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Best Practices for Operation andMaintenance of Photovoltaic andEnergy Storage Systems; 3rd EditionNational Renewable Energy Laboratory,Sandia National Laboratory, SunSpec Alliance,and the SunShot National Laboratory Multiyear Partnership(SuNLaMP) PV O&M Best Practices Working GroupNREL is a national laboratory of the U.S. Department of EnergyOffice of Energy Efficiency & Renewable EnergyOperated by the Alliance for Sustainable Energy, LLCThis report is available at no cost from the National Renewable EnergyLaboratory (NREL) at www.nrel.gov/publications.Contract No. DE-AC36-08GO28308Technical ReportNREL/TP-7A40-73822December 2018

Best Practices for Operation andMaintenance of Photovoltaic and EnergyStorage Systems; 3rd EditionNational Renewable Energy Laboratory,Sandia National Laboratory, SunSpec Alliance,and the SunShot National Laboratory Multiyear Partnership(SuNLaMP) PV O&M Best Practices Working GroupSuggested CitationNational Renewable Energy Laboratory, Sandia National Laboratory, SunSpec Alliance, andthe SunShot National Laboratory Multiyear Partnership (SuNLaMP) PV O&M Best PracticesWorking Group. 2018. Best Practices for Operation and Maintenance of Photovoltaic andEnergy Storage Systems; 3rd Edition. Golden, CO: National Renewable Energy Laboratory.NREL/TP-7A40-73822. https://www.nrel.gov/docs/fy19osti/73822.pdf.NREL is a national laboratory of the U.S. Department of EnergyOffice of Energy Efficiency & Renewable EnergyOperated by the Alliance for Sustainable Energy, LLCTechnical ReportNREL/TP-7A40-73822December 2018This report is available at no cost from the National Renewable EnergyLaboratory (NREL) at www.nrel.gov/publications.National Renewable Energy Laboratory15013 Denver West ParkwayGolden, CO 80401303-275-3000 www.nrel.govContract No. DE-AC36-08GO28308

NOTICEThis work was authored by the National Renewable Energy Laboratory, operated by Alliance for SustainableEnergy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. Fundingprovided by the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar EnergyTechnologies Office and SuNLaMP Agreement 32315.The views expressed herein do not necessarily representthe views of the DOE or the U.S. Government.This report is available at no cost from the National RenewableEnergy Laboratory (NREL) at www.nrel.gov/publications.U.S. Department of Energy (DOE) reports produced after 1991and a growing number of pre-1991 documents are availablefree via www.OSTI.gov.Cover Photos by Dennis Schroeder: (clockwise, left to right) NREL 51934, NREL 45897, NREL 42160, NREL 45891, NREL 48097,NREL 46526.NREL prints on paper that contains recycled content.

AcknowledgmentsThe National Renewable Energy Laboratory (NREL), Sandia National Laboratories (SNL),SunSpec Alliance, and Roger Hill were supported by the U.S. Department of Energy (DOE)Solar Energy Technologies Office (SETO) under Agreement 32315 in the production of thisreport. The authors would like to thank the following working group contributors to this report.Working Group CoordinatorDylan Tansy, SunSpec AllianceSupport TeamAmmar Qusaibaty, SETOAndy Walker, NRELEric Lockhart, NRELTravis Lowder, NRELKari Burman, NREL, ret.Geoff Klise, SNLRoger Hill, consultantTom Tansy, SunSpec AllianceTim Keating, SunSpec AllianceOlga Lavrova, SNLAnil Pochiraju, SunSpec AllianceJessie Deot, SunSpec AllianceBob Fox, SunSpec AllianceChuck Kurnik, NRELIntervieweesGreg Sellers, Clean Power FinanceJean Paul La Marche, Main Street PowerDirk Michaels, K & L GatesRue Philips, True SouthDavid Kenny, SunrunLeigh Zanone, MeteocontrolPaul Lanning, Lightbox EnergySarah Disch, Wells FargoAndrew Truitt, Distributed Resource VenturesMarco Lopez, AlectrisRoss Biesemeyer, First SolarLaks Sampath, AlectrisMark Berger, NextGrid TechnologiesiiiThis report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

