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Title: Investigation of a Wedge Adhesion Test for Edge Seals

Abstract

Many photovoltaic (PV) technologies have been found to be sensitive to moisture that diffuses into a PV package. Even with the use of impermeable frontsheets and backsheets, moisture can penetrate from the edges of a module. To limit this moisture ingress pathway from occurring, manufacturers often use a low permeability polyisobutylene (PIB) based edge seal filled with desiccant to further restrict moisture ingress. Moisture ingress studies have shown that these materials are capable of blocking moisture for the 25-year life of a module; but to do so, they must remain well-adhered and free of cracks. This work focuses on adapting the Boeing Wedge test for use with edge seals laminated using glass substrates as part of a strategy to assess the long-term durability of edge seals. The advantage of this method is that it duplicates the residual stresses and strains that a glass/glass module may have when the lamination process results in some residual glass bending that puts the perimeter in tension. Additionally, this method allows one to simultaneously expose the material to thermal stress, humidity, mechanical stress, and ultraviolet radiation. The disadvantage of this method generally is that we are limited by the fracture toughness of the glass substratesmore » that the edge seal is adhered to. However, the low toughness of typical uncrosslinked or sparsely crosslinked PIB makes them suitable for this technique. We present data obtained during the development of the wedge test for use with PV edge seal materials. This includes development of the measuring techniques and evaluation of the test method with relevant materials. We find consistent data within a given experiment, along with the theoretical independence of fracture toughness measurements with wedge thickness. This indicates that the test methodology is reproducible. However, even though individual experimental sets are consistent, the reproducibility between experimental sets is poor. We believe this may be due to inconsistencies in sample history, sample batch, or small changes in sample preparation/assembly from one month to the next. Because the fracture strength of typical edge seal materials is so low, they cannot be relied upon for mechanical strength. A small stress or strain on the edge seal is capable of promoting delamination or tearing causing the edge seal to fail. Because of this, edge seals are very dependent on the processing and construction parameters in the full size PV module such that any long term evaluation of their durability must be conducted on full size modules to be accurate.« less

Authors:
; ; ; ; ;
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:
1339608
Report Number(s):
NREL/CP-5J00-67126
DOE Contract Number:
AC36-08GO28308
Resource Type:
Conference
Resource Relation:
Conference: Presented at Reliability of Photovoltaic Cells, Modules, Components, and Systems IX: SPIE Conference, 28-29 August 2016, San Diego, California
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; adhesion; edge seal; hermetic; moisture ingress; permeation; wedge

Citation Formats

Kempe, Michael, Wohlgemuth, John, Miller, David, Postak, Lori, Booth, Dennis, and Phillips, Nancy. Investigation of a Wedge Adhesion Test for Edge Seals. United States: N. p., 2016. Web. doi:10.1117/12.2239161.
Kempe, Michael, Wohlgemuth, John, Miller, David, Postak, Lori, Booth, Dennis, & Phillips, Nancy. Investigation of a Wedge Adhesion Test for Edge Seals. United States. doi:10.1117/12.2239161.
Kempe, Michael, Wohlgemuth, John, Miller, David, Postak, Lori, Booth, Dennis, and Phillips, Nancy. 2016. "Investigation of a Wedge Adhesion Test for Edge Seals". United States. doi:10.1117/12.2239161.
@article{osti_1339608,
title = {Investigation of a Wedge Adhesion Test for Edge Seals},
author = {Kempe, Michael and Wohlgemuth, John and Miller, David and Postak, Lori and Booth, Dennis and Phillips, Nancy},
abstractNote = {Many photovoltaic (PV) technologies have been found to be sensitive to moisture that diffuses into a PV package. Even with the use of impermeable frontsheets and backsheets, moisture can penetrate from the edges of a module. To limit this moisture ingress pathway from occurring, manufacturers often use a low permeability polyisobutylene (PIB) based edge seal filled with desiccant to further restrict moisture ingress. Moisture ingress studies have shown that these materials are capable of blocking moisture for the 25-year life of a module; but to do so, they must remain well-adhered and free of cracks. This work focuses on adapting the Boeing Wedge test for use with edge seals laminated using glass substrates as part of a strategy to assess the long-term durability of edge seals. The advantage of this method is that it duplicates the residual stresses and strains that a glass/glass module may have when the lamination process results in some residual glass bending that puts the perimeter in tension. Additionally, this method allows one to simultaneously expose the material to thermal stress, humidity, mechanical stress, and ultraviolet radiation. The disadvantage of this method generally is that we are limited by the fracture toughness of the glass substrates that the edge seal is adhered to. However, the low toughness of typical uncrosslinked or sparsely crosslinked PIB makes them suitable for this technique. We present data obtained during the development of the wedge test for use with PV edge seal materials. This includes development of the measuring techniques and evaluation of the test method with relevant materials. We find consistent data within a given experiment, along with the theoretical independence of fracture toughness measurements with wedge thickness. This indicates that the test methodology is reproducible. However, even though individual experimental sets are consistent, the reproducibility between experimental sets is poor. We believe this may be due to inconsistencies in sample history, sample batch, or small changes in sample preparation/assembly from one month to the next. Because the fracture strength of typical edge seal materials is so low, they cannot be relied upon for mechanical strength. A small stress or strain on the edge seal is capable of promoting delamination or tearing causing the edge seal to fail. Because of this, edge seals are very dependent on the processing and construction parameters in the full size PV module such that any long term evaluation of their durability must be conducted on full size modules to be accurate.},
doi = {10.1117/12.2239161},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2016,
month = 9
}

Conference:
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  • In cold climates the increased edge-glass heat transfer at the perimeter of a sealed glazing unit creates a special problem. This is where condensed water and frost most readily occur. One mechanism contributing to edge-glass heat transfer is edge-seal conduction. Very few data are available regarding the thermal resistance of the various edge-seal configurations that are commercially available. An experimental procedure has been devised whereby the thermal resistance of an edge-seal can be directly measured using a guarded heater plate apparatus. Results are reported for nine edge-seal test samples. In addition, results from similar tests provide measured thermal conductivities formore » four of the materials used in the construction of the edge-seal test samples and commercially available edge-seals.« less
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