1207_surespracticepresentation_stachew

Development of Accelerated Photovoltaic (PV) Backsheet Testing and Evaluation

Elena M. StachewNicholas R. Wheeler Roger H. French

Solar Durability and Lifetime Extension (SDLE) CenterMaterials Science and Engineering DepartmentCase Western Reserve UniversityCleveland OH 44106

Crystalline Silicon (c-Si) PV module

SDLE Center, VUV-Lab, Materials Science & Engineering Department, Roger H. French © 2012 http://sdle.case.edu May 2, 2023, VuGraph 2

What is a backsheet and its function?

(1) DuPont Backsheet Offerings: DuPont Tedlar PVF Films, DuPont, 2009; (2) Roekens-Guibert, Hilde, Next Generation Tedlar* PVF Film for Photovoltaic Module Backsheets, DuPont, December 10th. 2007

Glass

Encapsulant

c-Si Cells / Interconnects

Encapsulant

Backsheet

• Electrical safety

• Protective barrier-O2,H2O, HAc

• Optical Properties • UV stability• Reduction of cell

operating temperatures

• Higher performance

Courtesy of Nick Wheeler

http://sdle.case.edu/


Typical tri-layer backsheet structures

Backsheet images from DuPont Photovoltaic Solutions, backsheets from various suppliers, chemical structures from Wikipedia

Fluoropolymers-UV stable, but expensive

Polyesters-electrically insulating

Polyolefins

Polyamides

Not UV stable, but cheap



The problem with current standard qualification testing

Czanderna & Jorgensen, NREL 1999

• Problem: • Not indicative of:

• true lifetime performance• real-world degradation

modes, pathways, rates and responses

• Solution: Develop a PV backsheet standard test methodology that reflects observed real-world degradation modes and rates

Carissa Plains Power Plant Failure • Test characteristics:• Initial performance, safety,

quality control• All important but lacking



Outline

Objective: Accelerated testing of PV backsheets must be cross-correlated with observed real-world degradation modes and rates using stress response (R(S)) framework

=

Accelerated testing

Development of outdoor testing infrastructure

Model development to refine R(S) framework

Tasks:



Model development

Accelerated testing

Model development to refine R(S) framework Development of

outdoor testing infrastructure

Recently submitted to BAPVC, courtesy of Roger French, Laura Bruckman, Nick Wheeler, Yang Hu

Model



1 acre SDLE SunFarm outdoor testing infrastructure

• 350 sample trays• Total: 8,000 samples

Tasks:• Wiring for sensors and

thermocouples for outdoor conditions

• Weight balance on trackers• Labeling infrastructure

Accelerated testing

Model development to refine R(S) framework

Development of outdoor testing infrastructure



Accelerated Testing

Chemical structures courtesy of Wikiipedia

Optical response measurements: Hunterlabs UltraScan Pro

• Haze• LAB Colorimetry

Accelerated testing



Materials:• Fluoropolymer derivatives:

• Tefzel 200, 210, 280• PFA 340, 350, 440• FEP 140

Tefzel derivative

• Polyamides:• Nylon-6,6

Exposure: QUV Accelerated Weathering Tester

1.55 W/m2/nm @ 340nm, 70°C for 96 hours



Haze

Computing Science, Simon Fraser University

• A measure of optical scattering through thickness of sample

• Total diffuse transmission (T) through sample

• Tdiffuse/Ttotal *100%

Tefzel 200 Tefzel 210 Tefzel 280 PFA 340 PFA 350 PFA 440 FEP 140 Nylon 6,650556065707580859095

100

Haze %Dose

FEP 140:Becoming more UV durable



LAB Colorimetry

Computing Science, Simon Fraser University, http://www.cs.sfu.ca/CourseCentral/365/mark/material/notes/Chap3/Chap3.3/Chap3.3.html

No significant change


102030405060708090

100

L* = Whitening

Dose


http://www.cs.sfu.ca/CourseCentral/365/mark/material/notes/Chap3/Chap3.3/Chap3.3.html

http://www.cs.sfu.ca/CourseCentral/365/mark/material/notes/Chap3/Chap3.3/Chap3.3.html


LAB Colorimetry


0.5

1

1.5

2

2.5

3

3.5

4

4.5

a* = Reddening

Tefzels first increase in redness then show a subsequent decrease

Dose


5

10

15

20

25

b* = Yellowing

Nylon-6,6 shows significant increase in yellowness---not UV durable

Dose



Conclusions and Future Work

1. Problem: Not indicative of true lifetime performance nor real-world degradation modes, pathways, rates and responses

2. Framework:

Accelerated testing



3. Solution: Develop a PV backsheet standard test methodology that reflects observed real-world degradation modes and rates

4. Future Work:• Continue collaboration with DuPont• Published literature review • R Project and R Studio for data analysis • Continue development of outdoor

testing infrastructure



Acknowledgements

This work was funded and supported by CWRU SOURCE, Dominion and the Case Alumni Association.

Thank you to Laura Bruckman, Myles Murray, Yang Hu and the rest of the VUV-lab group.

DuPont for their interest and collaboration on this project.

Replex Plastics for sample trays design and construction.

Thank you to Sheila Pedigo and Bethany Pope for coordinating the summer program.



Backgrounder


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