TY - JOUR
T1 - Field-Aged Glass/Backsheet and Glass/Glass PV Modules
T2 - Encapsulant Degradation Comparison
AU - Patel, Aesha Parimalbhai
AU - Sinha, Archana
AU - Tamizhmani, Govindasamy
N1 - Funding Information:
Manuscript received August 23, 2019; revised October 19, 2019 and November 26, 2019; accepted December 2, 2019. Date of publication December 27, 2019; date of current version February 19, 2020. This work was supported by the U.S. Department of Energy under Award DE-EE0008565. (Corresponding author: Aesha Parimalbhai Patel.) The authors are with Photovoltaic Reliability Laboratory, Arizona State University, Mesa, AZ 85212 USA (e-mail: appatel8@asu.edu; asinha42@ asu.edu; manit@asu.edu).
Publisher Copyright:
© 2011-2012 IEEE.
PY - 2020/3
Y1 - 2020/3
N2 - Ethylene vinyl acetate (EVA) is the predominant encapsulant in crystalline-silicon photovoltaic (PV) modules; however, its degradation is a subject of major concern, which causes significant power loss under field conditions. This article presents a comparison of EVA degradation in field-Aged PV modules with glass/backsheet (G/B) and glass/glass (G/G) architectures. Module-level characterization included UV fluorescence imaging and I-V measurements. Material analytical techniques, including colorimetry, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Raman spectroscopy, were performed to correlate the module performance parameters with EVA material properties. An intense EVA discoloration in G/G modules was observed, which was corroborated by higher module I-{sc} and Pmax degradation rates compared with its counterpart G/B modules. Higher power degradation was accompanied by a significant increase in EVA crosslinking, vinyl acetate content, yellowness index, and presence of functional groups containing unsaturated moieties that are linked to degradation products of photothermal reaction, and a higher decrease in the degree of crystallinity. The absence of a polymeric backsheet in hermetically sealed G/G modules, which restricts photobleaching and enhances the entrapment of volatile acetic acid and other degradation by-products, plays a major role in causing higher EVA degradation in G/G modules. This article concludes that EVA might have been a good choice of an encapsulant for the G/B modules over the decades, but it may prove to be an inappropriate choice for the G/G modules because of potential degassing, corrosion, and/or discoloration issues. Ionomers or polyester-based encapsulants like polyolefins could be best suited for G/G modules as it appears to be a current trend in the industry.
AB - Ethylene vinyl acetate (EVA) is the predominant encapsulant in crystalline-silicon photovoltaic (PV) modules; however, its degradation is a subject of major concern, which causes significant power loss under field conditions. This article presents a comparison of EVA degradation in field-Aged PV modules with glass/backsheet (G/B) and glass/glass (G/G) architectures. Module-level characterization included UV fluorescence imaging and I-V measurements. Material analytical techniques, including colorimetry, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and Raman spectroscopy, were performed to correlate the module performance parameters with EVA material properties. An intense EVA discoloration in G/G modules was observed, which was corroborated by higher module I-{sc} and Pmax degradation rates compared with its counterpart G/B modules. Higher power degradation was accompanied by a significant increase in EVA crosslinking, vinyl acetate content, yellowness index, and presence of functional groups containing unsaturated moieties that are linked to degradation products of photothermal reaction, and a higher decrease in the degree of crystallinity. The absence of a polymeric backsheet in hermetically sealed G/G modules, which restricts photobleaching and enhances the entrapment of volatile acetic acid and other degradation by-products, plays a major role in causing higher EVA degradation in G/G modules. This article concludes that EVA might have been a good choice of an encapsulant for the G/B modules over the decades, but it may prove to be an inappropriate choice for the G/G modules because of potential degassing, corrosion, and/or discoloration issues. Ionomers or polyester-based encapsulants like polyolefins could be best suited for G/G modules as it appears to be a current trend in the industry.
KW - Characterization
KW - crosslinking
KW - degree of crystallinity
KW - encapsulant degradation
KW - ethylene vinyl acetate (EVA)
KW - field aged
KW - glass/backsheet (G/B)
KW - glass/glass (G/G)
KW - photovoltaic (PV) module
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U2 - 10.1109/JPHOTOV.2019.2958516
DO - 10.1109/JPHOTOV.2019.2958516
M3 - Article
AN - SCOPUS:85077324734
SN - 2156-3381
VL - 10
SP - 607
EP - 615
JO - IEEE Journal of Photovoltaics
JF - IEEE Journal of Photovoltaics
IS - 2
M1 - 8944274
ER -