[londons_explore]

Todays grids don't have much need for energy storage on the sub-10 second timeframe. Ie. there is rarely any money to be made by taking power from the grid now and returning it in 10 seconds.

For technical reasons, thats because the 'spinning reserve' - which is momentum of every synchronous motor and generator across the nation - already adequately handles this.

Also, large generation stations are required to have a 'load line' which damps high frequency oscillations. The load line can best be described as 'whenever the grid frequency starts slowing down, generators must put more energy in automatically'. Things like wind and solar typically don't have the ability to do that.

For human reasons, it's because electricity markets tend to be minute by minute at most.

For all those reasons, I don't think you'll make any money with capacitor energy storage banks (not to be confused with capacitors for grid scale power factor correction, which can be profitable).

[fomine3]

Isn't it expected that 'spinning reserve' will be decreasing because we shutting down dirty power plants? Possibly it is needed in the future.