shallowpartnersonline

AnationallaboratoryoftheU.
S.
DepartmentofEnergyOfficeofEnergyEfficiency&RenewableEnergyNationalRenewableEnergyLaboratoryInnovationforOurEnergyFutureCost-BenefitAnalysisofPlug-InHybridElectricVehicleTechnologyA.
SimpsonPresentedatthe22ndInternationalBattery,HybridandFuelCellElectricVehicleSymposiumandExhibition(EVS-22)Yokohama,JapanOctober23–28,2006ConferencePaperNREL/CP-540-40485November2006NRELisoperatedbyMidwestResearchInstituteBattelleContractNo.
DE-AC36-99-GO10337NOTICEThesubmittedmanuscripthasbeenofferedbyanemployeeoftheMidwestResearchInstitute(MRI),acontractoroftheUSGovernmentunderContractNo.
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ntis.
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htmPrintedonpapercontainingatleast50%wastepaper,including20%postconsumerwasteCOST-BENEFITANALYSISOFPLUG-INHYBRIDELECTRICVEHICLETECHNOLOGY1ANDREWSIMPSONNationalRenewableEnergyLaboratoryAbstractPlug-inhybrid-electricvehicles(PHEVs)haveemergedasapromisingtechnologythatuseselectricitytodisplacepetroleumconsumptioninthevehiclefleet.
However,thereisaverybroadspectrumofPHEVdesignswithgreatly-varyingcostsandbenefits.
Inparticular,batterycosts,fuelcosts,vehicleperformanceattributesanddrivinghabitsgreatly-influencetherelativevalueofPHEVs.
Thispaperpresentsacomparisonofthecosts(vehiclepurchasecostsandenergycosts)andbenefits(reducedpetroleumconsumption)ofPHEVsrelativetohybrid-electricandconventionalvehicles.
AdetailedsimulationmodelisusedtopredictpetroleumreductionsandcostsofPHEVdesignscomparedtoabaselinemidsizesedan.
Twopowertraintechnologyscenariosareconsideredtoexplorethenear-termandlong-termprospectsofPHEVs.
Theanalysisfindsthatpetroleumreductionsexceeding45%per-vehiclecanbeachievedbyPHEVsequippedwith20mi(32km)ormoreofenergystorage.
However,thelong-termincrementalcostsofthesevehiclesareprojectedtoexceedUS$8,000,withnear-termcostsbeingsignificantlyhigher.
AsimpleeconomicanalysisisusedtoshowthathighpetroleumpricesandlowbatterycostsareneededtomakeacompellingbusinesscaseforPHEVsintheabsenceofotherincentives.
However,thelargepetroleumreductionpotentialofPHEVsprovidesstrongjustificationforgovernmentalsupporttoacceleratethedeploymentofPHEVtechnology.
Keywords:Plug-inHybrid;Hybrid-ElectricVehicles;Battery,SecondaryBattery;Modeling,Simulation;EnergySecurity.
1IntroductiontoPlug-InHybrid-ElectricVehiclesPlug-inhybrid-electricvehicleshaverecentlyemergedasapromisingalternativethatuseselectricitytodisplaceasignificantfractionoffleetpetroleumconsumption[1].
Aplug-inhybrid-electricvehicle(PHEV)isahybrid-electricvehicle(HEV)withtheabilitytorechargeitselectrochemicalenergystoragewithelectricityfromanoff-boardsource(suchastheelectricutilitygrid).
Thevehiclecanthendriveinacharge-depleting(CD)modethatreducesthesystem'sstate-of-charge(SOC),therebyusingelectricitytodisplaceliquidfuelthatwouldotherwisehavebeenconsumed.
Thisliquidfuelistypicallypetroleum(gasolineordiesel),althoughPHEVscanalsousealternativessuchasbiofuelsorhydrogen.
PHEVbatteriestypicallyhavelargercapacitythanthoseinHEVssoastoincreasethepotentialforpetroleumdisplacement.
1.
1Plug-InHybrid-ElectricVehicleTerminologyPlug-inhybrid-electricvehiclesarecharacterizedbya"PHEVx"notation,where"x"typicallydenotesthevehicle'sall-electricrange(AER)–definedasthedistanceinmilesthatafullychargedPHEVcandrivebeforeneedingtooperateitsengine.
TheCaliforniaAirResourcesBoard(CARB)usesthestandardUrbanDynamometerDrivingSchedule(UDDS)tomeasuretheAERofPHEVsandprovideafaircomparisonbetweenvehicles[2].
Bythisdefinition,aPHEV20candrive20mi(32km)all-electricallyonthetestcyclebeforethefirstengineturn-on.
However,thisall-electricdefinitionfails1ThisworkhasbeenauthoredbyanemployeeoremployeesoftheMidwestResearchInstituteunderContractNo.
DE-AC36-99GO10337withtheU.
S.
DepartmentofEnergy.
TheUnitedStatesGovernmentretainsandthepublisher,byacceptingthearticleforpublication,acknowledgesthattheUnitedStatesGovernmentretainsanon-exclusive,paid-up,irrevocable,worldwidelicensetopublishorreproducethepublishedformofthiswork,orallowotherstodoso,forUnitedStatesGovernmentpurposes.
toaccountforPHEVsthatmightcontinuetooperateinCD-modeafterthefirstengineturn-on.
Therefore,theauthorusesadefinitionofPHEVxthatismoreappropriatelyrelatedtopetroleumdisplacement.
Bythisdefinition,aPHEV20containsenoughuseableenergystorageinitsbatterytodisplace20mi(32km)ofpetroleumconsumptiononthestandardtestcycle.
