field study and analysis of backsheet degradation in 450mw ......field study and analysis of...

Field study and analysis of backsheetdegradation in 450MW+ PV installations

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Atlas-NIST Workshop 2017 December 4-6, 2017

Thomas Felder, Hongjie Hu, William Gambogi, Kaushik Roy Choudhury, Steven MacMaster, Lucie Garreau-lles, and T. John Trout

DuPont Photovoltaic Solutions

2Copyright © DuPont 2017. All rights reserved.

2

Agenda

• DuPont Global Field Assessment Program

• Solar panel defects observed in the field

- By component

- By climate

- By roof vs ground mounting

- By age and backsheet type

• Field examples of backsheet defects

- Frontside yellowing

- Airside Yellowing and mechanical loss

- Cracking

- Busbar corrosion and glass breakage

- Tedlar® PVF field results

• Conclusions



DuPont Global Field Assessment Program

5001000150020002500300035004000

-0.1

0

0.1

0.2

0.3

0.4

0.5

TEP UA Sharp 165 neq5e2u b_2012-11-30T11-08-32.spc

Wavenumbers [1/cm]

Abs

orba

nce

Backsheet

identification and

degradation using

FTIR spectrometer

Thermal Imaging IR

camera identifying

hot spots in modules

Multi-step Inspection Protocol

• Documentation of location, age, climate, module, energy production, visual & thermal imaging,

IR spectroscopy

• Defect categorization

Defect Analysis (FMEA) and Statistics

Working with many partners globally

By end of 2016, surveyed >190 global installations in NA, EU, and AP

45 module manufacturers, 450MW, 1,900,000 modules, newly commissioned to 30+ years in service



Cell defects• Snail Trails• Corrosion• ARC Delamination

EVA defects• Yellowing• Delamination

Other defects

Cracking

Delamination

Snail trails

Ribbon corrosion

ARC delamination

Yellowing

Delamination from cell

Delamination from glass

Cable corrosion

Glass breakage

Front side yellowing

Backsheet defects• Air Side Yellowing• Front Side Yellowing• Cracking• Delamination• Bubbling• Other

Air side yellowing

Field Degradation and Defect Categories

Jbox Melting



2016

Installations 197

Number of

panels

1,919,000

Average age

(years)

3.4

MW 453

No defect78.0%

Cell11.3%

Backsheet7.5%

Encapsulant2.7%

Other0.5%

2016 Analysis453MW inspected

Data size more than doubled from 2015 to 453 MW • All defects 22%• Cell related defects 11.3%• Backsheet defects 7.5%

0 200,000 400,000 600,000

all climates

Hot Arid

Tropical

Temperate

KW inspected

DuPont 2016 Field Analysis and Database - Overview

Climate sample sizes 2016



78.0%

11.3%7.5%

2.7%0.5%

No defectsCellBacksheetEVAOther defects

Cell and Metalization show less or small effect with ClimatePolymer Components (Backsheet and EVA) show stronger trend• Hot arid > Tropical > Temperate• Use Defect Rates to determine “harshness” of Climates?• Dominant factor is likely Temperature, then UV

Analysis of Climate on Defects Rates

Polymer trends

1

1 Temperate cell defects are dominated by Snail Trails, likely due to sampling

0 200,000 400,000 600,000

all climates

Hot Arid

Tropical

Temperate

KW inspected

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

Hot arid Tropical Temperate

% d

efe

cts

1

0.0

5.0

10.0

15.0

20.0

25.0

30.0

Hot arid Tropical Temperate

% d

efe

cts



Analysis of Defect Rates for Roof vs Ground Mounted Systems

63.0%

11.3%

25.3%

0.2% 0.1%

Roof mounted, 11.7MW

No defects

Cell

Backsheet

EVA

Other defects

78.4%

11.3%7.0% 2.8% 0.5%

Ground mounted, 441MW

Overall Higher defect rates for roof vs ground installations

• Backsheet defects are > 3X higher on roof systems

• Cell defects are similar for Roof and Ground

Differences are likely due to higher temperatures for roof systems

• Roof Systems are typically 15oC higher than Ground Mounted1

• This trend with temperature is similar to the effect seen in climates

1 Creep in Photovoltaic Modules: Examining the Stability of Polymeric Materials and Components(2010) 35th IEEE Photovoltaic Specialists Conference (PVSC ’10) Honolulu, David C. Miller, MichaelKempe



