A “sand battery” is a heat storage that warms sand or sand-like materials to a high temperature to store energy.

To call it a “battery” might mislead some people into assuming it stores electricity. Nobody would call a hot water tank a “water battery”. A better name might be “sand heat store”. So far as we know, the heat has not yet been used to generate electricity, but only to heat a swimming pool in Finland.

Sand is a good insulator so it can store heat at 500C for months. Sand is also abundant so its use as a heat store could easily be extended.

See also

https://www.bbc.co.uk/news/science-environment-61996520

https://www.marketplace.org/2022/07/29/could-the-sand-battery-make-renewable-energy-more-dependable