Sadly I begin to suspect that the only way to not have a prohibitive amount of water weight to carry around would be to have a closed system design.
I found an
example of a steam engine:
Quote:
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Our shop unit has been in use for the last 18 years producing 4000 watts an hour. It consumes about 250 pounds of water (that has been turned to steam) in one hour. 750 watts is considered one horsepower, and when you figure efficiency losses, that works out to about 47 pounds per horsepower hour (250 lbs divided by roughly 5.3 horsepower). Put another way, for every horsepower the engine produced, we evaporated 47 pounds of water to steam and passed it through the engine.
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250 pounds of water per hour to get 4 kwh out of the steam engine just puts some harsh weight restrictions on the amount of water that needs to be carried around.
If a closed system to recover the water vapor is too complicated / heavy ... perhaps as others have suggested a straight heat engine like a Sterling that just needs a temperature difference would work better... no water would need to be consumed.
Some useful books for learning more about Stirling:
http://www.freebookspot.me/Comments....ement_ID=23810
http://www.freebookspot.me/Comments....ement_ID=23809