Analysis of Backsheet Defects vs Age

Tedlar®-oldest installations, lowest defect percentage

• Defect rate is low and not increasing over time

PVDF and Polyester, highest defect percentages

• Defect rate is increasing with time

1Front side yellowing due to inner layer chemical treatment2 TPE, Weak inner layer adhesion led to delamination3 Slight Front side yellowing

Material (av. age in years)

Defect rate (MW basis)

Tedlar® (5.4) 0.1%

PVDF (2.3) 7%

Polyester(3.0) 8.6%

Defect Rates by Backsheet

PVDF PET PVF

1

2

3

>30 years

in the field



Field Examples of Backsheet Inner Layer Yellowing

Backsheet Yellowing on front side

2 year old fielded module in a desert region in USA- PVDF-based backsheet

9 year old fielded module in Tibet- PET-based backsheet-100% modules yellowed in 10kW field

Field examples of Backsheet Outer Layer Yellowing

27 26.1 25.9 26.4 25.8 25.5 24.9 25.6 26.4 26 26.2 26.8 24.8 25.2 25.8 25.4 25.8 26.3 25.6 25.5 25.6 25.8 25.5 25.7 24.5 25.3 26.1 24.9 25.2 25.8 26.3 25.6 25.2 25.7 25.1 24.6

26.5 25.8 25.7 26.2 25.5 25.1 24.8 25.2 25.9 25.5 25.7 26.5 23.9 24 25.1 24.3 23.9 25 25.6 25.1 25.8 26.2 25.7 25.3 23.9 24.9 25.8 20.2 23 25.3 26.2 25.3 25 25.6 24.5 24.3

26 24.8 24.7 24.9 24.8 24.1 24.5 25.2 24.7 26.2 22.9 23.4 24.1 22.8 24.5 26 25.3 26.1 25.3 25.3 23.3 23.1 24 20.6 23 25.2 24.4 24.3 24.8 24.3

26.1 24.9 24.5 24.8 24.4 24.4 24 24.3 25.1 24.9 24.7 25.9 22.5 22.7 23.7 22.8 23 24.2 25.7 25.2 26 25.5 25.5 25.2 23.9 23.9 24.7 23.5 22.9 24.2 24.6 24.2 24.3 25.8 25 24.6

24.2 22.7 22.5 22.9 22.4 22.4 21.9 22.4 23.4 22.4 22.6 23.6 19.9 19.9 21.2 20 19.6 21.4 24.3 23.8 24.2 23.6 24 23.5 21.9 22 23.2 22 21.1 22.5 22.8 22.6 23.1 24.9 24.7 24.2

23.4 20.9 19.8 20.3 19.7 21.1 20.3 19.7 20.8 19.6 20.9 23.1 18.6 16.4 17.8 16.8 17.6 20.8 23.4 20.7 20.4 19.7 20.1 21.2 21.8 20.7 21 20.1 19.4 22 21.9 20.3 21.7 24.7 24.7 24.3

23.1 20.4 18.6 19.2 18.4 20.6 19.5 18.5 19.4 18.6 20.1 21.9 18.3 14.8 16 14.6 16.6 20.2 22.9 19.7 18.6 17.9 18.4 20.3 21.6 20.1 20 18.1 18.6 21.3 21.4 19.6 20.8 24.8 24.6 24.3

