Getting to 100%：Six strategies for the challenging last 10%.docx

rerspectveGettingto100%:Sixstrategiesforthecha11enging1ast10%TrieuMai,*Pau1Denho1m,PatrickBrown,Wes1eyCo1e,E1aineHa1e,Patrick1amers,Cait1inMurphy,MarkRuth,BrianSergi,Danie1Steinberg,andSamue1F.Ba1dwinCONTEXT&SCA1EExpandingwindandso1ardep1oymentwhi1emaintainingtheexistingc1eane1ectricitygenerationhasemergedasthemostcost-effectivepathwaytosignificantIyreducee1ectricitysystememissions.Pathwaysforreachingmoreambitiouscommitments-inc1udingagrowingnumberca11ingfor100%renewab1eenergy(RE)or100%carbon-freee1ectricity-are1esscertain,withsomepathwaysre1yingonawiderangeofemergingtechno1ogiestomeetasma11fractionofdemand.Wegenera1izethisftna1incrementtodecarbonizethegridasthe1ast10%''whi1eacknow1edginguncertaintiesaroundtheprecisepercentageandwhentheseoptionswi11beneeded.Thisworkreviewssixtechno1ogystrategiesthatcou1dp1ayakeyro1einmeetingtheneedsofthe1ast10%andhigh1igh1sthecha11engesthataccompanyeachofthem.Thesetechno1ogiescanbepursuedindividua11yorasaportfo1ioofoptions.Thispaperseekstoimprovetheunderstandingofthetrade-offsandcharacteristicsofpossib1efutureso1utions,whichcou1dinformdecision-makingtoday.Thethresho1d(e.g.,REorCO21eve1)atwhichthiscostinf1ectionpointoccursdc-pendsonmanyfactors,inc1udinggridf1exibi1ity,techno1ogycosts,andhowcostisSUMMARYMeetingthe1astincrementofdemanda1waysposescha11enges,irrespectiveofwhethertheresourcesusedtomeetitarecarbonfree.Thecha11engesrimariIystemfromtheinfrequentuti1izationofassetsdep1oyedtomeethighdemandperiods,whichrequireveryhighrevenueduringthoseperiodstorecovercapita1costs.Achieving100%carbon-freee1ectricityobviatestheuseoftraditiona1fossi1-fue1-basedgenerationtechno1ogies,bythemse1ves,toservethe1astincrementofdemand一whichwerefertoasthe'1ast10%.,'Here,wesurveystrategiesforovercomingthis1ast10%cha11enge,inc1udingextendingtraditiona1carbon-freeenergysources(e.g.,windandso1ar,otherrenewab1eenergy,andnuc1ear),rep1acingfossifue1swithcarbon-freefue1sforcombustion(e.g.,hydrogen-anc1biomass-basedfue1s),deve1opingcarboncaptureandcarbondioxideremova1techno1ogies,anddep1oyingmu1tidaydemand-sideresources.Wequa1itative1ycompareeconomicfactorsassociatedwiththe1ow-uti1izationconditionanddiscussuniquechaiIengesofeachoptiontoinformthecomp1exassessmentsneededtoidentifyaportfo1iothatcou1dachievecarbon-freee1ectricity.A1thoughmanye1ectricitysystemsarea1ongwayfromrequiringthese1ast10%techno1ogies,researchandcarefu1considerationareneededsoonfortheoptionstobeavai1ab1ewhene1ectricitysystemsapproach90%carbon-freee1ectricity.INTRODUCTIONWindandso1artechno1ogiesareoftenidentifiedasthe1owest-costso1utionstoachievingadecarbonizedgrid.A1thoughthisgrowingbodyofresearchhasdemonstratedthatcost-competitivehighrenewab1eenergy(RE)systemsareachievab1e,ita1soidentifiesthedramaticincreaseincoststhatcanoccurassystemsapproach100%renewab1eor100%carbon-freee1ectricitymoregenera11y.Inthiswork,Wefocusoncarbon-freee1ectricityonanetbasis,whicha11owsforsomeemissionsthatareoffset,and,withtheexceptionofbioenergy,ondirectemissionson1y.Figure1showsexamp1esofnonIinearIyrisingcarbondioxide(CO2)abatementcostswhenapproachinga100%decarbonizedU.S.powersystem.7Thesecurvesareconsistentwithotherpub1ishedestimates.1.1Otherstudiessuggestthattheaveragecostofe1ectricity(withoutexterna1ities)canincreaseby20%-140%between90%and100%carbonfreedependingonstudydesignandmode1edtechno1ogies.-OCeIPressJouePerspectiveFigure 1. Non1inearIyrisingmargina1emissionsabatementcostswithdecreasingannua1emissionsI>atabasedoncapacityexpansionmodeIingsin1atingtrajectoriestodecarbonizethe11.S.powersector,withsensitivitiesreIatedtotechno1ogycosts,sitingandtechno1ogyavaiIabi1ityvanddemandgrowth.Themode1ingusesIhesameunder1yingframeworkas,butanupdatedversionof,theana1ysisfromCo1eeta1,5060708090IOCCO»reduction(%from20051vh)measured.WeUSesevera1quantitativeexamp1esfromtheUni1edSta1esthroughout1hisperspective,butthediscussionbroad1yapp1iesqua1itative1ytoa11majorcountries,economies,andPoWersystems.Whethercostsexceedbenefitswi11a1sodependonhowoneva1uestheemissionsreductions.Forexamp1e,therearewide-rangingestimatesofthesocia1costofcarbon.Giventhesesensitivitiesanduncertainties,thereisnoconsensusastowhenthisdramaticcostincreasewi11occurorwhetherincrementa1costsexceedbenefits.Withtechno1ogycostrcduc-tionsandimprovedmode1ing,the'4optima1,'RE1eve1andemissionsreduction1eve1,orthepointatwhichcostsbegin1oriseexponentia11y,hasshiftedtowardhighershares.ReCentestimatesrangefromapproximate1y80%to95%REfortheseinec-tionpoints.Whi1cacknow1edgingthesewide-rangingestimatesanduncer-tainticsfinthispaper,wegenera1izethischa11engeasthe'*1ast10%.''A1thoughexistingstudiesgenera11yhigh1ightthesamefundamenta1causesassoci-atedwiththe1ast10%prob1em,thereisa1ackofconsensusonthepreferredstrate-giesformeetingthischa11enge.Thisisnotsurprising,giventhediversityofpossib1eso1utionsandthespecu1ativenatureoftheircosts,giventheirear1ystageofdeve1-opment.ThisworksummarizesthechaiIengesassociatedwiththe1ast10%andhigh-1ightsthe