Brooms cause abrasions, especially when they are moving sand along glass or composite plastics. Non lubricated wipers are fine (but not ideal) for dirt / dust, but not at all comparable for sand.
Yeah, and as far as I am aware, they are all kept clean with water. I'm not aware of a single installation that isn't hooked up to water facilities, let alone plonked down in the middle of a desert.
I'm really not sure why you think washing them with water is vital to make a solar installation worthwhile. Panels have been getting / are dirt cheap, efficiencies have been going up, and that trend will continue for a long time. If $ cost to wash is more than $ increase from cleaner panels, we won't wash them.