[see Forum Thread
this is taken from for more]
How do you clean your panels? Got a tip for cleaning or maintaining panels? How do you deal with tree sap, gunk or other corrosion that happens?
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How to clean your solar panels
Before cleaning your panels with an ammonia based product (e.g., Windex, Sprayway) check the datasheet.
Not sure how serious it is, but I know panels have certifications for ammonia ratings (typically most important for farms where fertilizers are used).
; so that makes me think ammonia would be bad for some panels.
I've seen numerous warnings that cleaning by hosing them down should only be done while the panels are cool to avoid thermal shock.