Thermoelectric generator for small things

I've read through some posts about using thermoelectric generators for "the big stuff..." but it seems that it isn't necessarily cost effective or efficient in the end.  Still, it is something I think will continue to improve over time.

In our small store, we've been playing with a new-fangled contraption that we really love & so we've started selling it; but it only charges the "small stuff."  It's a thermoelectric generator in the form of a lantern that sits on your woodstove.  It's a lantern, a stove fan, and can power things like your phone, laptop, etc.

I shipped one out to someone who wasn't able to get it to work without the solar charger because, as it turns out, she has a double-walled stove.  I spoke to the company and found out that it's far more common on European designed stoves--not terribly common with American ones.  

So here's question #1: for those who have woodstoves, do you KNOW if you have a double-walled one or not, did you research it before purchase, & if so, why did you go with what you've got?

And, question #2:  Who on here has personal experience with thermoelectric generators? Mine is limited to the Stove Lite Pro (the lantern we sell).  My experience so far (apart from someone having a double-walled stove), has been fantastic in use & product quality.

I look forward to hearing from you!

Okay--for the life of me I can't figure out how to hyperlink so just in case someone wanted to see what I'm talking about, it's here:  http://pantryparatus.com/product/stove-lite-pro/

Very cool apparatus. I got one of 'em high efficiency stoves. It, I think is double-walled and doesn't like getting that hot.  It's got insulation between itself and the top, so I guess it isn't gonna work here.

Amit, that's what I'm wondering...the company told me that double-walled are very rare in their part of the country (Vermont) but I'm curious how common they might be.  The lantern can also have an optional solar charger, but then it just isn't as cool...

Insulated fireboxes increase efficiency and promote complete combustion of fuel.

I am torn on the two, as we love the radiant heat and it is part of our heat distribution system...no moving parts aside from radiation and convection!

Additionally we rely on our wood heaters flat heavy top as a cooking surface.

Highest efficiencies are available with the new firebox designs and i would like the best of both without having to use a wood fired cook stove as a seperate system.

This brings us to power take off applications as domestic water heating and thermoelectric generators.
Even at 40-75 watt power thermoelectrics work great for recovering lost heat energy, even at low efficiency.

45w x 18hrs is around 800 watt/ hrs. , daily and is as reliable as your fire-tending.
This can run the big stuff! Imagine a 400w version on your wood fired furnace, pricey but consistent.

Low efficiency scavenging is usually more desirable that just lost energy and we burn in a way that produces clear vapor from the flue 90- plus percent of its run time.

Not having an insulated firebox allows us to easily place take of devices within good contact with heat and without the extremes of the firebox interior.

A treasure here.
http://www.backwoodshome.com/extras/home-energy/

Technical article from sweden good stuff for diy and product selection.

https://triz-journal.com/generating-electricity-families-northern-sweden/

Good stuff for a hard drive somwhere.

We have a small unit that runs on t candles and is kind of a demonstration rather than practical power. It does produce 10x the light output of the candle that powers it, so cool trick.