lawrence berkeley national laboratory · 2019. 12. 19. · lawrence berkeley national laboratory...

Lawrence Berkeley National Laboratory

Review of DC Power Distribution in Buildings: A Technology and Market Assessment Vagelis Vossos, Karl Johnson1, Margarita Kloss, Mukesh Khattar2, Daniel Gerber3, and Rich Brown 1 California Institute for Energy and Environment, University of California at Berkeley, 2 Electric Power Research Institute, 3 University of California at Berkeley Energy Technologies Area May, 2017

http://doi.org/10.7941/S9159Z LBNL-2001006

ReviewofDCPowerDistributioninBuildings:

ATechnologyandMarketAssessment

May2017

VagelisVossos,KarlJohnson1,MargaritaKloss,MukeshKhattar2,DanielGerber3,andRichBrown

1CaliforniaInstituteforEnergyandEnvironment,UniversityofCaliforniaatBerkeley

2ElectricPowerResearchInstitute,3UniversityofCaliforniaatBerkeley

ThisworkwassupportedbytheCaliforniaEnergyCommission,ElectricProgramInvestmentCharge,underAgreementNo.EPC-14-015,andtheU.S.DepartmentofEnergy,OfficeofEnergyEfficiencyandRenewableEnergyunderContractNo.DE-AC02-05CH11231.

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Disclaimer

TheLawrenceBerkeleyNationalLaboratoryisanationallaboratoryoftheDOEmanagedbyTheRegentsoftheUniversityofCaliforniafortheU.S.DepartmentofEnergyunderContractNumberDE-AC02-05CH11231.ThisreportwaspreparedasanaccountofworksponsoredbytheSponsorandpursuanttoanM&OContractwiththeUnitedStatesDepartmentofEnergy(DOE).TheRegentsoftheUniversityofCalifornia,northeDOE,northeSponsor,noranyoftheiremployees,contractors,orsubcontractors,makesanywarranty,expressorimplied,orassumesanylegalliabilityorresponsibilityfortheaccuracy,completeness,orusefulnessofanyinformation,apparatus,product,orprocessdisclosed,orrepresentsthatitsusewouldnotinfringeonprivatelyownedrights.Referencehereintoanyspecificcommercialproduct,process,orservicebytradename,trademark,manufacturer,orotherwise,doesnotnecessarilyconstituteorimplyitsendorsement,recommendation,orfavoringbyTheRegentsoftheUniversityofCalifornia,ortheDOE,ortheSponsor.TheviewsandopinionsofauthorsexpressedhereindonotnecessarilystateorreflectthoseofTheRegentsoftheUniversityofCalifornia,theDOE,ortheSponsor,oranyoftheiremployees,ortheGovernment,oranyagencythereof,ortheStateofCalifornia.ThisreporthasnotbeenapprovedordisapprovedbyTheRegentsoftheUniversityofCalifornia,theDOE,ortheSponsor,norhastheRegentsoftheUniversityofCalifornia,theDOE,ortheSponsorpassedupontheaccuracyoradequacyoftheinformationinthisreport.

Acknowledgments

Theauthorswouldlikethankthefollowingpeopleandorganizationsfortheircontributionstothisproject:

• ThevolunteermembersofourprojectTechnicalAdvisoryCommitteeforvaluableinputandfeedbackforthedurationofthisproject;

• theSouthernCaliforniaNationalElectricalContractorsAssociation/InternationalBrotherhoodofElectricalWorkersElectricalTrainingInstituteinCommerce,CAforhosting,andSouthernCaliforniaEdisonforsponsoring,ourstakeholderworkshop;

• theworkshopattendeesandpresenters,oursurveyandinterviewparticipants;• theEMergeAlliance,andBrianPattersoninparticular,fortheEmergeAlliancelistof

codesandstandardsrelatedtoDCpower;• andNiraliMerchant,formarketresearchonDC-readyproductsandconverter

efficiencies.ThisworkwassupportedbytheCaliforniaEnergyCommission’sElectricProgramInvestmentChargeprogramandbytheAssistantSecretaryforEnergyEfficiencyandRenewableEnergy,BuildingTechnologiesProgram,oftheU.S.DepartmentofEnergyunderContractNo.De-AC02-05CH11231.

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TableofContentsAcknowledgments.......................................................................................................................................1

ListofFigures...............................................................................................................................................3

ListofTables................................................................................................................................................4

1.IntroductionandBackground..................................................................................................................5

2.LiteratureReviewandInformation.........................................................................................................7

EnergySavings.........................................................................................................................................7

CaseStudiesandDemonstrationProjects...............................................................................................9

Cost........................................................................................................................................................11

Non-EnergyBenefitsandBarriers.........................................................................................................12

3.StakeholderInput..................................................................................................................................14

A.SummaryofStakeholderWorkshop..................................................................................................14

B.HighlightsofStakeholderSurveysandInterviews.............................................................................15

OnlineSurveys.......................................................................................................................................15

TelephoneInterviews............................................................................................................................25

4.SummaryandDiscussion.......................................................................................................................27

MarketAdoption...................................................................................................................................27

EnergySavings.......................................................................................................................................28

Non-EnergyBenefitsandBarriers.........................................................................................................29

Cost........................................................................................................................................................29

Standards...............................................................................................................................................29

5.ConclusionsandFutureResearch..........................................................................................................31

References.................................................................................................................................................33

AppendixA:ReferenceList........................................................................................................................36

AppendixB:ConverterEfficiencyCurves...................................................................................................49

PowerOptimizers..................................................................................................................................49

Microinverters.......................................................................................................................................49

StringInverters......................................................................................................................................50

BatteryInverters....................................................................................................................................51

ChargeControllers.................................................................................................................................51

DC/DCConverters..................................................................................................................................52

LEDDrivers.............................................................................................................................................53

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Rectifiers................................................................................................................................................53

AppendixC:StakeholderWorkshop..........................................................................................................55

AppendixD:SurveyandInterviewQuestions...........................................................................................62

SurveyQuestions...................................................................................................................................62

InterviewQuestions...............................................................................................................................66

InitialQuestionsforAll......................................................................................................................66

Researchers:......................................................................................................................................66

Industry(DCHardwareandApplianceManufacturers):...................................................................66

A&EFirms&Contractors(Architects,Engineers,ElectricalContractors,SecuritySystems,Telecom/NetworkInstallers):............................................................................................................66

UtilityStaffandUtilityRegulators.....................................................................................................67

EnvironmentalOrganizations............................................................................................................67

Close-outQuestionsforAll................................................................................................................67

AppendixE:EMergeAllianceReferenceListforDCCodesandStandards................................................68

ListofFigures

Figure1.DirectIntegrationofDCGenerationandEnd-UseLoads.............................................................5Figure2.WorldwideDCCaseStudies........................................................................................................11Figure3.NumberofRespondentActivities(Q1).......................................................................................16Figure4.TypesofRespondentActivities(Q1)...........................................................................................17Figure5.Respondents’AnticipatedInvolvementinDCPowerintheForeseeableFuture(Q2)...............18Figure6.Respondents’AnticipatedMarketDevelopmentofDCPowerintheForeseeableFuture(Q3) 18Figure7.Respondents’RatingforApplicationsofDCPowerinBuildingsfortheNext3–5Years(Q4)....19Figure8.Respondents’RatingforEndUsesofDCPowerinResidentialBuildingsfortheNext3–5Years(Q5)............................................................................................................................................................20Figure9.Respondents’RatingforEndUsesofDCPowerinCommercialBuildingsfortheNext3–5Years(Q6)............................................................................................................................................................20Figure10.Respondents’RatingofBenefitsAssociatedwithDCDistributioninBuildings(Q7)................21Figure11.Respondents’RatingofBarriersAssociatedwithDCDistributioninBuildings(Q8)................22Figure12.Respondents’RatingofDCSystemvs.ACSystemCost(Q9)....................................................23Figure13.CategorizationoftheCriticalNextStepstoAccelerateAdoptionofDCPowerinBuildings,basedonRespondents’Feedback(Q10)...................................................................................................24Figure14.Respondents’RankingtheIdealCaseStudiesforDCinBuildingsCategorizedbyBuildingType(left)andEnd-UseApplication(Q11).........................................................................................................25

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ListofTables

Table1.DCSystemElectricEnergySavingsEstimatesforResidentialandCommercialBuildings..............8Table2.PowerSystemComponentPeakEfficiencies.................................................................................8

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1.IntroductionandBackground

California’senergypolicyenvisionsafutureenergylandscapethatcanbestberealizedthroughahighlyintegratedandinteroperablegridwithveryenergyefficientendusescombinedwithon-siteenergygenerationandstorage.Directcurrent(DC)powerdistributionarchitectureshavebeenproposedasawaytointegratethevariouselectricalcomponentswithinbuildingsthatareneededtorealizethisvision,atalowercostthantraditionalalternatingcurrent(AC)powersystems.Thisreport’spurposeistosummarizethecurrentstateofknowledgeaboutthefeasibility,costeffectiveness,marketbarriers,customerneeds,andsavingspotentialforDCorhybridDC-ACsystemstopowerzeronetenergy(ZNE)residencesandcommercialbuildings,subdivisions,andcommunities.Particularfocusisonresidentialandlight-commercialbuildingapplications.Theall-ACpowersystemsinusetodayweredevelopedduringatimewhennearlyallpowergenerationandend-usedeviceswerenativelydesignedforACpower.Increasingly,however,ourpowersystemsneedtointegrateresourcesandloadsthatarenativelyDC:distributedgeneration,storage(batteries),andend-usedevices(electronics,DCmotorswithvariable-speeddrives,etc.).DCoffersanidealintegratingplatformforthesemodernpowercomponents;offeringenergysavingsandimprovedreliabilitywithpotentialforlowerfirstcost.Furthermore,theefficiency,reliability,andeaseofcontrolofDCpowerdistributioncouldbealow-costelementtoachievingZNEbuildings,thushelpingCaliforniameetitsZNEandglobalclimatechangegoals.

Figure1.DirectIntegrationofDCGenerationandEnd-UseLoads

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VariousaspectsofDCelectricalsystems—includingDCmicrogrids,datacenters,residentialappliances,batteries,fuelcells,lighting,electronics,communications,andrenewablesources—havebeenstudiedorpromotedbyindustry.ThesestudiesandotherindustryeffortsgenerallyconcludethatDCpoweroffersenergysavings,potentialforlowercapitalcost,andpowerqualityandreliabilityimprovements.Theseresultsaresimilartothosefoundwithhigh-voltageDC(HVDC)transmissionsystemsusedintheUnitedStates,Europe,andAsia.However,thereisverylittleperformanceinformationonDCsystemsinU.S.residentialorcommercialbuildings.Thisreportfirststartswithareviewofexistingacademicandmarketliteratureonthedesign,availability,andperformanceofDCdistributionsystemsandequipmentinbuildings.Itthensummarizesnewinformationcollectedduringthecourseofthisstudythroughastakeholderworkshop,andasurveyandin-depthinterviewsconductedwithpowersystemresearchers,designers,andmanufacturers.Thereportconcludeswithasummaryofthefindingsandsuggestednextstepsbasedonalltheinformationcompiledandcollected.

