Pumped storage plants are like impoundment hydropower plants but with reservoirs above and below the turbine and with the capability of pumping water back uphill to refill the upper reservoir. This capability allows the same water to be reused many times to generate electricity.
Pumped storage facilities are used as a means of storing electricity. When demand is high the unit is used to generate electricity, and when demand is low or excess supply is available, electricity is used to pump water back uphill. Over time, pumped storage facilities are net consumers of power since it takes electricity to pump the water uphill, but on any given hour they can be an important and valuable source of generation when the water flows downhill. They are also valuable in “time-shifting” renewable energy generation.