Its an interesting challenge. Always makes me wonder best location. Here in Costa Rica, my friend cleaned his off in the dry season and was shocked by instant 20-30% increase in output. Obvious problem is water use. It's a complicated issue. Am wanting solar on next house but also want a hose on the roof and collect water through gutters to reuse.

Its often overlooked. There was a massive project (>500m USD) in Abu Dhabi called Shams. When they started phase 2, I think phase 1 was already down 60-70% production!