Progress Update: Task Group 5
Task Group 5 is focused on the effects of light and how these effects are related 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, 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 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 to different light sources. Studies include the determination of the activation energy (and corresponding acceleration factor) for EVA yellowing and adhesion, the attachment of edge seals (used in thin film modules), in addition to a back-sheet round robin test using different UV-test sources. A four-cell mini-module test program was recently completed in Japan in collaboration with Task Group 3, which is investigating test sequences combining irradiation intensity, temperature, and humidity. Creation of a strawman UV standard is anticipated by the end of 2014.