Notethatthisdefinitiondoesnotimplyall-electriccapabilitysincethevehicleoperationwillultimatelybedeterminedbycomponentpowerratingsandtheircontrolstrategy,aswellastheactualin-usedrivingcycle.
1.
2ThePotentialofPlug-InHybrid-ElectricVehiclesThepotentialforPHEVstodisplacefleetpetroleumconsumptionderivesfromseveralfactors.
First,PHEVsarepotentiallywell-matchedtomotorists'drivinghabits–inparticular,thedistributionofdistancestraveledeachday.
Basedonprototypesfromthelastdecade,PHEVstypicallyfallinthePHEV10-60range[3].
Figure1showstheUSvehicledailymileagedistributionbasedondatacollectedinthe1995NationalPersonalTransportationSurvey(NPTS)[4].
Clearly,themajorityofdailymileagesarerelativelyshort,with50%ofdaysbeinglessthan30mi(48km).
Figure1alsoshowstheUtilityFactor(UF)curveforthe1995NPTSdata.
ForacertaindistanceD,theUtilityFactoristhefractionoftotalvehicle-miles-traveled(VMT)thatoccurswithinthefirstDmilesofdailytravel.
Foradistanceof30mi(48km),theutilityfactorisapproximately40%.
Thismeansthatanall-electricPHEV30candisplacepetroleumconsumptionequivalentto40%ofVMT,(assumingthevehicleisfullyrechargedeachday).
Similarly,anall-electricPHEV60candisplaceabout60%.
Thislow-daily-mileagecharacteristiciswhyPHEVshavepotentialtodisplacealargefractionofper-vehiclepetroleumconsumption.
0204060801000102030405060708090100DailyMileage(mi)Probability(%)DailyMileageDistributionandUtilityFactorCurveDailymileagedistributionUtilityFactorcurveFigure1:DailymileagedistributionforUSmotoristsbasedonthe1995NationalPersonalTransportationSurveyHowever,forPHEVstodisplacefleetpetroleumconsumption,theymustpenetratethemarketandextrapolatethesesavingstothefleetlevel.
AsecondfactorthatisencouragingforPHEVsisthesuccessofHEVsinthemarket.
Globalhybridvehicleproductioniscurrentlyseveralhundredthousandunitsperannum[5].
Becauseofthis,electricmachinesandhigh-powerstoragebatteriesarerapidlyapproachingmaturitywithmajorimprovementsinperformanceandcosthavingbeenachieved.
AlthoughHEVcomponentsarenotoptimizedforPHEVapplications,theydoprovideaplatformfromwhichHEVcomponentsupplierscandeveloparangeofPHEVcomponents.
Finally,PHEVsareverymarketableinthattheycombinethebeneficialattributesofHEVsandbatteryelectricvehicles(BEVs)whilemitigatingtheirdisadvantages.
ProductionHEVsachievehighfueleconomy,buttheyarestilldesignedforpetroleumfuelsanddonotenablefuelsubstitution/flexibility.
PHEVs,however,aretruefuel-flexiblevehiclesthatcanrunonpetroleumorelectricalenergy.
BEVsdonotrequireanypetroleum,butareconstrainedbybatterytechnologiesresultinginlimiteddrivingranges,significantbatterycostsandlengthyrechargingtimes.
PHEVshaveasmallerbatterywhichmitigatesbatterycostandrechargingtimewhiletheonboardpetroleumfueltankprovidesdrivingrangeequivalenttoconventionalandhybridvehicles.
ThiscombinationofattributesisbuildingastrongdemandforPHEVs,asevidencedbytherecentlylaunchedPlug-InPartnersCampaign[6].
PHEVshavethepotentialtocometomarket,penetratethefleet,andachievemeaningfulpetroleumdisplacementrelativelyquickly.
Fewcompetingtechnologiesofferthispotentialcombinedrateandtimingofreductioninfleetpetroleumconsumption[7].
However,PHEVtechnologyisnotwithoutitschallenges.
Energystoragesystemcost,volume,andlifearemajorobstaclesthatmustbeovercomeforthesevehiclestosucceed.
IncreasingthebatterystoragebeyondthatofHEVsincreasesvehiclecostandpresentssignificantpackagingchallenges.
Furthermore,thecombineddeep/shallowcyclinginPHEVbatteriesisuniquelymoredemandingthanthatexperiencedbyHEVsorBEVs.
PHEVbatteriesmayneedtobeoversizedtolastthelifeofthevehicle,furtherincreasingcost.
GiventhatHEVsaresucceedinginthemarket,thequestionrelevanttoPHEVsis,"Whatincrementalpetroleumreductionscanbeachievedatwhatincrementalcosts"ThesefactorswillcriticallyaffectthemarketabilityofPHEVsthroughtheirpurchasepriceandcost-of-ownership.
Thispaperpresentstheresultsofastudydesignedtoevaluatethiscost-benefittradeoff.
2ModelingPHEVPetroleumConsumptionandCostThereductionofper-vehiclepetroleumconsumptioninaPHEVresultsfromtwofactors:1.
PetroleumdisplacementduringCD-mode,whichaspreviouslydiscussedrelatestothePHEVxdesignationbasedontheaddedbatteryenergycapacityofthevehicle.
2.
Fuel-efficiencyimprovementincharge-sustaining(CS)modeduetohybridization,whichrelatestothedegree-of-hybridization(DOH)oraddedbatterypowercapabilityofthevehicle.
HEVs,whichdonothaveaCD-mode,areonlyabletorealizesavingsviathissecondfactor.
ForaPHEVx,thesetwofactorscanbecombinedmathematicallyasfollows:()[]CVCSCVPHEVxFCFCxUFFCFC=1(1)whereFCPHEVxistheUF-weightedfuelconsumptionofthePHEVx,FCCVisthefuelconsumptionofthereferenceconventional(non-hybrid)vehicleandFCCSisthePHEVx'sCS-modefuelconsumption.
