Also for comparison: a single pumped-storage plant will often have storage capacity in the GWh; e.g. the Linth-Limmern pumped storage part in Switzerland can store 33 GWh and provides 1000 MW peak power.
Seeing the title, I jokingly thought of generating hydroelectric power off a dam, and storing excess power by pumping the water back up, Sisyphus like. I'm very surprised this is actually a thing.
It's also only slightly less efficient than batteries.
> GLIDES costs as low as $13/kWh and $346/kWh and roundtrip efficiencies as high as 80% can be achieved using depleted oil/gas reservoirs and high-pressure pipe segments as pressure reservoirs, respectively.
https://www.energy.gov/sites/prod/files/2019/12/f69/02_ORNL_...
Typically pumped storage uses two lakes, one high and one low. But points for creative thinking :)