KK6PD wrote:For me, it's mandatory, and I have a flat roof with 60 panels! It's all about the sun baby!
The flat roof is what makes it mandatory. My panels are mounted on my almost flat roof (about 4*). If I had frameless panels I could get away without cleaning, but as it is now I get up there a couple times a year and just wipe them down with a California duster when I see that panel production per panel starts varying a decent amount. Takes about 15 minutes. Doesn't get all the dirt off, but gets the bulk of it.
The problem with almost flat panels is that the lip of the frame traps a heavy layer of dirt/dust at the bottom edge which will eventually noticeably affect power output. If I were to do it again I'd make sure the panels were tilted up 10-15*, or as mentioned, used frameless panels.