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2.LiteratureReviewandInformation

TheresearchteamconductedareviewandanalysisofrecentexistingliteratureonDCpowerdistributioninbothentirelyandhybridAC-DCbuildings.Theliteraturereview,consistingofapproximately200references,focusedoninformationrelatedtoDCdemonstrationprojectsandbuildingcasestudies,energysavings,costs,non-energybenefits,currentmarketstatus,andmarketandtechnicalbarriers.Overall,wefoundthatalargenumberofstudiesconcentratedonestimatingpotentialenergysavingsfromDC,whilelessresearchhasbeenperformedonthecost-effectivenessofDCendusesandsystems,oronthequantificationofthelesstangible,non-energybenefitsofDCdistribution.Thischaptersummarizesourmainliteraturereviewfindingsrelatedtothesetopicsofinterest.SeeappendixAforalistofthereferencesusedinthisstudy.1

EnergySavings

SeveralstudieshaveinvestigatedthepotentialelectricalenergysavingsfromDCdistributioninbuildings,theresultsofwhicharebasedeitheronmodelingeffortsoronacombinationofanalyticalmodelsandmeasurementsinactualdemonstrationbuildingswhereenergyuseoftheDCsystemiscomparedside-by-sidetoanequivalentbuildingwithACdistribution.AsshowninTable1,energysavingsfromDCdistributioninbuildingsmayvary.Thepresenceofbatterystorage,whichisaDCsource,andEVsinthecommercialsector(primarilybecauseEVsarelargeDCloadsthatsynchronizewellwithPVgenerationinacommercialbuilding),canincreasesavings.Wealsonotethatmodelingstudiesproduceawiderrangeofenergysavingscomparedtoexperimentalstudies.Thisrangeinsavingsestimatesisdueprimarilytotheactualorassumedpowersystemcomponentefficiencies(AC/DC,DC/DC,DC/ACconverters),which,toalargeextent,determinetheenergysavingspotential.However,othersystemparameters,suchassystemconfiguration,DCvoltage,andcoincidenceofPVandbuildingloadsarealsoimportantfactorsforenergysavings.

Table2summarizesthepowersystemcomponentpeakefficienciesusedinenergysavingscalculationsfromrecentliterature,aswellasfromproductsurveys(seeappendixBformoredetailsontheconverterefficiencysurveys).Wenotethatconverterefficienciesaredependentbothonvoltageconversionlevels,aswellasconverterpowerratings.

1 These references are also publicly available at the project’s webpage: http://dc.lbl.gov/epic-research-project/reference-list

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Table1.DCSystemElectricEnergySavingsEstimatesforResidentialandCommercialBuildingsStudyType Scenario* ElectricitySavings

Modeling

GenericbuildingwithbatteryStorage 2%–3%[1]

All-DCbuilding(res.andcom.)Nobatterystorage

5%residential8%commercial[2]

All-DCresidentialbuilding

5%w/obattery14%w/battery[3]

All-DCresidentialbuilding 5.0%conventionalbuilding7.5%smartbldg.(PV-loadmatch)[4]

Experimental

LED**DCsystem(nobatterystorage) 2%measured5%potential[5]

LEDDCsystem(nobatterystorage) 6%–8%(modeled)[6]

All-DCofficebuilding;BatterystorageandEV 4.2%[7]

All-DCbuildingEV,Nobatterystorage 2.7%–5.5%dailyenergysavings[8]

*AllscenariosincludealocalDCsource,(typicallyPV).**LED=LightemittingdiodeNote:ReportedenergysavingsarecomparedforabuildingwithDCdistributionrelativetoabuildingwithACdistributionandequivalentenduses.

Table2.PowerSystemComponentPeak2Efficiencies

ComponentPeakEfficiencies(%)

LiteratureReview ProductSurveys(averagevalues)

AC-DCCentralRectifier 93.0[3],96.5[1],96.9[8],97.0[2][4],98.0[4] 97.5%(25kW)

DC-ACInverter 95.0[3],96.9[6],97.6[1] 96.9%

DC-DCConv.(380Vto24/48V) 95.0[3],[8]96.0[1] 90.6%(0-1kW)97.5%(1-5kW)

MPPT*andChargeController 97.4[5],97.6[1],[8],98.0[3] 98.3%

ApplianceAC-DCConv.(highwattage)

90.0[3],94.2[8],96.5[1] 93.7%

ApplianceAC-DCConv.(lowwattage)

87.0[3],87.9[7],91.7[8],95.0[1] 87.6%

LEDDriver 93.3[7],94.9[8],97–98[6] 92%

EVCharger 96.0[7],97.2[8] N/A*MPPT=maximumpowerpointtracker

2 Most studies use peak or nominal efficiencies when calculating potential DC system energy savings. For operational efficiencies, see appendix B, which includes efficiency curves for various converters.

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CaseStudiesandDemonstrationProjects

TherearenumerousemergingcasestudiesanddemonstrationsforDCsystemsinbuildings.Afewnotableexamplesaredescribedbelow,andshowngeographicallyinFigure2:

1. Bosch,incollaborationwiththeCaliforniaLightingTechnologyCenter(CLTC),isdevelopingademonstrationprojectinChino,California,fundedbytheCaliforniaEnergyCommission’sElectricProgramInvestmentCharge(EPIC)program.Theproject’sgoalistodemonstratethebenefitsofDCdistributionincommercialbuildingsbyimplementingaPVpowered,direct-DC,380Vdistributionsystempoweringlightingandforkliftchargers.[9]

2. TheAllianceforSustainableColoradoisdevelopingaretrofitofa40,000squarefootcommercialbuildingfromACtoDCdistributioninsidethebuilding.ThebuildingwillbefedbyPVpowerandotherrenewableDCsources,willincludebatterystorage,andwillbecapabletoactasaDCmicrogrid.Thisproject’sgoalistocreateascalabledemonstrationthatwillshowcasethebenefitsofDCdistributionincommercialbuildings.[10]

3. NextHomeinDetroit,Michigan,isademonstrationDCtestbeddevelopedbyNextEnergy,featuringPV-supplieddirect-DCpowerforLEDlighting,ceilingfans,aDCcomputingcenter,floorheating,homeappliances,batterystorage,andbi-directionalEVcharging.TheNextHomefeaturesaPVarrayprovidingdirect-DCviaamainDCbusoperatingat380Vtoa13.2kilowatt-hourbattery,steppeddownto24VDCattheloadlevel.[11]

4. AquionEnergy,anenergystoragecompany,andIdealPower,apowerconvertermanufacturer,havepartneredtoinstallamicrogridshowcasingtheirtechnologiesatStoneEdgeFarm,anorganicwineryinSonoma,CA.Thesystemincludesa32kWPVarray,a350kWhcapacityofbatterystorageprovidedbyAquion,anda30kWmulti-portconverterfromIdealPower.ThissystemdoesnotpowerDCend-uses,butusesaDC-coupledconfigurationbetweenthePVarray,themulti-portconverter,andthebatteries.[12]

5. BoschhasimplementedaDCmicrogriddemonstrationproject,fundedbytheU.S.DepartmentofDefense,inFortBragg,NorthCarolina,whichincludesa15kilowatt(kW)PVarraypowering44DCinductionlights,4DCceilingfans,anda100kWlithium-ion(Li-ion)batterystoragesystem.Aside-by-sideequivalentACsystemreportedlyuses8percentmoreelectricitycomparedtotheDCmicrogrid.AhighlightoftheBoschDCpowersystemconfigurationisthatmaximumpowerpointtracking(MPPT)isnotapplieddirectlyafterthePVarray,butratherattheAC/DCgatewayconverter,allowingforhighersystemefficiency.[6]

6. TheHawaiiNaturalEnergyInstituteisdevelopingahybrid500kWDC/ACmicrogridattheMokuoLo’e(Coconutisland)inHawaii.[13]TheprojectincludesDCpowersources(PV,fuelcells,wind)andbatterystorage,anddistributesDCandACpowertovariousDCandACend-useloads.ItsPartnersincludeNextekPowerSystems,theOkinawaInstituteofScienceandTechnology,andtheNavalResearchLab,andisexpectedtobecompletedby2018.

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7. PhilipsisdevelopingaPoE-poweredlightingsystematClemsonUniversity,whichwillincludemorethan45,000lightpoints.Thesystemisexpectedtoleadtoa70percentenergysavingsovertraditionallightingsystemsinsimilarbuildingsandwillfeatureluminaire-integratedcontrols,whichwillbeaccessibleandcontrollableremotelyviaawebinterface.[14]

8. ARDAPowerhasdesignedaDCmicrogridwhichwillbebuiltinBurlington(Ontario),Canada.Theprojectwillshowcaseamicrogridforamanufacturingandofficebuilding,andincludesDC(16kWPV)andAC(10kWdiesel/gasgenerator,microturbine),batterystorage,a30kWbi-directionalinverter,ACandDCloads.[15]

9. Philipshasimplementedagrid-connected,PV-poweredDCtestbedinstallationforanofficeLEDlightingsystemattheEindhoven(Netherlands)HighTechCampus,andcompareditsenergyperformanceagainstanequivalentACsystem.Thesitehasdemonstrated2percentelectricitysavingsand5percentpotentialsavingsfortheDCsystem.[5]

10. FraunhoferhasbuiltaDCofficebuildingtestbed,whichincludesagrid-connected,380Vdirect-DCsystem,batterystorage,DClighting,EVcharger,anda24VDCnanogridforelectronicloads.TheDCsystemdemonstratedelectricitysavingsrangingfromapproximately2.7percentto5.5percentoveranequivalentACsystem.[8]

11. TheBeijingUniversityofCivilEngineeringandArchitecture(BUCEA)isconductingresearchtodemonstratetheenergyandnon-energybenefitsofDCdistributioninbuildings.ResearchersatBUCEAhaveestimated11percentsavingsfromshiftingtoanall-DCsystemfromthecurrentACsystem.[16]

12. XiamenUniversityinChinaimplementedaDCmicrogrid.Thedirect-DCsystemconsistsofa150kWPVarray,30kWairconditioningsystem,40kWEVchargingstation,and20kWLEDlighting.ResearchersconcludedthatefficientDCmicrogridapplicationsshouldincludeabi-directionalinverterandbatterystorage,andthatahybridDC-ACbuildingdistributionsystemwouldbemoresuitablefortoday’scommercialbuildings.[17]

13. NTTFacilitiesisdevelopingademonstrationDCmicrogridforanofficebuildinginHokkaido,Japan.TheDCsystemincludesaPVarray,Li-ionbatterystorage,LEDlighting,arefrigerator,electronics,andanEV.NTTresearchersreportthattheDCsystemyields4.2percentelectricitysavingscomparedtothesamesystempoweredbyAC.[7]

14. TheIslandCityinFukuoka,Japan,hasmadeavailableademonstrationAC/DCresidentialproject.TheSmartHouseusesACdistributiontopowerelectricloadsthroughaninverterthatisinterfacingwiththeACgridanda380VDCsystemconsistingofaPVarray,windturbine,andbatterystorage.[18]

WenotethatthemajorityofthesedemonstrationprojectsarefocusedeitheronshowcasingbuildingDCdistributionsystemsasaproofofconcept,oronestimatingelectricitysavings.Asdiscussedinthenextsections,fewofthesestudiesaddresscostissues,orattempttoquantifynon-energybenefitsoftenassociatedwithDCdistribution,suchashigherpowerquality,reliability,andresiliency.

