Looking through this section I failed to see any references made to the Thermo-Mechanical Generator or TMG. The importance of this device is there's no hocus-pocus associated with it. It is based on a very real variation of the Stirling Engine known as the Ringbom type. The Ringbom is a displacer type stirling which has been simplified to the point where there are no linkages to drive the displacer itself. The displacer only moves by the different air pressures within the system, which in turn makes it more difficult to design as all the parameters have to be chosen carefully. This is especially so for the TMG as it needs to drive the output diaphram at a high enough frequency to generate AC current using a linear alternator.
I have seen a number of US patents related to this principle,
4345437
4408456
4511805
5329768
but not many suppliers:
http://www.infiniacorp.com/technology/how_stirling_works.htm
I was wondering whether there are versions of this machine that are affordable to the home experimenter.
Regards
Joseph