Many homeowners in Santa Clara County assume that occasional rain is enough to clean their solar panels—but rain alone doesn’t remove the grime that affects performance. In fact, rainwater often leaves behind mineral deposits, especially in areas like San Jose, where the water is hard and filled with calcium. It also spreads existing dirt into streaks rather than removing it. Bird droppings, tree sap, and pollen stick to panel surfaces and won’t wash away with a shower. In neighborhoods with dense trees, such as Cambrian Park and Evergreen, these substances collect quickly and reduce energy output. Professional solar panel cleaning is required to eliminate residue without damaging the system.