A Finnish sand battery can store green power for several months at a time in a low-cost, low impact way. The device is charged up using solar or wind power derived electricity. The sand stores the heat at around 500C in a steel container, generating hot air which is circulated in the sand by means of a heat exchanger. It can then warm homes in winter when energy is more expensive, and can be a source of consistent energy supply all year round.
www.bbc.com/news/science-environment-61996520