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Figure2.WorldwideDCCaseStudies

Cost

Arelativelysmallbutgrowingnumberofstudieshaveaddressedthecost-effectivenessofDCdistributiononretrofitornewconstructioninresidentialorcommercialbuildings.MoststudiescomparetherelativecostdifferenceofthepowersystemcomponentsrequiredbyACandDCsystems.Forexample,WillemsandAerts[4]madethiscomparisonandfoundthattheoverallhardwarecostfortheACsystemisslightlyhigherthantheonefortheDCsystem,mainlyduetothepresenceofAC/DCpowerconvertersattheappliancelevelandaPVarrayinverter(insteadofacheaperMPPT)fortheACsystem.However,theauthorsalsonotedthatacentralbi-directionalrectifierfortheDCsystemwasnotaccountedforinthecostcalculation.AnotherstudybyFosterPorteretal.[19]foundthatinamatureDCmarket,DCdistributionforelectronicendusesisbeneficialnotonlyfromanoperatingcostperspective,butalsofromtheperspectiveofcapitalupfrontcost.However,lighting,motor,andresistiveenduseswerenotcost-effectiveforconventional,code-compliantbuildings.ForZNEbuildings,duetothepresenceofthePVsystemandtheinverterfortheACsystem,allendusesotherthanresistiveloadswerecost-effective.Overall,thisstudyfoundthatelectronics,followedbyheating,ventilationandairconditioning(HVAC)werethemostcost-effectiveapplicationsforDCpowerinbuildings.Furthermore,accordingtoPlanasetal.[20],meteringcosts,converters,anddistributioncostsarelowerforDCsystems,althoughduetogenerallylowervoltagedistributionandtechnologymaturityinACsystems,systemprotectioncostsarehigherforDCsystems.

KingandBrodrick[21]reportthatelectricianstypicallychargebythenumberofreceptaclesintheresidentialsectorandstatethatduetoNECrequirementsfortherelativedistancebetweenreceptacles,thenumberofreceptaclesinaDChousewouldbesimilartotheoneforanAChouse,whileelectricianretrofitcosts(ofconvertinganexistingACbuildingtoDC)wouldbe

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higherthannewconstructioncosts.Regardingretrofitcosts,Glasgoetal.[22]estimatedthatthecostofanAC-toDCresidentialretrofitisapproximately$6,000to$10,000,andconcludedthatthehighcapitalcostsofsuchaconversionwouldnotberecoveredbytheenergycostsavingsofDCdistribution.Forlow-voltagedistribution(<50V),costscanpossiblybereducedbecausetheDCdistributionsystemcanuselessexpensivecablingandinstallationlaborthanatraditionalACsystem.

DClightingproductsandsystems,suchastheArmstrong24VDCcommercialceilinggrid[23],havebeeninthemarketforaboutadecade,andmayalreadybecost-competitiveinsomeapplications.Specifically,PoElightingsystemswithoccupancy,daylighting,temperature,andothercontrolscurrentlydevelopedandmarketedbyPhilips,Cisco,NuLEDS,andEaton,amongothers,claimsignificantcostsavingscomparedtotraditionalACsystems.AccordingtoPhilips,PoElightingcanleadtoa25percentreductionininstallationcostdueto87.5percentlessmainswiringcomparedtoconventionalwiringsystemsforlighting[24].Similarly,EatonclaimsthattheirPoEDClightingsystemscanleadtoa40percentreductioninmaterialsandinstallationscosts[25].

Non-EnergyBenefitsandBarriers

SeveralstudiesclaimthatDCsystemsinbuildingshaveimportantbenefits,suchaspowerquality,reliabilityandcontrollability,resilienceduringgridoutages,interoperability,andothers,comparedtoACsystems[2],[26]–[29].Sanninoetal[30]statethatDCsystemsofferthepotentialforbetterreliability,astheyareusuallycapableofbeingdecoupledfromthegrid.Inaddition,AlLeeandTschudi[31]claimthat,byeliminatingpowerdistributionunitsandtheinverterontheoutputoftheuninterruptiblepowersupply(UPS)system,datacentersusinga380VDCdistributionsystemare200to1,000percentmorereliable(whenestimatinguptime)thanequivalentACsystemswhenadirectconnectiontothebatterybusisavailable,andcitetelecommunicationssystems(operatingat48VDC)asanexample.However,regardingpowerquality,althoughDCdistributionsystemsinbuildingsareoftentoutedforfewerharmonicsandlowervoltagedistortioncomparedtoequivalentsystemswithACdistribution,Whaiteetal.[32]notethatDCdistributionsystemsmayalsoexperienceharmonicsduetothepresenceofpowerconvertersconnectingtheDCbustoanACgrid,orevenbyscalingupordownDCvoltagewiththeuseofbi-directionalDC/DCconverters.TherearemanyfundamentalandsystemicbarriershinderingthemarkettransformationtoDCandhybridelectricsystems:

• Safetyandfaultprotection:PerMonadietal.[33],faultdetectionandfaultresistancedetectionmethodsapplicabletoACsystemsarenotalwaysapplicabletoDCsystems.Therefore,theyrecommendfurtherresearchonprotectionschemes,groundingmethods,andDCcircuitbreakers(ofmediumtohighvoltage).

• Thelackofmaturestandardsandguidelines,whicharealsoanimpedimentfortheapplicationofprotectionschemesinDCsystems[20].

• LackofDC-readyappliances[19],[26],[28]andpowerdistributionsystemcomponents.

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• MarketandawarenessbarriersstemmingfromtheentrenchedACdistributionsystem.Customers,installersandcontractors,standardsandcodebodies,aswellaspolicymakersarelessfamiliarwithDCsystems,andthereforeunlikelytoembracethem.Anecdotally,arecentefforttodevelopaDCdemonstrationprojectinFortCollins,Colorado[34],washaltedwhenthecontractorfortheprojectcouldnotgetbonded,becauseoftheDCnatureofthedistributionsystem.Instead,theprojectproceededwithACdistributioninthebuilding.

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3.StakeholderInput

A.SummaryofStakeholderWorkshop

TheprojectteamheldastakeholderworkshoponMarch15,2016,attheLosAngelesElectricalTrainingInstitute(operatedbytheInternationalBrotherhoodofElectricalWorkers).Approximately30stakeholdersfromavarietyofinstitutions,includingmanufacturers,policymakers,non-profits,andresearchorganizations,attendedtheworkshop.Theworkshopsolicitedinputandadviceonthetechnology,policy,andmarketdevelopmentneedsforadoptionofDCandAC-DChybridsystemsinresidentialandcommercialbuildings.ItfocusedonZNEbuildingswithphotovoltaics(PV),batterystorage,andelectricvehicle(EV)charging.Keyfindings,recommendations,andquestionsfromtheworkshoparelistedbelow.Formoredetailsontheworkshopproceedings,seeappendixC

• StandardsandopenprotocolsshouldbedevelopedtojumpstartproductionofDCproductsbyindustry.Then,asdemandforDCproductsgrows,economiesofscalewillresultinreducedcoststoconsumers.

• StakeholdersneedtoreachagreementonDCvoltages,sothatproductscanbedesignedaroundinternationalDCstandards.Commonvoltagelevelsare24volt(V),48V,125V,and380V.

• DemonstrationsarecriticallyneededtoshowcaseDCperformanceatbothend-useapplicationsandtheZNEsystemsapplications.Also,realmeteringdataareneededtoresolvedifferingviewsaboutsavingspotentialofDCorhybridDC/ACversusall-ACbuildings.

• BatterystorageandEVs,duetotheirinherentlyDCnature,havesignificantadvantagesforintegratingwithZNEbuildingswithPVsandinterconnectingwithsmartgridsystems.

• MoreresearchisneededtounderstandandresolvepowerqualityissuesinbothACandDCsystems.

• Theindustryshouldexploit“Trojanhorses”(e.g.,plugloads,residentialelectronics,emergencylighting)togetDCintouseandexpandfamiliarityandcomfortofendusers.Fortheforeseeablefuture,largeACloadsmayneedtoremainonthegrid.

• PoweroverEthernet(PoE)lightingandotherapplicationsareemergingwithseveralcompanies(NuLEDS,VoltServer,Lumencache,andothers)offeringsolutionsthattakeadvantageofthedigitalpowerandembeddeddatacapabilities.

• IssuesrelatedtoZNEbuildingsincludetheneedtoagreeonacommondefinitionofZNE3,theenergyuserequirementsforZNEoverthebuilding’slifetime,thesizingofbatterystorage(i.e.,initialrequirementversuslikelyrequirementoverthelifeofthebuilding),andtheallocationofsharedrenewablesincommunity-scaleprojects.

3 We note that a report on this specific issue (A Common Definition for Zero Energy Buildings) was published in 2015. https://energy.gov/sites/prod/files/2015/09/f26/bto_common_definition_zero_energy_buildings_093015.pdf

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• Akeychallengeforretrofitsistheneedtodeveloptransformationalschemesforretrofits,whichmustinvolvetheentiresupplychainforbuildingretrofits,fromequipmentmanufacturersanddistributors,todesignersandarchitects,tobuildingcontractorsandtrades.Industryshouldtakeadvantageoflessintrusivetechnologiesandsolutions,suchasusingexistingwiringforDCdistribution.

• DC/ZNEbuildingshavemultiplestakeholders.Utilities,governmentagencies,andregulatorscanraiseconsumerawarenessanddemandthroughincentives(e.g.,rebates).Also,designers,builders,installers,andoperatorswillrequiretrainingandeducationinordertoacceptandimplementDCdistributioninbuildings.

ToprovideinsightabouttheimportantissueofcodesandstandardsforDCpower,BrianPattersonoftheEMergeAllianceprovidedasummaryofthecurrentstateofcodesandstandards.HefirstpointedoutthatDCandhybridAC/DCstandardsandsystemsarecommonforanumberofapplicationssuchastelecomfacilities,off-gridsystems,andmobiletransportation,includinglargeships(bothcommercialandmilitary).Mr.PattersonpointedoutthatcodesalreadyallowDCsystemsinanindirectway,throughthebasicelectricaldesigncriteria,butcomplianceforDCsystemsrequiresextracalculationandeffort,soitisimportantthatDCstandardsareadoptedexplicitlyintothecodebooks.Fortypicalbuildingsystems,specificDCstandardsarenowlistedintheInstituteforElectricalandElectronicsEngineers(IEEE),theInternationalElectrotechnicalCommission(IEC),andtheNationalElectricalCode(NEC).Thesestandardshavebeendevelopedinthelast10years,withtheEMergeAllianceleadingthewayinNorthAmerica.

B.HighlightsofStakeholderSurveysandInterviews

Asonepartofthisresearcheffort,wetappedtheknowledgeandexperienceofDCpowerexperts,thoughtleaders,andstakeholderstoidentifythestateofDCadoption,includingDCequipmentsuppliers,customers,designers,builders,industry,government,environmentalorganizations,regulatorybodies,policymakers,andutilities.Thisinformationgatheringhelpedtoassessthestateoftheartandidentifyindustryandcustomerneedsandbarriers.

OnlineSurveys

Wedevelopedacomprehensivestakeholderlist,ande-mailedtheseindividuals,askingthemiftheywouldliketovolunteertorespondtoanonlinequestionnaire(11questions).4Wereceived39surveyresponses,ofwhichfourwereincomplete.Asummaryoftheonlinesurveyresultsispresentedbelow.Toprofileandunderstandthespectrumofsurveyrespondents,thefirstquestionaskedaboutactivitiesrelatedtoDCpowerdistributionandaboutendusesinbuildingsinwhichtherespondentortheirorganizationwasinvolved.Activitiesincludedresearch,product

4 The survey questionnaire is available in Appendix D

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development,manufacturing,fielddeployment/installation,sales,codesandstandards/policies,other,andnotapplicable.ManyoftherespondentswereinvolvedinmultipleaspectsofDCpower,asreflectedbythefactthat39respondentsclaimedparticipationinover92activities.Onaverage,respondentswereinvolvedinmorethantwoactivities,andasmanyassix,although16respondentsindicatedthattheywereinvolvedinjustasingleactivity.(SeeFigure3.)

Figure3.NumberofRespondentActivities(Q1)

Figure4breaksdownthepercentageforeachtypeofactivity,asidentifiedbythesurveyrespondents.Nearly33percentoftherespondentsparticipateinresearchactivities,and17percentareactiveincodesandstandards/policies.Approximately15percentofrespondentsparticipateinfielddeployment/installationandproductdevelopment.Sales,manufacturing,and“other”eachtalliedunder20percentoftheresponses.

