sand
This works by a process called resistive heating, whereby heat is generated through the friction created when an electrical current passes through any material that is not a superconductor. The hot air is then circulated in the container through a heat exchanger.
The sand can store heat at around 500C for several days to even months, providing a valuable store of cheaper energy during the winter. When needed, the battery discharges the hot air - warming water in the district heating network. Homes, offices and even the local swimming pool all benefit in Kankaanpää, for example.
that doesn’t sound like it should work
It’s pretty much the same principle as a storage heater but on a massive scale. So long as you sufficiently insulate the thermal mass, the rate of energy loss can be reduced to be much lower than the rate at which power is used/produced, and given that the production here is renewable, a little inefficiency in exchange for much greater storage capacity is a good tradeoff. IIRC, thermal storage is actually more efficient at larger scales than at smaller ones. I’m not sure about the expense of these facilities though so it might not be particularly scalable at present, but still, very cool.
This I need to read on. Very interesting
