They do sell a solar cleaning chemical its made by winsol. It may help.save on your pure water. I would imagine tap would leave waterspots. It may not affect its performance but it probably also may not look like a professional job was done.
I strongly recommend using pure water. It will save you lots of time. The time you save will more than make up for the water cost. And, you’ll be leaving no residue, so those panels will stay clean for a longer period of time.
You can view a Waterfed Class episode on solar panel cleaning here: Mile High Window Cleaning Supply . Once there, scroll down to the blog section. Keep scrolling until you see the solar panel episode.
If it were a big project, I’d probably go wth a soap and pressure wash. Smaller residential, wfp. May depend on how bad they are and need some agitation to get clean. I’ve experimented with my wfp, then a week later just a good rinse with 400 tds water and they looked fine.
