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