NotethatthisexpressionbecomesapproximateforPHEVswithoutall-electriccapabilitybecauseuseoftheutilityfactorinthiswayassumesthatnopetroleumisconsumedinthefirstxmilesoftravel.
Figure2usesEquation1tocomparethepetroleumreductionofvariousPHEVdesigns.
Weseethereareavarietyofwaystoachieveatargetlevelofpetroleumreduction.
Forexample,a50%reductionisachievedbyanHEVwith50%reducedfuelconsumption,aPHEV20with30%CS-modereductionandbyaPHEV40with0%CS-modereduction(thislastexampleisunlikelysincePHEVswillshowCS-modeimprovementduetohybridization,notwithstandingtheincreaseinvehiclemassfromthelargerbattery).
TodemonstratethefeasiblerangeofCS-modereduction,Figure2comparesseveralcontemporaryHEVstotheirconventionalcounterparts(inthecaseoftheToyotaPrius,acomparisonismadetotheToyotaCorollawhichhassimilarsizeandperformance).
Atthelowendofthespectrum,the"mild"HEVSaturnVueachievesamodestreductionoflessthan20%.
The"full"HEVToyotaPriusachievesthehighestpercentagereduction(40%)ofallHEVscurrentlyonthemarketalthough,inadditiontotheplatformenhancementsemployedinproductionhybrids,italsousesanPotentialReductionofPetroleumConsumptioninPHEVsPrius(Corolla)CivicAccordHighlanderEscapeVue0%10%20%30%40%50%60%70%80%90%100%0%10%20%30%40%50%60%70%80%90%100%ReductioninCS-modePetroleumConsumption(%)TotalReductioninPetroleumConsumption(%)PHEV60PHEV40PHEV20HEVChallengingregionforHEVtechnologyFigure2:Potentialper-vehiclereductionofpetroleumconsumptioninPHEVsadvanced(Atkinson-cycle)enginetechnology.
NotethatnoneoftheproductionHEVsachievethe50%reductiondiscussedintheaboveexample,suggestingthatthereisanupperlimitonthebenefitofhybridizationalone.
Reductionsexceeding50%areavailablethroughCD-modeoperationinaPHEV,althoughincreasingPHEVxrangescanbeseentoprovidediminishingreturnsduetothenatureoftheUtilityFactorcurve(Figure1).
ThePHEVdesignspaceinFigure2characterizedbyCS/CD-modefuelconsumptionhasamatchingspacecharacterizedbybatterypower/energy.
ImprovingCS-modefuelconsumptionimpliesanincreaseinDOHandbatterypower,whileincreasingCD-modebenefitimpliesanincreaseinPHEVxanduseablebatteryenergy.
Movingineitherdirectionincursadditionalvehiclecosts.
However,thelinkbetweenbatteryspecifications,CS/CD-modereductions,andvehiclecostsisnotobviousandmustbeexploredthroughdetailedvehiclefuelconsumptionandcostmodeling.
Therefore,amodelwasdevelopedtopredictthepetroleumreductionsandcostsofcontrastingPHEVdesignscomparedtoareferenceconventionalvehicle.
Thedetailsofthismodelarepresentedinthefollowingsections.
2.
1ModelingApproachandScopeoftheStudyThePHEVcost-benefitmodelincludesseveralsub-models.
First,aperformancemodelcalculatescomponentsizesnecessarytosatisfytheperformanceconstraintslistedinTable1.
Second,amassbalancecalculatesthevehiclemassbasedoncomponentsizesdeterminedbytheperformancemodel.
Third,anenergy-usemodelsimulatesthevehicle'sgasolineandelectricityconsumptionovervariousdrivingcycles.
Thevehicleperformanceandenergy-usemodelsarecoupledtovehiclemass,sothemodelisabletocapturemasscompoundinginthesizingofcomponents.
Fourth,acostmodelestimatesthevehicleretailpricebasedonthecomponentsizes.
Allcostsarereportedin2006USdollars.
Finally,theresultspost-processingperformscalculationstoreportthevehicleenergyconsumptionandoperatingcostsinmeaningfulways.
ThemodelisimplementedinaniterativeMicrosoftExcelspreadsheet.
Theenergy-usemodelisadetailed,second-by-second,dynamicvehiclemodelthatusesareverse-calculationapproach[8].
Itisalsocharacterizedasapower-flowmodelsinceitmodelscomponentlosses/efficienciesasfunctionsofdevicepower,ratherthanasfunctionsoftorque/speedorcurrent/voltageasinmoredetailedmodels.
Thisreverse-calculation,power-flowmethodprovidesrapidestimationofvehicleenergyusageandenablesthecoupled,iterativespreadsheetdescribedabove.
Asolutionisobtainedinonlyafewseconds,meaningthatthedesignspacecanbeexploredveryquicklyandthoroughly.
SeveralhundredPHEVdesignswerethereforeincludedinthestudy.
Themodelperformssimulationsofbothconventionalvehicles(CVs)andHEVs(includingPHEVs)sothatside-by-sidecomparisonscanbemade.
Theperformanceandenergy-usemodelswerevalidatedforaToyotaCamrysedanandHondaCivicHybrid.
Inbothcases,errorsoflessthan5%wereobservedintheestimatesofvehicleperformanceandenergyuse.
Twopowertraintechnologyscenarios(Table2)wereincludedinthestudy.
Thenear-termscenario(2005-2010)representsvehiclesproducedusingcurrent-statuspowertraintechnologies,whereasthelong-termscenario(2015-2020)allowsforadvancedtechnologiesexpectedtoresultfromongoingR&Deffortsandhigh-volumeproductionlevels.
