I thought I'd start a new thread to follow up on my experiments with making electricity from my rocket mass heater. So far, I've easily been able to build my own little "ecofan" type fan units for the top of the barrel. This is probably the best use I've found so far for these cheap Peltier elements I'm using as the power source. I've also been successful building a "joule thief" circuit to power a group of LED lights with the same element. This is a bit more complicated than the fan, but works very well and was pretty straight forward. I'm only generating about .5v from one element, so it's pretty limited what you can do, but it's pretty cool to play with and so far has been cheap. Due to the low voltage, it's necessary to build the step up DC to DC converter to power even one LED, thus the "joule thief."
I would say that for sure the fan is worth while, since it performs a very useful function of moving the warm air off the barrel into the room, and helps break up stratification in the room. So far, the lighting is more novelty than very useful, but I am going to play with that a bit more tonight and see what's possible. I'll post more once I finalize some experiments and can give some better advice, but for now, here's a couple links:
Joule Thief circuit: You need this to run LEDs with one Peltier element.
http://www.evilmadscientist.com/2007/we ... ule-thief/
http://www.instructables.com/id/Make-a-Joule-Thief/
Homemade Eco Fan video: Not mine, obviously, but pretty much exactly what I did. Same heat sinks, even. This is a pretty awesome little project, since a store bought one is around $100 and up.
http://www.youtube.com/watch?v=g3fHGIPFqpY
Peltier element:
http://www.amazon.com/Tec1-12706-Thermo ... ds=peltier