How to remove and clean the photovoltaic panels

Spray the panels with a hose to remove loose dirt and debris. Scrub the panels with a soft brush and gentle cleaner, like dish soap and water. Rinse the residue off the panels with your hose. [pdf]
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Is it OK to use sand to clean photovoltaic panels

Probably not, it will probably be dust accumulated on the surface of the panel, perhaps as a result of a storm that has carried sand, sediment, or dust, or it could just be pollution. [pdf]
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How much tilt should photovoltaic panels have to be to be effective

To optimize performance, tilt your panels at an angle that is 10-15 degrees less than your latitude. For example, if you live at a latitude of 40 degrees, set your panels at about 25-30 degrees. [pdf]