2017 Working Group RosterEric Alderman, AirphrameCarlos Alves, Nextera Energy ServicesRob Andrews, Queen's UniversityJohn Balfour, High Performance PVStephen Barkaski, FLS EnergyJimmy Bergeron, SolarCityMichael Bolen, Electric Power Research InstitutePeter Bostock, VDE AmericasAlex Bradley, DuPontBill Brooks, Brooks EngineeringPaul Brucke, Brucke EngineeringJon Budreski, Air SharkKari Burman, NRELJoe Cain, Solar Energy Industries Assoc.(SEIA)Nathan Charles, Enphase EnergyDaisy Chung, Solar Electric Power Assoc. (SEPA)Joe Cunningham, CentrosolarJessie Deot, SunSpecSkip Dise, Clean Power ResearchRon Drobeck, System Operations Live View(SOLV)Nadav Enbar, Electric Power Research InstituteCary Fukada, OpTerra Energy ServicesCyrille Godenot, Schneider ElectricDanya Golan, Solar EdgeSteve Hanawalt, Power Factors LLCChris Henderson, AmerescoMartin Herzfeld, independent consultantRoger Hill, consultantBill Hoffer, Sunergy Engineering ServicesRebekah Hren, Solar Energy InternationalSandeep Jadhav, Mahindra SustenDirk Jordan, NRELRaymond Kaiser, Amzur TechnologiesJoe Kastner, Radian GenerationTim Keating, SunSpecJason Kechijian, SolBrightGeorge Kelly, Sunset Technology, Inc.Geoff Klise, SNLPramod Krishnani, Terraform PowerBhushan Kunjeer, EnersaasSarah Kurtz, NRELPaul Lanning, Lightbox EnergyOlga Lavrova, SNLRichard Lawrence, Institute for Building Technologyand Safety (IBTS)Eric Lockhart, NRELMike Loeser, Strata SolarJaya Mallineni, Nexamp Inc.Joseph McCabe, Renewable Energy ChampionRyan McCauly, Tritium3Dirk Michels, Ballard SpahrReegan Moen, SOLVJamie Mordarski, SMA AmericaJesse Moses, Swinerton Renewable EnergyMatt Murphy, Borrego SolarSean Murphy, SolBright Renewable Energy, LLCEric Nessl, Strata SolarChristina Nichols, DOEDon Nista, Cypress Creek RenewablesAngelo Purpura, SOLVMichael Rogerson, Solar EdgeAJ Rossman, Smart ResourceMary Rottman, Rottman AssociatesLaks Sampath, AlectrisJadhav Sandeep, Mahindra SustenRudy Saporite, IBTSKenneth Sauer, DNVGLThomas Sauer, ExxergyUlrich KW Schwabe, SEGIS-AC awardeesBill Shisler, NRGJeff Southard, Juniper Unmanned Inc.Jeff Spies, North American Board of Certified EnergyProfessionals (NABCEP)Kristy Straiton, American Society of Testing andMaterials (ASTM)Dylan Tansy, SunSpecTom Tansy, SunSpecAbhay Tilwankar, Mahindra SustenErnest (Ernie) Tom, Salt River ProjectWill Troppe, Power Factors LLCAndrew Truitt, Dividend FinanceAndy Walker, NRELCarter Wall, Franklin Beach EnergyJohn Williamson, Array TechnologiesGordon Woodcock, Taitem Engineering, PCLeigh Zanone, 8minutenergyivThis report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

