Loss persists after rainfall

This symptom is a weather-normalized production deficit that stays in place after rain instead of recovering, as ordinary dust soiling normally does. Its main known cause is widespread fungal soiling: biofilms and other persistent biological deposits on the module glass that rain does not wash off but manual cleaning removes. It is easy to mistake for ordinary dust, pollen or a weather-normalization error. Granular dust soiling usually recovers partly or fully after enough rain, so the lack of recovery after rain is the key difference. Some particles can become cemented to the glass, and rain may not remove them either. In that case active cleaning is needed. Check first by comparing rain events and cleaning logs with SCADA, irradiance and weather-normalized production. Look for a repeatable step-up after cleaning where rain did not bring output back. Confirm biofilm with a close visual inspection or handheld microscopy. Check several areas of the array, because biological deposits can be patchy. Where this loss is confirmed, add cleaning to the maintenance plan and base forecasts on cleaning results, not on the assumption that rain resets the loss.

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• sentence 4: support check: partial - u10 mentions the argument that rain doesn't remove cemented particles and active cleaning becomes necessary, but only as one side of a debate, not a firm statement. -->