For the most part solar panels are usually self cleaning. Though if you live in dry areas, dust, bird droppings, and dirt can build up over time and cause a problem for the amount of electricity is generated. Cleaning solar panels is not an easy job, but is do able on your own. There are safety precautions one should take before taking on this job. Make sure your solar system is shut down before starting. If you can’t clean your panels from the ground, it is best to hire someone to come out and do the job.
The best day to do the cleaning is on an overcast day in the early morning or evening. Early morning is a great time since the dew from overnight has softened the grime. Using a good quality soft brush and or squeegee with a plastic blade with a long extension is a great tool to use. Make sure your hose has a good nozzle for the stream to reach the panels. The glass that solar panels are made with are usually pretty solid quality which means that clean water and a little scrubbing should remove the grime.
Some things to watch for are oily stains. The best way to get rid of those is isopropyl alcohol as a spot cleaner. Also stay away from using any metal objects or abrasive products. Scratched glass on solar panels can affect the performance and the scratches can cast shadows, limiting the amount of light passing through.
for more about cleaning solar panels visit Energy Matters HERE