2016 Working Group RosterEric Alderman, AirphrameCarlos Alves, Nextera Energy ServicesRob Andrews, Heliolytics Inc.John Balfour, High Performance PVJimmy Bergeron, SolarCityMichael Bolen, Electric Power ResearchInstitute (EPRI)Peter Bostock, VDE AmericasAlex Bradley, DuPontBill Brooks, Brooks EngineeringPaul Brucke, Brucke EngineeringJon Budreski, Air SharkBen Compton, NextPhase SolarJoe Cunningham, CentrosolarSkip Dise, Clean Power ResearchRon Drobeck, SOLVNadav Enbar, EPRICary Fukada, OpTerra Energy ServicesJeff Gilbert, Vigilant Energy ManagementDanya Golan, SolarEdgeShannon Grein, Empyrean ElectricSteve Hanawalt, Power Factors LLCChris Henderson, AmerescoMartin Herzfeld, consultantRoger Hill, consultantBill Hoffer, Sunergy Engineering Services PLLCRebekah Hren, Solar Energy InternationalJoe Kastner, Radian GenerationJason Kechijian, SolBrightGeorge Kelly, Sunset Technology, Inc.Ken Kostok, AlectrisPramod Krishnani, Terraform PowerBhushan Kunjeer, SunEdisonSarah Kurtz, NRELPaul Lanning, Lightbox EnergyOlga Lavrova, SNLRichard Lawrence, National Accreditation Boardfor Certified Energy Professionals (NABCEP)Mike Loeser, Strata SolarJaya Mallineni, Nexamp Inc.Joseph McCabe, Renewable Energy ChampionRyan McCauly, Tritium3Scott McWilliams, SematechDirk Michels, Ballard SpahrReegan Moen, Swinerton Renewable EnergyJamie Mordarski, SMA America LLCJesse Moses, Swinerton Renewable EnergyMatt Murphy, Borrego SolarSean Murphy, SolBright Renewable Energy, LLCEric Nessl, Strata SolarChristina Nichols, DOEDon Nista, Cypress Creek RenewablesRue Phillips, True South RenewablesAngelo Purpura, Swinerton Renewable EnergyMichael Rogerson, SolarEdgeAJ Rossman, Smart ResourceMary Rottman, Rottman AssociatesLaks Sampath, AlectrisJadhav Sandeep, Mahindra SustenRudy Saporite, IBTSUlrich Schwabe, SEGIS-AC awardeesBill Shisler, NRGJeff Spies, NABCEPKristy Straiton, ASTMAbhay Tilwankar, Mahindra SustenErnest Tom, Salt River ProjectWill Troppe, Power Factors LLCAndrew Truitt, Dividend FinanceCarter Wall, Franklin Beach EnergyDavid Walter, Hartford Steam BoilerGordon Woodcock, Taitem Engineering, PCLeigh Zanone, MeteocontrolvThis report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

List of ternating currentadvanced metering infrastructureautomated meter readingAmerican National Standards InstituteAmerican Society of Non-destructive TestingAmerican Society for Testing and MaterialsBattery Lifetime Analysis and Simulation Toolcomputer-aided designcurrent transformerdata acquisition systemdirect currentdepth of dischargeU.S. Department of Energyenterprise asset managementengineering, procurement, and constructionethylene propylene diene monomerElectric Power Research Instituteenterprise resource planningethylene vinyl acetateFederal Energy Management ProgramFederal Energy Regulatory Commissionground fault interruptionglobal horizontal insolationgenerator ownergenerator operatorgenerator step-upInstitute for Building Technology and SafetyInternational Electrotechnical CommissionIEC Renewable EnergyInstitute of Electrical and Electronics Engineersinsulated-gate bipolar transistorInternet Protocolinternal rate of returninformation technologycurrent voltagekey performance indicatorthousands of Volts-Amps Reactivelithium carbonlevelized cost of energylithium iron phosphatelimited liability corporationlithium manganese oxidelithium titanatemulti-crystalline or multiple-connectorviThis report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

SCADASDOsfSTCTODTPOUAVULUNUPSUVVLAVRLAmaximum foreseeable lossmodule-level power electronicsmaximum power-point trackingNorth American Board of Certified Energy PractitionersNickel cobalt aluminumNetwork Control UnitNorth American Electric Reliability CorporationNational Fire Protection Agencynormal loss expectednickel-manganese-carbonNational Renewable Energy Laboratoryoriginal equipment manufactureroperations & maintenanceoutside management controlOccupational Safety and Health Administrationprobable maximum lossplane of arraypower purchase agreementpersonal protective equipmentperformance ratiophotovoltaicspolyvinyl chloridePhotovoltaic Power StationResource Conservation and Recovery Actrenewable energy certificateroot mean squarereturn on investmentSystem Advisor ModelSolar Access to Public Capitalstyrene butadiene styreneSupervisory Control and Data Acquisitionstandards developing organizationsquare footstandard test conditionTime of Daythermoplastic polyolefinunmanned aerial vehicleUnderwriters LaboratoriesUnited NationsUninterruptible Power Supplyultravioletvented lead acidvalve regulated lead acidviiThis report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table of ContentsAcknowledgments . iiiWorking Group Coordinator . iiiSupport Team . iiiInterviewees. iii2017 Working Group Roster . iv2016 Working Group Roster . vList of Acronyms . vi1 Introduction . 1234567891.11.2Purpose . 1Background—The PV O&M Working Group . 13.13.2Scope of O&M Guide . 5Prerequisites for a Successful O&M Program . 55.15.25.35.45.55.65.75.85.95.10Electrical System . 11Central, String, DC-Optimized, or Micro-Inverter Configuration . 12Roof Maintenance Related to PV System . 15Ballasted or Attached Rack .

NOTICE This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the U.S. Department of Energy (DOE) under