Some people think closed-loop hydro is the solution to electric grid storage. Somtimes this is also called Pumped Hydro Storage (PHS) or variations therefore.
It entails having two reservoirs: one on top of a mountain, one in the valley. To store electricity, pump water up the mountain. To release it, run the water down through generators.
The Australian study claims maybe 100 times the needed capacity exists on the planet. Perusing their atlas, they may be a little optimistic. However, they do exclude regions that are currently in other use like cities and much agricultural land, so not too bad, either.
Their atlas is really cool.
On the other hand, for the US now, NREL has a (perhaps) more realistic study, also with map and all.
Most pumped hydro storage is available in mountainous regions, like the Rockies or the Apalachians.
Northern and Western Europe doesn't have much capacity.