Pumped storage is the oldest kind of large-scale energy storage and works on a very simple principle - two reservoirs at different altitudes are required and when the water is released from the upper reservoir to the lower reservoir, energy is created by the downflow, which is directed through a turbine and generator to create electricity. The water is then pumped back to the upper reservoir.
Pumped storage hydropower provides a dynamic response and offers critical back-up during periods of excess demand by maintaining grid stability.
However, pumped storage is a net user of power - but used in conjunction with other forms of renewable generation to pump the water back up to the top of the reservoir, this can help to resolve intermittency issues associated with other renewable technologies.
Despite current electricity market mechanisms challenges, such as the absence of reward for capacity, which has historically led to some mothballing, the role of pumped staorge is becoming more critical looking forward.