21.3 19.2 17.6 18.9 17.5 18.8 16.7 16.6 18 16.7 17.8 19.3 15.9 13.7 15 13.4 14.4 17.7 20.7 18.3 17.7 17.3 17.7 18.6 18.9 18.6 19 17.2 17.3 19.7 19.8 18.5 19.7 23.6 24.3 24.2

23.3 20.9 19.2 19.7 19 20.9 18.4 18.4 19.4 18.4 19.2 21 17.3 13.9 15.4 13.8 15.2 19.2 21.9 19.2 18.2 18 17.9 20.3 20.6 19.5 19.3 17.6 18.1 20.9 20.7 19.1 20.2 24 24.5 24.6

21 20 20.3 17 18.1 19.9 18.1 18.3 19.1 17.3 19.5 21.1 18.5 15.9 17.1 15.5 16.6 20.3 18.4 16.7 17.6 14.5 15.1 18.3 22 19.7 18.3 17.9 18.8 20.1 20 18.6 17.4 25 24.9 24.9

18.7 18.3 18.5 16.1 15.5 17.4 15.9 16.4 17.8 16 16.1 18.4 17.3 14.6 17 15 14.5 17.4 16.6 15.4 17.1 14.2 13.1 15.2 20.3 18.4 16.8 17.2 17.4 17.2 19.1 17.8 19.4 23.5 24.1 24.3

20.4 19.2 18.8 16.5 19.7 18.4 17.4 18.5 19 21.4 18.7 15.6 17.4 16.7 20.6 18.5 16.3 17.7 14.2 18.1 22.2 19.6 17.8 18.6 20.8 20.4 18.8 20.6 24.7 25

20.9 20.2 20.2 18.8 18.5 20.6 19.4 19.3 20 19.2 20.2 22.2 19.7 18 19.2 18.5 18.3 21.4 19.3 18.5 19.5 17.5 17.3 19.6 22.8 21.1 19.7 20.2 20.5 21.6 21.2 20 21.2 24.6 24.8 24.6

21.1 21.5 21.7 21.2 20.4 21.5 21.1 21.6 22.1 21.3 21.4 22.4 20.7 20.9 21.9 21.1 20.6 21.9 20.3 20.9 21.9 20.8 19.8 21.1 22.8 22.6 22.2 22.5 22.6 22.4 22.2 22 22.7 24.3 24.4 24.7

23.5 23.6 24.3 23.6 23.1 24.4 23.3 23.5 24.4 23.6 23.6 24.6 23.2 23.3 24.1 23.6 23.1 24.5 23.1 23.1 24.2 23.4 22.9 23.9 24.7 23.9 24.5 24.7 24.5 24.3 24.2 23.8 24 25.2 24.6 24.4

24.4 24.5 25.4 24.8 24.7 25.4 24 24.3 25.5 24.8 24.9 25.5 24.3 24.7 25.5 25.1 24.6 25.4 24 24.3 25.4 24.5 24.4 25.1 25 23.7 24.6 24.9 24.8 24.6 25.2 24.7 24.4 25.4 24.4 24.4

24.7 24.9 25.8 25.5 25.3 25.7 24.6 24.9 25.6 25.6 25.4 26 24.8 25.2 26.2 25.8 25.7 26.1 24.6 25.1 26 25.4 25.4 26 24.7 24 24.3 24.5 24.6 24 26 25.3 25.1 25.3 24.6 24.1

25 25.7 26.5 26.7 26.3 26.5 25.4 25.6 26.3 26.3 26.2 26.6 25.1 25.7 26.3 26.3 26.5 26.8 25.6 25.9 27 26.5 26.7 26.9 26 25.4 25.9 26 25.6 24.9 26.6 26.1 25.7 26.1 25.3 25.2

A-Up7

A-Down7 A-Down1

A-Up6 A-Up5 A-Up4 A-Up3 A-Up2 A-Up1

A-Down6 A-Down5 A-Down4 A-Down3 A-Down2

E

Max High

27.0

24.2

21.4

18.7

15.9

13.1

Min Low

b* value

Yellowness measured on 12 rooftop modules deployed 15 years in Japan. Significant yellowing even on the interior of array (b* of 13-20)Highest yellowing is along edges with highest UV exposure (b* up to 27)

PET-based Backsheets

Detail of module from the installation shown on left

Source: Modules provided by AIST; DuPont analysis

Backsheet Yellowing on front side



Yellowing is an indication of polymer degradation and can place

modules at risk for failure and safety.