Thelong-termscenariodoesnot,however,includeadvancedenginetechnologiessincetheauthorwantedtoisolatetheimpactofimprovedelectricdriveandenergystoragetechnologiesontherelativecost-benefitofPHEVs.
2.
2VehiclePlatform,PerformanceandCostAssumptionsAllvehiclesincludedinthestudysatisfiedthesameperformanceconstraintsandusedavehicleplatformidenticaltothebaselineCV.
ThebaselineCVwasamidsizesedan(similartoaToyotaCamryorChevroletMalibu)andrelevantparametersarepresentedinTable1.
Mostparameterswerecalculatedfromsales-weightedaveragedataforthetopsellingUSmidsizesedansin2003[9].
Someparameters,suchasrollingresistance,accessoryloads,passingacceleration,andgradeability,wereengineeringestimates.
Thebaselinemanufacturer'ssuggestedretailprice(MSRP)ofUS$23,392wasusedincombinationwiththepowertraincostmodeltoestimatethebaseline"glider"cost(i.
e.
vehiclewithnopowertrain).
Thecostofa121kWCVpowertrainwasestimatedatUS$6,002,leadingtoanestimatedbaselineglidercostofUS$17,390.
Table1:VehiclePlatformandPerformanceAssumptionsforMidsizeSedanPlatformParametersGliderMass905kgCurbMass1429kgTestMass1565kg(136kgload)GrossVehicleMass(GVM)1899(470kgload)Dragcoefficient0.
3Frontalarea2.
27m2Rollingresistancecoefficient0.
009Baselineaccessoryload800Welec.
(4000Wpeak)PerformanceParametersStandingacceleration0-97kph(0-60mph)in8.
0sPassingacceleration64-97kph(40-60mph)in5.
3sTopspeed177kph(110mph)Gradeability6.
5%at88kph(55mph)atGVMwith2/3fuelconverterpowerVehicleattributesEnginepower121kWFuelconsumption10.
6/6.
7/8.
8Lper100km(urban/highway/composite)MSRP$23,392Table2:PowertrainTechnologyScenariosfortheCost-BenefitAnalysisNear-TermScenarioLong-TermScenarioBatteryChemistryNiMHLi-IonModulecostTwicethatoflong-termscenario$/kWh=11.
1xP/E+211.
1[14]Packcost$=($/kWh+13)xkWh+680[14]SameModulemassNiMHbatterydesignfunction[15],seeFigure6Li-Ionbatterydesignfunction[15],seeFigure6Tray/straps+thermalmgmt=0.
06kg/kg[15]PackmassHarness+busbars=0.
14kg/kW[15]SameEfficiencyEquivalentcircuitmodelbasedonP/Eratio,seeFigure5SameSOCwindowSOCdesignwindowcurve,seeFigure4Same(assumesLi-Ioncyclelife=NiMH)MotorMasskg=21.
6+0.
833xkW[13]kg=21.
6+0.
532xkW[14]Cost$=21.
7xkW+425[14]$=16xkW+385[14]Efficiency95%peakefficiencycurve,seeFigure5SameEngineMasskg=1.
62xkW+41.
8[9]SameCost$=14.
5xkW+531[14]SameEfficiency34%peakefficiencycurve,seeFigure5Same2.
3PowertrainArchitectureThetwothingsthatdifferentiateaPHEVfromanHEVaretheinclusionofaCDoperatingmodeandarechargingplug.
Therefore,aPHEVcanbeimplementedusinganyofthetypicalHEVarchitectures(parallel,series,orpower-split).
Forthisstudy,aparallelarchitecturewasassumedwiththeabilitytodeclutchtheenginefromthepowertrain(Figure3).
Thisparallellayoutprovidesgreaterflexibilityinengineon/offcontrolcomparedtoHonda'sintegratedmotorassist(IMA)parallelsystem[10]ENGINETRANS.
BATTERYMOTORFigure3:ParallelHEVpowertrainarchitecturewheretheengineandmotorarealwaysconnected.
Tocreatemoreflexibilityinengineon/offcontrol,itwasalsoassumedthatallaccessories(includingairconditioning)wouldbepoweredelectricallyfromthebattery.
2.
4ComponentSizingBatteryThebatteryisthefirstcomponentsizedbythemodelandthetwokeyinputsarethePHEVxdesignationandthebatterypower-to-energy(P/E)ratio.
Theuseablebatteryenergyiscalculatedusinganestimateofthevehicle'sequivalentelectricalenergyconsumptionperunitdistancemultipliedbythetargetPHEVxdistance.
TheelectricalenergyconsumptionisestimatedusingthePAMVECmodel[11].
ThetotalbatteryenergyisthencalculatedbasedontheSOCdesignwindow.
Finally,theratedbatterypoweriscalculatedbymultiplyingthetotalbatteryenergybytheinputP/Eratioandthende-ratingby20%toaccountforbatterypowerdegradationatend-of-life.
Toachievesimilarbatterycyclelife,differentPHEVxrangesrequiredifferentSOCdesignwindows.
Thedailymileagedistribution(Figure1)meansthataPHEV10isfarmorelikelytoexperienceadeepcyclethanaPHEV60.
Therefore,theSOCdesignwindowmustbechosensuchthattheaveragedailySOCswingisconsistentacrosstherangeofPHEVs.
Figure4showstheSOCdesignwindowsassumedinthePHEVcost-benefitmodel,basedoncycle-lifedatapresentedbyRosenkrantz[12]andatargetbatterylifeof15years(assumingonefullrechargeeachday).
Figure4alsoshowstheresultingaveragedailySOCswingwhichisconsistentacrosstherange.
