AltaRock Energy Melts Rock with Millimeter Waves for Geothermal Wells (2020)

Could this be used for tunneling too?

As an RF engineer, this is a very creative application of mmW and I hope can be successful, but is not without very significant challenges which the company has made no claims to have solved. The issue is, mm-waves (and all high frequency RF really) are very sensitive to distance and losses. As a random example [1] gives some numbers for theoretical and precision machined waveguides in these frequencies. In the very best case we're talking about 0.03dB/cm loss. That means in the first meter of ideal waveguide you've lost half the power! And not just disappeared, you just dumped 0.5MW into the pipe itself, meaning it would likely melt within minutes. Meanwhile, their concept is to bore 20km into the earth.

The only way I could imagine this working is to lower the gyrotron itself down the borehole, but there's presumably tradeoffs of physical dimensions and output power that make it challenging. Again maybe not impossible, but there's no indication they've made fundamental advances in miniaturizing the source, or producing lossless waveguide.

Related, another interesting company I came across is Petra [2], who is doing something similar -- plasma/heat based non-contact drilling. But because they fracture the rock instead of vaporizing it, there's essentially gravel/sand leftover which is hard to evacuate from a deep vertical shaft, hence their focus on power/fiber trenches not geothermal.

[1] https://www.nrao.edu/meetings/isstt/papers/2012/2012151153.p...

[2] https://petra.cc/

Things leak. It sounds like it should be easy to fix, but it really isn't. Not at scale, for a competitive price.

There was a fad to build homes into the sides of hills. It turns out if you want to do this, you have to do a significant amount of engineering and work if you don't want to have all your furnishings, electronics, books, and clothes to be ruined. I'm sure people will have examples where it has worked, but there are at least as many where it has not worked.

Similar for ground loop heat exchangers. It seems like it should be cheap and easy to put a pipe down and tap into that thermal mass, but it's just not cost competitive. It's not even a matter of externalities really - you can get better results by building with better insulation and more efficient heat pumps for the added cost.

Things like this can work if it's a community investment, but that's challenging to coordinate. It sounds like it shouldn't be, but it is.

tbh i don't know if anything could replace having windows for me. i have felt measurable changes in my mental state from living in places with few small windows and places with lots of large ones.

(i have also lived in places like houston where "some engineering challenges" become pretty absurdly difficult)

I'm thinking about the opportunity cost and the longevity of a solid-state rock, exo-"microwave oven" vs. drill bits.

How is it going to displace molten rock after it is softened?

And, if it's too hot for drill bits, how is it any better for electronics, power conducting cables, and cooling apparatus?

It seems like hammer technology in search of nails like flying cars and battleship rail guns.

One thing I do know is conventional microwaves heat the bejesus out of the edges of silicon dioxide objects like glass containers and ceramic bowls far sooner and better than they do food. Perhaps they have a dipole moment similar enough to water that it's unavoidable and typically enclose tasty vittles from spilling and sloshing all over.