In ground engine for cold climate question

[paulstef]

I'm new to this , please bare with me.

I would like to use the temperature difference from about 10ft deep ground to ambient air temperature in winter. Air temperatures in January, February go down to -15C to -20C (around 0F) on average, ground temperature at 10ft in these months will be around 5C (41F).

Has anybody built something like this? I realize this is a low temperature difference. If it doesn't exist, how would one go about building one?

Thanks for your ideas

[Bumpkin]

Hi paulstef. Certainly no practical knowledge here, but I think for minimal expectations your idea is certainly possible. You'd be limited to the conductivity of the dirt, so it'd probably need a big network of contact area. A loop dropped down a well into flowing ground water might make a more sustainable source. Assuming you could get the full temperature difference to the surface, that's still only about 7 %. It would take massive displacement and transfer area for such a small difference to be useful, but the engine design sure wouldn't be limited by any high-temp considerations, A roll-sock type large bore short stroke engine might work.

There've been some large-scale schemes to use ocean-depth temperature differences of a percentage similar to yours, and they have the disadvantage of having to pump cold water up. In your case gravity could do the pumping with a simple thermosyphon loop; probably still not cost-effective, but if you can speak bureaucrat and call it green-tech, you might get a big grant.

Bumpkin

[Ian S C]

I agree with Bumkin, the only thing stopping anyone trying is $$$$$$$$$ and maybe a bit more $$, I afraid that that's what stops most things like this.
Ian S C

[paulstef]

Thanks.

After reading a little more I realize that the main issue is low power density of such an engine and therefore this thing would need to be quite big = $$. Just as you pointed out.

It's still amazing that we can get out (in theory) usable energy only from a temperature difference....