[ttul]

Hmm. Why not talk to Etalim: https://www.etalim.com/

They invented and are very close to commercializing a direct heat-to-electricity converter that uses acoustic waves. No moving parts. Close to 30% efficiency.

[baybal2]

It is effectively another stirling, just with membrane instead of piston, and very high frequency of operation.

Sound == heat.

An AMTEC converter may be an another "fully self-contained" solution

[ttul]

No moving parts is the key advantage.