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Figure4.TypesofRespondentActivities(Q1)

Questions2and3ofthesurveyaddressedrespondents’anticipatedinvolvementinDCpoweractivities,aswellastheirperceptionofhowDCmarketswillevolveintheforeseeablefuture(overthenextonetotwoyearsandthreetofiveyears).

• Question2Responses:Respondentsanticipatethattheirparticipationwillincreaseinthenextonetotwoyears,andfurtheraccelerateinthenextthreetofiveyears.

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Figure5.Respondents’AnticipatedInvolvementinDCPowerintheForeseeableFuture(Q2)

• Question3Responses:Inthenextonetotwoyears,30percentofrespondents

anticipatea10to20percentincreaseinmarkets.Inthenextthreetofiveyears,approximately40percentoftherespondentsexpecta25percentormoreincreaseinmarkets.

Figure6.Respondents’AnticipatedMarketDevelopmentofDCPowerintheForeseeableFuture(Q3)

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Question4focusedonapplicationsforDCpowerinthebuildingsector,andquestions5and6askedaboutrespondents’ratingofDCpowerbyend-useapplicationinresidentialandcommercialbuildings,respectively.

• Question4Responses:Respondentsbelievethatnewconstruction(includingZNE),commercialbuildings,AC-DChybridbuildings,andoff-gridsystemsholdthemostpromise,whileretrofitsandall-DCbuildingsfacechallengessuchascost,availabilityofcomponents,andothers.

Figure7.Respondents’RatingforApplicationsofDCPowerinBuildingsfortheNext3–5Years(Q4)

• Question5Responses:RespondentsselectedEVcharging,backupandemergency

systems,andlightingasaffordingthegreatestDCopportunityinthenextthreetofiveyearsinresidentialbuildings;electronicswasaclosefourth.Notably,clothes/dishwashinganddrying,andwaterheatingwerelast.

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Figure8.Respondents’RatingforEndUsesofDCPowerinResidentialBuildingsforthe

Next3–5Years(Q5)

• Question6Responses:Respondentsmostfrequentlyselectedlighting,EVcharging,backupandemergencysystems,andelectronicsasthemostpromisingend-useapplicationsforcommercialbuildings.Spacecooling/heating,refrigeration,andsmallapplianceswereinthemiddle,andwaterheatinganddish/clotheswashinganddryingwerelast.

Figure9.Respondents’RatingforEndUsesofDCPowerinCommercialBuildingsforthe

Next3–5Years(Q6)

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• Question7Responses:Question7askedrespondentstoordertheimportanceofrolesthatDCdistributioncanplaytoacceleratechangeinbuildings.Respondentsrateddeploymentofrenewableenergysources,energystorage,andreductionofenergyusageandpercapitacarbonfootprintasthemostcriticalreasonstodevelopDCdistributioninbuildings.ImprovingreliabilityandflexibleinstallationofplugloadsandlightingwererankedastheleastpressingrolesforDCdistributioninbuildings.

Figure10.Respondents’RatingofBenefitsAssociatedwithDCDistributioninBuildings(Q7)

• Question8Responses:Question8askedrespondentstoordertherelativeimportance

ofbarriersinhibitingdevelopmentofDCsystemsinbuildings.Respondentsratedlackofmarket-readyDCappliancesandequipment,anentrenchedACdistributionsystem,thehighcostofaDCsystemandoverallretrofit,andlackoftechnologyandefficiencystandardsasthemostchallengingobstaclesimpedingdevelopmentofDCsystemsinbuildings.Lackofpowersystemcomponents,wirelossesatlowvoltages,andelectricalsafetyissueswererankedaslesspressingbarriersforDCdistributioninbuildings.

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Figure11.Respondents’RatingofBarriersAssociatedwithDCDistributioninBuildings(Q8)

Questions9,10,and11requestedopen-endedresponsesfromsurveyrespondents.

• Question9Responses:RegardingtherelativecostofDCsystemscomparedtoACsystems,ofthe31respondents,14statedthatDCfirstcostswouldbehigherthanAC;9thoughtthatDCsystemswouldhavehigheroperatingcostsbutloweroperatingorlife-cyclecosts,and4respondedthatDCsystemswouldhavelowerlife-cyclecostscomparedtoACsystems.Respondentsanticipatedcostsrangingfromsavingsof30percenttoincreasingcostsat500percent.SeeFigure12fordetails.

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Figure12.Respondents’RatingofDCSystemvs.ACSystemCost(Q9)

• Question10Responses:RegardingthenextcriticalstepstoaccelerateadoptionofDC

powerinbuildings,wereceived31responses.ThetopcategorieswerethedevelopmentofDC–readyproductsandcodes&standards,followedbytheneedforadditionaldemonstrationprojects.OtherrecommendedstepswerethedevelopmentofacompellingmarketpropositionforDC,theremovalofmarketbarriers,developmentandimprovementofpowerconvertersforDCsystems,andtheavailabilityofincentives.SeeFigure13.

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Figure13.CategorizationoftheCriticalNextStepstoAccelerateAdoptionofDCPowerinBuildings,

basedonRespondents’Feedback(Q10)

• Question11Responses:RegardingtheidealcasestudyfordeploymentofDCpowerinbuildings,thetopcasestudieschosenbyrespondentsfordeploymentofDCpowerwerecommercialbuildingsandwarehouses(includingbigboxretail,mediumtolargeofficebuildings,buildingswithlargerooftopareaforPVintegration,officebuildings),followedbyZNEbuildings(commercialandresidential),residentialbuildings,datacenters,andoff-gridapplications.Withregardtotheidealend-useloads,lightingwasthedominatingenduse,followedbybatterystorage,HVAC,EVs,andelectronics&plugloads.NotethatPVintegrationwasanoverarchingthemethroughoutresponses.

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Figure14.Respondents’RankingtheIdealCaseStudiesforDCinBuildingsCategorizedbyBuilding

Type(left)andEnd-UseApplication(Q11)

TelephoneInterviews

Attheendofthesurveyquestionnaire,participantswereprovidedafurtheroptiontoparticipateinanin-depthtelephoneinterview.5Fromtheindividualswhoelectedtobeconsideredforatelephoneinterview,weselected10respondents,representingarangeofbackgrounds.

Severalrespondentsmentionedcostasoneofthemainareaswherefurtherdataandresearchareneeded.TheyalsoidentifieditasoneofthemainfactorsthatwilldetermineDCadoptionintheforeseeablefuture.Forexample,anarchitectworkingonaDCretrofitproject,highlightedtheneedforcostinformationsincebuildingownersandinstitutionsmaketheirdecisionsprimarilybasedonfirstcost.AccordingtoJohnWangofABB,inprinciple,thecostofDCconvertersshouldbelessthantheirACcounterparts,butthisisnotalwaysthecaseinpracticebecauseexistingcomponenttopologiesandconfigurationsmayrequireredesign,whilethelackofdemandforDCproductsdoesnotcreatethenecessaryeconomiesofscaletoreducemanufacturingcosts.Inaddition,StevePantanoofCLASPnotedthatoneofthepotentialbenefitsofDCsystemsarefewercomponents(namely,AC/DCpowersupplieswithinappliances),whichcouldleadtoreducedmanufacturing,shipping,andconsumercosts.PeterMayOstendorpofXergyConsultingnotedthat,inordertodeterminefeasibilityofDCsystemsinthefuture,theactualcostsatmaturityforDC(includingbothoperationalandfirstcosts)shouldbeestimated. 5 The interview oral consent script and list of interview questions are available in Appendix D.

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Further,quiteafewintervieweespointedoutthatdemonstrationprojectsarekeytobettervalidatecostandperformanceofDCsystems,identifyandaddressintegrationanddesignissues,andraiseawarenessamongstakeholders.IntervieweesalsostatedthatthelackofsufficientofferingsofDC-readyproductsandpowersystemcomponentsareasignificantbarrierforDCsystems.Dr.SandraVanderstoep,whoisthedirectorfortheAllianceforSustainableColoradoDCproject,referredtotheunavailabilityofDCHVACsystemsasasignificantbarriertotheACtoDCbuildingretrofittheAllianceisimplementing.Further,JimSaberofNextEnergyemphasizedtheneedtoincreasethemarketshareofDC-readyappliances,butalsomentionedthatconvertingappliancestoacceptbothACandDC“wouldnotbeveryhard.”Forthisreason,StevePantanohighlightedtheAdaptinitiativeledbyCLASP,whichaimstoadvanceDC-readyappliancesbyraisingmanufacturers’andconsumers’awarenessandengagementinDCpower.Ontheotherhand,JohnWangstatedthatmanufacturersareunlikelytodevelopDCproductsaslongasDCstandardizationschemes,andprotectionstandardsinparticular,havenotbeendeveloped.Despitethesebarriers,manyparticipantswereoptimisticaboutDCinbuildings.Severalnotedtheincreasingnumberofestablished(Cisco,Philips,Eaton)andstart-up(Voltserver,Lumencache,NuLeds)companiesdevelopingDClightingsolutions(primarilythroughPoE)asasignofaDCresurgenceinlightingsystemsandcontrols.PeteHortonwithLegrand’selectricalwiringsystemsdivision,elaboratedthatcontrolsmanufacturersarecurrentlyanalyzinghowDCsystemscanhelpthemaddvaluetotheircustomersandaredevelopingpotentialproducts.Withregardtoend-useapplicationsforDC,respondentsmentionedDClightingapplications,IoTsystems,andDCdatacenters.Also,ondatacenters,andotherenergy-intensiveenduses(e.g.,refrigeratedwarehouses),StephenFrankwiththeNationalRenewableEnergyLaboratory(NREL)notedthatDCcanhaveacascadingeffectontheenergyusedbyHVACsystems.

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4.SummaryandDiscussion

ThisstudyfocusesonhowDCpowercanhelpmeettheAB32andrelatedCaliforniagoalsforZNEresidentialandsmallcommercialbuildingswithbatterystorageandEVcharging.ForthesetypesofZNEbuildings,aDCinfrastructurecansaveenergyandmayhaveother,non-energy,benefits,suchasincreasedresiliency,reliability,andpowerquality,andbetterintegrationofcommunicationsandcontrols.Inevaluatingthesebenefits,itiscriticaltounderstandthefullpictureofenergyandnon-energybenefits,cost-effectiveness,marketandtechnologicalbarriers,andcurrentmarketadoptionofDCdistributioninbuildings.Thissectiondiscussesourfindingsonthesetopics,basedonourresearchtodate,throughreviewoftheliterature,conclusionsfromthestakeholderworkshop,andfeedbackfromelectronicsurveysandinterviews.

MarketAdoption

AlthoughDCpowerisoftenperceivedasaradicaldeparturefrommainstreamelectricitydistribution,DCpowersystemshavebeenwidelyusedforalongtimeinvehiclesandboats.DCalsohaslongpoweredtraditionaltelephoneservice,andmorerecentlyUSB(universalserialbus)andPoEinbuildings.ThenumberofnativeDCsourcesandenduseshasbeenontheriseinthepastfewyears,withtheproliferationofPVsystems[35],batterystorage[36],LEDlighting[37],andconsumerelectronics.ThesedevelopmentshavespurredrenewedinterestinDCandAC-DChybriddistributionsystemsinbuildings.AsdiscussedinChapter2,anincreasingnumberofvariousDCcasestudiesanddemonstrationprojectsareunderwayandunderdevelopmentintheUnitedStatesandworldwide.Concurrently,DCsystemsarebeingcommerciallyimplementedindatacentersandforlightingsystemsincommercialbuildings,primarilywithPoE.Severalinternationalanddomesticorganizations(e.g.,EMergeAlliance,AlliancetoSaveEnergy,PassiveHouseInstitute,CLASP,andothersintheUnitedStates)areadvocatingforDC,spurringresearchandraisingawareness.

