The Sands of Time?

'Green' energies, like solar and wind power, have an inherent problem. How do you heat and light things, when the sun doesn't shine and/or the wind fails to blow? The creation of 'sand batteries' appears to offer a remarkably simple potential solution (https://www.bbc.co.uk/news/science-environment-61996520). 'Sand batteries' hold tons of sand in insulated buildings. The temperature of that sand can be raised to 500 degrees Centigrade, using electricity from solar panels and wind turbines. The 'sand battery' retains that heat for extended periods of time (months). The energy can be 'tapped', as and when it is required. The first commercially successful 'sand battery' is now operational in Finland. Finland is, of course, a country with long, dark, cold winters. 'Sand batteries' appear, however, to be a simple and relatively cheap means of storing 'green energy', usable anywhere.