For comparison with a gravitational battery, Dinorwig pumped hydro in north Wales has a max power output of 1.7 GW and storage of 9.1 GWh.

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ZeroGravitas 6 days ago | parent [-]

About 10-15 percentage points less efficient because of losses pumping the water uphill though, and slower to react (seconds vs milliseconds) which will probably force it out of the fast frequency response market which batteries have rapidly saturated.

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3eb7988a1663 6 days ago | parent | next [-]

Batteries are not perfect either. The EIA published numbers that grid scale batteries were something like 81% roundtrip efficiency.

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jacquesm 6 days ago | parent | prev [-]

It's pretty much tailor made for batteries and flywheels. 2 seconds is not feasible for pumped hydro, though it still is impressively fast at less than 30 seconds. It is interesting how all of these technologies have their sweet spots.

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ralphhughes 4 days ago | parent [-]

I've been inside Dinorwig Pumped Hydro plant back when they were doing tours. They keep the turbines spinning with compressed air to avoid the delay of having to spin up that large metal mass of turbine when they open the water valves.

	▲	jacquesm 3 days ago \| parent [-]
		Yes, the problem is that the changeover moment between 'tons of water moving uphill' and 'tons of water moving downhill' is inviting a serious case of water hammer if not managed properly. Typically it takes about 30 seconds for things to first quiet down and then to allow the flow to reverse. The turbines themselves are already spun up during that interval, either with compressed air or by temporarily using the generators as unloaded motors so they're already synchronized to the grid. The valves are then opened gradually to the point that the generators start leading the phases and hence put power into the grid. It's fascinating how mechanical all of this is. When stuff goes wrong with dams they really go wrong: https://en.wikipedia.org/wiki/Sayano-Shushenskaya_power_stat... Standing inside the turbine hall of one of these you can't help but think of the absolutely insane pressure from a water column typically 100's of meters high and half a meter or more across pushing down on a fairly simple valve. Engineering at its finest. To me the big dams are right up there with spaceflight.