However,despitethesedevelopments,DCpowersystemsinbuildingsarestillintheirnascentstage.TherearesignificanttechnologicalandmarketbarriersthatinhibitmarketadoptionofDCdistributioninbuildings,includingthefollowing:

• Alackofcost-competitive,market-readyDC-readyappliancesandpowerdistributionsystemcomponents,includingDCsystemprotectionschemes.

• AlackofmatureandDC-explicitstandardsandguidelines(e.g.,forelectricalprotection,physicalconnectors,etc.).

• LimitedawarenessofDCsystemsandtheirpotentialbenefitsamongpotentialspecifiersandpurchasers.

• HighcapitalcostsofretrofittinglegacyACsystems,whichpresentaparticularlylargebarrierforsuchapplications.

Discussionswithstakeholdershaverevealedthatthesebarriersareinterdependent.Forexample,manufacturersarelesslikelytodevelopDC-readyapplianceswhencomprehensive

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standardsarenotavailable.UtilitiesandregulatorybodiesarelesslikelytosupportandincentivizeDCsystemswhentheirpotentialbenefitshavenotbeensubstantiatedbysufficientresearchanddemonstrationprojects.Onabrightnote,theamountofresearch,thenumberofdemonstrationprojectsworldwideandintheUnitedStates,theincreasinginvolvementofapplianceandconvertermanufacturersenteringthisfieldinthepastonetotwoyears,andthewidespreadinstallationofon-sitePVsystemsmayleadtoacriticalmassforwidespreadadoptionofDCsystemsinbuildingsinthefuture.

EnergySavings

OneofthemainargumentsinfavorofDCdistributioninbuildingsisthepotentialforenergysavings.Ourliteraturereviewrevealsasignificantvarianceinenergysavings,whichismoreprominentinmodelingstudiesthaninexperimentalfindings.AsdiscussedinChapter2,calculatedenergysavingsfrommodelingstudiesrangebetween2and14percent,whereasinexperimentalstudiessavingsrangebetween2and8percent.

Thefollowingfactorscansignificantlyaffectenergysavings:

• Batterystorage:ThepresenceofbatterystoragecangreatlyincreaseenergysavingsthroughtheeliminationofpowerconversionsfromDCtoACandbacktoDC,whichcurrentlyoccurinatypicalACsystemwithPVandbatterystorage.

• CoincidenceofPVoutputandload:WhenpowerdemandoccursduringsolarPVgeneration,DCcanbefeddirectlyfromthePVarraytoDC-readyappliancesinthebuilding.Atthesametime,adirect-DCsystemwithhighcoincidenceofPVandloadusageuseslessrectifiedACpowerfromtheelectricgrid,whicheffectivelyreducestheDCsystem’senergylosses.

• Powersystemcomponentefficiencies:Theoperationalefficienciesofrectifiers(AC/DC),inverters(DC/AC),andDCconverters(DC/DC)—andspecifically,therelativeoperationalefficienciesofpowersystemcomponentsintheDCsystem(mostlytheefficienciesofDC/DCconvertersandcentralrectifiers)comparedtothoseintheACsystem(i.e.,efficienciesofinvertersandpowersupply/rectifierefficienciesattheappliancelevel)—candetermineenergysavings.IntheforeseeablefuturepotentialincreaseddemandandR&DforDCsystemswillleadtohigherefficienciesforDCsystemconverters.Ontheotherhand,technologyadvancementsandregulatorystandardsforinternalandexternalappliancepowersuppliesarealsoexpectedtoimproveefficienciesforsuchcomponents.Regardless,direct-DCsystemsrequirelesspowerconversionsthanACsystems(andmoresoinsystemswithbatterystorage),andarethereforeexpectedtokeeptheirtheoreticalefficiencyadvantage.

• DCVoltageandsystemconfiguration:DClinevoltage(typically380Vforhighpowerloads,and24Vor48VDCforlowpowerloads)canimpactwirelosses.

• Powersystemconfiguration:Finally,thepowersystemconfigurationandtopologies(i.e.,thetypeandnumberofcomponentsinthesystem,andhowthesecomponentsareelectricallyconnectedtoeachother)candeterminethenumberofpowerconversionswithinthebuildingandthereforeenergysavings.

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Non-EnergyBenefitsandBarriers

Accordingtoseveralstudies,DCpowerdistributioninbuildingshasimportantnon-energybenefitscomparedtoACpower.DCsystemsallowforeasierintegrationofpower,communications,andcontrolswithcertainDCstandards(PoEandUSB).Expandeduseofrenewablesalsoreducesgreenhousegasemissions,extendingtheenergysavingsofDCpowerinthiscriticaldimension.Inaddition,existingresearchinDCdatacentershasdemonstratedthattheeliminationofcertainpowersystemcomponentsinDCsystemscansignificantlyincreasesystemreliability.Furthermore,theabilityofDCsystemstoseamlesslyactasmicrogrids(i.e.,tobeislandedfromthegrid)canimproveresiliency,anincreasinglyvaluablecharacteristicasutilitiesandgovernmentagenciesareaddressingdisastermitigation.Furthermore,DCmicrogridsareeffectivelyde-coupledfromtheACgrid(evenwhennotcompletelyislandedfromthegrid),whichmakestheend-useequipmentontheDCmicrogridlesssusceptiblefromfrequencyandvoltagedisturbancesonthegrid.AlthoughsuchbenefitsarewidelydiscussedintheliteratureandamongDCpoweradvocates,theyhavenotbeenthoroughlyinvestigated,substantiated,orquantified.

Cost

AsdiscussedinChapter2,andbasedonsurveyandinterviewfeedback,DCsystemshavethepotentialofhavingalowerfirstcostcomparedtoACsystemsinbuildings,primarilyduetotheuseoflesscomponentsandsimplicityofcircuitry.However,thiswouldrequiretheappropriateeconomiesofscale.Forthecurrentmarket,certainend-useapplicationswhereDCpowerisstartingtoseesignificantadoption,suchasDCdatacentersandPoElighting,maybebettersuitedforcommercialization.Overall,firstcostisoneofthemainbarriersfordevelopers,designers,specifiers,manufacturers,andenduserstoimplementDCsystemsinbuildings.Fromaresearchperspective,thefewstudiesthataddressDCsystemscostfollowforthemostpartaqualitativeapproach,primarilyduetothelackofdataonDCappliances,converters,andactualinstalledsystems.However,bottom-upapproaches(i.e.,estimatingcostsfromcomponentstosystems),aswellastop-down(basedondatafromdemonstrationprojects)couldbeemployedtoestimatethecurrentandfuturecostsofDCsystems.

Standards

ManynewstandardsforDCpowerhavebeendevelopedinrecentyearsandmoreareinprocesswiththegoalofcreatinginternationalstandardsforDCpowersystemsandapplications.AnearlyleaderintheseeffortshasbeentheEMergeAlliance,whosemaingoalistohelpcreateDCstandardsdirectly,orbycatalyzingstandardscreationthroughotherorganizationslikeIEC,IEEE,theNationalFireProtectionAssociation(NFPA),andothers.Moststandardsdealingwithelectricity,andespeciallythosefocusingonsafety,alreadycoverthesubjectofDC.Unfortunatelytheydosoinsuchanindirectwaythatitmakesthemdifficulttointerpret,expensiveforpermitting,andunlikelytobeusedforDC,thushinderingtheadoptionofDCpower.Forthisreason,explicitandrapiddevelopmentofDCandAC-DChybridelectrical

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standardsandcodesarevitalforwidespreadmarketadoption.AnotherkeyfactorforDCstandardsistheincreasinguseofinformationtechnology(IT)standards—namelyPoEandUSB—fordistributionoflow-voltageDCpowerinbuildingstopowerDCproductssuchaselectronicsandlighting.AccordingtoarecentreportbytheIEC[38],themajorityofthestandardizationeffortsforDCrelatetotheadditionofprovisionsforDCintheexistingACstandards.However,thesamereportnotesthattherearespecificdifferencesbetweenACandDCthatshouldbeaddressedspecificallyforDC.Thoseincludethefollowing:

• StandardizationforDCvoltages,includingvoltagevariation,particularlyforapplicationwithbatterystorage.

• StandardizationofDCplugsandsockets.Suchproductsmustaddressarcingandloaddisconnectionwhileinactivemode.

• FurtherinvestigationofhumanhealtheffectsfromDCpower.• Otherdifferencessuchasprotectionagainstvoltageandcurrentsurgesovervoltageand

overcurrentprotection,faultdetection,groundingprinciples,arcing,andcorrosion.TheEMergeAlliancehasacodesandstandardsreferencelistforthenumerousDCandhybridstandardsandplanstoupdateitregularly.SeethelistinAppendixEandupdatesathttp://www.emergealliance.org.

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5.ConclusionsandFutureResearch

TosummarizethestateoftheindustryforDCpowerinbuildings,wehavedrawnonseveralinformationsources,includingareviewoftheacademicandindustryliterature,astakeholderworkshop,astakeholdersurvey,andin-depthstakeholderinterviews.SuccessfulmarketdevelopmentofDCsystemsinbuildingsrequirestheavailabilityofreliable,cost-competitiveend-useappliancesandequipmentthatcandirectlyuseandenableDCpower,aswellasmaturestandardsthataddressDCpowerdistributionvoltages,connectors,andprotectionschemes.Currently,theseelementsarelacking.Further,DCpowerdistributioninbuildingsappearstohavemultifacetedbenefitsthatcrosstraditionalboundaries.Whilethiswouldseemtobeanadvantage,nothavingasinglebenefitthatisaclearwinnerappearstobeanotherimpediment.Policymakersandadvocacygroupstypicallyfocusonaspecificattribute(e.g.,energysavings)whendecidingtopromoteandincentivizeaspecifictechnology.However,thestrategicvalueofDCpowerrequiresasystemsapproach—encompassingtheeasierintegrationofon-siterenewablegenerationwithdigitalbuildingcontrols,batterystorage,andEVcharging,toenergysavingsfromreducedpowerlosses,tothepotentialforincreasedresiliencyandreliability.Forthisreason,andasexpressedbystakeholdersduringtheworkshop,surveys,andinterviews,additionalfielddemonstrationsofDCpowerdistributioninlow-energybuildingsareneededtocarefullyevaluateandquantifythewholespectrumofpotentialDCbenefits.Demonstrationprojectsalsowouldhelptoaddressanyintegrationandsafetyissues,allowmanufacturerstofield-testtheirDC-readyproducts,andraisestakeholderawareness.Thesedemonstrationsshouldincludemultiplevendors’systemssotheresultscanbegeneralizedtoadvanceouroverallknowledgeofDCpowerinbuildings.ThedomesticmarketforDCpowerinbuildingscanlooktoadvancementsandlessonslearnedfromtheinternationalmarket.Japan,China,andseveralEuropeancountrieshaveinvestedinDCpowerandhavedevelopednumerouscasestudiesanddemonstrationprojects,withafocusonenergyefficiency,renewables,andresiliency.ReviewofinternationalcasestudiescomparedtotheU.S.marketshowsaconvergenceonthetypesofbenefitsandbarrierstoDCpower;however,theselectionandrecommendationofDCdistributionvoltagesandconfigurationscanvarybetweenprojectsindifferentcountries.Clearly,atthisearlystageofdevelopment,DCpowerdistributioninbuildingswouldbenefitfromacoordinatedefforttostandardizevoltagelevels—notonlytofacilitatestandardsdevelopment,butalsotoconcentratethemarketofpowerconvertersandDC-readyappliancesandfacilitatemanufacturersinstandardizingproductofferingsandreachingeconomiesofproductionscale.AnotherkeymarketfromwhichDCcanbenefitistheoff-gridmarket;andspecificallytheoff-gridsolarPVmarketforthedevelopingworldandruralapplications.Thereiscurrentlyalargenumberofdirect-DCappliancesandsolutionsfordirectcouplingwithPV[39],whicharesupportedbyinternationalandU.S.programs,suchastheGlobalLEAPinitiativeledbytheU.S.

