The world’s largest solar plants sure look amazing, but they raise one big question: how the hell do they keep all those panels clean? Nowadays, using robots like this!
This video shows the newly installed robotic cleaning system at Ketura Sun Solar Park. Until now, the panels covering the 20-acre site were only cleaned about nine times a year — a laborious task, performed infrequently due to expense — which in turn led to sub-optimal plant efficiency.

https://www.youtube.com/watch?feature=player_embedded&v=3-PWx9uE_GY

http://www.gizmodo.com.au/2014/04/this-is-how-they-clean-those-gigantic-solar-energy-plants/