"We will be able to inject or absorb up to 1.2 gigawatt-hours (GWh) of electricity in a few milliseconds"

1.2GWh in a few milliseconds? I'm pressing (X) to doubt.

An energy comparison: a semi tanker of gasoline hauls about 300 MWh of chemical energy potential.

That must be the total capacity and response time.

Nope. Total capacity is going to be 2.1GWh. The peak power will be 1.2GW, and milliseconds is the response time of the system. [1]

[1] https://flexbase.ch/en

I would assume it's a typo on GWh. It seems probable to me that the battery can supply/absorb 1.2GW on a millisecond response time, so it would be able to fully charge/discharge in a little less than 2hours, supplying/absorbing 1.2GW with 2.1GWh total capacity.

A vanadium one, which (as mentioned in the piece) is symmetric.

The 'Just Have a Think' channel did a video on the Swiss battery here - https://www.youtube.com/watch?v=CPAFeTvjVzY

The advantage of vanadium batteries, as I understand it, is that leakage does not corrupt the system. The vanadium gets converted to the right chemical species on either side.

They in theory combine well with pump-station powerplants where the medium is also the medium?