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DepartmentofEnergy(DOE)[40],thePowerAfricainitiativemanagedbytheUnitedStatesAgencyforInternationalDevelopment(USAID)[41],andtheWorldBank’sEnergySectorManagementAssistanceProgram(ESMAP).[42]Thesuccessofthoseprograms,andtheinvolvementofmanufacturersinthisfield,canhaveaspillovereffecttothedeveloped-worldoff-gridmarket,andfurthertothegrid-connectedbuildingsector.WiththeproliferationofdistributedDCgeneration,batterystorage,EVs,andefficientDC-internalappliances,thefutureofend-useloadsinthebuildingsectorisexpectedtobeDC.However,atthispoint,DCadoptionshouldfocusonspecificend-useapplicationsforDCinwhichthebenefitsarewellunderstoodandthebarrierstoadoption(informationandrisk)arelower.Thenextphaseofthisprojectwillfocusoncreatingsuchend-usedesignrecommendationsforasmallnumberofcase-studyDCpoweredbuildingsandonanalyzingtheenergyandcostimpactsofthesedesigns.

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49

AppendixB:ConverterEfficiencyCurves

ThisappendixaddressesefficienciesofpowerconvertersusedinpowerdistributionsystemsinbuildingswithACandDCdistribution,basedonmarketsurveys.Wecollectedefficiency,power,andvoltagedatafromvarioussources,includingmanufacturerwebsites,productspecsheets,andonlinedatabases.Thefollowingsectionsprovidebriefdescriptionsofthepowerconvertersusedinthebuildingdistributionsystems,andpresentefficiencycurves(efficiencyasapercentageofconvertermaxpower)foreachsurveyedconverter.ConverterssurveyedincludeDC/DCconvertersandMPPTs,AC/DCrectifiers,DC/ACinverters,fordifferentinputandoutputvoltagelevels,andpowerratings.

PowerOptimizers

PoweroptimizersareDC/DCconverters,typicallyconnectedtoindividualPVmodules,withthepurposeofmaximizingPVpoweroutputusingMPPT.PoweroptimizersarerelativelynewPVsystemcomponentsthatreplacethePVjunctionbox.TheycanbeusedbothwithACandDCbuildingdistributionsystems.PoweroptimizermanufacturersincludeSolarEdge,BlackMagic,eIQ,PikaEnergy,andothers.FigureB.1showsefficiencycurvesforpoweroptimizerswithpowerratingslessthan1kW.

FigureB.1.EfficiencyCurvesforPowerOptimizers(Vin<125VDC,Vout=48VDC,Pmax<1kW)

Microinverters

MicroinvertersconvertDCpowerfromthePVmodulestoACpowerthatistypicallysynchronoustothegrid.TheyincludeMPPT,andareconnectedtoindividualPVmodulestomaximizepoweroutputfromeachmodule.MicroinvertermanufacturersincludeAltenergy,Enphase,ABB,SMA,SolarBridge,Petra,LeadSolar,andothers.FigureB.2showsefficiencycurvesformicroinverterswithpowerratingslessthan1kW.

50

FigureB.2.EfficiencyCurvesforMicroinverters(Vin<65VDC,Vout=120/240VAC,Pmax<1kW)

StringInverters

Stringinvertershaveasimilarfunctionasmicroinverters.TheytypicallyincludeMPPT,andconvertDCfromthePVarrayintoACsynchronoustothegrid.Theyaremorewidespreadthanmicroinverters,andtheirmaindifferenceisthatinsteadofconnectingtoeachPVmodule,theyconnecttostringsofPVmodules(i.e.,modulesconnectedinseries).StringinvertermanufacturersincludeSMA,Fronius,SchneiderElectric,ABB,Solectria,andmanyothers.Powerratings,inputandoutputvoltagesvaryforstringinvertersdependingonthebuildingtype(residentialorcommercial,voltageservicetype(singlephase,orthree-phase,andtheloadservedbythePVsystem.FigureB.3showsefficiencycurvesforstringinverterswithpowerratingslessthan10kW.

FigureB.3.EfficiencyCurvesforStringInverters(Vin<600VDC,Vout=240/208VAC,Pmax<10kW)

51

BatteryInverters

BatteryinvertersconvertDCpowercomingfromthebuildingbatterystoragesystem,ordirectlyfromthePVarray,toACpowerthatissenttotheloadsortothegrid.Batteryinvertersincludeabuilt-inrectifiertoconvertACgrid-powertoDC,asrequiredforbatterycharging,buttheytypicallydonotincludeMPPT,asthisfunctionisgenerallyperformedbyanupstreamlocatedchargecontroller.Thebatteryinvertermarketissmallercomparedtothenon-batterybackupinvertermarket(i.e.,themarketforstringinvertersandmicroinverters).ManufacturersofbatteryinvertersincludeSchneiderElectric,SMA,Outback,Sigineer,Samlex,andothers.FigureB.4showsefficiencycurvesforbatteryinverterswithpowerratingslessthan10kW.

FigureB.4.EfficiencyCurvesforBatteryInverters(Vin<64VDC,Vout=120VAC,Pmax<10kW)

ChargeControllers

Chargecontrollersareusedinbatterybackupsystemstoregulatethecurrentsentto,orcomingfrom,thebattery,andtypicallyincludeMPPT.ChargecontrollermanufacturersincludeOutback,Morningstar,SchneiderElectric,SMA,MidniteSolar,andothers.FigureB.5showschargecontrollerefficiencycurvesforchargecontrollerswithMPPT,withpowerratingsbetween1-5kW.

52

FigureB.5.EfficiencyCurvesforChargeControllers(Vin<600VDC,Vout=48VDC,Pmax:1-5kW)

DC/DCConverters

DC/DCconvertersconvertDCpowerfromonevoltageleveltoanother.Theyarepredominantlyusedinlow-power,low-voltageapplicationsandarefoundinapplianceswithelectroniccircuits.DC/DCconvertermanufacturersincludeVicor,Emerson,Synqor,Eltek,andothers.HighpowerDC/DCconvertersaretypicallymoreefficientthanlowerpowermodels.FigureB.6showsefficiencycurvesforstepdownDC/DCconverterswithpowerratingslessthan5kWbutmorethan1kW.

FigureB.6.EfficiencyCurvesforDC/DCConverters(Vin<140-400VDC,Vout=48VDC,Pmax:1-5kW)

53

LEDDrivers

ACLEDdriverstypicallyconvertACpowertoalowervoltageDC.TheyalsoregulatevoltageandcurrentthroughtheLEDcircuit.DCLEDdriversoperatesimilarlytotheirACcounterparts,butdonotrequirerectification.ManufacturersofLEDdriversincludePhilips,DeltaElectronics,Meanwell,andothers.FigureB.6showsefficiencycurvesforACLEDdriverswithpowerratingslessthan500Wandinputvoltageat120V.6

FigureB.7.EfficiencyCurvesforACLEDDrivers(Vin=120VAC,Vout=48VDC,Pmax<500W)

Rectifiers

RectifiersareusedtoconvertACpowertoDC.IntheACdistributionsystem,rectifiersareusedinDC-internalappliances.IntheDCdistributionsystem,oneormorehigherpowerrectifierscanbeusedtoconvertACpowerfromthegridtoDCwhenpowerfromthePVsystemorthebatteryisnotsufficientforthebuildingloads.ManufacturersforrectifiersincludeEltek,DeltaElectronics,Murata,XPPower,Emerson,andothers.FigureB.8andFigureB.9showefficiencycurvesforrectifiersratedat0-1kW,and1-12kW,respectively.Asshowninthefigures,higherpowerrectifiersaremoreefficientthanthoseratedatlowerpower.

6 We note that although we did not obtain efficiency curves for DC LED drivers, their peak efficiencies were higher than those for AC LED drivers.

54

FigureB.8.EfficiencyCurvesforRectifiers(Vin=120VAC,Vout=48VDC,Pmax≤1kW)

FigureB.9.EfficiencyCurvesforRectifiers(Vin=120/277/480VAC,Vout=48VDC,Pmax:1-12kW)

55

AppendixC:StakeholderWorkshop

WorkshoponDirectCurrentasanIntegratingandEnablingPlatforminZNEBuildings

March15,2016

LosAngelesElectricalTrainingInstitute(ETI)6023S.GarfieldAve.,CityofCommerce,CA90040

Theworkshopsolicitedinputandadviceonthetechnology,policy,andmarketdevelopmentneedsforadoptionofDCandAC-DChybridsystemsinresidentialandcommercialbuildings,focusingonzeronetenergy(ZNE)buildingswithPV,batterystorage,andEVcharging.

WorkshopAgenda

8:30am-9:00am Check-inandnetworking

9:00am-9:30am Introductions

9:30am-10:15am OverviewofEPICresearchprojectandfindingstodate

10:15am-11:00am “Quickpitch”updatesfrompartners

11:00am-11:15am Break

11:15am-12:15pm Breakoutsession:“What’sneededtomaximizetheopportunitiesandovercomethebarriersforDCpowerintheseareas?”

• Technology• Policy• MarketDevelopment

12:15pm-1:15pm Lunchandtourofzero-netenergyfeaturesofETIbuilding

1:15pm-1:45pm Reportoutanddiscussionfrommorningbreakoutsession

1:45pm-2:00pm Reviewend-useapplicationsforDCandAC-DChybridpower

2:00pm-3:00pm Breakoutsession:“Whatfactors*affectZNEdesignstodayforourend-useapplications?”

• Smallloads(lighting,electronics,fans,…)• Largerloads(HVAC,waterheating,motors,EVs,…)• ZNEintegratedsystems(PV,storage,EVcharging,power

infrastructure)*e.g.,productavailability,buildingcodes,interoperabilitystandards,etc.

3:00pm-3:30pm Reportoutanddiscussionfrombreakoutsession

3:30pm-4:00pm Concludingsession:feedbackanddiscussion

56

TheworkshopwasfundedbytheCaliforniaEnergyCommissionEPICprogram,aspartoftheLBNL/EPRI/CIEEjointresearchprojecton“DirectCurrentasanIntegratingandEnablingPlatform.”CodesandStandardsBrianPatterson,EMergeAlliance

• Therearethousandsofrelatedcodesandstandards.Standardsgettranslatedintocodescenteredonsafety,notefficiency.

• MoststandardsbodiestreatDCcategorically:high,medium,low.Powersystemsarebeingtreated,notproducts.

• Firecodeisrevisedeverythreeyears.ThereismoreinterestinDC-relatedtopics.• MostcurrentstandardswrittenwithACinmind.Moststandard-settingbodiesarecomposedof

ACexperts.Moststandardsfocusonequipment,safety,ortesting;NOTsystemstandards.• ThestandardsarenotexplicitaboutthetechnicalrequirementsforDC.(Forexample,acode

inspectordoesn’tknowwhatyouaretalkingaboutwhenyoustarttalkingaboutinterpolatingtables.)

