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
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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
3Copyright © DuPont 2017. All rights reserved.
3Copyright © DuPont 2017. All rights reserved.
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
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4Copyright © DuPont 2017. All rights reserved.
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
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5Copyright © DuPont 2017. All rights reserved.
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
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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
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7Copyright © DuPont 2017. All rights reserved.
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
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8Copyright © DuPont 2017. All rights reserved.
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
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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
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10Copyright © DuPont 2017. All rights reserved.
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
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11Copyright © DuPont 2017. All rights reserved.
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
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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
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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
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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
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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