Reliability Issues for Photov

Reliability Issues for Photov

Modules

Sarah Kurtz

National Renewable Energy LaboraNational Renewable Energy Labora

Golden, CO

Funded by Department of Energ

NREL/PR-520-46481

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ PV Re

Octobe

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for S
Outline

• Solar – a huge success, but still a long way to • Key y approaches to solar electricity

• Solar thermal• Crystalline silicon• Thin film Thin film – amorphous silicon CdTe CIGS amorphous silicon, CdTe, CIGS• Concentrator – low- and high-concentration approac

• Importance of reliability to success of solar• Reliability issues specific to each approach

• Silicon – strong performance; continuous improvem

quantitative predictions quantitative predictions

• Thin film – uniform, large-area deposition for produc

development and sensitivity to moisture; metastabili

• Concentrator product development; simultaneous

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

• Concentrator – product development; simultaneous

optimization of multiple components
Growth of photovoltaic (PV) indu

Tons of Si passes

Area of Si passes 

Tons of Si passes

microelectronics

2006 

microelectronics

2001 

0.01%-0.1% of electricity now comes from PV - extrapolates to > 

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

competitive with conventional electricity for 0.1% - 1% of market; 

Rogol, PHOTON International A

3
Growth of PV industry

Annual replacement of electricity capacity for 20 yr cycle

100

ped

Annual new electricity capacity 1996-2006*

10

of PV ship If we can maintain 

1

GW 

If we can maintain the cu

growth rate, PV will reach 

milestones in less than 

If we can maintain 

current growth ratewill reach major 

milestones in < 10 

2000 2005 2010 2015 

Y

milestones milestones in less than 

in

< 10 

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

Year

*www.eia.doe.gov/emeu/international/electricitycapacity.html (4012-2981 GW)/10 yr
Solar energy is abundant

Convenient truth: small area can supply our energy needs Convenient truth: small area can supply our energy needs

5-6 kWh/sq m/day At 10% efficiency,

area needed 

for US 

electricity

>10 kWh/sq m/day >10 kWh/sq m/day

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

Sunlight reaching earth in 1 hour is enough to power the world for 1 year
Solar thermal electric

Parabolic trough is the primary technology todayResurgence of interest~ 400 MW installedCurrently generates ~ 0.01% of US electricit

y

Can generate electricity into the evening & use fuel into the night

8060

r in US

Sola

Parab

4020

completed/yr

0

MW c

1985 1990 1995 

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

Yea

4 GW planned in US by 
64 MW S l i P b li 64 MW Solargenix Parabolic 

Trough Plant in Nevada -

2007

1-MW Arizona Trough PTucson AZ 2006

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

Tucson, AZ - 2006
Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

8
Three key approaches to photovoltaic (P

Two strategie

semiconduc

Conventional approach

Front

Solar cell

2. Thi

Back 1. Silicon

Reduce cost by reducing use 

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

of semiconductor 3. Conc
Many technology choices

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

10
One “winner” or many technolo

Alka e lin

e Nickel cadmium Nickel met

Nickel met

Lithi i

Lead acid

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

Lithium ion

Different technologies for different applications 
Cost of electricity: two or three 

2 O ti d i t

65

1. Initial price (estimates*)

2. Operation an

d main

t

- Fuel cost (Coal

 PV



- Operation (Coal

 PV



- Maintenance (Coal

 PV

s ($/W)

54

s

3

t ($/W) e estimates PV is already competitive f

some locatio

321 Initial cos 3. Total electricity gene

- Ca

pacit

y factor (Coal

 

es of price

10

Old coal New coal Clean coal PV

py ( 

Coal ~100%; PV ~ 25%

- Life of plant (Coal

 PV



*Fortnightly’s

SPARK, p. 10, May 2008

Example

 Upfront costs for PV and coal plants are converging Ongoing costs are less for PV

o g y s S , p 0, ay 008

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

 Operation only during daylight hours increases cost by  Key remaining question is life of PV plant (30 years?) 
Importance of reliability & dura

1 0.0.8

costPerformance of good system

0.6

mance or Performance of systems with problems

0.4

ative perfor O ti d i t t O&M t 0.2

0.0

Rela

Operation an

d maintenance costs 

for systems with problems

O&M costs 

for good syste

Cost of solar electricity depends on degradation, lifetime, & ongoing costs 

0

5 10 15 20 

Year

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

Those paying for upfront investment want guarantee of system life
How to satisfy the investo