ElectricMotorThemotorpowerismatchedtothebatterypower,butwiththeresultingmotorpowerbeingslightlysmallerafteraccountingforelectricaccessoryloadsandmotor/controllerefficiency.
0%10%20%30%40%50%60%70%80%90%100%010203040506DailyMileage/PHEVx0DesignSOCwindowbasedonPHEVxAveragedailySOCswingbasedondailymileagedistributionDailymileageprobabilitydistributionFigure4:SOCdesignwindowforPHEVsEngineSeveralstepsarerequiredtosizetheengine.
First,therequiredpeakpoweroftheengineplusmotoriscalculatedusingthePAMVECmodel[11].
Thispoweristypicallydictatedbythestandingaccelerationperformanceandforthebaselinemidsizeplatformisapproximately120kW.
Themotorpoweristhensubtractedfromthetotaltoprovidearequirementfortheenginepower.
Thisproducessome"enginedownsizing,"buttherearedownsizinglimitsimposedbyotherperformanceconstraints.
Continuousperformanceevents(gradeabilityandtopspeed)determinetheminimumpermissibleenginesize.
Gradeabilityperformanceislimitedto2/3ofpeakenginepowerduetoenginethermalmanagementandnoise,vibration,andharshness(NVH)considerations.
Forthebaselinemidsizeplatform,theminimumenginesizeisapproximately80kW.
2.
5ComponentEfficiencies,Masses,andCostsEngineandElectricMotorAsdiscussedinsection2.
1,thePHEVenergy-usemodelisareverse-calculation,power-flowmodelthatsimulatescomponentlosses/efficienciesasafunctionofoutputpower.
Boththeengineandelectricmotorefficienciesaremodeledusingpolynomialexpressionsforcomponentinputpowerasafunctionofoutputpower.
Theenginecurveisbasedona4-cylinder,1.
9L,95kWgasolineengine.
A3rd-orderpolynomialwasfittedtodatafromanADVISORsimulation[8]usingthisengine.
Themotorcurveisbasedona50kWpermanentmagnetmachineanda9th-orderpolynomialwasfittedtodatafromanADVISORsimulationusingthismotor.
BothefficiencycurvesareshowninFigure5.
Theengineandmotormassesandcostsaremodeledaslinearfunctionsofratedoutputpower.
Theenginemassfunctionisderivedfromadatabaseof2003model-yearvehicles[9].
Thenear-termmotor-controllermassfunctionisbasedonthe2006currentstatuslistedintheFreedomCARandVehicleTechnologiesProgramPlan[13].
Thelong-termmotor-controllermassisbasedontechnologydemonstratedintheGMPreceptconceptvehicle[14].
Theenginecostfunctionisbasedonmanufacturers'dataprovidedtotheEPRIHybrid-ElectricVehicleWorkingGroup(HEVWG)[14].
Thenear-termandlong-termmotorcostfunctionsarealsobasedondatareportedbyEPRI[14].
PowertrainComponents-NormalisedEfficiencyCurves0%10%20%30%40%50%60%70%80%90%100%0%10%20%30%40%50%60%70%80%90%100%NormalisedPower(P/Pmax)Efficiency(%)EngineMotor-driveMotor-regenBatteryFigure5:EfficiencycurvesusedinthePHEVcost-benefitmodelBatteryBatteryefficiencyismodeledusinganormalizedfunctionforefficiencyvs.
inputpower(Figure5).
Thisrelationshipwasderivedfromanequivalentcircuitmodelusingrealisticvaluesfornominalopen-circuitvoltageandinternalimpedance.
Battery-modulemassforbothNiMHandLi-IontechnologyismodeledusingbatterydesignfunctionsdevelopedbyDelucchi[15]andshowninFigure6.
Theaddedmassofbatterypackagingandthermalmanagementwasalsobasedon[15].
Battery-module-specificcosts($/kWh)varyasafunctionofpower-to-energyratio(Figure6).
Thelong-termLi-IoncostcurveisbasedonestimatesfromEPRI[14].
Afterspeakingwithbatterysuppliersandotherexperts,itwasestimatedthatthenear-termspecificcostofNiMHmoduleswasapproximatelydoublethatofEPRI'slong-termprediction.
Thecostsofbatterypackagingandthermalmanagementarealsobasedonthoselistedin[14].
RechargingPlugandChargerPHEVsareassumedtobeequippedwithaninverter-integratedplug/chargerwith90%efficiencyandanincrementalmanufacturedcostofUS$380overthebaselineinvertercost[14].
BatteryDesignFunctions0200400600800100012001400160018002000050100150200SpecificEnergy(Wh/kg)SpecificPower(W/kg)NiMH(near-termscenario)LI-ION(long-termscenario)2520105BatteryCostFunctions020040060080010001200051015202530Power-to-EnergyRatio(1/h)ModuleSpecificCost($/kWh)NiMH(near-term)Li-Ion(long-term)Figure6:BatterydesignfunctionsandmodulecostcurvesassumedforNiMHandLi-IontechnologyRetailMarkupFactorsThecomponentcostfunctionsinTable2modelthemanufacturedcostofcomponents.
Toconvertthesetoretailcostsinavehicle,variousmarkupfactorsareapplied.
Amanufacturer'smarkupof50%anddealer'smarkupof16.
3%areassumedbasedonestimatesbyEPRI[14]2.
6PowertrainControlStrategyAgenericcontrolstrategywasdevelopedforthespectrumofPHEVdesigns.
Thiscontrolstrategyconsistsoffourbasicelements.
ThebasisofthestrategyisanSOC-adjustedenginepowerrequest:()ettdrivelinerequestengineSOCSOCkPParg=(2)WhentheSOCishigherthanthetarget,theenginepowerrequestisreducedtopromoteCDoperation.
