Gigawatt-hour storage does exist but it is limited in capacity.
Dinorwig can store ~11GWh and can provide that at 1.8GW (going from 0W to 1.8GW in under 2 minutes) and is ~75% efficient as a store, but it's only got a 6 hour capacity due to the limited size of the upper reservoir.
Something similar built at Itaipu or Three Gorges scale could provide some more serious capacity.
Dinorwig can store ~11GWh and can provide that at 1.8GW (going from 0W to 1.8GW in under 2 minutes) and is ~75% efficient as a store, but it's only got a 6 hour capacity due to the limited size of the upper reservoir.
Something similar built at Itaipu or Three Gorges scale could provide some more serious capacity.