NREL%is%a%na*onal%laboratory%of%the%U.S.%Department%of%Energy,%Office%of%Energy%Efficiency%and%Renewable%Energy,%operated%by%the%Alliance%for%Sustainable%Energy,%LLC.%

Observed(field(failures(and(

reported(degrada4on(rates((

Thin(Film(PV(Workshop,(

Golden,(CO

Dirk(Jordan,(Michael(Kempe,(David(Miller,(Corinne(

Packard,(John(Wohlgemuth,(Sarah(Kurtz(

2/28/2013(
2%

 Introduc*on%

 Degrada*on%Rates%

 IFV%parameter%distribu*on%%

 Field%Failure%

 Conclusion%

Outline(
3%

Degrada4on(Rates(–(Literature(Survey(

Most(modules(degrade(by(ca.(0.5(%/year(

Number%of%Degrada*on%rates%(Rd)%%

from%literature:%2128

Jordan%et%al.,%%“Degrada*on%Rates%–%An%Analy*cal%Review”,%Progress%in%PV,%2011%

Technology,%age,%packaging,%geographic%loca*on%

ca.%80%%below%1%/year%

>%100%publica*ons%from%32%countries%

Circle%size%=%number%of%data%

points%from%a%given%loca*on.%

0

50

100

150

200

250

Frequency

Degradation0Rate0(%/year)

Median:,0.5 %/year

Average:,0.8,%/year

#,reported,rates,=,2128
4%

Literature(Degrada4on(Rates(

Date%of%installa*on:%PreF%&%PostF2000%

Red%diamonds:%mean%&%95%%confidence%interval%

ThinTfilm(technologies(narrowed(gap(to(cTSi(in(last(10(years(

ITV(parameter(informa4on(for(ca.(50%((of(all(Rd(

a-Si CdTe CIGS mono-Si multi-Si

Pre Post Pre Post Pre Post Pre Post Pre Post

124 23 54 1323 550

Date of Installation (DoI): Pre 2000; Post 2000

DoI:

N:

31%

13% 22%

34%

Outdoor'IV

Indoor'IV

PVUSA

PR

>%50%%of%Rd%taken%by%IFV%curves%→%

Informa*on%on%%shortFcircuit%current%(Isc),%

openFcircuit%voltage%(Voc),%fill%factor%(FF),%

Imax,%Vmax%%

>%100%publica*ons%from%32%countries%

Number%of%Degrada*on%rates%(Rd)%%

from%literature:%2128
8%

ITV(Parameters(by(Technology(

MonoFSi% Mul*FSi% ThinFfilm%

Degrada4on(for(cTSi(Isc;(ThinTfilm(FF((

639

IV Parameter

Pmax Isc Voc FF

632 591 584

Degradation Rate (%/year)

42

IV Parameter

Pmax Isc Voc FF

36 31 33

Degradation Rate (%/year)

Pmax Isc Voc FF

476

IV Parameter

Pmax Isc Voc FF

475 473 397

Degradation Rate (%/year)

0.0

0.5

1.0

1.5

2.0

2.5

0 10 20

Current'(A)

Voltage'(V)

10/18/2000() 12(pm

10/15/2010() 12(pm

Smith%et%al.,%World%Renewable%

Energy%Forum,%May%2012%

NREL%study%–%May%2012%–%World%Renewable%Energy%Forum

Pmax%correlated%to%Isc%loss% Pmax%correlated%to%FF%loss%
9%

ThinFfilm%%show%high%FF%Rd%in%humid%climates%

cTSi(–(ThinTfilm(Comparison(

Different%longFterm%

performance%recommenda*on%

based%on%climate%

First%Solar%recommenda*on:%

F0.7%/year%for%hot%climate%

F0.5%/year%for%all%other%climates%

First%Solar%

Different(longTterm(recommenda4on(based(on(climate(

Strevel%et%al.,%17th%edi*on%Journal%Photovoltaics%

Interna*onal,%2012%

Hot%&%Humid%Climate%
10%

What(about(CIGS?(

2%reports%about%stable%CIGS%array%in%the%field%

1. Germany,%Musikowski%et%al.,%PVSEC,%2010,%3942%

2. NREL,%Jordan%et%al.%,%IEEE%PVSC,%2011%

Shell Solar E80-C modules deployed at NREL. 

