> Agreed, e-fuels seem to be far and ahead the front-runner.
For covering Dunkelflauten? Yes.
For seasonal storage with a prolonged discharge (so, low power/storage capacity ratio)? I think thermal storage wins there.
I just don't see it with thermal. You have to pay the Carnot tax, and you also need humongous amounts of material.
E.g. 100 GWh (4 days of 1GW thermal power) with a 100C temperature swing (you can't go down all the way to room temperature) will need around 3.6*10^4 tons of sand. That's a lot.
Honestly, power-to-gas sounds like the only reasonable way for now. In theory, with SOFC (Solid Oxide Fuel Cells) for power generation, it can beat the steam cycle.
Sure, thermal is great where it's possible. But there aren't that many places where district heating is viable.