Would plexi glass coating over solar panel...affect it's efficiency?

Question

are there any other ways of protecting solar panels from rain?

Answer 1

yes. in short, plexiglas will absorb some light at some wavelengths. If that light would have gone to generating electricity, then yes, you're losing efficiency.

I'd worry more about scratches and dirt accumulating on the plexiglas, making even less light reach the PV panel.

Why do you want to keep rain from getting on the glass panel? if anything it will help to clean it off. glass is also very scratch resistant and smooth, so it will last a long time unless you have sandstorms.