These are interesting, but the cost per kWh of storage capacity is still probably too high for true seasonal storage. Short term storage runs into competition with batteries.

I point again to Standard Thermal for an idea tailored to true seasonal storage. I wait for more news from them, particularly on their very low cost resistive heater technology.

https://www.orcasciences.com/articles/standard-thermal

Doesn't need to be seasonal, we have enough energy in general to go through winter. This is to help through week long cold snaps, when Finland is short on energy. Week-long storage is still eyewateringly expensive with chemical batteries.

Also the capex from sand battery goes to (mostly) local construction, while when buying chemical batteries all the money goes to china.

But thermal storage doesn’t wear out, unlike batteries, right? So less future maintenance. Plus there is no danger of battery puncture.

More directly this is a very cold area. Enough it might effect battery storage enough to be a real problem.