Drench the panel with water using a low pressure garden style
non-industrial hose.
Wipe the panel with a clean, soft cloth
or sponge using a solution of liquid dish washing detergent
and water (follow label instructions).
If the soap solution does not adequately clean the surface,
a non-solvent cleaner such as Simple Green may be used as a soap
replacement.
Rinse the soap solution off of the panel.
Wipe dry with a clean,
soft cloth.
NOTE:
Do not scrub with abrasive brushes. The brush fibers can penetrate
the surface layer of the FRP panels resulting in potential
short circuits and panel failure. Also, glass solar panels
will scratch,
reducing the power output of the panel so they should
be washed using the same approach.