That is what utilities need to be doing. Right now, they refuse to do much about energy storage, and home owners with solar or wind generation have to buy expensive batteries to buffer their production. That is stupid expensive for individual producers and is something a utility needs to take over. They just don’t want to because it’s more lucrative to burn fossil fuels and charge for that.

Stuff like this is so interesting. I remember reading about using decommisioned mine shafts as batteries a few years back, I think that idea uses sand as well. These kinds of adaptive reuse are really important for a sustainable future!

Why not just use a water reservoir which will also fill with water when it rains.