Mike Philips

In my estimation, perhaps the next most accessible way to generate electricity from wood may be to use a woodgas gasifier running a typical internal combustion engine (normally gasoline/petrol or diesel engine).  

There is a long history of vehicle use going back to at least WWII, and many online resources including from “All power labs”.

A system typically consists of: 1 ) a low-tar downdraft gasifier, vibratory shaker-grate. 2) Multi-stage filtration, 3 ) woodgas cooling heat-exchangers. 4 ) Carburetor, and optional automation at varying levels sophistication.

I suppose the advantages are that a lot of design & build resources are available and anyone can do it if they really want. It is relatively energy efficient compared to alternatives.  Disadvantages are that a large, multi-component system is required and significant operator labor (or expensive, complicated automation), and significant maintenance labor.  Cutting corners on this tends to gum-up the engine with tar.  

10 ) The TEG also makes essentially no noise, unlike an engine; an advantage that perhaps should not be underestimated if it will be used in your living room.

My thoughts on thermoelectric generator + rocket:

1 ) Expect ~4% efficiency. This could be justified if the fuel was going to be burned anyway for heat (aka “CHP”), otherwise it’s probably not efficient enough to be justified.

2 ) If you’re actually going to invest the $2-3/W, you might as well keep it running continuously if possible for the entire heating season.

3 ) RMH don’t burn much fuel. Say 1.5 cords/cold-season. Really not much thermal power to work with, especially at ~4% efficiency. To me this implies that all (or nearly all) of the heat should pass through the TEG. This is non-trivial to design, given the small area of the TEG device and the max temperature limitations.  Not saying it can’t be done, just non-trivial.

4 ) For max efficiency (already rather low), and max power, it should be run near the max temperature of the device.

5 ) Given these assumptions (moderately high temperature and constant temperature, continuously, I then look to the RMH properties and operation. Fluctuating temperatures and often not a lot of thermal storage at higher temperatures.

This makes me wonder: how could RMH temperature be made more constant?  

I was envisioning semi-automatic fuel conveyance. For instance a woodchip system, or perhaps a bundle of few sticks, several feet long, with a weight on top to gravity-feed the J-tube, and refilled once a day.

The batch-box style might work but could require more high-temp thermal storage and additional temperature regulating systems for optimal function.

6 ) From there, them one could think about ways to limit peak temp and heat exchanger design. Due to the high heat-flux requirement, liquid heat transfer on one or both sides of the TEG might well be needed or appropriate, (as mentioned above).  

7 ) Much like with solar cells (a very similar semiconductor device), clearly the TEG is enticing for its simplicity, solid-state reliability and low maintenance; that is, if it’s lower efficiency can be justified.  

8 ) The niche application would be for cold-climate off-grid use, especially in areas where solar and/or wind aren’t particularly abundant.  

9 ) The availability of off-the-shelf TEG components is excellent (especially compared to steam or Stirling heat engines).  The safety is probably also considered much better.

Someone spent many thousands of dollars on a lidar survey.  what value did it gain? Beforehand, you had thousands of dollars and a map accurate to 20 cm, afterward, you don’t have that thousands of dollars anymore but your map is now accurate to 2 cm.  Was it worth it?  Is your permaculture practice that much better as a result?  Did anyone pause to consider the purchase, or was it just technology that was impulsively applied?  

I ask because I want to know what role high-tech plays or doesn’t play here. I did a survey on asking folks to describe “appropriate tech” but there was no trend or correlation.  Sometimes folks embrace high-tech, other times they shun it. Is there any rhyme or reason to this?

I think there’s more to learn. Don’t you?

Most plastics aren’t heat resistant. I’d rather use metal, wood, ceramic/brick, even cardboard.