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memo
To: IEPR Committee (Chair Weisenmiller and CommissionerDouglas)
Date: April 29, 2011
From: KEMA, Inc. Karin Corfee, David Korinek, WilliamCassel, Christian Hewicker, J org Zillmer, Miguel PereiraMorgado, Holger Ziegler, Nellie Tong, David Hawkins, and
J orge Cernadas
Copy: Otto Tang
Subject: Distributed Generation in Europe PhysicalInfrastructure and Distributed Generation Connection
KEMA is pleased to submit the attached memo (Memo #1) on distributed generationapplications in Europe. This memo specifically focuses on the physical infrastructure anddistributed generation connection. This memo is the first of three memos that will serve asinterim deliverables for the European Distributed Generation Infrastructure Study. The threememos will eventually be rolled into one consultant report.
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TABLE OF CONTENTS
Introduction...............................................................................................................................................
1
SECTION1: PhysicalInfrastructureinGermany.............................................................................. 2RegionalandQuantitativeAllocationofRenewableEnergyinGermany.................................... 2WindEnergy....................................................................................................................................... 4SolarEnergy........................................................................................................................................ 4BiomassinCogenerationPlants...................................................................................................... 4HydroPower...................................................................................................................................... 5
Network
Structures
in
Germany
..........................................................................................................
5
GridandVoltageLevels................................................................................................................... 5TransmissionGrid............................................................................................................................. 6
ConclusionforGridConnectionofDistributedGeneration.......................................................... 10ImplicationsofDGonGridPlanningandOperation................................................................ 10GridDimensioning.......................................................................................................................... 11GridOperation................................................................................................................................. 11
GeneralandTechnicalRequirementsinGermany......................................................................... 12GeneralRequirements..................................................................................................................... 12TechnicalRequirements.................................................................................................................. 13
TechnicalOptionstoEnsureSecureGridOperation...................................................................... 15General.............................................................................................................................................. 15MostFrequentApplicationofOptionsinGermany................................................................... 18
RecentNetworkPlanningPoliciesandStudies............................................................................... 19SECTION2:PhysicalInfrastructureinSpain................................................................................... 21OverallSystemPlanningandDevelopment.................................................................................... 22NetworkStructuresinSpain.............................................................................................................. 22GridandVoltageLevels................................................................................................................. 22TheSpanishTransmissionSystem................................................................................................ 23TheSpanishDistributionSystem.................................................................................................. 26
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HVDistributionGrid...................................................................................................................... 26MVDistributionGrid...................................................................................................................... 27LVDistributionGrid....................................................................................................................... 30
RenewableEnergySources(RES)inSpain....................................................................................... 31DistributedGeneration................................................................................................................... 32RegionalandQuantitativeAllocationofRenewableEnergy.................................................... 33
RESCompensationArrangementsinSpain..................................................................................... 36InterconnectionTechnicalRequirementsinSpain...................................................................... 37
ImplicationsonPowerGridOperation............................................................................................ 38ConnectionProcesstoTransmissionNetworkinSpain................................................................. 38ConnectionApplicationPhase....................................................................................................... 38
ConnectionProcesstoDistributionNetworkinSpain................................................................... 40RESInstallations(Nonsolar)......................................................................................................... 40PhotovoltaicInstallations................................................................................................................ 41
MainReasonsforSuccessofRESinSpain....................................................................................... 42RemainingBarrierstoDevelopmentofDGinSpain...................................................................... 43ImpactofDGonSpainsNetworkInfrastructure........................................................................... 44
SECTION3: ComparisontoGridInfrastructureinCalifornia..................................................... 46SECTION
4:
Summary
of
Key
Lessons
Learned
..............................................................................
51
ListofFigures
Figure1:GenerationMixinGermanyatEndof2009(AllDatainPercentages)............................. 2Figure2:RelationshipbetweenNetworkConnectionLevelandTechnologyforInstallationsEligibleunderthe2008RenewableEnergyAct..................................................................................... 3Figure3:MediumvoltageGridLayouts a)NormallyopenLoops;b)CircuitswithTwoSourceStationsandNormallyopenContactatOneStation............................................................................ 7Figure4:TypicalUrbanLowvoltageGridLayout............................................................................... 9Figure5:TypicalRuralLowvoltageGridLayout.............................................................................. 10Figure6:VoltageIncreaseCausedbyDistributedGeneration......................................................... 14Figure7:SpanishTransmissionSystem................................................................................................ 25Figure8:LoopedHVGrid(SingleSourcePoint)................................................................................ 26
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Figure9:BridgeConfiguration(HVGridFedfromTwoPoints)..................................................... 27Figure11: UrbanMVGrid:ReflectionPointandSupportCircuitDesign..................................... 28Figure12:UrbanMediumVoltageGrid:DistributionPointdesign................................................ 29Figure
13:
Rural
MV
Grid
Structure
......................................................................................................
30
Figure14:LVGridStructure.................................................................................................................. 31Figure15:BreakdownoftheTotalInstalledCapacitybyTechnologyattheEndof2010............31Figure16:AnnualGrowthofSpainsInstalledPowerGeneration(GW)........................................ 32Figure17:BreakdownoftheTotalRenewableInstalledCapacitybyTechnologyattheEndof2009............................................................................................................................................................ 33Figure18:WindCapacityGeographicDensityinSpain................................................................... 34Figure
19:
Installed
Solar
Power
(MW)
in
the
Autonomous
Communities
of
Spain
by
End
2009
a)PVandb)SolarThermal..................................................................................................................... 35Figure20:DGConnectionProcess........................................................................................................ 40
ListofTables
Table1: GeneralRulesforSelectingtheVoltageLevelofthePointofCommonCoupling,accordingtotheRatedPowerofGenerationPlants............................................................................. 3Table2:HydroPowerPlantsinGermany,CategorizedbyNumberandInstalledPower............5Table3:OverviewofVoltageLevelsinGermany................................................................................. 6Table4:MostFrequentlyUsedOptionstoIntegrateDistributedGenerationinGermany..........18Table5:OverviewofVoltageLevelsinSpainperIECDefinitions.................................................. 23Table6:ComparisonofACVoltageLevelsinCaliforniaandEurope............................................ 46
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INTRODUCTION
AsreflectedintheEnergyCommissionspreviousIntegratedEnergyPolicyReportproceeding,theEnergyCommissionwantstodeterminehowcertainEuropeancountriesintegratelargequantitiesofintermittentrenewableelectricityintotheirelectricdistributionsystemswhilestill
maintainingsystemcontrolandreliability.ThismemoaddressesthisissuebyprovidingacomparisonbetweentheelectricdistributionsystemsinEuropeandCaliforniawiththeultimategoalofcapturingkeylessonslearnedtofacilitateCaliforniasintermittentrenewabledistributedgeneration(DG)intoitselectricdistributionsystem.
ThismemodescribesthephysicaldistributioninfrastructureandtherequirementsandprocessesforinterconnectingDGtothedistributioninfrastructureinGermanyandinSpain.ItcomparestherelevantcharacteristicsintheseEuropeancountriestothecorrespondingcharacteristicsinCalifornia.Theanalysisfocusesonmedium andlowvoltagedistributiongridsandoutlinesrelevantaspectsandimpactsofrenewablegenerationathighervoltagelevels.
Theresearchfocusedonaddressingthefollowingquestions:
HowaretheelectrictransmissionanddistributionsystemsconfiguredinGermanyandSpain?DoesthistopologyincreaseopportunitiesforrenewableDGintegration?
HavegridoperatorschangedtheconfigurationoftheirdistributionsystemstoallowforgreaterpenetrationofrenewableDG?Whatarethechangesfromaqualitativesense(whathavetheydone)andaquantitativesense(howmuchofithavetheydone,howaretheytreatingcostallocation,whatisthequantitativerelationshipbetweenchangesininfrastructureandDGpenetration)?
Do
grid
operators
use
ancillary
technologies
(i.e.,
battery
storage,
flywheel)
and
policy
leversthatallowforgreaterbackflowsonthedistributionsystemwithoutthreateninggridstability(e.g.,protectiondevices,curtailment)?Ordotheysimplyallowgreaterpenetrationundersomecircumstanceswithoutconcern?
IshigherpenetrationofrenewableDGlikelytocausevoltageissuesandpotentialbackfeedissues?HowdoestheelectricdistributionsystemofGermanyandSpainaddressthebackfeedissueinlightofactivepowerflowfromthemediumvoltagecircuitsuptothetransmission/subtransmissionhighvoltagecircuits?
Thismemoisorganizedasfollows:
Section
1
reviews
the
current
state
of
physical
infrastructure
in
Germany.
Section2reviewsthecurrentstateofphysicalinfrastructureinSpain.
Section3providesacomparisontogridinfrastructureinCalifornia.
Section4providesasummaryofkeylessonslearned.
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SECTION 1:Physical Infrastructure in Germany
Atoftheendof2009about16percentoftheGermanelectricalenergyproductioncamefrom
renewableenergysources.1ThegrowthofrenewableDGinGermanycontinuesunabated.Germangridoperatorshavedealtwiththechallengeofsignificantrenewableintegrationforthelastfiveto10yearsandhavedevelopedtechnicalrulesandguidelinestoensuresecurenetworkoperation.AnexaminationoftheGermanpowersystemisthereforeusefulforacomparativeanalysis.
Regional and Quantitative Allocation of Renewable Energy inGermany
Theextentofdeploymentofeachtypeofrenewablegenerationdependsonmanyfactorssuchaslocalclimateconditions,landutilization,andpopulationlevels.AcomparisonofalltypesofinstalledgenerationcapacityinGermany,includingbothrenewablesandconventionalgenerationisshowninFigure1.
Figure 1: Generation Mix in Germany at End of 2009 (All Data in Percentages)
Source: BDEW: German Energy Market, 2010
1GermanStatisticsofRenewableEnergySources,December2010.
13
13
18
15
12
29
Generation capacity(total: 153.8 GW net)
Nuclear Lignite
Hard coal Natural gas
Oil, Pump storage hydro, other Renewables
23
24
18
13
6
16
Net electricity generation(total: 561 TWh net)
56
10
10
21
3
Renewable generation capacity(total: 44.6 GW)
Wind
Biomass
Hydro
Solar
others
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Thetypeofrenewableenergysourceoftenaffectsthesizeofthegenerationplantsandtherebythetype(voltagelevel)ofthegridconnection.AsageneralrulefortheGermangrid,thevoltagelevelatthepointofcommoncouplingforDGplantsfollowstheschemashowninTable1.
