Solar Panels are constantly exposed to the elements by Dirt, Dust, Bird Droppings, Salt from the sea and wind. The residue left behind on the Solar panel surface will limit the amount of Sunshine the panels receive, therefor reducing the efficiency of the Solar panels, which means the less Electricity they will produce.
Cleaning is especially neccesery where the rainfall is quite low and airborne dust high. A layer of dust will build up on the modules causing a drop off in generation of electricity production
Does Rain Clean Solar Panels ?