Thanks a lot for the references! But do you realize that I was speaking of 20% output and not of a 20% reduction (i.e. 80% output) which makes my speculation w

Thanks a lot for the references! But do you realize that I was speaking of 20% output and not of a 20% reduction (i.e. 80% output) which makes my speculation worse than what it is actually in the Middle-East? In my opinion, on a huge solar grid, 50% is still pretty much helpful (solar is roughly forever free energy, modulo the maintenance cost). > How about indoors? We sweep/vaccum away plenty of dust. Do you people not have to do that? We're speaking of enough dust hanging on a smooth sloppy surface (not a floor, but a plane with an angle) and thick enough to block more than 80% of the light (for dust, that makes very thick).