 Historically, degradation & failure mechani

have been found in the field that were not f

accelerated testing

 Predictive models need to be validated wit

data

 Big challenge: How can we give 30-year 

predictions for degradation & failure rates wproduct has only been in the field for 1-2 y

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO
Silicon modules

SiliconS

G

Si module cross 

EE

Bac

Silicon cell 

Common encapEVA - Ethylene 

Ethylene 

PET - polyethylPVF - poly viny

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO
History of Si module qualification tes

JPL (Jet Propulsion Lab) Block b

Test I II III IVYear 1975 1976 1977 1978 Th l erma 100 l 50 l 50 l 50 l Cycle (

°C)

100 cycles

-40 to +90

50 cycles-40 to +90

50 cycles-40 to +90

50 cycles

-40 to +90

Humidity 70 C, 90%RH, 68 hr 5 cycles 40 C 90%RH 5 cycles 40 C 90%RH 5 cycles 54 C 90%RH 

68 hr 40

C, 90%RH 

to 23 C

40

C, 90%RH

to 23 C

54

C, 90%RH

to 23 C

Hot spots -

-

- - 

Mechanical load

- 100 cycles 

± 2400 Pa

100 cycles ± 2400 Pa

10000 cyc. ± 2400 P

H il a --- 9i t mpac

ts 

3/4” - 45 mph

NOCT - - - Yes 

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PO

High pot - < 15 μA 

1500 V

< 50 μA 

1500 V

< 50 μA 

1500 V
JPL Block buys led to dramatic impro

• O t d l i d (Whi l 1993) One s

t

u

dy c

l

a

ime

d (Whipp

le, 1993)

:

• Pre-Block V: 45% module failure rate

• P t os

t

-Bl k V oc

k

V: 

<0 1%. mod l f il 

d

u

le 

failure ra

• Studies of c-Si modules show that modul

are small (i t d i t h t 

ll (inverters 

dom

ina

te when cos

t

Unscheduled maintenance costs

69% 

Currently, most repo

that c-Si module fai

dominated by im

Inverters

dominated by im

installation, lightnin

critters, etc

21% 

System

P

V

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

(Prog. PV 2008; 16:249)

10% 
Today’s qualification standa

are similar to JPL are similar to JPL

 IEC 61215 - Crystalline silicon design qual

includes 18 test 

procedures 

Thermal cycling - 200 cycles -40

°C to +85

°

C

Humidity freeze - 10 cycles +85

°C, 85% RH to 

D ht amp 

hea

t - 1000 h t +85 1000

hrs a

t +85

°C 85% RH C, 85% RH

Wet leakage current - Wet insulation resistance 

40 M

Ω

m

2 at 500 V or system voltage

Requirement is typically to retain 95% of origin

production

IEC 61646 (thin film) and IEC62108 (

IEC 61646 (thin film) and IEC62108 (

are similar

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

www.iec.ch
Silicon modules – remaining cha

 New materials (reduce cost, improve perfo

– will these have same reliabilit

y

?

 Continued quality assurance (e.g. impuritie

give light-induced degradation)

 Arcing, grounding, power conditioning, oth

system-related problems

 Confident, long-term, quantitative predictio Typical degradation rates are 0-1%/yr (diff

measure); field failure rates are often < 0.1

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

 Proven module does not guarantee new pr
Past success does not guarantee 

future success

C-Si

70% Thin film Thin film

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

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20 About two-thirds of degradation rates are measured as 

33rd PVSC, Tamiz
Measurement of degradation rates tak

1200 

DC 

power -0.14%/yr

1000

g (W)

inverter replaced

p

800

ower rating 

inverter efficiency

600

Po

 ASE Americas Si modules

400 

2003 2005 2007

 Xantrex Suntie 2500

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PO

Need precise measurement of irradiance, temperature, etc. 21

Time
Thin-film approaches on the m

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

CuIn(Ga)Se CdTe Amorpho
Thin-film approach

• First Solar (Toledo, OH) - 5th bigge

PV com

p y an

y in world in 200

7

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO
Thin-film structures

Glass

CdTe uses superstrate

Glass for protec

CuInGaSe uses substra

ITO or TCO

Glass for protec

CdS

CdT

ZnO or TCO

CdS Not to 

e scale

Metal

CuInGaSe

Molybdenum

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PO

Glass for strength Glass
Monolithic module integrat

5 x 

Contact

Cell

(I ti )

Active Cell

+

(Inactive) 

w

Glass

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

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Hurdle for thin films: uniformity of de

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

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Hurdle for thin films: uniformity of intercon

