Pumped hydraulic energy storage :STEP

Energy storage by pumping was developed to optimize the operation of large power plants in interconnected grids, in the face of variable electricity demand over time (peak/off-peak hours). At the start of the 21st century, this type of energy storage is the subject of a major new wave of development, linked to the growth of renewable energies.

Pumped storage is the most economical means of generating electricity, provided that suitable sites are available: a reservoir can be built or used at high altitude, which can be connected by pipes and galleries to another body of water at a lower level. The key components are turbines and pumps, or turbine-pumps combining both functions. The latest pump-turbines feature variable speed drives for greater operating flexibility in both pumping and turbining. Several examples of high-power installations are given in this article.

Pumped storage is currently the most widely used stationary energy storage method in the world, with global installed capacity of pumped storage plants already at around 140,000 MW in 2010. In France, there are 6 STEP pumped storage stations (stations de transfert d'énergie par pompage).

In addition to its primary use, which is to "store" electricity for use at times when it is needed, pumped energy storage contributes to a host of services for power grids and systems, and provides backup in the event of grid problems. It is currently undergoing rapid development to help compensate for the intermittent nature of renewable solar and wind energy, not only in Europe, but also in other countries such as China and the United States.