Alternatively,whentheSOCislowerthanthetarget,theenginepowerrequestisincreasedtorechargethebattery.
Theadjustmentisgovernedbythefactorkwhichissetproportionaltototalbatterycapacity.
Anelectric-launchspeedof10mph(16kph)isalsospecified,belowwhichthestrategytriestooperatethevehicleall-electricallybysettingtheenginepowerrequesttozero.
However,boththeSOCadjustmentandelectriclaunchcancausethepowerratingsofthemotortobeexceeded.
Therefore,athirdelementofthestrategyistoconstraintheenginepowerrequesttowithinacceptablelimitssuchthatnocomponentsareoverloaded.
Finally,thereisengineon/offcontrollogic.
Theengineistriggeredonwhenevertheadjustedenginepowerrequestbecomespositive.
Onceon,however,theenginecanonlyturnoffafterithasbeenonforatleast5minutes.
Thisfinalconstraintisdesignedtoensuretheenginewarmsupthoroughlysothatrepeatedcoldstartsareavoided.
Theaimofthiscontrolstrategyistoprioritizedischargingofthebatterypack.
Giventhenatureofthedailymileagedistribution,thisapproachensuresthatthemaximumpetroleumwillbedisplaced.
However,thestrategydoesnotexplicitlycommandall-electricoperation.
Rather,itdischargesbatteryenergyatthelimitsofthebattery/motorpowercapabilitiesandusestheengineasneededtosupplementtheroadloadpowerdemand.
Therefore,thevehiclebehaviorthatresultsistotallydependentonthepowerratingsofcomponents.
Vehicleswithhigherelectricpowerratingswillhaveall-electriccapabilityinmoreaggressivedriving,whereasvehicleswithlowerelectricpowerratingswilltendtooperateina"blended"CD-modethatutilizesbothmotorandengine.
Formorediscussionofall-electricvs"blended"operation,thereaderisdirectedto[16].
2.
7DrivingCyclesThecost-benefitmodelsimulatesCVs,HEVs,andPHEVsovertwocycles–theUrbanDynamometerDrivingSchedule(UDDS)andtheHighwayFuelEconomyTest(HWFET)–usedbytheUSEnvironmentalProtectionAgency(EPA)forfueleconomyandemissionstestingandlabeling[17].
2.
8FuelEconomyMeasurementandReportingThePHEVfueleconomiesandoperatingcostsaremeasuredandreportedusingaprocedurebasedonamodificationoftheSocietyofAutomotiveEngineers'(SAE)J1711RecommendedPracticeforMeasuringtheExhaustEmissionsandFuelEconomyofHybrid-ElectricVehicles[18].
ThisproceduremeasuresthefuelandelectricityuseinbothCDandCS-modesandweightsthemaccordingtotheUtilityFactor(UF),assumingthePHEVsarefully-rechargedeachday.
Furtherdiscussionofthisprocedureforfueleconomymeasurementandreportingisprovidedin[17].
3ResultsPHEV2,5,10,20,30,40,50,and60vehicleswereconsideredinthestudy.
Also,anHEV0wasmodeledasaPHEV2withitscharger/plugremoved.
P/EratioswerechosentovaryDOH(definedastheratioofmotorpowertototalmotorplusenginepower)acrossarangeofapproximately10%–55%.
NotethattheenginedownsizinglimitcorrespondstoaDOHofapproximately32%,andthatDOHhigherthanthisresultsinexcesselectricpowercapabilityonboardthevehicle.
Figure7showsthebatteryspecificationsforthespectrumofPHEVsinthelong-termscenario.
Thetotalbatteryenergyvariesfromapproximately1.
5kWhfortheHEV0/PHEV2toapproximately25kWhforthePHEV60.
Thebatterypowervariesfromapproximately10–100kWacrosstherangeofDOH.
Figure7includesdashedlinesofconstantP/Eratio,whichvariedfromapproximately1–50.
Figure7alsoindicatestheminimumbatterypowerrequirement(approximately45kW)forthePHEVstohaveall-electriccapabilityontheUDDStestcycle.
Thebatteryspecificationsforthenear-termscenarioaresimilartoFigure7buthaveincreasedpowerandenergyrequirementsduetomass-compoundingfromthelowerspecificenergyofNiMHbatteries.
BatteryPowervsEnergyforPHEVs020406080100120051015202530TotalBatteryEnergy(kWh)BatteryPower(kW)PHEV2PHEV5PHEV10PHEV20PHEV30PHEV40PHEV50PHEV6011064220UDDSall-electricUDDSblendedFigure7:BatteryspecificationsforthespectrumofPHEVdesigns(long-termscenario)Figure8presentsthereductionsinannualpetroleumconsumptionandincrementalcostsforthespectrumofPHEVsinthelong-termscenario.
Takingamacroscopicview,weseethatincreasingPHEVxprovidesincreasingreductioninpetroleumconsumption.
RelativetothebaselineCV,whichconsumes659gal(2494L)ofpetroleumbasedon15,000mi(24,100km)eachyear,theHEVsreducepetroleumconsumptionby20%–28%.
ThePHEVsreducepetroleumconsumptionfurther,rangingfrom21%–31%forthePHEV2supto53%–64%forthePHEV60s.
However,theseincreasingreductionscomeatincreasingcosts.
TheHEV0sareprojectedtocostUS$2,000–$6,000morethanthebaselineCV,whereasthePHEV60sareprojectedtocostUS$12,000–$18,000more.
Thenear-termtrendisquitesimilartoFigure8,exceptthatpetroleumreductionsareslightlyreducedandvehiclecostincrementsaremuchlargerduetothegreatermassandsignificantlyhighercostofnear-termNiMHbatteries.