Photo credit: Harin Ullal, NREL PIX 14725 

0 20 40 60

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

0 500 1000 1500 2000

Time%(Months)

Daily%Performance%Ratio

Monthly%Performance%Ratio

Time%(Days)

Daily

Monthly

Performance%Ra*o%

2(reports(of(CIGS(arrays(w/o(measurable(degrada4on(

Shell%Solar%System%F%NREL%
11% 11%

Device(Performance(Measurement(

3%Measurement%techniques:%

1.%LACSS:%Large%area%con*nuous%solar%simulator%

2.%SOMS:%Standard%outdoor%measurement%system%

3.%Spire%240A%pulsed%simulator%

Only Module 61 shows clear signs of degradation 

Representative 

Uncertainty bar 

SN: Serial 

Number 
12% 12% National Renewable Energy Laboratory Innovation for Our Energy Future 12 

(a) (b)

Module(61(

Hot spot developed along presumed manufacturing defect 

Hegedus%et%al.,%“ThinFFilm%Solar%Cells:%Device%Measurements%and%Analysis”,%Progress%in%PV:%2004,%12,%155.%

Palm%,%“Second%Genera*on%CIS%Solar%Modules”,%Solar%Energy,%77,%2004,%757–765.%

Shunt resistance 

Optical image Infrared image 

Plot dJ/dV near Jsc 

 Rshunt

Scratch across cells Hot spot at the end of 

scratch 
21%

Module(ITV(Distribu4on(

100 10

Number of 

Modules

500

Color:%IFV%parameter%

Size:%Number%of%modules%in%study%

Coefficient%of%Varia*on%(CoV):%Standard%devia*on/%Mean%

Distribu*on%width%% Distribu*on%symmetry%%

Coefficient(of(Varia4on((%)(

Distribu4on(Skewness(

Years( Years(

Distribu4ons(widen(and(skew(with(field(exposure
31%

Israel%–%1995%–%7%years% Japan%–%2003%–%10%years% Sweden%–%2006%–%25%years%

CA%–%2011%–%%

11%&%20%years%

ITV(Distribu4ons(

Spain%–%2011%–%12%years%

Tunisia%–%2008%–%25%years%

MA%–%2010%–%30%years% Italy%–%2010%–%%

23%&%30%years%

Switzerland%–%2010%F20%years% CO%–%2012%–%15%years%
33%

Israel%–%1995%–%7%years% Japan%–%2003%–%10%years% Sweden%–%2006%–%25%years%

CA%–%2001%–%%

11%&%20%years%

ITV(Distribu4ons(

Spain%–%2011%–%12%years%

Tunisia%–%2008%–%25%years%

MA%–%2010%–%30%years% Italy%–%2010%–%%

23%&%30%years%

Switzerland%–%2010%F20%years% CO%–%2012%–%15%years%

0

50

100

150

200

250

Frequency

Degradation0Rate0(%/year)

Module(Parameter(Distribu4ons(similar(to(Rd(Distribu4on
38%

Skewed%distribu*on%with%2000%data%points%

Very%few%studies%inves*gate%that%many%modules%

%FF>%take%50%random%sample%%

Outlier(may(be(indica4ve(of(skewed(distribu4on(

Takes(sufficient(field(exposure(&(sample(size(to(see(it((

System(Performance(

Power((W)(
40%

0

50

100

150

200

250

300

Frequency

System-Degradation-Rate-(%/year)

CoV=1,+Skewness=0

CoV=2,+Skewness=21.1

CoV=8,+Skewness=0

CoV=8,+Skewness=22.6

Why(do(we(care?(

Monte%Carlo%Simula*on:%%

Assump*on:%modules%0.5%/year%degrada*on%over%25%years%

20kW%array,%200W%modules,%100%modules,%10%strings,%10%modules/string%%

Distribu4on(of(module(degrada4on(affects(system(degrada4on((
41%

Yellowing/browning Front%grid%oxida*on Discolora*on

Terminal+junc*on%box%

oxida*on Glass Soiling

Hot%spot Internal%electrical%circuit Metalliza*on%discolora*on

broken/cracked%cells Cells arc

Backsheet%detachment Encapsulant%&%backsheet String%interconnect

Encapsulant%delamina*on Bubbles backsheet%crumbling

Sealant%penetra*on Delamina*on Tedlar%detachment

Grid%oxida*on Frame arc%damage%to%earth

Insula*on%(dry) Corrosion JFbox%cracking

Insula*on%(wet)

