Pumped storage hydroelectricity is a method of storing and producing electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand, excess electrical capacity is used to pump water into the higher reservoir. The advantages of pumped storage power plant are given below: 1) Pumped-storage plants are unlike conventional hydro facilities in that they are a net consumer of electricity. In reality, pumped-storage plants function as transmission facilities because their primary purposes are storage, grid balancing, and providing ancillary services – not generating electricity. These plants can be very economical, from an overall system operation perspective, due to peak/off-peak price differentials and the provision of ancillary services. 2) Pumped-storage plants have been used to balance system load and to allow large thermal generating sources to operate at optimum conditions. Pumped storage is the largest-capacity and most cost-effective form of grid energy storage available. Pumped-storage plants also provide ancillary grid services, such as network frequency control and reserve generation. This is due to the ability of pumped-storage plants, like other hydro plants, to respond to load changes within seconds. 3) Pumped storage is now being applied to firm the variability of renewable power sources, such as wind and solar. Pumped storage can absorb excess generation (or negative load) at times of high output and low demand and release that stored energy during peak demand periods. 4) A net reduction in greenhouse gas emissions can be realized with pumped storage when the fuel providing electricity for pumping has a lower carbon content (or no carbon content as in the case of wind energy or nuclear power) than the fuel being displaced by the pumped storage generation.