pumped-storage system

…the load on the generators, pumped-storage hydroelectric stations are occasionally built. During off-peak periods, some of the extra power available is supplied to the generator operating as a motor, driving the turbine to pump water into an elevated reservoir. Then, during periods of peak demand, the water is allowed to…

Electricity must be used as soon as it is generated; there are no economical means of storing large quantities of electric energy. Thus hydroelectric plants built for near-maximum power consumption during daytime peak hours would have to operate at low efficiency during nighttime…