A new industrial-scale 'sand battery' has been announced for Finland, which packs 1 MW of power and a capacity of up to 100 MWh of thermal energy for use during those cold polar winters. The new battery will be about 10 times bigger than a pilot plant that’s been running since 2022.
They didn't say, but I'm wondering what the loss is when you convert the heat back into electricity. I assume they're boiling water and turning turbines with it- I can't imagine they're losing too much.