Solar panels normally use glass on the top surface. I know they are working on plastics, but I don't know if these are in production. So, check the documentation on the panels.
If the spots are small, then they probably wont affect the panels output. Again depends on the panel design. If the spots are coin size or larger, then they may still be okay. Some panels are resistant to dirt and leaves where only part of it might stop producing power. The older, cheaper varieties stop producing on the whole panel !
Otherwise Use detergent and water with a plastic scraper. If that doesnt work, and the surface is definitely glass then try a metal scraper meant for glass (paint shops and hardware stores have them).
I would try chemicals like turps or paint thinners as a very last resort and only if the spots are larger. Because you could spill it elsewhere and it may take paint off the sides of the panels.
Google will tell you IPA will work, but I struggle to see how IPA will take paint off.