• DCiscurrentlyonlyaddressedinspecificenduses—transport(railway),marine,telephony(DCusedfor>50years).TransmissionofwaterisDC-i.e.,ThreeGorgesinChina,alsoEurope.

• Heavycommercializationwaitsforstandardsdefinition.• EMergeisrewritingstandardstoacceleratetheprocessforDCorhybridsystems.InGermanyin

particularandEuropeingeneral,moreworkhasbeendonewithrenewables.• EMergefocusesonstandardsdefinition,inpreparationforinternationalstandardsbodiestaking

thisup(whatPattersoncallsa“vanguard”organization).VanguardorganizationslikeEMergedothecoordinationworktogetinitialversionsofstandards,thenworkwithotherstospreadadoption,shareinfo,etc.Industryneedstoleadtheeffortifrapidchangeisdesired;thenproductscanbebuiltaroundthenewstandards:technicaloperations,safetystandards,buildingenergycodes,performancecodes(notgreenstandards).

“QuickPitch”UpdatesRajendrahSingh,ClemsonUniversity

• Disagreeswithmuchsaid;driveristhecarbonissue;utilitytodecentralizedpowergeneration;electrificationofthetransportsector.Notinfavorofworkingwithexistingsystems—justgotoDCpower.

• Savingscangoupto30%–50%.Thereare25%lossesinAC-DCconversionifbelowpeakpower.Partloadinverterefficiencyis30%–40%

• UseexperiencecurvesforfuturepricesofbatteriesandPV.Wewillneedfactoriestoproduceatlargescaletodecreaseunitprices.

PeterMayOstendorp/StevePantano,CLASP

• CurrentresearchfocusedonidentifyingthelikelypathsforDCinhomes;conductgapanalysistoaddressshortcomings.

• CLASPconveningagroup“DemandDC.”• Lookatend-points-appliances,etc.;howtoincentivizethesevaluepropositions.• Adoptionpaths:Inthenextdecade,whatarethemostlikelyclustersofproductsinthehome—

entertainment,homeoffice,garage,others?• Whatisdoableinayear?• Focusingonnon-energybenefits;energyefficiencywon'tmotivatethechangetoDCwith

consumers.ProbablyPV+storageisstrongerincentive;1/3ofwhatisinhomeisDC-compatible,andthispercentageisrising.

57

• Markettransformation—whatwillittake?Howshouldwebemotivatingthistransition?Thereareuniqueopportunities—verticalintegratorsmakemultipleendpointspossible.

PeteHorton,Wattstopper-Legrand&AlliancetoSaveENergy• Legrandisa$6Bglobalenterprise—U.S.,Europe,India.• AlliancetoSaveEnergy-DCisoneofthelargestworkinggroupsinAlliance.Spenttwelve

monthslookingatsystemefficienciesforlighting,HVAC,multi-systemeffectsinbuildinglevelDC.

• Creatingadraftdocumentonsystemefficiency,whichwillbeoutnextmonth.• AllianceisfocusingonDOEcarbonneutraltarget.Whatdoescarbonneutralhome/buildinglook

likeinthefuture?Consideringbothsavingsandcost,alsotransactionalmarkets.Whoareearlyadopters?Howcanwegetthere?

• EVswillhelpbringdownbatterycosts.Efficiencywon’tgetusthere.• Codesandstandards—developenoughtogetgoing.

HenryLee,ADCEnergy

• DCenergydeterioratestheminuteitisgenerated.ADCofferstwoapplications:o ACandDCtransmissiononexistingwire;o Permitslongdistancetransmissionwithoutdeterioration.

DaveGeary,DCFusionandAllianceforSustainableColorado

• DenverAllianceforSustainableColorado:In2016,theDCMicrogridProjectisconvertingTheAllianceCenterfromalternatingcurrentACtoaself-containedDCsystem.Stampeddrawinginpermittingnow.360Engineering.Optimizewhatwecandotomorrow.

• DC-FusionjoiningPowerAnalytics.ModelDCinsoftware,sameasAC.Evolvethisfromdesigntocontrol;thenevolvetotransactionalmarketparticipation.

• DC-NexusWebsitetrackingcurrentevents.http://dc-nexus.comDanLowe,Voltserver

• VoltservermakeshighvoltageDCsafetotouch.Sensesenergyleakageofcurrent,andshutsoffcurrent;whilecheckingsystemforsafety,cansimultaneouslysendcontroldata.

• WaitingforDCproductsisnotnecessary.• SBIRPhase2,energyefficiencyupto99%.Focusingonmobilecommunications.Inresidential

30%–40%overallsavings.BrianPatterson,EMergeAlliance

• EMergehasnewboardmembers;partneredwithIEEE.• EMergeiswritingstandardforResidentialDC;draftinonemonth,finalinoneyear.• EMergeiscoordinatingdemonstrations:

o GreenCononDCEnerneto LightFairCavaDCasanetworktechnologyo IECSEG4-LowvoltageDCo SolarPowerInternational,LasVegas-demotwomicrogridsinSmartCommunity

Pavilion;mostrapidgrowthatsolarshowisstorageexhibits.Marriageofrenewableandstorageiscritical.

o GreenbuildLA—LargedrawofDCmicrogrid,alsohybrid.

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BreakoutSession1:“What’sneededtomaximizetheopportunitiesandovercomethebarriersforDCpowerintheseareas?”A.TechnologiesKeytakeaways:Direct-DCtechnologiesareemergingincertainareaslikemotors,pumps,ceilingfans,PoEapplicationsforcharging,lightingandotheruses;hybridACandDCelectricoutletsallowingmorePoEapplications;forlightingandheatpumps,computerserversandelectricvehiclecharging.DCpoweradvantagesforemergencybackuplighting,resiliency,islandingfromthegridmaybe“Trojan-horses”forintroducingDCmicrogridsintoresidentialandcommercialbuildingsespeciallyforZNEbuildings.Thereisalsoaneedforrevenue-gradetwo-waynetmeteringforDCmicrogridsandforbettermodelingprogramsfordesigningDCsystems.

• AvailableTechnologies:o PoEdevicesandapplicationsareexpandingsignificantlywiththecurrentabilitytohave

50wattsperchannel,whichisexpectedtogoto90wattslaterthisyear.o DCmotorsandpumps—size,control,efficiencyandcostofownershipadvantages(need

largervolumetobringpricesdown.o Ceilingfans:DCmotorswithLEDlightsnowavailableo DCLighting:SamsungDCsmartlightingplatform;CREESmartcast

• Technologygapsandotherbarriers:o Improvedbi-directionalinverterso Revenuegrademeteringandtwo-waynetmeteringforDCo Systemoperationandcontrolmanagement—analysisandmodelingo AgreementonresidentialDCvoltageo AC/DCdualoptionsbuilt-inbymanufacturersonhomeandofficeapplianceso PerformanceanddemodataplusULandotherlistingso ImprovedDCsystemdesignmodelingsoftware

• Barrierscanbeaddressedindemos• “TrojanHorses”forDCpower:

o E.g.:Emergencylighting:Transformsdeadassettoactivemanagemento UPSsystemso Audiovisualequipmento Cellphonetowers(asDCmicrogridtestbeds)

B.PoliciesKeytakeaways:

• Energysavings:Perceptioninthepolicycommunitythattherearenotenoughenergysavings• Thereisno“home”currentlyforDC• Non-energybenefits:

o Bipartisansupportcanpotentiallybedrawnfromnon-energybenefitssuchasresilienceandreliability(e.g.,theabilityforbuildingstoswitchto“resilientmode”).

o Ourexistingcodesandstandardsnetworkdoesnottakeintoaccountfactorssuchasresiliencyandreliability

o Interoperability:DCenablescommunications• Title24-California:CEClooksatfeasibilityandcost-effectiveness(life-cyclecost)• Forutilities,theimportantaspectsofDCwouldbefunctionalityandfirstcostsavings.(e.g.,can

DCmakethatheatpumpcheaper?)

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• Needmetricstocomparebuildingsonallfactors.Forexample,fortransformers,thecurrentmetricusedis“wattslost”

• DCalsoenableswatermeasures:Reduceswaterdesalinationplantcosts• GovernmentincentivesareneedformanufacturerstomakeDC-readyappliances• Convergenceisneededonvoltagestandardsto24,48,and380VDC• Potentialpolicyforvoluntarystandards:ProvidingacreditforDC-readiness,orthegoldencarrot

incentive• Sandy-microgrid-PSE&G• DCProducts:Lookatproductsinthedevelopingworld• Storage:Therearebenefitstotheutilityproviders.

C.MarketDevelopmentKeytakeaways:

• Retrofitchallengescomefrom:o UnavailabilityofDCinfrastructure/DCpowero Lackoftraining/education(design,construction/installation,operation)o Lackofretrofittransformationalschemeo Powerdistributionchallenges;noonelikesexistingwalltearingo PotentialROI/paybacko Deferinitialcosts:Incentives/rebatesfromutilities/government;Multiplestakeholders,

consumers/utilities/regulators• EnergySavings

o Whataretheenergysavings?Moreresearchisneeded(claimsrangefrom3%–30%)o Considertotalcostofownership,notjustenergysavings

• ProductAvailabilityo DCproductsavailability/awarenesslimitedo Competitive,cost-effectiveproductsneededo Make“hip”/coolproducts,e.g.,Teslatodrivemarketo Distributionproducts(e.g.,plugs,switches,circuitbreakers)needed

• Worldwidestandardso DC-specificstandardsarerequiredo Standardswouldgreatlyincreasevolume/reducecosts

• AbilitytoachieveZNEo CommondefinitionofZNEisdesiredo Howtoaddresssharingofcommunity-scalerenewables?o Needtoarticulateconsumerdriverso Drivedemand(throughincentives,regulations,etc.)

• Integrationo DCiseasiertointegratethanACo Nofrequencyregulationrequirement

• Safetyo Emergingissuesdependuponvoltageandcurrento Safetyneedstobeaddressedalongwithstandards

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BreakoutSession2:“Whatfactors*affectZNEdesignstodayforourend-useapplications?”A.SmallLoadsMostsmallloads,especiallyplugloadappliances,arealreadydigitaldevicesandhaveAC/DCconvertersthatprovidetherequiredDCvoltagetothedigitalappliance.Thisincludesadjustablespeedmotors,fans,andpumps,aswellaselectronicballastsandLEDlighting.Forplugloads,dualACorDCpowerinputsfromthemanufacturersorDCnetworksthatcanintegratethedeviceslikePoEsystemsareneededformarketadoption.Theefficiency,reliability,interoperability,andcontrollabilityofDCmotorsprovideimportantfeaturesforZNEbuildings.Keytakeaways:

• Plugloads—somekeyissuesare:o HowtoconnecttoZNEbuildingsystemandsmartgrido HowtooptimizetheenergyuseforclustersofDCdevicesforentertainmentand

workstations.• Heatpumps

o KeytechnologyforHVACinZNEbuildingso Products:Carrier-PVpoweredheatpumpsystem;Japan-Mitsubishi,Sharpresidential

DCminisplit• Lighting

o PoEo Armstrong24Vmicrogridceilingsystemo Cove,tasklighting,etc.—alreadyDCforlowvoltagelightingprovidetargetapplications

• NeedimprovedDCsystemsdesignandanalysistoolsformanufacturersandforengineeringofZNEbuildings.

• DCVSDmotors• NeedtohavestandardDCvoltagesandstandardDCdesignsforappliances,plugloaddevices,

andothersmallelectricloads• MajorappliancedesignersneedtoprovideDC/ACcapabilities• Demandresponse(DR)canimprovewithDCnetworksandeasiercontrolandInternetofThings

(IoT)access• Load-balancingDR,with“grid-friendly”appliancesispossibleandhasbeendemonstratedtobe

effective,butmanufacturersneedtobemotivatedtoaddthesecontrols—mostlikelybylegislation.

