43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun20161

MechanicalLoadTestingofSolarPanels– BeyondCertificationTestingAndrewM.Gabor1,RobJanoch1,AndrewAnselmo1,

JasonL.Lincoln2,HubertSeigneur2,ChristianHoneker3

1 BrightSpot AutomationLLC,Westford,MA,USA2 FloridaSolarEnergyCenterattheUniversityofCentralFlorida,

Orlando,FL,USA3 Fraunhofer CSE,Boston,MA,USA

This material is based upon work supported in part by the U. S Department ofEnergy’s Office of Energy Efficiency and Renewable Energy, in the Solar EnergyTechnologies Program, under Award Number DE-EE0004947.

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun20162

Motivation• Hatredofcrackedcells– Transitionfrom300to180micronthickwafers

• Areweconfidentinthedegradationrateofpanelsmadeinthelastdecade?–Whattestingarewedoingnowtoexaminedegradationrelatedtocrackedcells?

–Whatnewtestingisneeded?

Wecandobetter!

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun20163

Content• Mechanicalloadtestingbackground• Cellcrackingandpaneldegradation• LoadSpot tool• FiniteElementModelingofstressvsload• Conclusions

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun20164

MechanicalLoadTesting• Replicatestressesrelatedtosnowandwindloads

• PartofpanelcertificationtestingsequencessinceearlyJPLBlockVTests(1981)

• IEC61215– Statictest:3cyclesof2400Pa,1houroneachsideofpanel(static)

• IEC-TS-62782– Cyclic(dynamic)test:3-7cycles/min,+/- 1000Pa– WilllikelybefoldedintoIEC61215incomingyears

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun20165

ProblemsRevealedbyLoadTesting• Permanentdistortionofframingelements

• Edgesealfailure• Shatteringofcover-glass

• Fatigueofinterconnectwires

• Solderjointfailure• Delamination• Crackingofcells

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun20166

Cellcrackinginthefield• Verycommonaftershiftinwaferthicknessto<200µm

• Reportsofhighdegradationsrates

[Kottantharayil,IIT,LessonsLearnedfromtheAllIndiaSurveyofPhotovoltaicModules,NRELPVMRW2016]

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun20167

CellCracking/DegradationModel• Mostcellsarefineinthefactory– EveniftherearecrackstheyaretightlyclosedandcausenopowerlossandweakifanyELsignal

• Windgustorheavysnowinfield(orabuseduringshipping/installation)putscellsintotensilestress– Microcracks formedduringthesolderingprocesspropagateintocracks

• Snailtrailscanformrelativelyquickly• Overyears,closedcracksgraduallybecomeopenleadingtopowerdegradation

[Kontges, ISFH, PVSEC 2010]

[Sander, Fraunhofer CSP, Solar Energy Materials & Solar Cells 2013]

HumidityFreezeCycling

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun20168

ShortcomingofIEC61215• NewestversionofIEC61215stilldoesnotfollowloadtestingwithenvironmentalchambertestingtoopenupcracks– Mostcracksremaintightlyclosedwithoutpowerloss

• PVQATtestingdoes [Wohlgemuth, NREL, PVSC 2014]

[Beck,Siva,NRELPVMRW2016]

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun20169

CellCrackingSolutions

[Gabor, BrightSpot Automation, NREL PVMRW, 2015]

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201610

LoadTestingMethods• Sandbags– Timeconsuming,staticonly,uniformity?

• Airbladder– Singlesided

• Suctioncups– Dominantmethodforcyclic,uniformity?

• Vacuum/Air-Pressure– Veryuniform,littleattention,canconstraintheedges

[Gade, Jabil, NREL PVMRW, 2015]

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201611

PointLoadingwithSuctionCups• Reportsofmorecellcrackingseenundersuctioncupslocations

• IEC-TS62782cyclicloadingtestrequirescenter-to-center distancebetweensuctioncupsbe<20cm– Goodenough?– StaticloadinginIEC61215?