Table 1: General Rules for Selecting the Voltage Level of the Point of Common Coupling,according to the Rated Power of Generation Plants
Rated power of the generation plant Voltage level of grid connection
Up to 30 kW Low-voltage grid without verification
30 to 200 kW Low- or medium-voltage grid
0.15 to 20 MW Medium-voltage grid
15 to 80 MW High-voltage grid
80 to 400 MW Extra-high voltage grid
Source: Potentialermittlung fr den Ausbau der Wasserkraftnutzung in Deutschland, Bundesministerium fr Umwelt, Naturschutzund Reaktorsicherheit (BMU), September 2010 [Capacity of hydro power in Germany, September 2010]
InactualpracticetherecanbedeviationsfromthegeneralrulebasedontheresultsofspecificstudiesforDGinterconnection.Figure2showsthebreakdownofgenerationtypesinstalledateachvoltagelevelasapercentageofthetotalgenerationcapacityinstalledatthatvoltage.Thesizeofthegeneratorisakeyparameterasitrequiresacorrespondingcapacitybothatthenetworkconnectionpointandfortransportingtheelectricityproducedfromthatpointtothesystem.Forinstance,solarpowerinstallationstendtoberathersmall(mainlyroofbasedinstallations)andaremostlyconnectedtothelowvoltagenetwork.Ontheotherhand,windprojectsaredevelopedoveramuchwiderrangeofsizes(e.g.,windfarms)andthereforeareconnectedatmanydifferentvoltagelevels.
Figure 2: Relationship between Network Connection Level and Technology for InstallationsEligib le under the 2008 Renewable Energy Act
2
Source: Bundesnetzagentur EEG-Statistikbericht 2008 (Translated Regulators EEG Statistical Report, 2008)
2Installedgeothermalcapacityisnegligible.Gasesreferstowastegasprojects(e.g.,minegas,etc.)
0% 20% 40% 60% 80% 100%
Extra high voltage
Extra high/ high voltage
High voltage
High / medium voltage
Medium voltage
Medium/ low voltage
Low voltage
Hydro
Biomass
Gases
Geothermal
Wind
Solar
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AdditionalgeneralobservationsinregardtonetworkintegrationofDGontheGermannetworkareasfollows:
Wind Energy
Ahighconcentrationofwindenergyplantsappearsinrural,sparselypopulatedareasinnorthernGermany.Theindividualgeneratingunitsmostlyhavearatedpowerfrom1MWto3MW.Hence,thepointofcommoncouplingismostoftenlocatedonamediumvoltagegrid.However,whenindividualunitsarecollectedintowindfarmswithratedpowerfrom20MWto80MW,theyareusuallyconnectedtothehighvoltagegrid.Afewlargewindfarmsgenerate80to400MWofelectricpowerapieceandaredirectlyconnectedtotheextrahighvoltagegridviaseparatesubstations.
Solar Energy
Eventhoughthepercentageofelectricalenergygeneratedbysolarpowerwasonlyabout
7
percent
of
all
renewable
energy
by
the
end
of
2009,
solar
power
has
had
the
strongest
growth
rateforthelasttwoyears.AsignificantamountofsolarenergygeneratingunitshasbeeninstalledparticularlyinsouthernGermany.Theinstalledsolargenerationcapacityincreasedby3,800MWin2009andbyabout6,500MWin2010,bringingthetotalinstalledsolarcapacitytoapproximately10GW.
Inurbanareas,smallsolargenerationplants(photovoltaicmodulesandconverters)areinstalledonroofsofresidentialhomes(ratedpower3kWto5kW)orcommercialandpublicbuildings(100kWto1MW).Accordingtogridcode,smallunitsupto5kWpeakcanbeconnectedasasinglephasecustomerataservicepoint.3Unitsupto30kWareallowedtoconnectasathreephasecustomeratanypointontheLVgridwithouttechnicalverification.
However,thepresenceofmultipleDGprojectswithinanindividualrurallowvoltagegridcancauseseverevoltageorpowerqualityissues(seeMemo#2forfurtherdiscussion).
Biomass in Cogeneration Plants
Bytheendof2009,thefractionofrenewableelectricalenergygeneratedfrombiomasswasroughly30percentofallrenewableenergyproduction.Hence,biomassisthenextmostimportantrenewableenergysourceafterwindinGermany,andalsohashighgrowthrates.CogenerationplantsforbiomassareinstalledalloverGermany,particularlyinruralareas.Smallunitswithelectricpowerupto150kWareconnectedtothelowvoltagegrid.Themajorityofunitsrangesfrom500kWto5MWandisconnectedtothemediumvoltagegrid.Largeunitswithconsiderablymorethan5MWexistandareconnectedtothemedium orhighvoltagegrid
3EigenerzeugungsanlagenamNiederspannungsnetzRichtliniefrdenAnschlussundParallelbetriebvonEigenerzeugungsanlagenamNiederspannungsnetz;VWEWEnergieverlagGmbH;September2005[GermanTechnicalGuidelineGeneratingPlantsConnectedtotheLowVoltageNetwork,September2005]
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accordingtotheirratedpower.Sincebiomassisconsistentlyavailable,itislesscriticalfornetworkoperationthanfluctuatingresourcessuchaswindandsolarpower.
Hydro Power
HydropowerresourcesareconsideredtobewelldevelopedinGermany.Therefore,the
amountof
hydro
power
has
remained
nearly
constant
over
the
last
few
decades
since
most
of
thepotentiallocationsarealreadyutilized.HydropowerstationsofvarioussizeshavebeeninstalledinmountainousareasandalongriversincentralandsouthernGermany.Currently,hydrogenerationisabout25percentofallGermanrenewableenergygeneration.
Severallargepumpedstoragepowerplantsconnectedtotheextrahighvoltagegridcontributetotheloadbalancingandfrequencycontrolofthetransmissionsystem.Table2providesanoverviewofthenumberofgenerationplantsinseveralpowercategoriesandtheinstalledpower.
Table 2: Hydro Power Plants in Germany, Categorized by Number and Ins talled Power
Hydro power unitswith less than 1 MW
Hydro power unitswith more than 1 MW
Pumped- storageplants
Number of units ~6,500 ~400 ~30
Installed Power ~600 MW ~3,400 MW ~6,600 MW
Network Structures in Germany
Inthenextpartofthememo,thebasictechnicallayoutsandconfigurationsofGermantransmissionanddistributiongrids,includingsubstationsandsecondarysubstationsaredescribed.ThenthegeneralandtechnicalrequirementsfortheinterconnectionofDGfroma
Germanperspectivearethenconsidered.Finally,themostcommonnetworkupgradeoptionstomanagetheintegrationofrenewableenergysourcesandcomplywithtechnicalrequirementsareexamined.
Grid and Voltage Levels
TheEuropeanpowergridisathreephasealternatingcurrentgridoperatedatafrequencyof50Hertzatallvoltagelevels.4Fourcommonvoltagegroups(EHV,HV,MV,andLV)havebeenestablishedintheGermanpowergridperInternationalElectrotechnicalCommissiondefinitions.TheexistinggridvoltagesforeachofthesegroupsinGermanyareshowninTable3.
4Therailwaypowergridisdistinguishedfromthepublicpowergridbyfrequencyandgeneration.ItisatwophaseACgridoperatedat16.7Hz.
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Table 3: Overview of Vol tage Levels in Germany
Name(IEC Definition) Abbreviation Rated Voltage Role
Extra-high voltage EHV 380 kV, 220 kV Transmission grid
High voltage HV 110 kV
Distribution gridMedium voltage MV 30 kV, 20 kV,15 kV, 10 kV
Low voltage LV 400 V
Transmission Grid
TheEuropeantransmissiongridisoperatedprimarilyat380kVandpartiallyat220kV,butthelatterisonthedeclineandprovidesthebasisfortheelectricalenergytransportbetweenlargescalepowerplants,theconnecteddistributiongrids,andneighboringcountries.TheEuropeantransmissiongridisanintegratednetworkdesignedtoensurereliable,efficient,andsecureelectricalenergysupplybasedontherulesoftheOperationHandbookoftheEuropean
Network
of
Transmission
System
Operators
for
Electricity
(ENTSO
E).5
According
to
the
GermanTransmissionGridCode,6themaintaskofthetransmissiongridoperatorsistoassumeresponsibilityforthewholesystemofelectricalenergysupply,including:
Thebalanceofloadwithinacontrolarea,especiallyincaseofaresourcecontingency,andtherebymaintainingsystemfrequencystability
Networksecurity,i.e.,thesecurityofsupply,secureoperation,thecompliancewithvoltageandotheroperationallimitsandthe(n1)criterion
Theongoingevaluationofsystemoperatingconditionsandinitiationofrequiredcorrectivemeasuresthatwillinvolvetheassociateddistributiongridoperatorsasneeded
Thetransmissiongridisameshedsystemwithhighstandardsforsystemstability(frequency,voltage,dynamicstability)andsecurityofsupply.ThetransmissioninfrastructureinGermanyispredominatelyoverheadconstruction.
Distribution Grid at the High Voltage Level
The110kVhighvoltage(HV)gridservesasthetransportgridformediumdistancesandcarriestheelectricenergyfromexchangepointsonthetransmissiongridtowardsurbanorruralmediumvoltagegrids.Therequirementsconcerningsecurityofsupplyareagaincoveredbycompliancetothe(n1)contingencycriterion.Thegridismeshedandconsistsmainlyofoverheadlines.Inurbanareas,undergroundcablesareofteninstalledat110kV.Highloads
5UCTEOperationHandbook(OH),version2.5,levelE,dated24.06.2004,UnionfortheCoordinationofTransmissionofElectricity(UCTE);Brussels.
6TransmissionCode2007,Netz undSystemregelnderdeutschenbertragungsnetzbetreiber,Version1.1,August2007,VerbandderNetzbetreiberVDNe.V.beimVDEW,Berlin[TransmissionCode2007,NetworkandSystemRulesoftheGermanTransmissionSystemOperators,August2007]
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withhighdemands(e.g.,largeindustrialloads)andgeneratingunitsexceedingapowerlimitofabout20MWareprimarilyconnectedtothisgridlevel.
Distribution Grid on Medium Voltage Level
Themediumvoltagegrid(MVgrid)mainlycomprisesthevoltagelevels30kV,20kV,15kV,
and
10
kV.
Urban
and
rural
medium
voltage
grids
significantly
differ
in
their
characteristics.
Ahighdensityofloadsandrelativelyhighdemandthatcauseshighutilizationoftheequipment(transformers,cables)istypicalforurbanareas.Appropriatefortheserequirements,urbanmediumvoltagegridsinGermanyconsistlargelyofcableswithatypicalcablecrosssectionof150to300mm(nominallyequivalenttoarangeof300kcmilto636kcmil)andwithacomparablyshortcablelength.TheurbanMVgridsaregenerallyoperatedatvoltagelevelsof10kVand20kV.Theyaresetupasloopednetworkswithopenloopsundernormaloperatingconditions(seeFigure4),wherethesmallercirclesrepresentnormallyopenswitchgearandthelargercirclesrepresentsubstationtransformers.
a) b)
Figure 3: Medium-voltage Grid Layoutsa) Normally-open Loops; b) Circuits w ith Two Source Stations and Normally-open Contact at One
Station
Source: KEMA
TheMVgridsareconnectedtothehighvoltagegrid(110kV)viasubstationswithtwoormoreHV/MVtransformersinaratedpowerrangefrom31.5MVAto63MVA.Thepowertransformersaretypicallyequippedwithtapchangersandautomaticvoltagecontrolto
110 kV
110 kV
20 kV20 kV
20 kV20 kV
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guaranteeafixedvoltageatallmediumvoltagebusbars.Aslinktothelowvoltagegrids,thesecondarysubstationsmainlyconsistofsingleMV/LVtransformersinaratedpowerrangefrom400to1,000kVA.Fordirectcustomerconnections,transformersupto1,600kVAcanbeused.Asaresultofthehighinstalledpowertransformercapacityandtherelativelyshortcableswithlargecrosssections,thenetworkimpedanceiscomparablylowthroughoutthewhole
urbanmediumvoltagegrid.Hence,voltagedropandpowerqualityissuesrarelyoccur.
