I have more questions than answers.

Does the article describe how the heat gets from the mound to the houses or buildings it plans to heat, or factor in the cost of that?

Naively, I'd assume that would like 90% of the cost.

I know that physics is under no obligation to be intuitive, but it's also surprising to me that it's so easy to heat and keep dirt this temperature (600C / 1100F) throughout Winter, and I didn't see how that piece worked either, though I'm willing to assume that part is figured out and factored in.

Apparently the insulation value (R value) of dirt and soil is between .25 and .8 per inch (depending on moisture content). That wouldn’t be great if it was a material like fiberglass, but since it’s dirt cheap (ba-dum-tssh) and easy to pile up in large quantities with little to no ongoing maintenance in this kind of context, it matters.

A 10 ft pile of dirt (assuming 10 ft between heat exchanging pipes and the outside air) has an R value of 24 to 96, which is extremely significant.

I expect there would still be notable losses trying to keep it at 1100F indefinitely, but 10 ft of dirt will have insulation values approximating many feet of fiberglass insulation.

You’d want a very large mass to heat however, scaling matters a lot. You’d want the ratio of surface area to mass to be as small as possible, and that means as large a volume with as thermally dense a material as possible inside. Surface areas increases by the square, while volume increases by the cube.

Also, no matter what you do, you would eventually cook whatever was at the surface or underground, so don’t do this where you want trees - or where there are underground coal seams

I think there have been about 5 different contexts over the years where I've been surprised by how good an insulator a pile of dirt is.

> Pipes run through the pile, and fluid flowing through them removes heat to supply the customer.

Dirt keeps a constant temperature year round quite close to the surface that’s a ~60 degree difference between summer and winter in many areas. So 600c would just be a tradeoff between depth, heat loss, and thermal efficiency. However, what they aren’t saying is electricity > heat > electricity is quite lossy and even just using the heat directly is far less efficient than a winter heat pump.

they mention that demand source should be close by to reduce losses in transportation