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.

April 10, 2026 - 08:41 UTC

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Alternative is to store heat in the subsoil at much lower temperature, a few degrees (like a ground source heatpump does). That needs a much bigger volume of soil, so long and expensive heat absorber pipes or boreholes. Better match for individual buildings, than for this 2MW district heat network.
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Yes I've spoken to Polar Night before - they insulate the tanks really well and they store at a high temp. It is possible to charge the ground with heat during summer that you use in winter, though! Has some ecological risks, possibly. Nowhere near the same density of energy storage.
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