlocalâlevel,âandâmaintainingânetworkâassets.âMovingâforward,âsystemâoperatorsâmustâprepareâforâpotentialânewâinvestmentâandâmaintenanceâpriorities,âincreasedâcollaborationâwithâfellowâoperators,âorâtheâneedâtoâadoptânewâbusinessâstructures.âEmployingâallâofâtheseâstrategiesâandâgettingâreadyâtoâadoptânewâdevelopmentsâwillâbeâessentialâtoâfurtherâintegratingârenewableâenergyâsourcesâintoâtheâelectricâpowerâsystem.
12â CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH ZurichââChangingâenergyâmixâandâitsâimpactâonâgridâstability
Acronyms
AC:âAlternatingâCurrent
ACER:âAgencyâforâtheâCooperationâofâEnergyâRegulators
AEMO:âAustralianâEnergyâMarketâOperator
BESS: BatteryâEnergyâStorageâSystem
CIGRE:âInternationalâCouncilâonâLargeâElectricâSystems
DC:âDirectâCurrent
DSO:âDistributionâSystemâOperators
DSM:âDemandâSideâManagement
ENTSO-E:âEuropeanâNetworkâofâTransmissionâSystemâOperatorsâforâElectricity
HVDC:âHighâVoltageâDirectâCurrent
ISO:âIndependentâsystemâoperators
NERC:âNorthâAmericanâElectricâReliabilityâCorporation
PV:âPhotovoltaic
RES:âRenewableâEnergyâSource(s)
RTO:âRegionalâtransmissionâoperators
TSO:âTransmissionâSystemâOperator
CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH Zurich âChangingâenergyâmixâandâitsâimpactâonâgridâstabilityâ 13
Disclaimer
Theâentireâcontentâofâthisâreportâisâsubjectâtoâcopyrightâwithâallârightsâreserved.âTheâinformationâmayâbeâusedâforâprivateâorâinternalâpurposes,âprovidedâthatâanyâcopyrightâorâotherâproprietaryânoticesâareânotâremoved.âElectronicâreuseâofâtheâdataâpublishedâinâthisâreportâisâprohibited.âReproductionâinâwholeâorâinâpartâorâuseâforâanyâpublicâpurposeâisâpermittedâonlyâwithâtheâpriorâwrittenâapprovalâofâSwissâRe,âandâifâtheâsourceâreferenceâisâindicated.âCourtesyâcopiesâareâappreciated.âAlthoughâallâtheâinformationâusedâinâthisâreportâwasâtakenâfromâreliableâsources,âSwissâReâdoesânotâacceptâanyâresponsibilityâforâtheâaccuracyâorâcomprehensivenessâofâtheâinformationâgivenâorâforward-lookingâstatementsâmade.âTheâinformationâprovidedâandâanyâopinions,âprojectionsâandâotherâforward-lookingâstatementsâmadeâareâforâinformationalâpurposesâonlyâand/orâsolelyâtheâviewsâorâopinionsâofâtheâauthor(s),âandâinânoâwayâconstituteâorâshouldâbeâtakenâtoâreflectâSwissâReâsâposition,âinâparticularâinârelationâtoâanyâongoingâorâfutureâdispute.âInânoâeventâshallâSwissâReâbeâliableâforâanyâlossâorâdamageâarisingâinâconnectionâwithâtheâuseâofâthisâinformationâandâreadersâareâcautionedânotâtoâplaceâundueârelianceâonâforward-lookingâstatements.âUnderânoâcircumstancesâshallâSwissâReâorâitsâGroupâcompaniesâbeâliableâforâanyâfinancialâand/orâconsequentialâlossârelatingâtoâthisâreport.âSwissâReâundertakesânoâobligationâtoâpubliclyâreviseâorâupdateâanyâforward-lookingâstatements,âwhetherâasâaâresultâofânewâinformation,âfutureâeventsâorâotherwise.âThisâreportâdoesânotâconstituteâlegalâorâregulatoryâadviceâandâSwissâReâgivesânoâadviceâandâmakesânoâinvestmentârecommendationâtoâbuy,âsellâorâotherwiseâdealâinâsecuritiesâorâinvestmentsâwhatsoever.âThisâdocumentâdoesânotâconstituteâanâinvitationâtoâeffectâanyâtransactionâinâsecuritiesâorâmakeâinvestments.
14â CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH ZurichââChangingâenergyâmixâandâitsâimpactâonâgridâstability
Contributors
ETH ZĂŒrich
Prof.âDr.âGiovanniâSansavini
Dr.âPaoloâGabrielli
Dr.âBlazheâGjorgiev
BehnamâAkbari
LindaâBrodnicke
KateâLonergan
RaphaelâWu
Swiss Re
Dr.âThomasâKocher
JanâBerger
WernerâCollenbergâ
CoauthoredâbyâSwiss Re Corporate SolutionsâandâETH Zurich âChangingâenergyâmixâandâitsâimpactâonâgridâstabilityâ 15
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