1. Principles and description

The principle of this energy storage system is to pump water from one reservoir to another at a higher altitude, during periods when electricity is abundant. Then, at times when demand is higher than production, this water is pumped down through turbines to generate electricity. This requires two water reservoirs at different altitudes (figure 1 ), tunnels, pipes or conduits linking the two reservoirs, pumps and turbines, as well as ancillary structures.

Energy is stored in the form of potential gravity energy. A volume of water V existing at a certain altitude h above the sea corresponds in effect to a potential energy :