5 x 

Contact

Cell

(I ti )

Active Cell

+

(Inactive) 

w

Glass

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO
Module metastability: Reversi

vs irreversible changes

• Amorphous silicon degrades in light and recov

when annealed in the dark

• CIGS d CdT h t i t CIGS an

d CdTe can s

how 

trans

ien

ts

9

Rated efficiency

8

%)

June 

2003

July

Jan 2009

0.2 kWh/m 2

Jan 2009

0.2 kWh/m 2

0.25 kWh/m 2

start test

76

Efficiency (%July 2008 Dec 2008 July 2008 2.75 kWh/m 2 tested same day 3.15 kWh/m 2 tested next day 3.15 kWh/m 2 tested next day 50°C overnight 50°C overnight 0°C 

65

tested next day

overnight

0 C

overnight

CIGS d l

 CIGS no exposure

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

4

CIGS 3-year exposure in Florida CIGS mo

d

ules
Damp heat can cause degrad

 ZnO (and other transparent conductors

with moisture, causing increase in serie

resi t s

tance

 CuInGaSe may react with moisture

T t C d ti O id Transparen

t

Con

ductive 

Oxides

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO
Many possible failure mechan

• CdTe has shown instability of back contact 

( ) diffusion?

)

• Edge seal may allow water into glass/glass mo• Partial shunts or conducting diodes may be se

scribe lines or other defected areas

• Adhesion to glass can be problem• Role of sodium is important in CuInGaSe modu

Role of sodium is important in CuInGaSe modu

but sodium can move

• Currently, gg the biggest effort with CuInGaSe is t

put it on a flexible substrate – requires excellenbarrier coating unless cell can be hardened to moisture

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO
Range of concentrator approa

Amonix JX Crystals

High concentration Low concentration

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• 35% 

- 40% cells

• 400X – 1500 X

• 15% - 25% cells• 2X – 100 X
CPV challenges – many interact

 CPV can fail in many ways, but it can be d

understand where the 

problem is and to fix 

problem without creating a new problem

• Tracking – optics must be aligned with the 

• Optics – durability can be problem, soiling; 

affect rest of system

• Cell – must be encapsulated, but not affec

UV; size of cell affects rest of system

• Heat sink – must be electrically isolated, bu

excellent thermal contact

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

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• Modularity may be benefit!
UV transmission

Analysis of transmitted optical spectrum enabling accelerate

CPV designs

SPIE 2009 David Miller, et al

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Bonds to heat sink and opt

Optic Optical bond with 100% Transmission

Electrical 50 W/sq cm

Cell

H t ik

contact

Small 

T (<10

°C)

Electrical isolation

Hea

t s

in

k No voids

T cycle OK

• Borrowing experience from power electronics and DBC (direct bonded copper) makes this a smaller 

IR im

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

issue• Intense UV may be a substantial problem, but optics may not transmit UV

Bos
Concentrators – reliability chal

• Wide variety of designs• Qualification test is not well establishe

Qualification test is not well establishe

• Companies spend time developing th

accel t dt t t d d t lera

t

e

d

tes

ts 

to spee

d pro

duc

t

development cycles

• Very few companies have heritage w

testing

• Everyone wants to bring a product to 

immediatel

y

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO
Concentrator technol

Creative

optical 

designs?

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO
Summary

• Solar is growing rapidly and could become a 

si ifi t f l t i it ithi 10 ignificant source of electricity within 10-20 yrs

• Silicon modules are performing well in the field

reliability testing of new designs is still importareliability testing of new designs is still importa

• CdTe and CuInGaSe modules are sensitive to 

moisture, so must be carefully sealed; only amorph Si d l il bl i fl ibl 

hous Si modules are available in flexible 

• Concentrator PV is in product development sta

is benefiting from expertise in other industries is benefiting from expertise in other industries

• In general, PV industry can benefit from the re

testing experience of the microelectronics indu

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

Let’s work together to help PV grow!
Planet powe

renewable e

By year 2100 o

Thank y y ou for your attention!

Thank you to :Dave AlbinGlenn AlersNick BoscoJoe del CuetoChris DelineEd GelakSteve GlickPeter HackeDirk JordanMike KempeTom Moricone Tom MoriconeBill MarionDavid MillerMatt MullerJohn PernJose Rodriguez

Sarah Kurtz ASTR 2009 Oct 7 – Oct 9, Jersey City, NJ

PO

g

Bill SekulicRyan SmithKent TerwilligerDavid Trudell