[ZeroGravitas]

UK is up there in the world rankings for batteries.

I think they have slightly more grid batteries installed than California. UK have more people, but less money and less electricity used so I'd say they're doing better than California on battery deployment.

[tialaramex]

I do not think so. There is BESS here and it's hard to be sure from the available data but it sure looks like less than 10GWh of BESS, maybe much less. There is now more BESS here than pumped storage, which was installed as a Black Start† rather than specifically storage but it's just not very much compared to California from what I can see. So maybe I'm wrong about how much capacity it is, because the Pumped Storage is like 20GWh top to bottom.

† Most modern power stations perversely need electricity in order to start them, so if your whole grid goes offline you're fucked, you go dark and your civilisation is now on a clock - a Black Start facility is a station which can go from black (no electricity) to running. In the case of Britain's pumped storage that's because "all" we need to do is allow the water to run through the generator. Once one or two Black Start sites are up you can use that power to start the other generators and restore supply to residents, and things get back to normal in a few hours.

[Edited to say that since we know there's about 20GWh of PSH the larger BESS can't be as small as I thought unless it's run a lot harder...]

[ZeroGravitas]

It hard to get exact numbers because the rollout is fast in both places but it looks like they have strikingly similar targets for 2030 and 2040 in terms of GW but California both started earlier so is still ahead in GW deployed and their regulations mean that 4 hour is more common so they're actually about 2x on storage duration in California.

Both doing well, but UK would need much more of a handicap for GDP than I thought to claim a win. Solar and batteries do generally pair better than wind.