In the forum topic 'A fuel source you may not have considered', Rachell Koenig asked what if we could run a device from the heat we produce to power a fuel feeder?
My suggestion 'without much thought' is how about a Stirling engine, also known as a hot air engine.
Low temperature/efficiency stirlings are quite simple to build,
however efficient stirlings are very demanding
as they need very high temperature differences.
