I have looked at the solar idea and I just don't think it will work
. Not enough output and high set up cost.
Diesel/ kerosene/s propane
is still by far the cheapest sourse of energy.
The Still wouldn't have to be very large, I would envisage a small bilge pump
, pumping salt water
up to a continuously supplied boiler and a condensor with something like a small camping stove
to supply the heat, and maybe hang it over the stern of the boat
. As I said $4,000-$6,000 buys a lot of camping fuel
. Also it would be a lot more reliable than RO's