why use sand when you could just use the subsoil on the site? why make a big tank when you could just leave it in the ground?

April 10, 2026 - 07:25 UTC

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Any evidence on how this would work specifically? How would you be able to store heat at hundreds of degrees in the subsoil?
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There is a Finnish company heliostorage.com/products/btes/
doing just that, storing heat in the subsoil, but not at elevated temperatures above 100. Not sure how successful the technology is as no recent breakthroughs are reported and the even the site in Drake Landing is now dismantled.
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I was hoping you might do the analysis. But surface to volume ratio seems important here. if we are storing cities worth of heat then the self insulation of baked soil might be plenty. sketch: dig deep hole, bury big resistor, cook in summer, collect surface heat in winter.
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Presumably because, in order to retain the heat the tank has to be well insulated.
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This! And also, to store heat at hundreds of degrees the sand must be very dry. Ever a small infiltration of ground water or rain would absorb your heat and boil up into steam.
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I don't think this is true. if you are storing 1TWh of heat then you need something in the order of a skyscraper's foundations, at that scale the surface to volume ration is quite small and a layer of gravel (or shattered fired subsoil) is sufficient.
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