Compressing air takes energy that can be released when the air decompresses. I read about another storage mechanism that heats vast bins of basaltic pebbles and then generates electricity with that heat. Glad folks are thinking outside the battery box.
During off peak hours, water is pumped up to it.
During peak hours, water from the lake is run h=through turbines to produce electricity.
I do too, Outside the box is the way. But air compressed is heated when it is compressed and once it cools it losses about 50% of it’s pressure and stored energy capacity.
Freeflow without any pressure such as heat exchange thermal mass is different. That works well to help maintain an even keel. :)