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Proceedings Paper

Examination of an optical transmittance test for photovoltaic encapsulation materials
Author(s): David C. Miller; Jaione Bengoechea; Jayesh G. Bokria; Michael Köhl; Nick E. Powell; Michael E. Smith; Michael D. White; Helen Rose Wilson; John H. Wohlgemuth
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Paper Abstract

The optical transmittance of encapsulation materials is a key characteristic for their use in photovoltaic (PV) modules. Changes in transmittance with time in the field affect module performance, which may impact product warranties. Transmittance is important in product development, module manufacturing, and field power production (both immediate and long-term). Therefore, an international standard (IEC 62788-1-4) has recently been proposed by the Encapsulation Task-Group within the Working Group 2 (WG2) of the International Electrotechnical Commission (IEC) Technical Committee 82 (TC82) for the quantification of the optical performance of PV encapsulation materials. Existing standards, such as ASTM E903, are general and more appropriately applied to concentrated solar power than to PV. Starting from the optical transmittance measurement, the solar-weighted transmittance of photon irradiance, yellowness index (which may be used in aging studies to assess durability), and ultraviolet (UV) cut-off wavelength may all be determined using the proposed standard. The details of the proposed test are described. The results of a round-robin experiment (for five materials) conducted at seven laboratories to validate the test procedure using representative materials are also presented. For example, the Encapsulation Group actively explored the measurement requirements (wavelength range and resolution), the requirements for the spectrophotometer (including the integrating sphere and instrument accessories, such as a depolarizer), specimen requirements (choice of glass-superstrate and -substrate), and data analysis (relative to the light that may be used in the PV application). The round-robin experiment identified both intra- and inter-laboratory instrument precision and bias for five encapsulation materials (encompassing a range of transmittance and haze-formation characteristics).

Paper Details

Date Published: 24 September 2013
PDF: 12 pages
Proc. SPIE 8825, Reliability of Photovoltaic Cells, Modules, Components, and Systems VI, 882509 (24 September 2013); doi: 10.1117/12.2024372
Show Author Affiliations
David C. Miller, National Renewable Energy Lab. (United States)
Jaione Bengoechea, Fundación CENER-CIEMAT (Spain)
Jayesh G. Bokria, Specialized Technology Resources, Inc. (United States)
Michael Köhl, Fraunhofer-Institut für Solare Energiesysteme ISE (Germany)
Nick E. Powell, Dow Corning (United States)
Michael E. Smith, Arkema Inc. (United States)
Michael D. White, The Dow Chemical Co. (United States)
Helen Rose Wilson, Fraunhofer-Institut für Solare Energiesysteme ISE (Germany)
John H. Wohlgemuth, National Renewable Energy Lab. (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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