Show us the dirtiest solar panel pics you have come across.
These are so bad that they are white colored on the surface. I think it is some sort of mold or something. I have only seen this once. The solar panel monitoring service called the customer to let them know they needed to come out and take a look because their solar productivity had dropped dramatically.
Hera is another good one I found in the archives. I was real happy that she did not ask me to clean the gutters. They were completely full with pigeon poop. One of the few gutter cleanings I just would not du or should I say du du.
The problem I have with the hogs hair brush is that you have to lift it off the panels to get a good clean rinse. I prefer a Monofillament brush because you do not have to lift it off the panels for the final rinse.
I will share a free tip for cleaning those really dirty solar panels. Instead of wasting time with Relatively lower pressure DI water, hook up to tap water first with a quick connect. Pre treat them with a soap if you like, but do the main cleaning with tap water ( lots if natural pressure) . Then for final polish / rinse use DI water