The temperature swing can be much greater than 100 C. Heat can be extracted as a wave passing through the store, then heat added back by reversing the flow. It would operate like a counterflow heat exchanger.
View another way: if we hook several piles in series, then lukewarm air from a first mostly discharged pile can be directed into later piles for more heating. In the continuous limit this is the concept I described above.
> The temperature swing can be much greater than 100 C.
No, because your steam will be at a lower temperature as you draw down the heat, bringing down efficiency.
Realistic designs for this can achieve 450C delta t. Your energy store can store at ~1000C (slightly below rock melting point), and run steam turbines with a hot side of 600C and a cool side of 150C.
Over the season, your sand drops from ~1000 to ~600 (which is fine since your power needs drop in the spring)
Sorry, but 1000C is wildly unrealistic. There are no bulk materials that can be used to construct heat exchangers for this kind of environment. 600C is already a stretch.
At 1000C steel will react with _water_.
To be clear, I'm not talking about cooling a small crucible but a structure that is at least 20 meters in size.
At 600 C one can use stainless steel, but things rapidly become expensive and problematic beyond that. 1000 C would require Inconel or something.
That is wrong, and I already explained why.