Did the Cleaning Crew Crack Your Modules? Before-and-After EL as the Only Way to Tell

ⓘ This article is currently published in Chinese. An English version is being prepared — read the Chinese original.

Module cleaning is routine O&M, but the act of cleaning is itself a mechanical-loading event: robots tracking across glass and frames, high-pressure jets concentrating force on edges and corners, cold water hitting hot modules at midday, grit dragged under brush heads, and technicians stepping or leaning on panels. None of this leaves a visible mark, and short-term I-V curves rarely move — yet cracks initiated during cleaning quietly propagate through later thermal and wind cycles. This article explains the four mechanical pathways by which cleaning induces hidden cracks, why only EL imaging can see the result, and how to run a defensible before-and-after EL comparison: shooting a baseline before the crew arrives, holding camera position, current and grading criteria constant, sampling by cleaning method and by edge rows, closing the time window so no storm or hail can be blamed instead, and reading crack morphology to separate load-induced patterns from pre-existing random ones. It closes on writing EL acceptance into the cleaning contract, and on why daytime UAV EL makes same-day verification practical at plant scale.