RuralMediumvoltageGridsRuralareasarecharacterizedbylargergeographyandlowloaddensity.Thisresultsinlonglines,highnetworkimpedances,andlowutilizationoftheequipment.InruralmediumvoltagegridsinGermany,undergroundcablesandoverheadlinesareinstalledinnearlyequalshares.Typicalundergroundcablecrosssectionsrangefrom120to240mm(nominallyequivalenttoarangeof4/0AWGto400kcmil).Thecrosssectionsofoverheadlinesrangefrom70to120mm(nominallyequivalenttoarangeof2/0AWGto4/0AWG).
RuralMVgridsareoperatedatvariousvoltagelevels;mostcommonare10kV,15kV,20kV,
and30kV.Likeurbanareas,ruralMVgridsaresetupasloopednetworkswithopenloopsundernormaloperatingconditionsorinsomecases,linesareconnectedbetweentwostationswithanormalopencontactatoneend(seeFigure1).Usually,thegridsareconnectedtothehighvoltagegrid(110kV)viasubstationswithtwoHV/MVtransformersinaratedpowerrangefrom16to40MVA.Thepowertransformersaretypicallyequippedwithtapchangersandautomaticvoltagecontroltoguaranteeafixedvoltageatallmediumvoltagebusbars.ThesecondarysubstationsconsistofsingleMV/LVtransformersinaratedpowerrangefrom100to400kVA.
Inafewcases,intermediate30kVgridsoperatetosupplyremote,lightlyloadedareas.These30kVdistributiongridsformclosedloopsandsupplylowervoltage10kVgrids.
Duetothelonglines,smallcrosssectionsandthecomparablylowinstalledtransformercapacity,thenetworkimpedanceincreasessignificantlytowardstheremotelineterminal.Voltagedropandpowerqualityissuesfrequentlyoccur(seefurtherdiscussioninMemo#2).
Low Voltage (LV) Distribution Grid
Thelowvoltagegrid(LVgrid)isa400Vnetworkandremainsathreephasegrid(orthreephaseplusneutralphase)uptotheservicepoints(endcustomers).Ingeneral,outgoingcableunitsinsecondarysubstationsarefusedbyalowvoltage,highloadbreakingcapacityfuse.Servicepointconnectionsareprotectedforamaximumpermissiblecurrentof63A(equalto25kVA).Similartomediumvoltagegrids,urban,andrurallowvoltagegridshavedifferentgrid
characteristics.
UrbanLowvoltageGridsAccordingtothehighspatialdensityofurbanloads,lowvoltagegridsintheseareasconsistofrelativelyshortgridcableswithtypicalcablecrosssectionsof150to240mm(nominallyequivalenttoarangeof300kcmilto400kcmil).Fromthegridcables,servicepointcableswitha
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crosssectionof3550mm(nominallyequivalenttoarangeof#2AWGto#1AWG)branchofftocustomers.
TheurbanLVgridsareoperatedasmeshedgridsconnectedbymeansofcabledistributionboxes.TheLVgridscanbefedbyasinglesecondarysubstationorbyoneortwoMVcircuits
(see
Figure
4).
The
urban
secondary
substations
contain
about
10
outgoing
cable
units.
The
meshedgridstructureensureshighservicereliability,allowsforhighutilization,andreducesvoltagedropsandpowerqualityissues.Unfortunately,thegridassemblyisunclearandthemaintenanceeffortisrelativelyhigh.
Figure 4: Typical Urban Low-voltage Grid Layout
Source: KEMA
RuralLowvoltageGrids
Withrespecttotheexpansionofthesupplyzoneandthelowloaddensity,rurallowvoltagegridsinGermanyaremainlyradiallystructuredcableoroverheadlinegrids.Forthegridlines,typicalcablecrosssectionsrangefrom95mmto150mm(nominallyequivalenttoarangeof3/0AWGto300kcmil).Thecrosssectionsofoverheadgridlinesrangefrom50to95mm(nominallyequivalenttoarangeof#1AWGto3/0AWG).Theservicepointconnectionsaretypicallyrealizedthrough35mmcables(nominallyequivalentto#2AWG).Occasionally,overheadlineswithcrosssectionof25to35mm(nominallyequivalenttoarangeof#4AWG
to
#2
AWG)
are
used.
Theruralsecondarysubstationscontainuptoeightoutgoingcableunits.TheruralLVgridsareoperatedasradialgridsfedbyasinglesecondarysubstation(seeFigure5).Thelonglinesanddecreasingcrosssectionstowardsthelineendscausehighnetworkimpedances.Thus,thesensitivitytovoltagedeviationandsystemperturbations(powerqualityissues)significantlyrises.
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Figure 5: Typical Rural Low-voltage Grid Layout
Source: KEMA
Inadditiontothestandardtaskofsupplyingendusecustomersthedistributionoperators(DSO)mustconnectdistributedgeneratingunitsinthemostcostefficient,technicallysecureway.Therefore,theDSOfirstutilizesanyexistingreservecapacityinthegridforconnectingaDG.Ifthesereservesareexhausted,thepointofcommoncouplingcaneitherbemovedtoahighervoltagelevelgrid(dependingontheDGsize),orthelowervoltagegridmustbeupgradedtoaccommodatethenewDG.Inthecaseofagridextensionorupgrade,thegridplannerconsidersexistinggridexpansionrequirementsandnetworkplanningdirectivesin
conjunction
with
the
technical
rules
for
the
grid
connection
of
distributed
generation
in
order
to
comeupwiththeoveralllowestcostgridexpansionplan.
Conclusion for Grid Connection of Distributed Generation
Implications of DG on Grid Planning and Operation
Eventhoughtheincreasingproductionofrenewableenergyfromdistributedgeneratingunitsaffectsthegridatallvoltagelevels,nofundamentalchangesinthegridstructureandplanningstandardshavebeenmadeinGermany.However,duetothescaleofdistributedgenerationgrowthinthelastdecade,thelevelofDGoutputonmedium andlowvoltagegridsnowexceedslocalloadinmanyplacesinGermany.Hence,backfeedconditionsoccurinsomeregionsofthenetwork.Ingeneral,backfeedsarepermittedinGermany.Themeteringandprotectionhastobedesignedforbidirectionalflow.Afourquadrantmeterisnecessaryandtheprotectionsystemhastoallowbackfeeds.
Networkconnectionsandupgradesareplanned,basedontheexpectedlevelofbackfeed,sothatthisconditioncausesnooverloads.Therefore,abackfeedconditionduringnormal
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operationsshouldnotleadtocurtailmentortrippingtheDG.Infact,undertheGermanrules,TSOsmustfirstexhaustallotheravailablemarketoptionsbeforecurtailingrenewableDG.RulesapplyingtoDGcurtailmentbyDNOsarenotasclear,andtheDNOsalsohavefeweroptionsthantheTSOs.However,ifarenewableDGiscurtailedbyeitheraTSOoraDNO,theDGstillreceivesitsnormalfeedintariffremunerationforanycurtailedenergy(i.e.,itdoesnot
reducetheDGsrevenue).
SincethecostsofnetworkupgradesinGermanyaresocialized,networkplannersseekthelowestcostplanofupgradetosatisfyDGintegrationneeds.Uptonow,theplanningforDGintegrationhasgenerallybeendoneaspartoftheregulargridexpansionplanningprocesswithnormalexpansionplanningandreplacementneedsconsideredfirst,thenDGintegrationsecond.
Grid Dimensioning
Inthepast,medium andlowvoltagegridsweredesignedanddimensionedbasedonthepeakloadscenario.Thegriddimensioningandoperationnowhavetoaccountforthefollowingfour
scenariosforloadandDGoutput:
Peakload/lowDGoutput
PeakDGoutput/lowload
Peakload/peakDGoutput
Lowload/lowDGoutput
Thefirsttwoscenarioshavebecomethemostcriticalcasesforgridplanningandoperation.Thepowerlinesandtransformersofeachvoltagelevelofthegridmustbesizedtomanagetheemergingrenewablepowerproduction.
Protectionaspects
TheprotectiondevicesandsettingsinGermandistributiongridsgenerallyallowforbackfeeds.Theoverloadprotectiondependsontheloadinglimitsoftheassetsandisindependentoftheflowdirection.
Distributedgenerationplantshavetobeequippedwithovervoltageandundervoltageprotection.ThetimedelayoftheprotectiondeviceshastobeadjustedtoallowforthetimedelayoftheautomatictapchangersonHV/MVpowertransformerssupplyingthatpartofthenetwork.Additionally,distributedgenerationplantsinmediumvoltagegridsandabovemustbeequippedwithunderfrequencyandoverfrequencyprotection.Furthermore,apowercircuitbreakerwithintheDGplantmustguaranteethedisconnectionofthedistributedgenerationprojectfromthegridincaseofashortcircuitintheplant.
Grid Operation
OperationalissuesduetothehighconcentrationofwindandphotovoltaicgenerationplantsthataremanagedmainlyatthehighvoltageandextrahighvoltagelevelinGermanyinclude:
Theloadforecastandgenerationschedules,definedinthetraditional15minuteschedulingintervals,getperturbedbyfluctuatingrenewableoutput.
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Theconsiderablebackfeedsfromlowload/highDGareasmustbetransportedtolargeloadcentersandcancausecongestioninthetransmissiongrid.
Thecurtailedutilizationofconventionalpowerplantsreducestheavailablefrequencycontrolandshortcircuitdutyandaffectsthedynamicstabilityofthesystemduetoareductioninrotationalinertiaconnectedtothesystem.
AccordingtotheGermanlawEnWG,gridoperatorsatallvoltagelevelscaninvokegenerationcurtailmenttocopewithcongestionandothercriticaloperationalsituationsthatjeopardizethenetworksecurity.Forthispurpose,distributedgenerationplantswithratedpowerofmorethan100kWmustbeequippedwithremotecontrolcapabilitytocommunicatetheirrealtimeoutputtothegridoperatorandallowforthegridoperatortosendautomaticpowerdispatchcontrolinstructionstothegenerators.Whilesuchtelecommunicationfacilitiesarenothighvoltagefacilities,theystillareanessentialcomponentoftheinfrastructurerequiredforreliableoperationandcontrolofthehighvoltagegridinGermany.
