Wood Burner Back Boiler

[renewablejohn]

On 07/04/2022 at 22:28, openspaceman said:

TEGS designed for the job, rather than Peltier coolers pinched for things like stope top fans, will work up to 300C because they are joined with a harder solder. Petier devices can be used as TEGS  but tend to be made with softer solder that melts at around 200C.

 

Peltier coolers are available at  nearly an order of magnitude cheaper than proper TEGS.

 

It's a compromise whether one should go with a much larger array of Peltier coolers and arrange for the same heat flux to go through a lower delta T (say 200 through to 40C) or stump up for a smaller number of higher temperature TEGs and a smaller surface area with the heat flux fro 300 down to maybe 70C and heat water for traditional DHW or radiators.

 

I don't understand the science enough really.

 

What I would like to see is a stove manufacturer to design a wood burner incorporating a Stirling genset, like the free piston Microgen one British Gas were trialing. I think this was developed originally by Sunpower to sit at the focus of a parabolic mirror.

 

Harwell actually had a long life Stirling  which was further developed for powering light buoys, which had no sliding surfaces, using a diaphragm instead of a piston, One apparently ran for nearly three years with only re-gassing (helium) required every 6 months, it converted 10% of the heat flux to electricity  so again the stove wouldn't give out heat directly but a traditional wet system could circulate hot water from it. It hummed rather loudly.

Personally I have always been down the high temperature thermal oil route at upto 230C then two distinct cycles a conventional steam followed by an ORC cycle the waste heat for UFH. Its made easier now with screw expanders.