In fact a slight haze on a sunny day is the best light you can get. We get several amps more under those conditions.
That is interesting. I suppose instead of a concentrated "image" of the sun hitting a small area on the panels the haze is spreading the energy more evenly over the panel.
Water cooling definitely sounds like a bad idea in Oz. I saw photo of a sign from the Nullarbor that said "please don't ask for water as refusal can offend"!
I wonder if you could put an infra-red filter in front of panels, or would that block the frequencies the PV cells use?