Accelerated weathering screening

Accelerated weathering screening is a preventive lab test. Backsheet materials or whole modules are exposed to combined light, temperature and moisture so weaknesses show up before the product reaches the field. To screen for backsheet chalking, the backsheet goes through accelerated weathering and is then checked with a simple wipe test for loose powder. Backsheet cracking has not appeared in standard IEC 61215-2 qualification testing. Newly designed indoor tests that apply UV, humidity, temperature and thermo-mechanical load, either together or in sequence, have reproduced polyamide backsheet cracks and can check new backsheets for crack susceptibility during product development. Common procedures include cyclic xenon-arc exposures to ASTM G155 and D7869 and the steady-state polymer weathering conditions of IEC 62788-7-2, such as the A3 condition. Combined accelerated stress testing applies several natural stressors at once. Besides backsheet cracking, it has revealed backsheet delamination, discoloration, corrosion and cell cracking. Encapsulant and backsheet materials should be tested both separately and together in the complete laminate, because incompatibilities between them can cause problems such as delamination. Screening has limits. There is no way to predict whether chalking will lead to later cracking or insulation loss, and long-term outdoor experience is still missing for some newer materials. Screening does not fix modules already in the field. Cracked backsheets there need a repair coating or film, or the modules must be replaced.

<!-- review notes

• sentence 1: support check: partial - Passages say weathering tests apply temperature, light and moisture and are used on backsheets/polymeric materials, but 'preventive' and 'whole modules' and 'before reaching the field' are only loosely supported.
• sentence 8: support check: partial - u6 says affected modules must be repaired with coating or film or repowered/replaced, but the framing 'screening does not fix modules' is not stated and repair is not possible for squared cracks. -->