Pv panels ( except a few small cheap ones ) are made to withstand the weather , and have a 20/25 year warranty . They have to withstand strong rain , hail stones , snow ect. Having paid for my own panels , I have no worry about cleaning them with my water fed , or trad on my small ones .
Solar thermal tubes , same as above , but are not flat so harder to clean with brush , and it Would be possible if not careful to hit them with the stock of the brush .I do clean my own tubes , but would not do it for customer .