General and Technical Requirements in Germany
General Requirements
TheimplementationofrenewableenergysourcesisanimportantpoliticaltargetoftheGermangovernment.Inthiscontext,thefederalgovernmenthasdevelopedlegalboundaryconditionsforthedevelopmentofdistributedgeneration.Asaresult,importantnewlaws(EnWG7andEEG8)wereenacted.TheselawsdefineapriorityofrenewableenergysourcesincontrasttoconventionalenergysourcesandobligatetheGermangridoperatortoconnectdistributedgeneration.Thegridoperatorhastoensurethatdistributedgeneratingunitsareabletofeed
into
the
grid
and
that
the
total
installed
power
can
be
transmitted
under
normal
conditions.
Furthermore,thepointofcommoncouplingshouldbeascloseasreasonabletothelocationoftheindividualdistributedgeneratingunit,giventechnicallimitations.
Anexceptionisdefinedfordistributedgeneratingunitswithaninstalledpowerlowerthan30kW.Fortheseunitsthepointofcommoncouplingissimplydefinedasthelowvoltagegridclosesttotheserviceconnectionoftheownerofthegeneratingunit.
7EnWG ZweitesGesetzzurNeuregelungdesEnergiewirtschaftrechtsvom7.Juli2005;BundesgesetzblattJahrgang2005TeilINr.42,ausgegebenzuBonnam12.Juli2005[SecondGermanLawontheEnergyIndustry,July2005]
8EEGGesetzzurNeuregelungdesRechtsderErneuerbarenEnergienimStrombereichundzurnderungdamitzusammenhngenderVorschriftenvom25.Oktober2008;BundesgesetzblattJahrgang2008TeilINr.49,ausgegebenzuBonnam31.Oktober2008[GermanLawontheRenewableEnergySources,October2008]
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Regardingtheevaluationofthetechnicallyreasonablepointofcommoncoupling,differenttechnicalnormsandrulesweredevelopedinthepast.Theserulesweredevelopedinconsiderationofthefollowingtargets:
ThepointofcommoncouplingshouldbeclosetothelocationoftherespectiveDG.
Asecure
grid
operation
must
be
maintained
under
all
conditions,
including
the
full
outputofthedistributedgenerator.
TheoperationofDGshouldhavenegligibleimpactonothercustomers.
Specificpowerqualityparametershavetobemaintained.
Giventhiscontext,distributedgenerationplantsareconnectedatvariousvoltagelevelsdependingonthetypeofenergysourceandtheinstalledpower.Thefollowingsummarydescribesthetechnicalnormsandrulesregardingdistributedgenerationconnectedtomediumvoltageandlowvoltagegrids.
Technical Requirements
Toensureasecureoperationofthegridunderallconditionsthefollowingmainpointsshouldbeconsidered:
Allcomponentsusedintheinterconnectionshouldbeproperlydimensionedforthesizeoftherenewableproject.
Thevoltagelevelatthepointofconnectionshouldbewithinanacceptablerange.
Utilization and Overload
Theutilizationoftheelectricalinterconnectioncomponentsmustnotexceedtheratedcurrentoftheelectricalcomponents.Theratedcurrentsofthecomponentsaredefinedthroughindustrynorms.Inaddition,gridoperatorsinGermanyhavedefinedrelatedrules.Distributedgeneratingunitsthatareconnectedtothemediumvoltageorlowvoltagegridsshouldnotcauseoverloads,undervoltages,orovervoltages.
Permissible Voltage Range
Thepermissiblevoltagerangeformedium andlowvoltagegridsisdefinedinthenormDINEN50160.9Ontheonehand,themaximumvoltageshouldnotexceedtheinsulationleveloftheelectricalcomponents.Ontheotherhand,theminimumvoltageateachserviceconnectionpointmustallowanundisturbedoperationofallconnecteddevices.Inthiscontext,thevoltageateachserviceconnectionpointshouldbeinarangeof10percentoftheratedvoltageundernormaloperatingconditions.
9DINEN50160MerkmalederSpannunginffentlichenElektrizittsversorgungsnetzen;April2008[GermanNorm50160VoltageCharacteristicsofElectricitySuppliedbyPublicDistributionNetworks,April2008]
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Power Quality
Additionally,distributedgenerationplantsshouldnotinterferewithothercustomers(consumersorgeneratingunits).Toensureacceptablepowerqualityparameters,thefollowingsystemperturbationsassociatedwithaDGshouldbeconsidered:
Voltage
increase
at
point
of
connection
Flicker
Harmonics
Admissiblelimitsforvoltagedeviation,nonsymmetry,flicker,andharmoniclevelsarealsodefined(seeMemo#2).Technicalrulesexistforthegridconnectionofgeneratingunitstothemediumvoltagegrid10andtothelowvoltagegrid11,respectively.
The Most Critical Issue: Voltage Increase
Generally,voltageincreaseisthemostcriticalissueatthepointofcommonconnectionfordistributedgeneratingunits.Voltageincreasesarecausedbytheinjectedpowerofgenerating
units.Thepowertransmissionoverthenetworkimpedancecausesavoltagedropfromthefeedingtothereceivingend.Themagnitudeofthevoltagedeviationrelatestothesizeoftheimpedance.Asaresult,thevoltagedeviationsinthegridvarydependingontheDGsize.ThiseffectisillustratedinFigure6.
Figure 6: Voltage Increase Caused by Distributed Generation
Source: KEMA
10.ErzeugungsanlagenamMittelspannungsnetzRichtliniefrdenAnschlussundParallelbetriebvonErzeugungsanlagenamMittelspannungsnetz;VWEWEnergieverlagGmbH;Juni2008[GermanTechnicalGuidelineGeneratingPlantsConnectedtotheMediumVoltageNetwork,June2008]
11.EigenerzeugungsanlagenamNiederspannungsnetzRichtliniefrdenAnschlussundParallelbetriebvonEigenerzeugungsanlagenamNiederspannungsnetz;VWEWEnergieverlagGmbH;September2005[GermanTechnicalGuidelineGeneratingPlantsConnectedtotheLowVoltageNetwork,September2005]
servicepoint
load
G
distributedgenerationplant
circuitlinetransformer
voltage
lengthpeakload
peakfeedin
voltageincrease
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ThemaximumdifferencebetweenreceivedvoltageswithandwithoutDGoperationaredefinedintheGermangridrules(seeMemo2).Alldistributedgeneratingunitsthatareconnectedonacommonsectionofgridhavetobeconsidered.
Theshortcircuitdutyatapointofcommoncouplingservesasameasureforthenetwork
impedance.
High
short
circuit
duty
reflects
a
low
network
impedance
and
vice
versa.
Therefore,
inareaswithlowshortcircuitpower(i.e.,ruralareas),theoccurringvoltageincreaseishigherthaninareaswithahighershortcircuitpower(i.e.,urbanareas).Ifthevoltageincreaseexceedsthelimitvalue,eithergridupgradesarerequiredtoreducethenetworkimpedance,orthedistributedgeneratingunithastobeconnectedtoanotherpointofcommoncoupling.
Inaddition,othertypesofsystemperturbations(i.e.,flicker,harmonics,etc.)arealsoevaluatedinregardtotheshortcircuitpoweratthepointofcommoncoupling.AlloftheperformancerulesareconsideredbytherespectiveTSOorDNOduringplanningstudiesforeachDGconnectionandappropriateplanningoptionsareemployed,asdiscussedinthenextsection.
Technical Options to Ensure Secure Grid Operation
General
Becauseofthedistinctelectricalcharacteristicsofeachmedium andlowvoltagegrid,themaximumacceptablelevelofDGcapacitycanbelimitedatanygivenpointinthenetwork.Toensuresecuregridoperationdifferentgridplanningoptionscanbeusedtoincreasetheacceptableamountofconnecteddistributedgenerationinagivenpartofthenetwork.However,Germannetworkplannersconsiderallpossibilitiesinordertodeterminetheminimumlevelofgridinvestment.Generally,whentheconnectionpointisinadequate,the
technical
options
include:
DirectlyconnectingtheDGintoasubstation
UpgradingofthenetworkcircuitthermalcapabilitytotheDGlocation
Upgradingofupstreamtransformercapacity
Reroutingthecircuittoreducecircuitlength
Relocationofthenetworkloopnormallyopendisconnectpoint
Setpointadjustmentofautomaticvoltagecontrolonnetworktransformers
Usingreactivepowercapabilitiesofdistributedgeneratingunits
Constructionof
anew
substation
Changestonetworktopology
Upgradeofthenetworksratedvoltagelevel
Installationofsupplementalreactivepowercompensationequipment
Implementationofrotatingandnonrotatingenergystoragesystems
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Thesepossibilitiesaredescribedinmoredetailbelow.
Direct Connection at a Substation
Ifthevoltageincreaseexceedsthelimitvalue,otherpointsofcommoncouplingshouldbejustified.Inthiscontext,thedirectconnectionofadistributedgeneratingunittoanetwork
substation
is
one
of
the
most
commonly
used
solutions
in
Germany.
This
option
can
also
be
usedifothersystemperturbationfactorsexceedthepermissiblelimits.ItrequiresrelocationoftheplannedDGtoasiteadjacenttothenetworksubstationorconstructionofagentielinefromtheDGsitetothenetworksubstation.
Upgrade of Conductor Size
AnupgradeofgridundergroundcableoroverheadlinescanbeusediftheconnectionoftheDGtothenearestgridlineexceedscriticalperformanceparameters.Dependingonthegridload,thisapproachmayallowadditionaldistributedgeneratingunitstobeintegratedintothegrid.InGermany,thissolutionisoftenusedforoldergridlines,andconductorreplacementneededduetotheageofthegridlinecansometimesbecombinedwithintegrationof
distributedgeneration.Thissolutionisalsousedinordertoraiseshortcircuitdutyatthepointofcommoncoupling.Therefore,thisoptioncanalsobeusedtosolveproblemsregardingcriticalvoltageincreases.However,Germanyavoidsupgradingofthedistributiongridsolelyforintegratingdistributedgenerationmany.DependingontheamountofDGprojectsaddedtoaportionofthegrid,upgradeoflineconductorsmayonlybeashorttermoption.Inallcases,relevantneartermandlongtermgridplanningfactorsshouldbetakenintoaccount.
Upgrade of Transformer Capacity
Similartolineupgrades,theupgradeofupstreamtransformercapacityisalsousedinGermanyforsomeDGinterconnections.Thisoptionmaybepreferable,especiallyforoldertransformersandallowsmorepoweroutputbydistributedgeneration.
Reduction of the Circuit Length
Thisoptioncanberealizedbyreplacinggridline(s)totheDGsitewithanalternativeroutethatcreatesashortercircuitlengthandlowernetworkimpedance.However,thefeasibilityofthisoptiondependsonthegeographyofthespecificgridarea.Moreover,theresultantbenefitsinmanycasesarerelativelylow.
Relocation of the Network Normally-Open Disconnect Point
Ashorttermoptiontoreducevoltageincreasesongridlinescanbetherelocationofthenormallyopendisconnectpointofagridloop.12
In
Germany
this
option
is
only
a
short
term
solution
and
is
used
more
from
the
grid
operation
side.Theimpactoftherelocationofthedisconnectionpointontheabilitytointegratedistributedgenerationiscomparablylowandmayincreasethenetworkelectricallosses.Withrespecttothedynamicgrowthofrenewableenergygeneration,therearesuperioroptionsformediumtermorlongtermgridplanning.
