Many PV modules are self-cleaning according to their manufacturers. This is true, as long as one takes into account the limitations of what is technically feasible because manufacturers in this sector are confronted with a certain dilemma. They can either seal the modules with an extremely smooth layer of high-strength glass, which reflects quite strongly and thus slightly reduces the efficiency, though at the same time it is relatively diet-repellent. But if the layer of glass is coated with a non-reflective plastic coating the module's efficiency initially increases but the dirt-repellent effect is less. Whatever the design of the module and no matter how dirt-repellent the surface is, dirt will accumulate in time due to pollen, dust, bird droppings, traffic, agriculture, etc. To make matters worse, the cleaning effect of snow and rain is much lower than originally assumed (please refer to the long-term study of Prof. Häberlin, FH Bern).
In Germany the losses incurred by solar farms due to soiling are around 3 percent per year. With an installed output of 1 MW, the feed loss can be up to € 10,000 p.a. depending on the year of commissioning.Since the losses are much higher in Sothern Europe on account of the additional soiling factors and higher solar irradiation a different basis has to be assumed for the calculations. The losses here are around 6-8 percent per year, corresponding to a feed loss of around€ 26,000 per year.
