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Title: Encapsulation and backsheet adhesion metrology for photovoltaic modules

Photovoltaic modules are designed to operate for decades in terrestrial environments. However, mechanical stress, moisture, and ultraviolet radiation eventually degrade protective materials in modules, particularly their adhesion properties, eventually leading to reduced solar cell performance. Despite the significance of interfacial adhesion to module durability, currently there is no reliable technique for characterizing module adhesion properties. We present a simple and reproducible metrology for characterizing adhesion in photovoltaic modules that is grounded in fundamental concepts of beam and fracture mechanics. Using width-tapered cantilever beam fracture specimens, interfacial adhesion was evaluated on relevant interfaces of encapsulation and backsheet structures of new and 27-year-old historic modules. The adhesion energy, Gc [J/m 2], was calculated from the critical value of the strain energy release rate, G, using G = βP2, where β (a mechanical and geometric parameter of the fracture specimen) and P (the experimentally measured critical load) are constants. Under some circumstances where testing may result in cracking of brittle layers in the test specimen, measurement of the delamination length in addition to the critical load was necessary to determine G. Relative to new module materials, backsheet adhesion was 95% and 98% lower for historic modules that were exposed (operated in the field)more » and unexposed (stored on-site, but out of direct sunlight), respectively. Encapsulation adhesion was 87-94% lower in the exposed modules and 31% lower in the unexposed module. As a result, the metrology presented here can be used to improve module materials and assess long-term reliability.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1]
  1. Stanford Univ., Stanford, CA (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Report Number(s):
NREL/JA-5J00-66410
Journal ID: ISSN 1062-7995
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
Progress in Photovoltaics
Additional Journal Information:
Journal Volume: 25; Journal Issue: 1; Journal ID: ISSN 1062-7995
Publisher:
Wiley
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; adhesion; reliability; delamination; photovoltaic; encapsulation; backsheet
OSTI Identifier:
1351446
Alternate Identifier(s):
OSTI ID: 1401879

Tracy, Jared, Bosco, Nick, Novoa, Fernando, and Dauskardt, Reinhold. Encapsulation and backsheet adhesion metrology for photovoltaic modules. United States: N. p., Web. doi:10.1002/pip.2817.
Tracy, Jared, Bosco, Nick, Novoa, Fernando, & Dauskardt, Reinhold. Encapsulation and backsheet adhesion metrology for photovoltaic modules. United States. doi:10.1002/pip.2817.
Tracy, Jared, Bosco, Nick, Novoa, Fernando, and Dauskardt, Reinhold. 2016. "Encapsulation and backsheet adhesion metrology for photovoltaic modules". United States. doi:10.1002/pip.2817. https://www.osti.gov/servlets/purl/1351446.
@article{osti_1351446,
title = {Encapsulation and backsheet adhesion metrology for photovoltaic modules},
author = {Tracy, Jared and Bosco, Nick and Novoa, Fernando and Dauskardt, Reinhold},
abstractNote = {Photovoltaic modules are designed to operate for decades in terrestrial environments. However, mechanical stress, moisture, and ultraviolet radiation eventually degrade protective materials in modules, particularly their adhesion properties, eventually leading to reduced solar cell performance. Despite the significance of interfacial adhesion to module durability, currently there is no reliable technique for characterizing module adhesion properties. We present a simple and reproducible metrology for characterizing adhesion in photovoltaic modules that is grounded in fundamental concepts of beam and fracture mechanics. Using width-tapered cantilever beam fracture specimens, interfacial adhesion was evaluated on relevant interfaces of encapsulation and backsheet structures of new and 27-year-old historic modules. The adhesion energy, Gc [J/m2], was calculated from the critical value of the strain energy release rate, G, using G = βP2, where β (a mechanical and geometric parameter of the fracture specimen) and P (the experimentally measured critical load) are constants. Under some circumstances where testing may result in cracking of brittle layers in the test specimen, measurement of the delamination length in addition to the critical load was necessary to determine G. Relative to new module materials, backsheet adhesion was 95% and 98% lower for historic modules that were exposed (operated in the field) and unexposed (stored on-site, but out of direct sunlight), respectively. Encapsulation adhesion was 87-94% lower in the exposed modules and 31% lower in the unexposed module. As a result, the metrology presented here can be used to improve module materials and assess long-term reliability.},
doi = {10.1002/pip.2817},
journal = {Progress in Photovoltaics},
number = 1,
volume = 25,
place = {United States},
year = {2016},
month = {9}
}