ReductioninFuelConsumptionvsPowertrainCostIncrement-MidsizeSedans$-$2,000$4,000$6,000LookingcloselyatFigure8,weseearepeatedtrendintherelativecost-benefitofPHEVswithvaryingDOH,andthereisanoptimumDOHforeachPHEVx.
FortheHEV0s,theoptimumDOH(32%)coincideswiththelimitofenginedownsizing.
ForthePHEVs,theoptimumDOHishigher(35%)tocoincidewiththeminimumbatterypowerrequiredforall-electriccapabilityontheUDDScycle(themaximumpowerrequirementontheHWFETcycleislower).
Thisall-electriccapabilityallowsvehiclestoavoidengineidlinglossesthatwouldotherwisebeincurredduetoengineturn-oneventssubjecttothe5-minuteminimumengineontimeconstraint.
TheoptimumHEVsandPHEVsforthenear-termandlong-termscenariosaresummarizedinTables3and4.
$8,ailCostIn000$10,000$12,000$14,000$16,000$18,000$20,0000100200300400500600ReductioninAnnualPetroleumConsumption(gals.
)RetcrementHEV0PHEV2PHEV5PHEV10PHEV20PHEV30PHEV40PHEV50PHEV60UDDSAERvehiclesFigure8:IncrementalcostsandannualpetroleumconsumptionforthespectrumofPHEVdesigns(long-termscenario)ItmustbeemphasizedthattheseoptimumDOHarehighly-dependentonthevehicleplatform/performanceattributesandthenatureofthedrivingpattern.
Theanalysisshouldberepeatedforotherbaselinevehicles(e.
g.
sport-utilityvehicles)toseehowthePHEVdesignswillvary.
Furthermore,PHEVsshouldbesimulatedoverreal-worlddrivingcyclestoidentifydifferencesinthepetroleumdisplacementandall-electricoperationcomparedtostandardtestcycles.
SuchfurtheranalysesshouldprovidetheunderstandingneededtooptimizePHEVsforthemarket.
Table3:Near-TermScenarioPHEVSpecifications–OptimumDOHVehiclesVehicleCurbMassEnginePowerMotorPowerDOHBatteryEnergyP/ERatioSOCWindowFuelCons.
Elec.
Cons.
RetailCost(kg)(kW)(kW)(kWh)(1/h)(L/100km)(Wh/km)(US$)CV142912210.
3---23,392HEV01451783833%1.
533.
437%7.
5---28,773PHEV21451783833%1.
533.
437%7.
3729,435PHEV51505804235%3.
615.
939%7.
11731,447PHEV101571824435%6.
98.
641%6.
73334,180PHEV201678854735%12.
74.
947%6.
06038,935PHEV301759894936%17.
23.
853%5.
48442,618PHEV401824915136%20.
83.
359%4.
810445,655PHEV501880945236%23.
92.
966%4.
511848,162PHEV601923965336%26.
42.
773%4.
113350,184Table4:Long-TermScenarioPHEVSpecifications–OptimumDOHVehiclesVehicleCurbMassEnginePowerMotorPowerDOHBatteryEnergyP/ERatioSOCWindowFuelCons.
Elec.
Cons.
RetailCost(kg)(kW)(kW)(kWh)(1/h)(L/100km)(Wh/km)(US$)CV142912210.
3---23,392HEV01412773632%1.
532.
837%7.
4---26,658PHEV21412773632%1.
532.
837%7.
2727,322PHEV51445784134%3.
515.
739%7.
01728,365PHEV101481794235%6.
68.
541%6.
53229,697PHEV201531814335%11.
84.
947%5.
75831,828PHEV301569824435%15.
93.
753%5.
07833,533PHEV401598834535%19.
03.
259%4.
59634,839PHEV501618844535%21.
62.
866%4.
110835,857PHEV601636844635%23.
62.
673%3.
712036,6813.
1EconomicsofPHEVsThePHEVcost-benefitanalysisalsoincludesasimplecomparisonofcost-of-ownershipoverthevehiclelifetime.
Thecomparisonincludestheretailcostofthevehicleandthecostofitsannualenergy(fuelandelectricity)consumption,butdoesnotaccountforpossibledifferencesinmaintenancecosts(foramorethoroughanalysisoftotalPHEVlifecyclecosts,thereaderisdirectedto[14]).
Figure9presentseconomiccomparisonsforthenear-termandlong-termscenarios.
Incalculatingannualpetroleumandelectricityconsumption,allvehiclesareassumedtotravel15,000mi(24,100km)peryeartobeconsistentwiththeassumptionsoftheUSEPA.
Thenear-termcostofretailgasolineisassumedtobeUS$3pergallon(US$0.
79perL),whereasahighergasolinecostofUS$5pergallon(US$1.
32perL)isassumedfortheprojectedscenario.
ThecostofretailelectricityisheldconstantatUS$0.
09perkWhbasedonthe2005USaverageretailpriceandhistoricaltrends[19].
Nodiscountratewasappliedtofuturecashflows.
Inthenear-termscenario,theHEVachievesalowercost-of-ownershipthantheCVafterapproximately10years.
However,thePHEVsneverachievealowercost-of-ownershipthantheCVnortheHEVoverthe15-yearvehiclelifetime.
Thelong-termscenarioprovidesasignificantcontrast,withtheHEVprovidinglowercostthantheCVafterapproximately4yearsandthePHEVsprovidinglowercostthantheHEVafterapproximately12years.
CumulativeVehicleplusEnergy(Fuel/Elec.
)Costs$-$10,000$20,000$30,000$40,000$50,000$60,000051015CumulativeVehicleplusEnergy(Fuel/Elec.
