Boiling a fluid to make a inverse water wheel?
Ok, how about this;
Submerge a waterwheel type structure with cups facing downwards on one side. Under the cups you have some kind of heating element. The fluid is methanol or some other low boiling fluid. A very small amount of heat from the element will produce bubbles, which rise and are caught in the cups, the wheel turns and can generate electricity or whatever.
I'm using this principle in another application, but thought it could be quite an efficient means of generating electricity from heat. If the meths is sitting at forty something degrees and boils around 50, it shouldn't take hardly any energy to tip it over. And since you're effectively generating force from gravity (the weight of the fluid on the other side of the wheel) you're kind of getting ten times your force back. ie producing one litre of bubbles will give you 9.8 Newtons of force (for water, 8ish for meths).
So (excuse my dodgy maths) 125 litres of bubbles in an hour would give you 1 kiloWatt hour?
One cola bottle per minute, doesn't sound very much and that much energy could easily be produced through concentrated solar. Slight risk of explosion...
How efficient do you think it would be, overall?