There's already some wood pellet boilers on the market which can integrate a sterling engine, to supplement off-grid battery-backed photovoltaic solar panels for local electricity generation. The power output of the sterling engine isn't stellar, but that's to be expected, it's just to help when it's less sunny and you need space heating anyways.

For example: https://www.oekofen.com/en-gb/pellematic-condens/