)Costs$-$10,000$20,000$30,000$40,000$50,000$60,0000510YearsafterpurchaseCumulativeCostYearsafterpurchaseCumulativeCost15PHEV40PHEV20PHEV10HEV0CVPHEV40PHEV20PHEV10HEV0CVNear-termLong-termFigure9:EconomiccomparisonofPHEVsinthenear-termandlong-termscenariosSeveralobservationscanbemadefromthesecomparisons.
Itisclearthatthese"payback"analysesaresensitivetothecostofgasolineandalsothevehicleretailcosts,whicharestronglyaffectedbythebatterycostassumptionsineachscenario.
ItisalsoclearthattheeconomicsofPHEVsarenotpromisingifgasolinepricesremainatcurrentlevelsandbatterycostscannotbeimproved.
However,itdoesseemthatacompellingbusinesscaseforplug-inhybridscanbemadeunderascenarioofbothhighergasolinepricesandprojected(lower)batterycosts,atleastfromtheperspectiveofthesimpleconsumereconomiccomparisonpresentedhere.
DespitetheuncertaintyofPHEVeconomics,thereareotherfactorsthatmayjustifytheincrementalPHEVcost.
Examplesincludetaxincentives;reductionsinpetroleumuse,airpollution,andgreenhouseemissions;nationalenergysecurity;reducedmaintenance;fewerfill-upsatthegasstation;convenienceofhomerecharging;improvedaccelerationfromhigh-torqueelectricmotors;agreenimage;opportunitiestoprovideemergencybackuppowerinthehome;andthepotentialforvehicle-to-gridapplications.
Alternativebusinessmodels—suchasbatteryleasing—alsodeservefurtherconsiderationsincetheymighthelptomitigatethedauntingincrementalvehiclecostandencouragePHEVbuyerstofocusonthepotentialforlong-termcostsavings.
4ConclusionThispaperhaspresentedacomparisonofthecosts(vehiclepurchasecostsandenergycosts)andbenefits(reducedpetroleumconsumption)ofPHEVsrelativetoHEVsandCVs.
Basedonthestudyresults,thereisaverybroadspectrumofHEV-PHEVdesignswithgreatlyvaryingcostsandbenefits.
Furthermore,thePHEVcost-benefitequationisquitesensitivetoarangeoffactors.
Inparticular,batterycosts,fuelcosts,vehicleperformance,anddrivinghabitshaveastronginfluenceontherelativevalueofPHEVs.
Giventhelargevariabilityanduncertaintyinthesefactors,itisdifficulttopredictthefuturepotentialforPHEVstopenetratethemarketandreducefleetpetroleumconsumption.
However,thepotentialforPHEVstoreduceper-vehiclepetroleumconsumptionisclearlyveryhigh.
Reductionsinexcessof45%areavailableusingdesignsofPHEV20orhigher.
Thiscomparesfavorablywiththe30%maximumreductionestimatedforHEVsHowever,itseemslikelythattheaddedbatterycapacityofaPHEVwillresultinsignificantvehiclecostincrements,eveninthelongterm.
Fortheprojectedscenariointhisstudy,aretailcostincrementofUS$3,000wasestimatedforamidsizesedanHEV.
Incontrast,thelong-termcostincrementsforamidsizePHEV20andPHEV40wereestimatedatUS$8,000andUS$11,000respectively.
Withoutknowingthefuturecostsofpetroleum,itisimpossibletodeterminethefutureeconomicsofPHEVs.
Butitdoesseemlikely,basedontheresultsofthisstudy,thatitwillbequiteachallengetojustifythePHEVcapitalcostpremiumonthebasisofreducedlifetimeenergycostsalone.
OtherincentivesandbusinessmodelsmayberequiredtocreateanattractivevaluepropositionforPHEVmotorists.
However,thelargepetroleumreductionpotentialofPHEVsofferssignificantnationalbenefitsandprovidesstrongjustificationforgovernmentalsupporttoacceleratethedeploymentofPHEVtechnology.
AcknowledgementTheauthorswouldliketoacknowledgetheprogrammaticsupportoftheU.
S.
DepartmentofEnergyOfficeofEnergyEfficiencyandRenewableEnergyFreedomCARandVehicleTechnologiesProgram.
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AuthorAndrewSimpson,VehicleSystemsEngineer,NationalRenewableEnergyLaboratory(NREL),1617ColeBlvd,GoldenCO80401USA;Tel:303-275-4430;Fax:303-275-4415;andrew_simpson@nrel.
gov.
AndrewjoinedtheAdvancedVehicleSystemsGroupatNRELin2005andhiscurrentfocusisplug-inhybrid-electricvehicles.
HeholdsaBachelorofMechanicalEngineering(2000)andPh.
D.
inElectricalEngineering(2005)fromtheUniversityofQueensland,Brisbane,Australia.
PriortoNREL,AndrewworkedasaCFDconsultantforMaunsellAustralia.
Healsoco-foundedtheSustainableEnergyResearchGroupatTheUniversityofQueenslandandwasacoordinatingmemberoftheUniversity's"SunShark"solarcarteamwhichracedsuccessfullyfrom1996-2000.
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SUPPLEMENTARYNOTES14.
ABSTRACT(Maximum200Words)Thispaperpresentsacomparisonofvehiclepurchaseandenergycosts,andfuel-savingbenefitsofplug-inhybridelectricvehiclesrelativetohybridelectricandconventionalvehicles.
15.
SUBJECTTERMSplug-inhybridelectricvehicles;PHEVs;fuelsavings;fueleconomy;vehiclecosts16.
SECURITYCLASSIFICATIONOF:19a.
NAMEOFRESPONSIBLEPERSONa.
REPORTUnclassifiedb.
ABSTRACTUnclassifiedc.
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