Different purpose. A swimming pool sized silo of sand can heat a few hundred apartments or well insulated homes through winter using summer energy. Make it a fe

Different purpose. A swimming pool sized silo of sand can heat a few hundred apartments or well insulated homes through winter using summer energy. Make it a few tens of metres high/deep and a handful will power a town. If there is going to be curtailment anyway then the energy is effectively free (or has negative cost). Or if you'd need to use something like pumped hydro or chemical storage then the heat pump only gives you a COP of 1-2 once you include storage losses.