Smelly Old Engines
I've had some professional (engineering) association with the design of Stirling cycle engines, and have been working on this particular engine design during long flights for many years.
The first prototype engine, completed last December, (image above) has now run for more than a hundred hours and goes really well. One of its possible applications is to generate a KW or so of electricity using anything that will burn: wood, agricultural waste, dead books even. And, in case you're wondering which books are the most powerful when judged by the Rev Robert Stirling's engine, no it's not bibles or similar, nor even encyclopaedias. No, indeed, it's Mills and Boon style bodice rippers- because of their unclayed paper. In addition to generating electricity this engine can also simultaneously provide for cooking or water heating- or anything else that needs heat. I probably should publish the plans, but don't have any (it just grew), and then there'd be endless impossible questions to answer anyway, so maybe I'll just 'move on' each prototype when I've had my fun from it, and suggest people copy it- seems to work for kites, even without the suggestion!