12Thedisconnectionpointdefinesthenormallyopenpointinanetworkloop(seeFigure1a).
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Adjustment of Automatic Voltage Control Set Point on Transformers
Anadjustmentofthetransformervoltagecontrolsetpointisalsoconsideredashorttermoption,butinsomecasescanbeusedtokeepthevoltagelevelatadownstreamDGconnectionpointwithinthepermissiblerange.
ThisoptioncanonlybeusedinmediumvoltagegridsinGermanybecauseonlytheHV/MVpowertransformersareequippedwithautomaticvoltagecontrolsystems(tapchangingunderload).Therefore,applicationislimitedtolargerDGfacilitiesthatneedtoconnecttoMVnetworks.ThisoptionisoccasionallyusedinGermany.
Using Reactive Power Production Capabilities of Distributed Generation Plants
Somedistributedgeneratorsareequippedwithautomaticvoltageregulatorsthatcanabsorbreactivepowerfromthegrid(underexcitedoperation)orprovidereactivepowertothegrid(overexcitedoperation)UnderexcitedDGoperationcanbeusedtodecreaseconnectionvoltage,whileoverexcitedoperationcausesvoltageincrease.InGermany,thisoptionisbeing
usedwithincreasingfrequencyaspartofthelongtermgoalfordistributedgeneratingunitstocontributetothevoltagecontrolofthegrid.Inthepast,numerousDGunitswerenotcapableofproducingreactivepower.Therefore,differenttechnicalruleshavebeendevelopedthatincludetherequirementforDGcapabilitytoprovidereactivepowerandtocontrolvoltage.
Construction of a New Substation
AnewsubstationcanbenecessaryifseveralcomponentstransformersandgridlinesreachcriticalutilizationlevelsduetoDGintegration.Theconstructionofanewsubstationimpliesextensivegridextensionmeasures.ItisthemostcostlyoptionandisthereforeavoidedinGermany.However,thisoptionmaybenecessaryinareasexperiencingacomparablyhighlevelofDGinstallationconcentratedinonelocation.ThishasbeenthecaseinthenorthernpartofGermanywheresomeHV/MVsubstationshavebeenconstructedexclusivelyfordistributedgeneration(windfarmconnection).
Change to the Network Structure
ChangestoexistingnetworkstructuresarecarriedoutinGermanyonlyifneededaspartofacomprehensivegridexpansionplan.WhiledistributedgenerationaloneisnotconsideredthemainreasonforchangingnetworkstructureinGermany,itisoneofthemanyfactorsconsideredinlongtermgridexpansionplanning.
Upgrade of the Rated Voltage Level
TheratedvoltagelevelofmediumvoltagegridsinGermanyhasbeenupgradedinsomeareas.
Inmostcases,theupgradewasfrom10kVto20kV.Theseupgradesallowforagreaterpenetrationofdistributedgeneration.However,whenthisoptionhasbeenuseditwasselectedduetoitscompatibilitywiththeoverallgridexpansionplanningneeds.DistributedgenerationwasnotbeenusedasthesoledriverforthisoptioninGermany.
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Installation of Supplemental Reactive Power Compensation
Theimplementationofsupplementalreactivepowercompensationsystems(e.g.,shuntreactors,FACTS),ishardlyeverusedformediumvoltageandlowvoltagegridsinGermany.Testsregardingtheimplementationofreactivepowercompensationsystemsarebeingcarriedout.Whethertheinstallationofmorereactivepowercompensationsystemsinmediumvoltage
andlowvoltagegridswilltakeplaceinGermanyisunclearatthistime.
Implementation of Rotating and Non-rotating Energy Storage Systems
Energystoragesystemscanstoreoutputfromfluctuatingrenewableenergysourcesattimeswhentheyexceedtheneedsofthegrid,andthestoredenergyisreleasedbackintothegridatalatertimewhenneeded.However,storagesystemshavenotbeenusedinmediumvoltageandlowvoltagegridsinGermanyforDGintegrationtodatebecausethecostsofsuchtechnologiesarenoteconomicallyjustified.However,pumpedstoragehydroprojectshavebeenusedextensivelyontheEHVgridforregulatingpurposes.
However,implementationofstoragesystemsforrenewableintegrationonHVandMVgridsis
consideredtobealongtermpossibilityinGermany.
Most Frequent Application of Options in Germany
ThemostfrequentlyusedoptionsaresummarizedinTable4andarecategorizedaccordingtothemostcommonfieldsoftheirapplication.
Table 4: Most Frequently Used Options to Integrate Distributed Generation in Germany
Option Grid overloadCritical voltage
variationPower quality
issues
Direct connection
to a substation
Upgrade of gridcircuit conductors
Upgrade of upstreamtransformer capacity
Reduction of thegrid circuit length
Relocation of the loop normally-open disconnect point
Set point adjustment of transformerautomatic voltage control (tap changer)
Using reactive power capabilitiesof distributed generation plants
Construction ofa new substation
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Automatic Curtailment Option
Ingeneral,thegridoperatorsofmedium andlowvoltagegridsinGermanyhavenotusedautomaticcurtailmentofDGasanoptionforexpansionplanning.However,thisoptionhasrecentlybeenunderdiscussion.Inthisscenariothedistributedgenerationplantwouldneedtobecapableofautomaticallyreducingtheiroutputintheeventofspecificovervoltageor
overloadcondition,evenwithoutaremotecontrolsignalfromthegridoperator.Technicalruleshavenotyetbeenestablishedforthispotentialoption,butitmightbeimplementedinthefutureasanoption.
Recent Network Planning Policies and Studies
Eventhoughtheincreasingproductionofrenewableenergyfromdistributedgeneratingunitsaffectsthegridatallvoltagelevels,nofundamentalchangesintheapprovedgridstructureandplanningdirectiveshavebeenmadetodate.Technicalguidelineshavebeendevelopedto
ensureasecure
operation
of
the
grid
under
all
conditions
while
connecting
distributed
generationinaneconomic,leastcostmannerfromtheperspectiveofgridexpansionoptions.Anylargescalegridexpansionandredesignmeasuresinthepasthavebeendrivenprimarilybyoveralllongtermgridplanninggoals,andnotprimarilybydistributedorrenewablegeneration.However,recentpolicyinitiativesandstudiesinGermanysuggestthatanewgridinvestmentparadigmmaybedeveloping.ThisisdueperhapsinparttoconcernsoverthelevelofdependenceonnuclearresourcesinGermanyslongtermenergyplanandthepossibilityofsignificantlyreducingthisdependencethroughintegrationofevenhigherlevelsofrenewables.
MostrelevanttothecurrentKEMAinvestigation,recentlypublishedGermanstudyreportsconcludethatamajorincreaseinthescopeofdistributedandrenewablegenerationwould
requireconsiderableexpansionofexistingtransmissionanddistributionnetworks.Accordingtoonemajorwindresourceexpansionstudy13completedin2010,inthebaserenewableexpansionscenariostudiedupto3,600kmofnewtransmissionlinesareneededtoaccommodaterenewablegrowth,particularlylargeoffshorewind,by2020.Thiswouldrequireapproximately1billion/yearinadditionalgridexpansioncostsfornewtransmissionlines.Anotherexpansionscenarioconsideredincreaseduseofhightemperaturetransmissionconductorswhichwouldreducethemileageofnewlinestosome1,700km,butwouldalsorequiresome5,700kmofexistinglinestobemodified.Thisscenariowouldincreasetheexpansioncoststo1.6billion/year,whichisthehighestofallthescenariosanalyzed.
TheseresultsarecomplementedbyanotherdraftstudybyamajorGermanindustryassociation
(BDEW)whichquantifiesthenetworkexpansionnecessarytomeetmidtermrenewablepolicygoalsandforecast.14Whilethegovernmentsenergystrategypublishedin2010envisionsatotal
13DeutscheEnergieAgenturNetworkStudyIIPlanningoftheGridIntegrationofWindEnergyinGermanOnshoreandOffshoreuptotheYear2020(DenaGridstudy),2010.
14DraftreportbytheFederalAssociationoftheGermanEnergyIndustry(BDEW),March2011.
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installedsolarpowercapacityofapproximately33GWin2020(i.e.,doublingthecurrentinstalledsolarpowercapacity),theFederalMinistryofEnvironmentestimatesthatby2020therewillbeanother52GWofinstalledcapacityaddedfromsolarpowerandsmalleronshorewindparks.Giventhisforecast,theBDEWdraftstudyconcludesthatby2020theywouldneedtobuild195,000kmto380,000kmofadditionallinesontheGermanHVandMVdistribution
voltagenetworks.Theassociatedcapitalcostisestimatedtobe13billionto27billion.
Duetothedelayandconsiderableamountoftimeneededofthepermittingprocedureforplannedandnewtransmissionlines,theGermangovernmenthasalsorevealedpotentiallegalchangesinordertoaccelerateandsimplifytheplanningandpermittingprocedure.
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SECTION 2:Physical Infrastructure in Spain
Inrecentyearsdistributedgeneration(DG)hasreceivedincreasingattentionasitcancontribute
tothevariousgoalsofEUenergypolicy.Enhanceddiversityofsupply,areductioningreenhousegasemissions,efficiencygainsandmoreflexibilityininvestmentsaresomeofthemajorbenefitsassociatedwithDG.However,whentheamountofdistributedelectricitysupplyofrenewableenergysources(RES)surpassesaparticularlevel,itcannolongerbeignoredinplanningandoperationoftheelectricitysupplysystem.Therefore,improvementsoftheregulatoryframeworkoftheelectricitysupplysystemsarerequiredalongwiththegrowthoftheelectricitysupplyfromdistributedgeneration.
Basicprinciplesforachievingsustainabledevelopmentfromaneconomic,social,andenvironmentalpointofviewinSpaintodayincludereducingdependenceonforeignenergy,betteruseofavailableenergysources,andagreaterawarenessoftheenvironment.Thesegoals
increasinglydemandthedeploymentofrenewablesourcesofenergy,increasedefficiencyinelectricgenerationandareductioningreenhousegasesinaccordancewiththecommitmentsacquiredonsigningtheKyotoprotocol,bymeansofasearchforenergyefficientgenerationofelectricity.
CreationofthespecialregimeforthegenerationofelectricitymeantanimportantmilestoneinSpainsenergypolicy.TargetsforrenewableenergyandcombinedheatandpowerarecoveredintheRenewableEnergyPlan20052010andintheStrategyforEnergySavingandEfficiencyinSpain(E4),respectively.Inviewoftheabove,althoughgrowthinthespecialregimeforelectricitygenerationhasbeenoutstanding,incertaintechnologiesthetargetsarestillfarfrombeingreached.