SandBags SuctionCups

[Mülhöfer,ISE,PVSEC2013]

[Baek, Samsung SDI, NREL PVMRW, 2014]

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201612

ELUnderFrontSideLoad• Lightpressure– Opensuppre-existingcracks– Cracksrecloseuponreleaseofpressure

• ELandIVtestingcancomparethese2states– Predictdegradationoncecracksopenupthefield

[Gabor, Evergreen Solar, PVSEC 2006]

[Sander, Fraunhofer CSP, Solar Energy Materials & Solar Cells 2013]

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201613

LoadSpot a better way to bend

• Rear-sidevacuum/air-pressurecavity– FrontsideopenforIV/EL– Sealwithoutconstrainingedgesofpanel

• CanperformIECloadtests• Flexiblepanelsize(upto72cells)• +/- 5400Pa• Fasterthan2seccyclicmode• Deflectionmonitoring• Constraintsat4mountingpointsusingdesiredclamps

• FirstunitshipstoFSEC,July2016– Availableforordersnow

~35 cycles/min

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201614

Window– openexistingcracks• Newcracksstartformingabove1000Pa• Stillopenat600Pa

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201615

InteractionwithShading• Pre-existingcracks• Shadingloss~9%at0Pa

• Incrementalshadingloss~12%at800Pa

• Explanation– Littlepowerlossbelow10%inactivearea

– Inactiveareasfromshadingandopencracksareadditive

[Kontges, ISFH, PVSEC 2010]

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201616

FiniteElementModeling@2400Pa

• Highstresseswithstandardconstructionandmounting

• Loadtestingwithedgeconstraintsdoesnotaccuratelyreplicaterealconditions

• MinimalstresstoSiinglass/glass(neutralaxis)

• MinimalstresstoSiifsubstituteperimeterAlframemasswith3gluedbackrails

MPa605550454035302520151050-5-10-15

a) b)

c) d)

A)Standard B)EdgeConstrained

C)Glass/Glass D)BackRails

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201617

WalkingonSunshine• Assumptions– Standardpanelconstruction

– 180lbs ononefootincenterofpanel

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201618

WalkingonSunshine• Assumptions– Standardpanelconstruction

– 180lbs ononefootincenterofpanel

• >80MPaincenter!• Doesnot”feelgood”to

thepanel

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201619!

LoadSpot-PROconcept• Testeverymoduleinproductionline(30stakt time)• EL&IVinbentandunbentstates

– Minimalpressuretomainlyopenpre-existingcracks(<800Pa)?• Afewsecondsvsweeksofenvironmentalchambertime

– Higherpressurestodemonstratewhateverloadsmightbeexpectedinthefield?• Burn-intesting- Commoninotherindustries (e.g.– PCB)

• Statisticalprocesscontroltohelpoptimizefactoryperformance

• IVdeltadatacanbeprovidedtocustomersasdemonstrationofpanelquality– RatemoduleWattsondegradedstate?

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201620

ComparisonofLoadingMethods

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201621

Conclusions• Modeledcellstressunderfrontsidepanelload

– Importanttonotconstraintheedgeduringtesting– PotentialforlowerstressusingAlmassinbackrailsratherthanperimeter

frames– Glass/glassmoduleconstructionisvastlysuperiorregardingcracking

• DemonstratedLoadSpot operation– Mechanicalloadtestingwithvacuumandairpressure– SatisfyIECstaticandcyclicloadtestingdefinitionsforpanelcertification

• IEC61215doesnotmakesenseregardingloadtesting– Anyloadtestshouldbefollowedbyenvironmentalchambertestingto

openupthecrackscreated• PVQATsequence• Differentloadlevelsfordifferentapplications?

– Howmanymodulesonthemarketwouldpasscertificationwithsucharequirement?

• ELimagescapturedinthefactoryprovidelittleconfidenceregardingfuturecrackinganddegradationinthefield

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201622

Beyondcertificationtesting• EL/IVonpanelunderloadtoquicklyquantifyfutureimpactofexistingcrackedcellsoncecracksopenupinthefield– Faster,cheaper,non-destructivealternativetoenvironmentalchambertesting

• Statisticalprocesscontrolofpanelfactory• Burn-intesting:loadmodulesinthefactorytolevelstheywilllikelyseeinthefieldandquantifythepotentialimpactofnewlyformedcracks

• Interactionbetweenshadingandcrackedcells

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201623

NextSteps• TransferthemodelingfromSolidWorkstoAbacusand

replacethesiliconsheetwithdiscretecells• NewLoadSpot variations– LoadSpot-PRO:In-lineQConeverypanelinfactory– LoadSpot-Mobile:Testpanelspriortoinstallationinfield

– LoadSpot-Field:Testinstalledpanels• TestpanelsatFSEC– Correlatecrackopeningtesttoenvironmentalchamberdegradation

– Hubert.Seigneur@uspvmc.org• Morefieldstudiesneededtrackingtheevolutionofcrackedcellsandpowerdegradation

43RDIEEEPHOTOVOLTAICSPECIALISTSCONFERENCE- 10Jun201624

Thankyouforyourattention!

gabor@brightspotautomation.comwww.brightspotautomation.com