Clive Arthur wrote:
Figures from BBC article...

'Bigger than Olympic swimming pool'. Say twice as big, so 5000 m^3

'2.5 x density of water' so 12500 T or 12.5E6 kg

'200m high' so 200 * 12.5E6 * 9.81 joules = 24.5E9 J

/3600 = 6.8 MW-h

'700 sites around the country' so 4.77 GW-h

Is that right?

Sounds about right. You could imagine a larger volume - for example a
warehouse 100m x 50m x 5m, but that's only a factor of 5.

I wonder how it compares with flow batteries? You need a different kind of
TechnoGloop (TM), but the batteries don't need a hillside. So you could have
two adjacent tanks, or one tank with some kind of diaphragm to keep the
charged and uncharged gloop separate. And you could build that anywhere you
wanted, at any scale.

(you could even combine the two techniques...)

Theo