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Comment by grecy | Hacker News Reader

Many people here in the far north have extensive solar setups and live completely off-grid. Unfortunately in winter, we only get ~4 hours of sunlight, and it's a pain to sweep snow off the panels every day at ~ -30C to -40C

We don't get much wind, and rivers are only liquid for ~4-5 months, so wind and hydro are not popular.

I've been investigating commercial thermoelectric couplings as a source in the winter. Everyone has a BIG wood stove burning 24x7 for ~6 months. My best research shows it shouldn't be hard to see +400C on the top surface of the stove. My plan is to have a radiator outside, run anti-freeze in the system and get an approx 400 deg C temperature drop.

Now, my interest is peaked in this approach from NASA. I wonder how long it will be until I can buy or build such a thing?

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I absolutely wouldn't recommend it.

Thermoelectric generators are far far less efficient than simple generators (say a Stirling engine). The benefit to them is that a) they are very compact and b) they need no mechanical parts.

It makes sense to put a thermoelectric generator in a satellite or rover because the mechanical parts found in a traditional engine are typically very heavy and more likely to fail.

So if you aren't concerned with a couple dozen pounds and the occasionally maintenance call, just use a wood-burning generator. You'll save about an order of magnitude on costs.

edit: what you're looking for is micro-cogeneration (http://en.wikipedia.org/wiki/MicroCHP)

Piqued your interest, just as an aside

This might interest you. http://www.biolitestove.com/campstove/camp-overview/features...

Who knew steampunk inventions were environmentally friendly?

Thanks.

I looked into that a while ago (and a similar one), and it looks like any power produced from the TEC is considered a bonus, and is in the range of 1-5W, probably only enough to charge a phone, etc.

I'm looking to produce a sustained 150W + to charge deep cycle batteries.

Tech specs show the biolite to have about a 2.5in radius and (approx) 6.5in high fuel compartment, which is about 2.1L (http://www.wolframalpha.com/input/?i=volume+of+a+vertical+cy...). Using its design you can get about 2W continuous power at 5V.

Scaling this up, roughly, you would need about 157.5 liters of fuel space, though probably much less if your fuel was more compact (obv you don't fill up exactly 2L of space in the canister while burning twigs). The realistic output of heat/power based on space is probably much more efficient than something this large, considering they say 46 grams of fuel can boil 1 liter of water, and 46 grams is approx 0.046 liters (based on water density).

Somebody please correct my horrible assumptions, but basically, fill an oil drum up most of the way with wood and build a thermoelectric generator and you should be good to go.

(Also, if you're charging deep-cycle batteries, i'm assuming you're not going camping? Maybe solar would be simpler? http://www.mdpub.com/SolarPanel/index.html) (Edit again: I forgot your original post, no solar)

More edit: Check this page for an adaptable thermoelectric generator: http://www.tegpower.com/

And more edit: https://www.youtube.com/watch?v=bUH1HA3EnZE (i'll stop posting links now!)

Sorry, this is the one I meant to link to (probably the similar one you mention). Might be a better design to scale up. Don't know if the TEC is any more efficient though.

http://www.kickstarter.com/projects/tpod1/tpod1-thermoelectr...

My understanding of the problem is that nuclear sources tend to be nasty stuff and not the sort of thing that one really wants lay people responsible for discarding.

Looking through the Wikipedia page on RTGs, there is a noted risk classified by the US-DOD that Beta-M RTGs could be used as dirty bombs, which is about what I expected. =/ I wonder if this risk extends to other RTGs in the wrong hands? I imagine so, but I honestly don't know.

Basically a RTG converts nuclear decays into power by absorbing the nuclear decay products, generating heat. This is quite similar to the process of radiation poisoning, where chemical bonds are destroyed by the decay products. So for a rather handwaving estimate, we can assume that the processes are the same.

The lethal dose of radiation is about 3-5 Sv, that is 3 to 5 J/ kg absorbed radiation (times some factors, which describe how the radiation is absorbed and which type of radiation). Therefore assuming full body irradiation and gamma particles, the lethal dose for an adult would be received in a matter of minutes ( 60kg irradiated by 1 W would be 1 Sv/minute). Note however, that a more realistic scenario for a dirty bomb from a RTG involves ingestion of alpha emitting particles for a rather large number of bystanders. ( And therefore the effects vary a lot by the details of the bomb and the radio isotopes used. )

So already with the radioactive material from a rather small RTG you can build a quite potent dirty bomb, rather independent of the exact type of the RTG used.

I think the OP is looking at using their stove as the heat source, not a nuclear battery.

On that note, the idea you're talking about was actually considered for a little while for public use until the dangers were found to outweigh the benefits.

Right now I'm thinking about a stove, but this nuclear battery has me thinking.

I am wondering if it would be possible to buy or build such a nuclear battery.

Certainly to build one the theory behind it wouldn't be tough, it'd operate on the same principles as the stove setup. To buy though? There's a story of a boy scout who did something similar as part of a personal experiment in the 90's. (Before getting raided out of fear by the FBI) Will have to find that story again.

In almost every country the materials required are tightly regulated and getting permission even in a lab environment is tough work. If you can work out the legalities and safety, I'd be interested too!

The book is The Radioactive Boyscout

http://www.amazon.com/The-Radioactive-Boy-Scout-Backyard/dp/...

I read the book. from what I remember he started with smoke detectors and worked his way up from there. Just a few letters to some supply houses saying he was a researcher or something. he effectively mail ordered his radioactive sources I think.

Governments tend to frown on the personal acquisition of radioactive isotopes. Well, there's a tiny bit in your smoke detector, but if you managed to get the eleven pounds that are in the MSL's RTG you'd make the international news.

Pu-238 isn't naturally occurring, and nobody makes it anymore. The US bought the plutonium that went into the MSL from the Russians, who are starting to run out themselves.

The other problem with RTGs is they get less efficient as they get larger. The one in the MSL only produces 125 watts, which will decay to about 100 watts at the end of its 14 year lifetime. That's not a lot of power.

The sensible way to get electricity out of burning wood would be a steam turbine or stirling engine-based micro CHP (https://en.wikipedia.org/wiki/Micro_combined_heat_and_power).

Toshiba makes a small nuclear reactor for your home: http://www.engadget.com/2007/12/19/toshibas-building-a-micro...

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