Surface soiling

Surface soiling is dust, dirt, pollen, bird droppings, algae, moss or other material that settles on the module front surface and blocks light from reaching the cells. The particles scatter and absorb light, so module current and plant output fall; the loss is mostly reversible by cleaning and is not a true module failure. Uneven soiling causes current mismatch and hotspots that in extreme cases can permanently damage a module, and soiling can speed up ongoing potential induced degradation. It drives granular dust soiling losses and general soiling losses, and frequent cleaning or sandstorms can abrade the glass and reduce transmittance over time. Losses are worst in arid regions during dry periods, at low tilt angles, and near sources such as railways, farming, mining, roads or construction; humidity and dew can cement dust to the glass. Soiling can also build up slowly in rainy temperate climates, for example as a dirt strip along the lower frame edge. Exposure is reduced by site selection, higher tilt, anti-soiling coatings suited to the local dirt, and cleaning schedules based on measured soiling rate and cleaning cost. Clean with methods the module manufacturer recommends, because careless cleaning can damage components or anti-reflective coatings.

<!-- review notes

• sentence 5: support check: partial - The passages support arid dry periods, low tilt, nearby sources, and humidity/dew cementation, but they do not say roads, mining or construction make losses worst; the sources are mentioned only as origins or as causes of spatially uneven loss.
• sentence 7: support check: partial - Site selection, tilt, anti-soiling coatings suited to the soiling type, and cleaning optimized by soiling rate and cost are supported, but the passages do not state that higher tilt reduces soiling in those words; u22 only says soiling increases as tilt decreases. -->