Pumped-storage hydroelectricity is 130 years old technology
" Low-cost surplus off-peak electric power is typically used to run the pumps. During periods of high electrical demand, the stored water is released through turbines to produce electric power. Although the losses of the pumping process makes the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest.
50 years ago it was a nice idea to use low-cost surplus off-peak el;ectric power from coal fired power stations
but today, there is no low-cost or surplus off-peak electric power, since generators in coal fired power stations and and other generators can be controlled to lower electric power output by 50% or increase by 100% at peak times, so in modern power energy systems there is no surplus or off-peak electric power to to run the pumps.
Grid has been developed these days to such an extend, energy from one country can be sent to another country, so surplus electric power from large wind farm in one coun try can be easily transferred to another country ( Europe, Asia)
Since claimed efficiency of a new PSH targets 70-80%, so 20-30% of electric power gets lost.
You can easily verify the above stated facts about state-of-the-art in PSH of today, buying and operating pico hydro PSH for your homehttps://en.wikipedia.org/wiki/Pico_hydro
Since intelligent grids don't require new PSH installations any more
Money invested in the development of new PSH projects is money lost since large Li-Ion battery energy backup systems are readily available and at more affordable price. easy to install and operate, not generating investment overheads ( bank loans)