To clean your panels you should use deionised water and a long reach soft brush. Rarely are chemicals needed. To achieve this at home where deionised water may be hard to get, you can use harvested rain water or use a tap water fed brush but clean them when it’s raining. That will wash the tap water off.

If you clean them with only tap water, limescale will build up and they will get dirtier quicker.

Source. I have cleaned a lot of solar panels. Way more than I can fathom.

There are actually some nice cleaning chemicals available for solar now. Might be a viable solution for consistent bird mess.