Cell%or%Interconnect%

break Milky%papern

Soiling Diodes Mortar%soiling

Interconnects Mechanical%damages Burn%marks

Frame%defects LID

Electrochemical%

weathering

AR%coa*ng%oxida*on Mismatch Weathering

Field(Failures(T(Literature(

Lack(of(consistent(terminology(
42%

• Uses(IEC/UL(standard(terminology(

• Aeempts(to(balance(collec4on(of(sufficient(detail(for(failure(

mode(evalua4on(against(minimizing(recording(4me(per(

module(

• Consists(of(14(sec4onsT(based(on(module(component(

• Long%form%&%short%form%evalua*ons%

42%

Development of a Visual Inspection Data Collection Tool 

for Evaluation of Fielded PV Module Condition

C.E. Packard, J.H. Wohlgemuth, S.R. Kurtz 

Additional detail can be found in the 

full NREL report TP-5200-56154 

Visual(Inspec4on(Data(Collec4on(Tools(
43%

Field(Failure(T(Literature(

Is(it(consistent(with(our(own(field(observa4on?(

Front%glass/cover%%moves%up%–%but%not%a%lot%of%sta*s*cs%

Number%of%References% Number%of%References%

All%Technologies% ThinFfilm%

Almost%70%references%
44%

BP((Solarex)(Array(T((AZ(

Most%common%failure/degrada*on%modes:%

 Shading%%

 Delamina*on%@%hot%spot%

 Soiling%at%periphery%(frame)%

 Delamina*on%%

Also:%

 Site%wiring%

 Broken%glass%

Modules:%

 M/N%MSTF43MV%

 51W%max,%45W%rated.%

 Manufactured%July%2000%to%May%2001%

 Total%of%~10,000%%BP%modules%

BP(Solar(array,(facing(north((top)(

and(facing(south((boeom)(

aTSi(
45%

Broken(Glass(

 Wide%variety%of%fracture%morphologies%and%

extent%of%damage%

 Neither%front%or%back%glass%is%tempered.%

 Front%side:%6/400%modules.%

 Back%side:%11/400%modules.%

 Both%sides:%5/400%modules.%

Severely%broken%front% Less%severely%broken%front%

Broken%back%
46%

Broken(Glass(–(different(System(

Op*cal%image%of%only%damage%at%base%of%module% Op*cal%image%of%less%damaged%module%

Op*cal%(les)%&%IR%(right)%image%%

 Fracture%did%not%always%couple%to%the%back%

from%the%front%

 Extent%of%damage%varied%widely%

 Usual%hot%spot%may%not%be%observed%on%

modules%with%broken%glass%

 Rela*ve%occurrence:%3/450%in%original%(old%

edge%seal)%modules.%

 Minimal%thermal%signature%%

 (diode%is%probably%on)%
47%

Delamina4on(at(hot(spot(

 Localized%delamina*on%observed%at%top%of%

module%(over%jFbox)%

 Thot%spot%~%50°C;%Tfront%glass%~%45°C%%

 Rela*ve%occurrence:%every%module%

 Delamina*on%corresponds%to%a%hot%spot%

observed%on%every%module%

Op4cal(image(of(delamina4on(at(module(top( IR(image(of(mul4ple(modules(within(the(array(
48%

Permanent(Soiling(

 A%narrow%(0.5”)%region%at%the%bopom%of%

the%area%was%typically%soiled%

 Loca*on%corresponds%to%where%frame%

would%retain%water%runoff%

 The%contamina*on%is%extremely%difficult%

to%remove%

 The%orienta*on%of%the%modules%(and%cells)%

minimizes%shading%loss%at%the%soiled%

region;%also%minimizes%shading%loss%from%

grass,%plants,%etc.%%

 Rela*ve%occurrence:%every%module%
49%

Delamina4on(

Effected(region(

iden4fied((circle)(on(

module(

Detail(of(the(effected(region(on(the(same(

module(

Rela*ve%occurrence%128/400%modules%
50%

Less(damaged(region,(photo(from(back(

 all%“extruded”%modules%have%at%least%bubbles.%

 “Extrusion”%could%result%from%O2%or%N2%absorp*on%in%sieve%in%seal%or%

outgassing%from%residual%peroxide%in%EVA%

 No%evidence%of%damage%on%replacement%modules,%all%with%edge%seal.%

 (change%in%material%by%manufacturer?)%

 3/450%“extruded”%modules%cracked.%

“Edge(seal”,(from(front(

Severely(damaged(region,(

photo(from(back(

Other(Observa4ons(

Edge(Seal(Extrusion
51%

Other(Observa4ons(

Shading%

Weathered%interconnect%system%

Delaminated%relief%pad%

Cell%defects%
52%

Any(other(observa4ons(
53%

Any(other(observa4ons(

27 

months 

Packard.%et%al,%EU%PVSEC,%2012%

Dhere%et%al.,%PVMR%2011%
54%

Summary(

1. Degrada4on(rates(

 cFSi%Pmax%decline%is%most%strongly%correlated%with%Isc%,%less%FF%

 ThinFfilm%are%characterized%by%much%higher%FF%degrada*on%(do%not%

have%a%lot%of%field%data)%

 Module%distribu*ons%widen%and%skew%with%increasing%field%exposure%%

→%can%have%significant%impact%on%system%performance%

 ThinFfilm%systems%with%no%measurable%degrada*on%have%been%shown%

2. Field(Failure(

 Need%to%use%standard%approach%to%characterize%field%failures%

 Need%more%data,%par*cular%percentage%breakdown%of%failures%
55%

Acknowledgments(

Thank%you%to%:%

Chris%Deline%

Josh%Stein%

NREL%T&M%team%

Rest%of%the%NREL%reliability%team%

Thank%you%for%your%apen*on%

Na*onal%Renewable%Energy%Laboratory%

15013%Denver%West%Parkway,%MS%3411%

Golden,%CO%80401,%USA%

dirk.jordan@nrel.gov%

This%work%was%supported%by%the%U.S.%Department%of%

Energy%under%Contract%No.%DEFAC36F08FGO28308%

with%the%Na*onal%Renewable%Energy%Laboratory