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Proceedings Paper

Linking accelerated laboratory and outdoor exposure results for PV polymeric materials: a mechanistic study of EVA
Author(s): Xiaohong Gu; Yongyan Pang; Chiao-Chi Lin; Kaipeng Liu; Tinh Nguyen; Jaonnie W. Chin
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Paper Abstract

Linking accelerated laboratory test to field performance for predicting the service life of polymeric materials are being investigated at NIST using the reliability-based methodology. Based on this methodology, a successful linkage between the laboratory and field exposure data for a model polymeric material has been made. Recently, this methodology, for the first time, was introduced to the lifetime assessment of PV polymeric materials. In this paper, a mechanistic study of the degradation of three unstabilized model ethylene vinyl acetate (EVA) systems---uncured EVA, cured EVA and laminated EVA---was carried out under accelerated laboratory exposure and outdoor exposure. The NIST SPHERE (Simulated Photodegradation via High Energy Radiant Exposure) was used for the accelerated laboratory tests, and the outdoor exposure was conducted in Gaithersburg, Maryland. Simultaneous multiple stresses, including temperature, relative humidity and UV radiation, were applied individually or in combination during SPHERE exposure. The effects of the environmental factors on the main degradation mechanisms of different EVA systems were investigated. The results showed that the UV radiation was the most important factor for the degradation of EVA and a synergistic effect occurred between UV radiation and relative humidity. A slower degradation rate was observed for the laminated system as a result of limited diffusion of O2 and H2O into EVA. It was also found that the substantial chemical changes of the uncured EVA system did not yield yellowing, which was dramatically different from the peroxide cured EVA system. Additionally, the chemical degradation modes of the three EVA systems exposed outdoors appeared to be similar to those exposed to the SPHERE. The implication of this work to the current test standards was discussed.

Paper Details

Date Published: 24 September 2013
PDF: 15 pages
Proc. SPIE 8825, Reliability of Photovoltaic Cells, Modules, Components, and Systems VI, 88250L (24 September 2013); doi: 10.1117/12.2024532
Show Author Affiliations
Xiaohong Gu, NIST (United States)
Yongyan Pang, NIST (United States)
Chiao-Chi Lin, NIST (United States)
Kaipeng Liu, NIST (United States)
Tinh Nguyen, NIST (United States)
Jaonnie W. Chin, NIST (United States)

Published in SPIE Proceedings Vol. 8825:
Reliability of Photovoltaic Cells, Modules, Components, and Systems VI
Neelkanth G. Dhere; John H. Wohlgemuth; Kevin W. Lynn, Editor(s)

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