Solar panels rely 100% on the light generated by the sun. Each panel has dozens of solar cells which absorb the sun’s light and transform it into electricity through the photovoltaic effect. With, anything that builds upon the top layer of the panel will cause a slight decrease in their efficiency and ability to generate power for your home. Some materials that cause this buildup include dirt, dust, pollen, leaves, ash, bird droppings, smog, or a combination of all these light-blocking objects.