• DCnetworkedentertainmentandelectronics/officesystemsclusternetworksarebeingdeveloped—someundertheEPIC15-310and15-311grants

B.LargerLoadsKeytakeaways:

• Potentialloadso Waterheating:Heatpumpwaterheatero HVAC:Splitsystemheatpumpo Pumpsandfans:DCmotors

• IssueswithDCMotorso DoestheOEMorthemotormanufacturerassemblethee.g.,compressorassembly?

HoweasyisitgoingtobefortheproducttobeconvertedtoDC-ready?o Fromtheutility’sperspective,youwanttohavemostofthedispatchableloadsonthe

microgrid

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o WhatistheDCvoltagethatDCmotorsrunon?Is380Vtherightvoltage?o Part-loadefficienciesshouldbeaccountedfor(bothforACandDCsystems)

• Electricvehicleso Fastchargingdirectat600Vtaking380VfromDCandboostingto600Vo Whatisthevoltageattheinputofthechargecontroller?Isit380V?o PVtoEVcoincidence:Doesitmakesenseintheresidentialcasestudy?

C.ZNEintegratedsystems(PV,storage,EVcharging,powerinfrastructure)Keytakeaways:

• Loadrequirementso Fixedloadso Variableloads/miscellaneouso Automobile

• Issueso SizingofPVo Spacelimitationo VirtualnetmeteringforsharedPVallocationo Building—passive,lowconsumption,efficiento Storage/batterytostabilizeafternoonloadIntegrationofpowersystemcomponents:

Inverters,rectifiers,circuitbreakers,DC-DCconverters,etc.• Supplyvoltages(standardization)

o 380VDCo 24/48VDCo 125/250V(currentlyusedinindustrialapplications)

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AppendixD:SurveyandInterviewQuestions

SurveyQuestions

66

InterviewQuestions

InitialQuestionsforAll• Feedbackonquestionsfromelectronicsurvey:Requestfurthercomment,discussclarifications

onresponses.• WhatisthemostexcitingnewdevelopmentthatyouknowaboutDCpowerinbuildings?• WhatisyourcurrentinvolvementinDCpowerandcomponents?

Researchers:• Whatarethemostpressingresearchquestionsthatshouldbeaddressed?• Couldyounamethe“top”(3-5)papersinthefield?(withregardtoenergysavings,benefitsand

barriersofDCdistributionsystemsatthebuildinglevel).Canyousummarizethemajorfindingsofthesepapersandsenduslinks?

• Pleasesummarizeyourpast,current,andfutureresearchfindingsonDCdistributioninbuildings.Canyousenduspdfs/links?

Industry(DCHardwareandApplianceManufacturers):• Whatcomponents/appliancesdoyoucurrentlymanufactureorsell(bycomponenttype:end-

useequipment,distributionequipment,generation/storage/conditioningequipment).• Whatfactorsdotheyconsiderwhendecidingtoparticipate/expandinthemarket?(i.e.,market

demand,standards,profitability,etc.)WhatkeysignswouldyouneedtoseetoparticipateintheDCmarket?

• Whatcomponents/appliancesarecurrentlyunderdevelopment?Doyouhaveanyfutureplansthatyouwouldliketoshare?

• AtwhatscalewillDCproductionbecomecompetitivewithAC?• AtwhatscalewillhybridAC-DCbecomecompetitivewithAC?

A&EFirms&Contractors(Architects,Engineers,ElectricalContractors,SecuritySystems,Telecom/NetworkInstallers):

• Doyouhaveanyplanstodesign/install/constructaDCsystematthebuildinglevel?• Imagineforyounextprojectyouwereaskedtodesignadcsystem.Whatwillbeyourbiggest

challengesandopportunities?Indesigning/installing/constructingaDCsystem,whatarethemostimportantconsiderationsthatshouldbetakenintoaccount?

• HowdoyouthinkDCpowercanbeusedmosteffectivelyinZNEbuildings?• WhatwouldkeepyoufromputtingDCinyournextbuilding?Whatisthetypicalprofileofa

clientwhowouldbeinterestedinDC?WhatisyourperceptionofhowyourclientsrespondtoDCsystems(safety,convenience,availability,etc.)?

• AtscaledoyouthinkDCwillbemore/less/equallyexpensiveasDC?• Doyouhaveanycostdata?

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UtilityStaffandUtilityRegulators• Whatareyourupcomingandlong-termplansforDCpoweronthecustomersideofthemeter?• WhatroledoesDCpowerplayinanyZNEprogramsyouhave?• DoyouthinkthatDCapplicationsanddeploymentcouldhelpinimprovingtheresilienceand

reliabilityoftheexistinggrid,and,ifso,how?• Howwouldanintegratingtechnology,likeDCpower,betreatedinprograms?• Arethereanyotherprojectsthatweshouldbeawareof?

EnvironmentalOrganizations• What’sthemosteffectivewaytoaccelerateDCuptake?(policyandmarketdevelopment,etc)• WhataretheenvironmentalprosandconswithDCpowerinbuildings(airquality,toxics,EMF)?

Whatarepotentialmitigations?

Close-outQuestionsforAll• Isthereanythingyouwouldliketoadd,ortellusabout?• Arethereanyotherprojectsthatweshouldbeawareofortalkto?• Wouldyoulikeustouseyournameifwequoteyou?

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AppendixE:EMergeAllianceReferenceListforDCCodesandStandards

MANDATORYSTANDARDS-applytoallelectricalinstallations

Standard Description Region Status

NFPA70 USNationalElectricalCodeAddressesfundamentalprinciplesofprotectionforsafety.AppliestoLVDC

(under1000V).

US 2014versionreleased

Article250SectionVIII

Grounding&Bonding-DirectCurrentSystems-Articles250.160-250.169


Article393 Low-VoltageSuspendedCeilingPowerDistributionSystems


Article408 Switchboards,Switchgear,andPanellboards US 2014versionreleased

Article480 StorageBatteries US 2014versionreleased(2017

revisions)

Article690 PVSystemsover600Volts US 2014versionreleased(2017

revisions)

NFPA70E Standardforelectricalsafetyintheworkplace-IncludesLVDC.


NFPA70B Recommendedpracticeforelectricalequipmentmaintenance.


GENERALAPPLICATIONSTANDARDS

EMergeOccupiedSpaceV.2.0

DCpowerdistrib.Req'mtsforcommercialbldg.interiors

Global Released

EMergeResidentialV1.0

DCpowerdistrib.Req'mtsforresidentialbldgs. Global ScheduledRelease2016

EMergeCommercialBldg.

V1.0

DCpowerdistrib.Req'mtsforcommercialbldg.andCampus

Global ScheduledRelease2016

USB-PD ExtraLowVoltageDCforDesktopandPersonalElectronics

Global Released

PoE ExtraLowVoltageDCforICTEquipment24&48V Global Released

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DC;35Watts

EUROPEANANDGLOBALSTANDARDS

DINVDE0100-100:2009-06

Low-voltageelectricalinstallations–Part1:Fundamentalprinciples,assessmentofgeneral

characteristics,definitions

Europe Released

DINVDE0100-410:2007-06

Low-voltageelectricalinstallations–Part4-41:Protectionforsafety-Protectionagainstelectricshock

Europe Released

DINVDE0100-530:2011-06

Low-voltageelectricalinstallations–Part530:Selectionanderectionofelectricalequipment–Switchgearand

controlgear

Europe Released

DINVDE0100-540:2012-06

Low-voltageelectricalinstallations–Part5-54:Selectionanderectionofelectricalequipment–Earthing

arrangementsandprotectiveconductors

Europe Released

DINEN61557-2:2008-02

Electricalsafetyinlowvoltagedistributionsystemsupto1000Va.c.and1500Vd.c.–Equipmentfortesting,measuringormonitoringofprotectivemeasures,Part2:

Insulationresistance

Europe Released

DINEN61557-8:2007-12

Electricalsafetyinlowvoltagedistributionsystemsupto1000Va.c.and1500Vd.c.–Equipmentfortesting,measuringormonitoringofprotectivemeasuresPart8:

InsulationmonitoringdevicesforITsystems

Europe Released

DINEN61557-9:2009-11

Electricalsafetyinlowvoltagedistributionsystemsupto1000Va.c.and1500Vd.c.–Equipmentfortesting,measuringormonitoringofprotectivemeasuresPart9:EquipmentforinsulationfaultlocationinITsystems

Europe Released

IEC60050-614 InternationalElectrotechnicalVocabulary-Part614:Generation,transmissionanddistributionofelectricity-

Operation

Global Released

IEC60034-1 Rotatingelectricalmachines-Part1:Ratingandperformance

Global Released

IEC61362 Guidetospecificationofhydraulicturbinegoverningsystems

Global Released

IEC60308 Hydraulicturbines-Testingofcontrolsystems Global Released

IEC61992 DCswitchgear Global Released

70

IEC60038:2009 StandardVoltages Global Released

IEC62848-1 DCSurgearresters Global Released

IEC62924

StationaryenergystoragesystemforDCtractionsystems

Global Released

IEC62053-41/Ed1 ELECTRICITYMETERINGEQUIPMENT(DC)-PARTICULARREQUIREMENTS

Global Released

IEC61378-3Edition1.0(2006-04-27)

Convertertransformers Global Released

IEC62620 Performanceoflithiumionbatteriesforindustrialapparatus(unitbattery/batterypack)

Global Released

IEC/TS62735-2 D.C.Plugsandsocket-outletstobeusedinindooraccesscontrolledareas

-Part2:Plugandsocket-outletsystemfor5,2kW

Global Released

IEC61869-14 SpecificRequirementsforDCCurrentTransformers(CDV)

Global Released

IEC61869-15 SpecificRequirementsforDCVoltageTransformers(CDV)

Global Released

IEC61180/Ed1 HIGH-VOLTAGETESTTECHNIQUES FORLOW-VOLTAGEEQUIPMENT

Definitions,testandprocedurerequirements,testequipment

Global Released

IEC60947-2 Low-voltageswitchgearandcontrolgear–Part2:Circuit-breakers

Global Released

IEC60947-3 Low-voltageswitchgearandcontrolgear-Part3:Switches,disconnectors,switch-disconnectorsandfuse-

combinationunits.

Global Released

IEC61439-X LOW-VOLTAGESWITCHGEARANDCONTROLGEARASSEMBLIES–PartX:Assembliesforphotovoltaic

installations

Global Released

TELECOMANDDATACENTERS

ETSIEN300132-3-0 Powersupplyinterfaceattheinputtotelecommunicationsanddatacom(ICT)equipment

Europe Released

ETSIEN3061605 Eartingandbondingfor400VDCsystems Europe Released

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ITU-TL.1200 SpecificationofDCpowerfeedinginterface Global Released

EMergeData/TelecomV.1.1

DCpowerdistributionrequirementsindatacenters/telecom

Global Released

YD/T2378-2011 240VDCsystems China Released

YD/TXXXX-201X 336Vdirectcurrentpowersupplysystemsfortelecom China Approvalprocess

ATIS-0600315.01.2015

Voltagelevelsfor400VDCsystems US Released

IEC62040-5-3 DCUPStestandperformancestandard Global Scheduledrelease2016

IEC62040-5-1 SafetyforDCUPS Global Workstarted

IECTS62735-1 400VDCplug&socketoutlet Global Released

YD/T2524-2015 336VHFswitchmoderectifierfortelecommunication China Approvalprocess

ELECTRICALVEHICLECHARGING

CHAdeMO DCfastcharging Released

SAE/CCS DCcharging Released