Yellowing: Indicates Polymer Degradation

Correlates with loss of Mechanical Properties

• Yellowing is often observed on the backsheet air side in the field.

• An extensive study comparing yellowing with elongation loss showed a correlation

• Loss of elongation can lead to cracking

4yrs solar farmPET-based backsheet

Yellowness correlates with Loss of Elongation



Cracking: Backsheet Loses Insulation and Places Modules at

High Risk for Failure and Safety

PVDF-based Backsheet cracking & delamination 57% of modules cracked

PET-based Backsheet cracking with ~15-20% of modules cracked. 80% power loss

PA-based Backsheet large amount of cracking with ~40% of modules cracked.

4yrs solar farm NA: 40kWPVDF-based backsheet

4yrs solar farm China: 20MWPA-based backsheet

9yrs rooftop Arizona: 35kWPET-based backsheet

Backsheet cracking observed in 3 classes of backsheets



4yrs solar farm NA: 40kWPVDF-based backsheet

9yrs rooftop Arizona: 35kWPET-based backsheet

Breakage, busbar corrosion, and power loss in glass-glass modules

Observation: Bus bar Corrosion, EVA browning

Power loss

Location: Danzhou (China), Time: 15 years

Observation: Bus bar Corrosion

Power loss

Location: Shanghai (China), Time: 5 years

• Multiple failures: Power Loss & Breakages across regions, applications (roof+ground)

• Believed higher corrosion rates are due to trapping of acetic acid by the glass backsheet

Observation: Bus Bar Corrosion,

Power loss

Location: Okinawa (Japan), Time:11 years

Observation: Extensive breakage

Location: Yannan (China), Time: 10 years



Tedlar® Field Case: 18yrs Old Tedlar® TPT Installation in Beijing

Low Power Loss and No Sign of Degradation

18yrs field module with TPT backsheet shows low power loss rate (0.7%/yr)

Tedlar® film shows no degradation after 18yrs field service

TPT backsheet maintains 160.8% elongation and 92.1 Mpa tensile strength, excellent retention of properties

Standard PVF

Tedlar® from field after 18yrs



Tedlar® Protecting Modules for over 35 years

Beijing, China 1999

SMUD, USA 1984SUPSI, Switzerland 1982

SYSU, China 1985

Nara, Japan 1983

Mt Soleil, Switzerland 1992 Tamil Nadu, India 1995

Vermont, USA 1985


15

Conclusions

• Results of >190 site inspections shows 22% of modules have defects

- Cells (11.3%) and backsheets (7.5%) are the leading categories

- Hot arid climate shows greatest polymer defect frequency

- No climate trend for cells and metallization

- Backsheet defects are 3X greater frequency on roof vs ground mount

• Backsheet defect analysis

- Defect rates are

- 7% for PVDF backsheets

- 8.6% for PET-based backsheets

- 0.1% for PVF-based backsheets

- Defects rates for PVDF and PET-based backsheets are increasing with time, rate is

not increasing for PVF

- Yellowing is observed on both front and airsides of backsheets

- Backsheet airside yellowing is correlated with backsheet cracking

- Glass breakage, bus bar corrosion, and power loss is seen in glass-glass modules

- Tedlar® PVF stable

• Tedlar® PVF offers the best protection for PV modules

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field study and analysis of backsheet degradation in 450mw ......field study and analysis of...

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