As most panels are laid at relatively flat angles, relying on the rain to clean them won’t be sufficient enough to agitate and remove the greasy and stubborn residues. Having your solar panels cleaned once or twice a year using only pure filtered water and specially designed soft brushes will enable your panels to work efficiently. The main benefit of using pure water is that no mineral or detergent deposits are left on the surface, this in turn helps to keep them cleaner for longer as the dirt has less to take hold of.