Attheendof2010Spainhadatotalinstalledelectricpowerproductioncapacityof97.5GW(peninsularsystem).Thetotalinstalledcapacityinsolarandwindpowerproductionwas23.8GW(24percentofthetotalinstalledcapacity).Thistotalincludesapproximately9GWfromwindprojectsand4GWfromsolarPVprojectssmallerthan20MW.Continuedgrowthofdistributedrenewablegenerationseemsunabated.
Therefore,Spanishgridoperatorsinrecentyearshavedevelopedtechnicalrulesandguidelinestomaintainsecurenetworkoperationwithlargeamountsofrenewables.AccordingtotheseextensiveexperiencestheSpanishpowerdistributionsystemissuitableforacomparativeanalysis.
TheSpanishMinistryofIndustrythroughtheInstituteforEnergyDiversificationandSaving(IDAE)hasdevelopedthewebsiteRenovables(Renewables)MadeinSpain,http://www.renovablesmadeinspain.com/withtheobjectivetoinformtheworldaboutthesignificantpenetrationofrenewableenergiesinSpainandtheleadershipofSpanishcompaniesandorganizationsthathavemadethispossible.
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InthefollowingsectionstheresearchteampresentsthemainvoltagesofthetransmissionanddistributionnetworksinSpain.Thenwedescribetherelevanttypesofrenewableenergysourcesbyregion,alongwiththecharacteristicsofthegenerationplantsandtheirimplicationsforthegrid.Finally,weaddressthemostfrequentlyusedtechnicaloptionsandfacilitiestomanagetheintegrationofrenewableenergysourcesandtherebytocomplywithtechnical
requirementsandguidelines.
Overall System Planning and Development
InMay2008,theSpanishMinistryofIndustry,TradeandTourismpassedthe20082116planningdocumentforthegasandelectricitysectorstoensurethesafetyandqualityoftheenergysupply.Thisplansetsoutasubstantialprograminvolvingtheconstructionofnewpowerinstallations.
In2009RedElctricadeEspaa(REE),theSpanishcorporationthatoperatesthenationspower
transmissionsystemandelectricitygrid,continuedtodrawupforecaststudies,bothforpowerdemandandcover.REE,asoperatoroftheinsularandextrapeninsularsystems,likewisedrawsupboththedemandandpowerpeakforecastsandtheestimatesofgeneratingequipmentneedsforthesesystems.
REEiscarryingoutinvestmentsaimedatreinforcingthegridmeshinordertocoverincreasesindemandinsomeareasofthemainlandandtofacilitatetheestablishmentofthenewgenerationinstalled,mainlycombinedcyclesandwindpowerplantsand,toaneverincreasingextent,solarthermalplants.
Network Structures in Spain
ThispartofthereportdescribesthebasictechnicalconfigurationsofSpanishdistributiongridsincludingsubstationsandsecondarysubstations.Theanalysisfocusesonmedium andlowvoltagedistributiongrids.ItalsooutlinesrelevantaspectsofdistributedgenerationathighervoltagelevelsinSpain.
Grid and Voltage Levels
TheSpanishpowergridatallvoltagelevelsisathreephasealternatingcurrentgridoperatedatafrequencyof50Hertz.FourcommonvoltagelevelshavebeenestablishedintheSpanish
powergrid
as
shown
in
Table
5.
This
classification
of
voltages
is
according
to
the
IEC
definitions.
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Table 5: Overview of Voltage Levels in Spain per IEC Definitions
System Name
(IEC Definition)Abbreviation Rated Voltage Role
Extra-high voltage EHV 400 kV, 220 kV15 Transmission grid
High voltage HV132 kV, 110 kV
66 kV, 45 kV
Distribution gridMedium voltage MV
30 kV, 20 kV,15 kV, 13.2 kV,
11 kV
Low voltage LV 400 V
Spanishlegislation(RoyalDecree223/2088)givesasimilarclassificationforlinesabove1kV:
Specialcategory:Linesofnominalvoltageaboveorequalto220kV,ortheonesoflower
voltagethatareoperatedbytheTSO. Firstcategory:Linesofnominalvoltagebelow220kVandabove66kV
Secondcategory:Linesofnominalvoltageequaltoorbelow66kVandabove30kV
Thirdcategory:Linesofnominalvoltageequaltoorbelow30kVandabove1kV.
Thecharacteristicsandfunctionsofthemainvoltagelevelsarediscussedbelow.
The Spanish Transmission System
ThetypicalvoltagelevelsforthetransmissiongridinSpainare400kVand220kV.The
internationalconnectionsarealsoconsideredasapartofthetransmissionsystem.REEistheTransmissionSystemOperator(TSO)andownsabout99.8percentofthe400kVpowerlinesand98.5percentofthe220kVpowerlines.AccordingtocurrentSpanishregulationsall220kVmustbetransferredtotheTSO.
TheElectricitySectorAct54/1997confirmedtheroleofREEasacornerstoneofsystemoperation.Thislawcreatedawholesalepowermarketthatrequiredaneffectivelymanagedtransmissiongridtoworkproperlyandacoordinatedoperationofthegenerationtransmissionsystemtoensurethatdemandwouldbesatisfiedatalltimes.
Act17/2007of4JulyinSpainamendedthepreviouslawtoadaptittoEuropeanDirective
2003/54/CEwhich
established
the
common
guidelines
for
the
domestic
power
market.
This
law
hasresultedinthedefinitiveconsolidationoftheREEsTSOmodel.Inthisregard,REE,asthesystemoperator,guaranteesthecontinuityandsecurityofthepowersupplyandtheproper
15Inthepast,theDSOscontrolledpartsofthe220kVnetwork,butithasmostlybeenmovedtotheTSO.
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coordinationoftheproductionandtransmissionsystem,performingitsfunctionsbasedontheprinciplesoftransparency,objectivity,andindependence.
REEisnotjustthemanager(operator)ofthetransmissiongridbutlikewisehasexclusiveresponsibilityfordevelopmentandmaintenanceofthegrid.Thisisquitedifferentfromthe
German
case
where
several
transmission
grid
owners
and
operators
coexist.
LikeGermany,SpainispartoftheEuropeanNetworkofTransmissionOperatorsforElectricity(ENTSOE),andthereforeoperatesaccordingtorulesintheOperationHandbookofENTSOE.Thetransmissiongridisameshedsystemwithhighstandardsforsystemstability(frequency,voltage,dynamicstability)andsecurityofsupply.Overheadlinesdominatethegridinfrastructure.Figure7illustratestheSpanishtransmissionsystemwith400kVlinesrepresentedinredand220kVlinesrepresentedingreen.
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Figure 7: Spanish Transmission System
Source: REE (http://www.ree.es/transporte/mapa_red_transporte.asp)
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The Spanish Distribution System
ThetypicaldistributionvoltagelevelsinSpainare132kV,110kV,66kV,45kV(highvoltage),30kV,20kV,15kV,13.2kV,11kV(mediumvoltage),and380V(400Vinthelatestregulation,RD842/2002,lowvoltage).
InSpain
the
main
distribution
companies
are
Iberdrola,
Endesa,
Gas
Natural
Fenosa,
Hidrocantbrico,andE.Onwithamarketshareof40percent,39percent,15percent,2.5percent,and2.5percenteach,whichcombinedrepresent99percentofthetotaldistributionactivity.
HV Distribution Grid
SpanishHVgridsareofmeshedtopology(moreorlesscomplex)andcanbeoperatedalsoinameshedphilosophy(closedloop)orradial(openloop).Theexceptionareafewradialbuiltnetworksinruralareas,butevenintheseareasthemostcommontopologyistheopenloop,sothereispossibilityofsupportthroughasecondline.ThisgridisusedtofeedthedistributionsubstationsthatareconnectedtotheMVgrid.ThelayoutoftheHVbusbarofthese
distributionstationsdependsontheareatheyarebuilt.MostoftheHVgridcomplieswithn1securitycriterion(fortransformersandlines).Securitycriterian2canbeappliedforHVgridsassociatedtourbanareas,whenthereareforexamplesubstationsfedbycriticaldoublecircuitlines.Figures8through10illustratedifferentnetworktopologiesappliedattheHVlevelinSpain.
Figure 8: Looped HV Grid (Single Source Point)
Source: KEMA
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Figure 9: Bridge Configuration (HV Grid Fed from Two Points)
Source: KEMA
Figure 10: HV Mesh Configuration
Source: KEMA
MV Distribution Grid
TheSpanishmediumvoltage(MV)grid)inSpainisdifferentiatedbyurban,semiurban,and
ruralareasthathavedifferentpowerquality,reliability,andcontinuityofsupplyrequirements.
Urban Medium-voltage Grids
UrbanMVgridsinSpainservehighdensityurbanareasfedbyundergroundcables.Thetypicalcablecrosssectionis240to400mm(nominallyequivalenttoarangeof400kcmilto750kcmil),butthereisasignificantheterogeneityofcrosssectionespeciallyinthelargecitiesduetodecadesofdifferentplanningcriteriaandnetworkdevelopmentcriteria.
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ThedesignphilosophyofMVgridsinSpainistoservetheMV/LVstationsinawaytheycanalwaysbefedfromatleastfromtwodifferentpoints.ThereshouldnotbeMV/LVstationsonsingle,radialMVsources.Thisisachievedbyapplyingmainlytwostandardnetworkdesigns:
Reflectionpointandsupportcircuit
Distributionpoint
Figure11illustratestheconceptbehindthereflectionpointandsupportcircuitdesign.Theideaistohaveanormallyopenbackupcircuit(CircuitodeApoyo)thatincaseoffaultinoneofthemainfeederswillbeabletocloseintothereflectionpointandfeedtheloadonthehealthyportionofthefaultedfeederafterthefaulthasbeenisolatedbyremotecontrolledswitches.TheseswitchesareassociatedtoRMUs(RingMainUnits)intheMV/LVstations(circlesinthefigure).IntheexampleshowninFigure11,afault(indicatedbythelightningbolt)hasoccurredonthefirstsectionofCircuit1nearthesourcestation(ST),whichhasbeenisolatedandtheremainderofthecircuitloadpickedupfromthereflectionbusviathebackupcircuit(greenindicatesaclosedbreaker,andwhiteindicatesanopenbreaker).
Figure 11: Urban MV Grid: Reflection Point and Support Circuit Design16
Source: Universidad Pontificia Comillas: Master Thesis by Trinidade Moya
Figure12illustratesthedistributionpointdesignthatisusedmainlyinhighdensityloadareas.Reliabledistributioncentersarebuiltascloseaspossibletotheloadcenterandtwoormorehighcapacitytrunkfeeders(circuitosallementadores)areconstructedfromtheremoteHV/MVtransformationsubstationstothedistributioncenters.Noloadisconnecteddirectlytothetrunkfeeders.MultipledistributioncircuitsemanatefromeachdistributioncenterandfeedmultipleMV/LVstationswithinthehighloaddensityarea.Figure12illustratesaconfigurationwithtwosuchdistributioncenters,butothercombinationscanbeused.TheMV/LVstationsnormally
consist
of
transformers
above
400
kVA,
with
one
or
more
transformers
per
station.
16STmeanssubstation.CircuitodeApoyomeansbackupcircuit.CXmeansreflectionpoint;abuswithcircuitbreakersandgroundswitchesusedtogroundthecircuitswhenthebreakersareopen.
