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Title: Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability

Abstract

The width-tapered cantilever beam method is used to quantify the debond energy (adhesion) of encapsulant and backsheet structures of 32 modules collected from the field. The collected population of modules contains both those that have remained intact and those with instances of either or both encapsulant and backsheet delamination. From this survey, initial threshold values (an adhesion value above which a module should remain intact throughout its lifetime) for encapsulant and backsheet interfaces are proposed. For encapsulants this value is ~ 160J/m 2 and for backsheets ~ 10J/m 2. Here, it is expected that these values will continue to be refined and evolve as the width-tapered cantilever beam method gets adopted by the PV industry, and that they may aid in the future improvement of accelerated lifetime tests and the development of new, low-cost materials.

Authors:
ORCiD logo [1];  [1];  [1]; ORCiD logo [2];  [2]
  1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Stanford Univ., Stanford, CA (United States)
Publication Date:
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)
OSTI Identifier:
1405279
Report Number(s):
NREL/JA-5J00-69023
Journal ID: ISSN 2156-3381
Grant/Contract Number:
AC36-08GO28308
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
IEEE Journal of Photovoltaics
Additional Journal Information:
Journal Volume: 7; Journal Issue: 6; Journal ID: ISSN 2156-3381
Publisher:
IEEE
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 42 ENGINEERING; adhesive strength; reliability; photovoltaic cells

Citation Formats

Bosco, Nick, Eafanti, Joshua, Kurtz, Sarah, Tracy, Jared, and Dauskardt, Reinhold. Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability. United States: N. p., 2017. Web. doi:10.1109/JPHOTOV.2017.2746682.
Bosco, Nick, Eafanti, Joshua, Kurtz, Sarah, Tracy, Jared, & Dauskardt, Reinhold. Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability. United States. doi:10.1109/JPHOTOV.2017.2746682.
Bosco, Nick, Eafanti, Joshua, Kurtz, Sarah, Tracy, Jared, and Dauskardt, Reinhold. 2017. "Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability". United States. doi:10.1109/JPHOTOV.2017.2746682.
@article{osti_1405279,
title = {Defining Threshold Values of Encapsulant and Backsheet Adhesion for PV Module Reliability},
author = {Bosco, Nick and Eafanti, Joshua and Kurtz, Sarah and Tracy, Jared and Dauskardt, Reinhold},
abstractNote = {The width-tapered cantilever beam method is used to quantify the debond energy (adhesion) of encapsulant and backsheet structures of 32 modules collected from the field. The collected population of modules contains both those that have remained intact and those with instances of either or both encapsulant and backsheet delamination. From this survey, initial threshold values (an adhesion value above which a module should remain intact throughout its lifetime) for encapsulant and backsheet interfaces are proposed. For encapsulants this value is ~ 160J/m2 and for backsheets ~ 10J/m2. Here, it is expected that these values will continue to be refined and evolve as the width-tapered cantilever beam method gets adopted by the PV industry, and that they may aid in the future improvement of accelerated lifetime tests and the development of new, low-cost materials.},
doi = {10.1109/JPHOTOV.2017.2746682},
journal = {IEEE Journal of Photovoltaics},
number = 6,
volume = 7,
place = {United States},
year = 2017,
month =
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on October 4, 2018
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  • The width-tapered cantilever beam method is used to quantify the debond energy (adhesion) of encapsulant and backsheet structures of 27 modules collected from the field. The collected population of modules contains both those that have remained in-tact and those with instances of either or both encapsulant and backsheet delamination. From this survey, initial threshold values (an adhesion value above which a module should remain intact throughout its lifetime) for encapsulant and backsheet interfaces are proposed. For encapsulants this value is about 60 J/m2 and for backsheets about 20 J/m2. It is expected that these values will continue to be refinedmore » and evolve as the width-tapered cantilever beam method becomes adopted by the PV industry, and that they may aid in the future improvement of accelerated lifetime tests and the development of new, low-cost materials.« less
  • MDRC Techniques are used for the detection of the vulnerability in specific regions in a PV module. They can also be useful as quality control tools. PV modules were selected randomly at the factory floor over a sixteen month period. Adequate number of samples were extracted at predetermined locations in the middle, periphery, and bus line regions from a selected cells of each module. Adhesive shear strength was measured during the extraction of the samples. Care was taken to verify that the data was statistically significant. Consistently high values of adhesive strength are desirable in all the regions. There wasmore » a smaller spread of values in the batches with higher adhesive strengths. On the other hand, the data showed wider fluctuations in the batches of lower average values of adhesive shear strength showing that inhomogeneity from one region to other may be leading to overall low values. The techniques were found to be useful for assuring quality. The information may be useful for determining warranty period. {copyright} {ital 1999 American Institute of Physics.}« less
  • Presented at the 2001 NCPV Program Review Meeting: Measurements of backsheet moisture permeation and encapsulant-substrate adhesion. At the March 2001 NCPV workshop on ''Moisture Ingress and High-Voltage Isolation'', industry participants identified several properties associated with PV module durability that are critical for commercial success. These include interface conductivity, adhesion of encapsulants to substrate materials as a function of in-service exposure conditions, and moisture permeation through backsheet materials as a function of temperature. Electrical data is discussed in a companion paper; adhesion and water vapor transmission rate (WVTR) measurements are presented herein.
  • 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 andmore » 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) 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