Dark surface deposits

Dark deposits on the module glass can come from sub-aerial biofilms, mainly black fungi. These organisms grow into dark masses and trap other particles. The deposits reduce how much light passes through the glass. The resulting soiling loss can change over time, and in humid subtropical regions it can stay at 5 to 11 percent of production. To tell fungal soiling apart from granular dust, look at how production responds to rain. Dust losses usually recover partly or fully after rain, while fungal deposits stay attached until targeted cleaning removes them. Check first whether irradiance-normalized production stays low after rain but steps up after a manual cleaning. Compare cleaning records against SCADA, irradiance and weather data to confirm this. Confirm the contaminant with a close visual inspection or a handheld microscope. The deposits can be patchy, so inspect several areas of the array rather than one representative module. Where deposits persist, clean as routine maintenance and update the production forecasts using the cleaning results.