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Figure 12: Urban Medium Voltage Grid: Distribution Point design17
Source: Universidad Pontificia Comillas: Master Thesis by Trinidade Moya
Rural Medium-voltage Grids
Spainhasmadeadifferentiationbetweenconcentratedanddispersedruralareas.Botharefed
mainly
by
overhead
lines,
though
dispersed
rural
areas
have
longer
lines,
commonly
causing
voltagedropproblemsrelatedtothelargeimpedanceofthelongoverheadlines.Thedesignnormallyconsistsofamainfeederwiththesameconductorcrosssectionoveritsfulllength,
17CentrodeRepartoCR1and2meansDistributionCentersNo.1and2,SubestaciaonTranformadorameansTransformationSubstation,TrafoT1andT1meanBank1and2.
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fromwhichseveralderivativefeeders(branches)aresuppliedtypicallywithsmallerconductors.
SimilarlytotheUnitedStates,theruralnetworksinSpainareequippedwithswitchesalongthelines(reclosersandsectionalizers)inordertomoreefficientlyisolatefaultysectionsandrestore
the
supply
to
the
healthy
ones.
The
main
feeders
of
the
rural
network
can
be
fed
from
two
alternativesubstationsoperatinginanopenloopmanner(makinguseofanormallyopenpointbymeansofaswitch),resemblingtheloopconnectedwithnormalopencontactphilosophythatisusedinGermany.Thisallowstheuseoflooprestorationschemesincaseoffaults.ThetypicalSpanishruralMVgridstructureisillustratedinFigure13.Unlikeurbanareas,MV/LVstationsinruralareasareusuallysuppliedfromasinglecircuit.
Figure 13: Rural MV Grid Struc ture
Source: KEMA
LV Distribution Grid
Thelowvoltagegrid(LVgrid)isathreephase400V,comprisingalsoaneutralwire.Thesegridsarebuiltandoperatedinaradialway,regardlessofbeingurbanorrural.Urbangridsaredominatedbyundergroundcables,whileruralgridsaredominatedbyoverheadlines.Ruralgridsaremoreexposedtovoltagedeviations(droporrise)duetotheirhigherperunitimpedancecombinedwithlongerlength.ThetypicalSpanishLVgridstructureisillustratedinFigure14.
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Figure 14: LV Grid Structure
Source: KEMA
Renewable Energy Sources (RES) in Spain
Electricityproducers
in
Spain
are
subjected
to
different
legislation
depending
on
the
technology
andenergysourceused.Producersareclassifiedintwomaingroups:specialregime(ex:renewableenergysources)andordinaryregime(ex:conventionalpowerplantssuchasnuclearpowerstations).Figure15showsabreakdownofthetotalinstalledcapacitybytechnologyattheendof2010.Figure16showstheannualevolutionoftheinstalledpowerbytechnologyfrom2005to2010.
Figure 15: Breakdown of the Total Installed Capacity by Technology at the End of 201018
Source: REE (Red Elctrica de Espaa)
18ThecategoryOtherSpecialRegimeincludescogenerationandwastetoenergyplantsbelow50MW.
Installed Pow er (GW)
Combined cycle; 25,2
Fuel/Gas; 2,9
Coal; 11,4
Nuclear; 7,7Hydro; 16,7
Wind; 19,8
Solar; 4,0
Other Special Regime;9,8
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Spainhadatotalinstalledcapacityinelectricpowerproductionof97.5GW(peninsularsystem)bytheendof2010.Thetotalinstalledcapacityinsolarandwindpowerproductionwas23.8GW(24percentofthetotalinstalledcapacity)attheendof2010.Nexttocombinedcycleplantsat25.2percentofthetotalresourcecapacity,windwasthenextlargestblockat19.8percentoftotal.
Figure 16: Annual Growth of Spains Installed Power Generation (GW)
Source: REE (Red Elctrica de Espaa)
Distributed Generation
Generally,distributedgenerationcomprisesgenerationplantsthatareconnectedtolow and
mediumvoltagedistributiongridsclosetoenergyconsumersandgenerationplantsforselfsupply.However,thisdefinitionassuchisnotusedinpracticeinSpain.Althoughtherearedifferentremunerationschemesforgeneratorsofdifferentsize,whichthereforewillbeconnectedtodistinctvoltagelevels,themainsplitinSpainismadebetweenthesocalledordinaryandthespecialregime.Thetechnologieseligibleforspecialregimearecogeneration,renewableenergysourcesandwaste.AccordingtotheSpanishlawRD661/2007,therenewableenergysourcesgroupisdividedineightsubgroupsasfollows:
b.1:solarenergy
b.2:windenergy
b.3:waves,geothermic,tides
b.4:andb.5:hydropower
b.6,b.7,andb.8:biomassandbiogas
Installationswithaninstalledcapacitylargerthan50MWarenotincludedinthespecialregime.However,iftheseinstallationsproducerenewableenergytheyreceiveapremiumequal
Installed Pow er (GW)
12,2
15,5
21,0
21,7
23,1
25,2
6,6
6,6
4,8
4,4
3,0
2,9
11,4
11,4
11,4
11,4
11,4
11,4
7,9
7,7
7,7
7,7
7,7
7,7
16,7
16,7
16,7
16,7
16,7
16,7
8,7
11,6
14,8
16,2
18,7
19,8
8,4
9
9,7
12,6
13,3
13,8
0 10 20 30 40 50 60 70 80 90 100
2005
2006
2007
2008
2009
2010
Combined cycle Fuel/Gas Coal Nuclear Hydro S.R. Wind S.R. Other
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tothatpaidtosmallerrenewableprojects(i.e.,thoselessthan50MW),butdiscountedby2080percent.DuetothisfinancialdisincentivetherearenoindividualrenewableenergyprojectsinSpainwithinstalledcapacityover50MW.
Point of Common Coupling
The
definition
of
point
of
common
coupling
in
Spain
is
similar
to
Germany,
i.e.
it
is
the
grid
connectionpointofagenerationplant.Itslocationdependsontheratedpowerofthegenerationplantandtechnicalandeconomicaspectsofthepowergrid(voltagelevel,utilizationofassets,networkimpedance,etc.).
Regional and Quantitative Allocation of Renewable Energy
In2009,thegeneratorsoperatinginthespecialregimesupplied32percentofthegrosselectricalconsumptioninSpain.Windfarmsalonesupplied14.5percentofSpainsgrosselectricalconsumptionin2009.
Figure17showstheshareofthedifferentrenewabletechnologiestothetotalinstalledcapacity
in
renewable
electricity
production
for
the
special
regime
(S.R.).
Figure 17: Breakdown of the Total Renewable Installed Capacity by Technology at the End of 2009
Source: REE (Red Elctrica de Espaa)
Wind Energy
WindpoweristherenewablesourcethathasexperiencedthelargestdevelopmentinSpain.ThepopulationdensityinlargeareaswithgoodwindresourceismuchlowerthaninGermany,
whichhas
provided
opportunities
to
build
larger
wind
farms.
The
development
has
taken
place
throughlargeinvestorssuchaselectricityandconstructioncompanies.Recently,thetrendisfornonelectriccompaniestoselltheirinstallationsduetotheincreasingtechnicalrequisitesinthissector.Thedevelopmentofthewindpowersectorgoesinthedirectionoflargerwindfarmsconnecteddirectlytothetransmissiongridduetothetechnicaldevelopmentofwindturbinestechnologyandtheavailablecapacityinthetransmissiongridtotransportmoreelectricpower,gettingbetterprices.Whentheinstallationcapacityislargerthan50MW,promotersdivideintoseveralinstallationsunder50MWinordertogetthehighestpayment.About60percentofthe
Installed Power (% Total Renewable i nstalled Power)
S.R. Hydro 7,8%
S.R. Wind 75,1%
S.R. Solar 13,9%S.R.Biomass 2,6%
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totalinstalledwindpowerisconnectedtothetransmissiongrid.Oftheremaining40percentconnectedtodistributionthelargemajorityisconnectedtothe132/110/66kVgrids.Only25percentisconnectedtotheradialoperateddistributiongrids(30kVandbelow).Windpowerisdistributedalloverthecountry,butthereissignificantincidenceoflargewindfarmsinthenorthernregionsofGaliciaandtothesoutheastinCastillaLaMancha.Figure18showsthe
installedwindcapacitydensity(kW/km2)inSpain.
Figure 18: Wind Capacity Geographic Density in Spain
Source: REE (Red Elctrica de Espaa)
Spainswindproductionishighlyvariablebothhourbyhouranddaytoday.Forexample,Spainsrecordhighwindproductionwasabout11:00amonFebruary24,2010at12,916MW,andtherecordlowwasonJune3,2009at164MWintheearlyafternoon.Onmostdays,windproductionpeaksatnight,andreachesaminimumbetweennoonand2:00pm.Downwardrampsinwindproductioninthemorningsoftenincreasemorningrampupsofconventionalgenerationinthesummeralongwithdispatchofpumpedhydroplants.SomekeyfactsaboutwindpowerinSpain:
RenewableenergyplanforSpain(20052010):~20,000MW(accomplished)
Officialnetworkplanningfor2016:29,000MW
Furtherincreaseexpectedfor2020incompliancewithproposedECinitiatives Productionrecords:54percentofdemand at3:50amonDecember30,2009
Solar Energy
Spainleadstheworldinthedevelopmentofsolarenergy,asitisoneofthesunniestcountriesinEurope.Morethan95percentofthetotalPVinstalledcapacityisconnectedtothe
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distributiongrid(below220kV)aswellasabout35percentofthetotalthermal(conventional)installedgeneratingcapacity.
Figure19showsthedistributionofsolarPVandsolarthermalpowerintheSpanishautonomouscommunities,byend2009.Atthistimetherewereabout3.3GWofsolarPVwere
connected
to
the
grid.
While
solar
thermal
is
present
only
in
the
communities
of
higher
solar
radiationexposure,suchasAndalucia,solarPVismuchmoreuniformalongthecountry,althoughstilldominatedbythesoutherncommunities.
a) b)
Figure 19: Installed Solar Power (MW) in the Autonomous Communities of Spain by End 2009a) PV and b) Solar Thermal
Source: REE and ASIF (Associacion Industrial Fotovoltaica)
AtpresenttheTSOhasnoremotemonitoringorremotecontrolcapabilityforanyofthe3.3GWofPVpowergenerationbecausetelemetrytotheTSOisonlyrequiredforDGprojectsof10MWorlarger,andtherearenoPVprojectsofthissizeinSpain.AstheinstalledMWofsolarPVexpands,thelackoftelemetryontheseprojectswillcreategreateroperatingproblemsfortheTSO.Also,SpainswinterpeakdemandisintheeveningwhenPVmakesnocontribution.Inthewintertheuseofmoltensaltenergystorageandhybridizationwithnaturalgas19canenablesuchsystemstoproduceduringthepeakdemandhours.Ontheotherhand,concentratingsolar
thermalhasapositivecorrelationwithSpainssummerpeakdemand.
