It’s a pretty neat system:

• can be set up anywhere
• can supply high grade heat (process heat, not space heating heat)

However, heat stores are subject to scaling laws which don’t favour sand on the large scale. Large thermal stores benefit from storing heat in water, and placing the water deep underground so the boiling point rises.

For comparison Helsinki (.fi) has a 10 GWh underground thermal store. Where I live, Tallinn (.ee) will soon get a 1 GWh thermal store. And Vantaa (.fi) will soon complete a whopping 90 GWh thermal store that’s located 100 m underground, so their water will boil at 140 C instead of the usual 100 C.