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chr writes:

Finnish researchers installed first working 'sand battery' that can store energy as heat for months. See article in BBC: https://www.bbc.com/news/science-environment-61996520

In short:

1. Use excess/cheap electricity to heat up sand.
2. Store the hot sand and thus the energy for later use. Article says it can be done for up to several months.
3. Later use the warm sand as a heat source for district heating, i.e. heat up water that's transported to e.g. residences.

The BBC article is light on technical details: The installation in Kankaanpää in Finland uses about a 100 tonnes of sand heated to 500 deg C.

Their company is called Polar Night Energy: https://polarnightenergy.fi/ Extracting information from there; the unit in Kankaanpää has 100 kW heating power and 8 MWh capacity.

Didn't see details of cost. Seems like it could scale well in principle. However, IIRC, construction sand might become a scarce resource in the future, so I hope their solution works with other types of "sand".

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