It depends on how one is storing the energy.
In Wales there are “hollow Hills” as a result of coal mining. Water is pimped there at night while the country sleeps and then drained to power turbo-electric generators during the day when demand is high. This balances the demand for power. It only makes sense because the ‘Hollow Hills” are already there. If we had to excavate those ‘reservoirs’ specifically for this purpose then the energy costs would be too high.
As it is, this kind of storage works best with nuclear power plants which are run at near constant output.