Geographic batteries (potential energy sinks, eg storing water in a reservoir at a higher altitude and releasing it through turbines to a lower one) have operated for decades.

Dinorwig in Wales operates a 9GWh capacity at 1.7GW. Far from insignificant, much cheaper (and safer) than the equivalent lithium cells.

https://youtu.be/6Jx_bJgIFhI

To be clear, Dinorwig is not only powered by green methods, but it could.

There's quite a few large working ones: https://en.m.wikipedia.org/wiki/List_of_pumped-storage_hydro... It looks like 60s/70s were pretty good for building initial low-capacity ones.

Now it looks like the plans for new ones are entirely dominated by China. (Or were projects in other countries just not researched/included?)

The less favourable the existing geography, the harder it will be for a state to "just" build a pumped storage facility like Dinorwig. Dinorwig is basically ideal, the mountain was already right there, with a nice lake at the bottom and a quarry that had closed or was about to close that could be re-used as the top lake. It's far enough away to reduce the amount of random BANANAs‡ who get involved yet not so far as to make the infrastructure cost prohibitive (for HV power lines to the facility). The UK hasn't built lots more because it doesn't have dozens of other mountains with lakes next to them just kicking about for the work, and any it does have are deemed environmentally important (e.g. something rare lives in the lake or on the mountain).

China has two advantages: One it's fucking enormous, there are bound to be places with mountain lakes that weren't needed for anything else more important. Two under an authoritarian government there's no prospect of protest against the plan even if it's catastrophic for some groups.

‡ NIMBYs but more so, Build Absolutely Nothing Anywhere Near Anyone.

> Far from insignificant, much cheaper (and safer) than the equivalent lithium cells.

Pumped storage "batteries" have one disadvantage though, they are nowhere near as reactive as solid-state batteries can be - think of milliseconds instead of dozens of seconds.

You can chain in a relatively small lithium battery to smooth load.

That's true, but power grids have managed to track demand with production that reacts over dozens of minutes.

Not very important as long as you have a good power grid and some other form of backup power.