UV, Temperature, and Humidity: Task Group 5
Task Group 5 is focused on the effects of UV light radiation and how these are coupled to temperature and humidity.
Light (especially UV light) can cause changes in modules including solarization of the glass, light-induced degradation in the cells, discoloration, embrittlement, and reduced adhesion at interfaces. Unfortunately, application of light in large areas is expensive, so an often-used historical strategy has been to apply the stresses to either material coupons or a smaller version of a module. The group, however, aims to standardize the test conditions (including the UV sources, UV irradiance, temperature, and humidity) used to age specimens of all sizes. This scope is closely related to the scope of Task Group 3.
Having surveyed equipment that is being used for UV exposure testing in the industry, experiments are being conducted to compare the degradation of a set of samples aged using different light sources. Studies include the determination of the activation energy (and corresponding acceleration factor) for EVA yellowing and encapsulant adhesion, the attachment of edge seals (used in thin film modules), in addition to a back-sheet round-robin test (examining discoloration and cracking) using different UV-test sources. A four-cell mini-module test program was recently completed in Japan in collaboration with Task Group 3, comparing test sequences including separate UV exposure, thermal cycling, and dynamic mechanical load steps. A Task Group 5 effort was started in China in 2014. A strawman UV aging standard for encapsulation is anticipated by the end of 2014.
IEC 62892-1 "Comparative testing of PV modules to differentiate performance in multiple climates and applications—Part 1: Overall test sequence and method of communication," is being developed by IEC Technical Committee 82. The first committee draft is being reviewed. The general concept being proposed for inclusion in the IEC Comparative Testing Standard was presented at the SOPHIA workshop and at the 40th IEEE PVSC:
Wohlgemuth, J. S. Kurtz, T. Sample, M. Kondo, and M. Yamamichi "Development of Comparative Tests of PV Modules by the International PV QA Task Force." IEEE PVSC, Denver, CO. June 2014.
Michael Koehl — Fraunhofer ISE, Overall Task Group 5 leader
Jasbir Bath — SEMA, representing the Americas
David Miller — NREL, representing the Americas
Tsuyoshi Shioda — Mitsui, representing Japan
Ganxin Jie — China National Electric Apparatus Research Institute, representing China