19HybridizationwithnaturalgasislimitedbySpanishregulationsto15percentofsolarthermalplantcapacity,whereashybridizationwithbiomassorbiogasisallowedupto50percent.
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RES Compensation Arrangements in Spain
RESrevenuescanbedeterminedbyoneofthetwofollowingalternatives:
Feedintariff:thepricepaidpereachkWhproducedbyaRESinstallationisregulatedandfixedtoaconstantvalue,independentofmarketfluctuations.TheannualevolutionofthistariffdependsontheevolutionoftheaveragereferenceelectricitytariffinSpain(RT),asfeedintariffs(FIT)aresetasapercentageoftheRT.Thetariffisfixedforacertaincontractduration(e.g.,15years).TheregulatedfeedintariffforeachREStechnologydependsonthetypeofthetechnologyandontheyearwhentheinstallationisputonservice.Thisalternativeisaheritageofthepreviousregulation.RESfacilitiesgreaterthan10MWarecommittedtogivetodistributioncompanies(DISCOs)aproductionschedule30hoursinadvance,beingallowedtoadjustsuchschedule1houraheadofeachintradailymarket(sixcallsduringaday).HourlyenergydeviationsfromtheproductionschedulearepenalizedatapriceperkWhdeviatedequalto10percentoftheRT.Thispenalizationdoesnotapplyinadeadbandof20percentoftheproduction
scheduledforRESfacilities.Thisrule,whichimpliesabigchangeinRESregulationfromthepreviousframework,willapplytowindfarmsonlysinceJanuary1,2006.AsthegovernmentREStargetsarereached,theFITdecreases.WhentheFITcontractperiodforagivenRESprojectisover,itsenergyissoldatthemarket(pool)price.
Wholesalemarket:RESaregivenincentivestojointhewholesalemarket,followinginthiscasepracticallythesamerulesasordinarygenerators.AstheRESwillfacenewtechnicalandeconomicconstraintsbydoingso,theirremunerationschemeprovidesanadditionaleconomicincentive.Thetotalincomeisthesumofthemarketsellingprice,plusapremiumthatrepresentstheexternalitiesinasimilarwaytopreviousregulation,plustheabovementionedadditionalincentivetoaccessthemarket.Thepremiumand
theadditionalincentivearesetalsoasapercentageoftheRT.AsRESareintegratedinthewholesalemarket,theyhaveaccesstoalltherestofelectricitymarkets(daily,intradaily,ancillaryservices,etc.).Theycanearnmoneyiftheyareabletoparticipateinsuchmarketsorpayiftheyusesuchservices,beingthemostimportantthecostofproductiondeviationsfromthepredictions.Inthiscase,thereisnodeadband,andthepriceissettledthroughmarketmechanisms.
REShaveanadditionalincomeassociatedtoreactivepowerthatdependsonthetimeperiod(peak,flat,orvalleyhours)anditcanbepositiveornegativedependingonthepowerfactorthe
unit
is
providing.
This
income
encourages
RES
to
consume
reactive
power
(lagging
power
factor)invalleyhoursandtosupplyreactivepower(leadingpowerfactor)inpeakhours.Inpreviousregulationstherewasanincentivetokeepthepowerfactorequaltoone.
AninterestingaspectofcurrentSpanishlegislationistheeconomicincentivethathasbeenfixedforwindfarmstobeabletocopewithvoltagedipswithouttripping.Thisisoneofthemaintechnicalproblemsforwindgenerationexpansion,withhighpenetrationlevelsofwindgenerationthatcanalltripatonceifthereisavoltagedipinthetransmissionnetwork,
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threateningsystemstability.Thereisaneconomicincentiveof5percentofRTtoeachkWhsoldbyeachimmunizedwindparkagainstvoltagedipsduringaperiodoffouryears.
Interconnection Technical Requirements in Spain
RESproducersthatwishtoconnectattheEHVlevelmustconnectaminimumcapacityof100
MWat
any
one
point
of
interconnection
to
the
220
kV
grid
or
at
least
250
MW
at
any
one
point
ofconnectionwithtothe400kVgrid.ItispossibleseveralforsmallerprojectdeveloperstomakeajointapplicationtotheTSOtofulfillthisrequirement.RD436/2004definesadditionalcriteriaandareagainstatedagainintheRD661/2007(annex11)withsomemodifications:
1. Thecombinedcapacityofallspecialregimegeneratorsconnectedtoonelineofthedistributiongridcannotexceed50percentofthecapacityoftheline.
2. Thecombinedcapacityofallspecialregimegeneratorsconnectedtoonesubstationorsubstationtransformercannotexceed50percentofthecapacityoftherespectivesubstationortransformerservingthatvoltagelevel.
3. Forproducerswithoutstoragecapabilitiesornotabletodirectlymanagetheiroutput,
suchaswindpowerandPVproducers,itisalsoestablishedthattheMWcapacityoftheproducerorgroupofproducerssharingaconnectionpoint(pointofcommoncoupling),willnotexceed5percentofthegridshortcircuitduty(atthatpointonthesystem)expressedinMVA.Fordispatchablegenerators(biomass,solarthermal),theMWcapacityshallnotexceed10percentofthegridshortcircuitduty(atthatpoint)expressedinMVA.ThisisintendedtolimitthemaximumvoltagedeviationduetoDGoperationtotherangeof510percentofthelocalgridsnominalvoltage.
BecauseoftheabovelimitationsingridimpactsduetoDG,veryfewbackfeedsituationshave
developed
in
Spain.
In
practice,
the
criteria
above
only
restrict
the
connection
to
the
distributiongridandarenottheconnectiontothetransmissiongrid.Basedonutilityexperienceregardingconnectiontothedistributiongrid, criteria1and2fromthelistabovelimitthecapacitythatcanbeconnectedinabout10percentofthecases,whilecriteria3islimitinginapproximately90percentofthecases.DGprojectsinSpaindonothavemuchexperienceconnectingtotheMVdistributiongrid,sotheselimitationsmayneedtobereviewedinthecomingyearsaswell.Distributioncompaniesgenerallyconsiderthesecriteriatobeadequate,althoughtherehavebeensuggestions/discussionsontheinclusionoflocalloadasalimitingfactorfortheinterconnectionofspecialregimegenerationduetoconcernaboutbackfeedintoHVandthetransmissiongrid.
Photovoltaicplants
smaller
than
100
kVA
and
connected
to
low
voltage
networks
(below
1kV)
havespecificconnectionrequirementsenactedintheRoyalDecree1663/2000.Themostrelevantrequirementsofthislegislationaretheobligationstomaintainvoltageattheinterconnectionpointat5percentofthenominalvoltageandoperateatapowerfactorascloseaspossibletounity.
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Implications on Power Grid Operation
REE(TSO)has,alongtheyears,beenexperiencingwindgenerationtripsduetovoltagedips.Asaresult,ithasbeenmonitoringvoltageandgeneratorperformancesince2005.AnoperationalprocedurehasbeenimplementedaspartoftheSpanishgridcodethatestablisheswhen
generatorsmustremainconnectedinordertoallowridethroughintheeventofafault.StartingJanuary1,2008,allnewwindfacilitieshadtocomplywiththisvoltageridethroughregulation.Mostexistingplantshavemadethenecessaryretrofitstocomply,andonlysome1,000MWto1,500MWplantsstillneedtobeadapted.REEnowrunsrealtimesimulationtomodelscenariosofthreephasefaultsin70ofits400kVsubstations.ThesesimulationsallowtheTSOtotakeactionsfromadedicatedcontrolcentreinordertoensuresafesystemoperationandavoidfurthergenerationtripping.
Voltagecontrolforconventionalgenerationistypicallydoneatthesubstation.Thatisnotsufficientwherealargepenetrationofrenewablegenerationexists.REEhasinstitutedasystemtoincentiverenewablegeneratorstoprovidereactivepower:Generatorsreceiveabonusor
sufferapenaltyfor+8percentto 4percentof78.44perMWh,dependingonthepowerfactor.Thesystemoperatorissuesinstructionstomodifythepowerfactorsettings.
SinceApril1,2009,REEhasorderedallDGunitsabove10MWtooperateatpowerfactorsbetween0.98and0.99inductiveinordertoeliminatesuddenchangesinthevoltageprofileandavoidhighvoltages.REEbelievesthattheultimatesolutionistoenablevoltageschedulingcapabilityforallgeneratorsgreaterthan10MW.AkeyissueremainsastowhenandhowtoautomateDGvoltagecontrolandwhetherthisrequiresalocal,regional,ornationalstructure.
Connection Process to Transmission Network in SpainConnection Application Phase
Therearetwodifferentstages,accordingtoP.O12.2ofREE:
1 Requestforaccesstothetransmissiongrid.
2 Requestforconnectiontothetransmissiongrid.
Forstage1,thegeneratormustsubmitarequestforaccesstoaspecificnetworklocation(node)andsupplyavarietyoftechnicaldataaboutitsgeneratingplantfromratedpowertoPSS/E
controlblock
models
for
dynamic
analysis.
REE
also
requests
the
seasonal
generation
patterns.
Itisacompletesetofdataonthegeneratingunit,whichiscomplementedwithdataoninterconnectionlinesandalsowithdataonstepuptransformers.Furthermoretherearedifferentrequestsdependingonthegenerationtechnology.REEP.O12.1annexeslistallthenecessarydatafordifferentgenerationtechnologies.Afterreceivingtherequestforaccessaccompaniedbythegeneratordata,theSpanishTSOhastwomonthstodetermineifthesystemcapacitywillsupporttheconnection.Ifso,thegeneratoradvancestostagetwo.
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Atstagetwothegeneratormustsubmitthebasicdesignofitsinstallation,theconstructionprogramandareportshowingthattheinstallationfulfillsalltheconnectionrequirementsinInstalacionesconectadasalareddetransporte:Requisitosminimosdediseoyequipamiento.Thisdocumentdefinesprotectionrequirements,groundingrequirements,switchgeararrangements,etc.Thegeneratorhasonemonthtodeliverthesedocumentsafter
receivingapositivestage1approval.Initsturn,theTSOhasonemonthtodecideifthegeneratorsdocumentationisadequate.
Thegeneratordoesnothavetoperformanystudiesitself,sincethestudiesarecarriedoutbytheTSOusingdatasuppliedbythegenerator.ThegeneratorisfreetoasktheTSOforinformationaboutaparticularlocationornodeofthegridifhewishestoperformhisownstudiestoevaluatethefeasibilityoftheinterconnectioninagivennode.The[decidingauthority]usestheTSOstudiesforitsdecision.
Ifthestateoneproposalfails,thegeneratorcanproposealternativeconnectionpointsorrequestinformationonthegridreinforcementcostsnecessarytoeliminatetherestrictions.Ifthe
developeris
willing
to
pay
for
these
reinforcements,
while
advancing
to
stage
two,
he
must
pay
upfrontfor20percentofthesecosts.
Commissioning Phase
Twomonthsbeforetheplannedinterconnectiondate,thegeneratormustprovidetheTSOwithat
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