[ekr]

Stirling engines built into a wood stove is a mature technology capable of delivering lots of power (kWs for a regular wood stove found in a home). Simple to build.

As for pollution, no-one can deny that, but the rocket stove bunch claim much reduced emissions compared to even modern wood stoves (which I personally find hard to believe). But still, billions of people are still using wood to heat their homes; that's not going to change soon. Reusing that to produce electricity as a byproduct is something that some people call 100% efficient.

[1] http://volodesigns-sterlingproject.blogspot.com/

[2] http://www.oekofen-e.com/en/engine/