We can collect light from a large but far away fusion reactor to generate electricity.
A better way could be to use the heat from the nuclear reactor we inhabit.
But in order to do this we would need to drill holes up to 10km deep through granite in many places
and this is a surprisingly difficult problem.
Surprisingly, because we are able to dig tunnels through mountains and we can drill deep enough holes to produce oil and gas.
However, existing rotary drilling technology is not sufficient to unlock geothermal energy in most places.
A research project at the University of Leoben, Austria, investigates an alternative drilling technology using water jets, which looks promising.
But perhaps it will take a billionaire and plasma jets (YouTube, fwd to 43:30) to solve this problem: link.
6 comments:
Drilling a well into hot rock isn't a problem. Recovering heat from that rock in sufficient quantity to generate much electricity is a problem. The thermal conductivity of granite or most other rocks is very low so you need a great deal of surface area to continuously heat the working fluid flowing through the system to a given temperature. That requires not just a hole in the ground but also a very highly fractured formation. Various countries around the world have been been putting quite a lot of effort and money into heat recovery from hot dry rock since the mid 70's, right after the first Arab oil embargo. So far the results have been exceptionally unimpressive. The commercial geothermal energy sources that are in production worldwide are typically in fluid filled highly fractured formations. Our ability to fracture not previously fractured rock to the degree needed for geothermal so far has been very limited.
50mW/m2 of geothermal vs 100W/m2 of solar.
Good explanation here (it's only 4 pages, but the whole book is very good):
https://www.withouthotair.com/c16/page_96.shtml
I listened to Friedland and I was pretty confused. Why does he want large diameter wells regardless of whether they are horizontal or vertical in hot dry rock? The surface area for heat transfer goes up linearly with the radius while the volume you are trying to heat goes up as the radius squared. That doesn't make much sense to me when he's essentially talking about a shell and tube heat exchanger where the shell side can't transfer heat very efficiently. Existing geothermal reservoirs are very highly fractured with an extremely large surface area per unit of open volume. What I'm calling the open volume is filled with a fluid, usually liquid water, but sometimes dry steam as in the cases of The Geysers field in Northern California and the Larderello field in Northern Italy. Although there has been a lot of work done trying to replicate that that sort of fracturing in hot dry rock there hasn't been anything so far that has come close to being commercial. And not to nit pick too much but I'm a little skeptical there is much nuclear fission going on in the core of the earth. I thought the earth was mostly heated from radioactive decay. Maybe I am wrong.
The high pressure jet technology you also link to seems to me to hold more promise in terms of developing existing geothermal resources. Drilling rigs are paid for by the day and they are expensive. Anything that would reduce the time to complete the well would reduce it's cost as long as the cost of implementing the technology wasn't more than you would save by reducing the time to drill it.
Thanks for the comments and link - I learned something ...
You may not be interested, but below is a link to an article where injection into what is basically hot dry rock from an external water source really has resulted in additional heat recovery from that rock. The injection is into a geothermal field called The Geysers which was, and I think probably still is, the largest geothermal field in the world. It's a vapor dominated reservoir meaning the wells produce only dry steam and no liquid. I think the benefits from injection of the external water source ended up being greater than those projected in the link.
https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2005/2420.pdf
The DEEP project in Canada seems promising. They only drill 3.5km deep and 2km horizontal from what I see ...
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