I want to try something like this too at some point. I have been reading about absorption chillers recently. My new word of the month that I stumbled across is trigeneration
. Basically, you get heating, cooling, and power generation all as part of a single process.
So the absorption chiller uses the sun's heat to say freeze water. Naturally, this process causes it to get very hot at the "exhaust" side. Here you place your motor that runs off of heat (i.e. steam engine / stirling engine). These things also have an "exhaust" which transferred to somewhere that needs heating.
Now if you thought that it was a pain to try can augment your house's hot water, just wait until you try this.
Definitely a crazy idea to try in your backyard.