Powder transfer in wipe test

Rubbing a finger over the outer backsheet surface leaves white powder on it. That powder transfer is the signature. The powder wipes off, and the backsheet underneath usually looks rough or dull. The powder comes from backsheet chalking. UV light and oxygen break down the polymer in the outer backsheet layer, and the filler inside is released. A simple wipe test is enough to check for chalking on modules in the field. The same wipe test can also be used on backsheet samples after accelerated weathering tests, as a preventive check. Chalking only affects the surface. It is not directly linked to backsheet insulation resistance and has no direct effect on module reliability or system performance. Sometimes chalking is an early sign of microcracking that can later turn into deep backsheet cracking. However, nothing reliably predicts this, and cracking has been seen with and without chalking. If no powder transfers, that does not rule out cracking. For example, PVDF-based backsheets can crack while usually showing no chalking.

<!-- review notes

• sentence 3: support check: partial - Photo-oxidative degradation (UV plus oxygen) of the outer layer polymer releasing inorganic filler is stated; the passage does not say the powder itself is the filler beyond 'release of filler', which is close, so only minor wording differs.
• sentence 4: support check: partial - Wipe test for field checking and use after accelerated weathering are stated, but 'enough' to check chalking is not claimed, and PVDF cases show chalking may be absent. -->