What is pumped storage?

Pumped storage is a way of storing energy by turning electrical energy into stored (or potential) energy and back again to electrical energy. The system uses electricity to pump water from a lower reservoir to a higher reservoir. This pumping happens at times when there is more energy being produced on the grid network than is needed. This energy is stored until it is required, when the water is allowed to flow back through a hydro-turbine, generating electricity to meet sudden or predicted spikes in consumer demand.

This cycle of pumping and generating repeats on a daily basis as required. Pumped storage utilises excess generated electricity when consumer demand is low and generates electricity when demand requires.
It can be used at very short notice to provide what the Directors consider to be a flexible and valuable balancing service to the relevant distribution network operator.

A typical conventional pumped storage hydro power plant consists of four components:

Water reservoirs: normally two interconnected water reservoirs.
Water piping: tunnels that allow moving water from one reservoir to another.
Powerhouse: facility with one or more pump/turbine and motor/generator assemblies that allow pumping water into the upper reservoir at off-peak hours, and discharging water into the lower reservoir.
Grid connection: power transmission lines to move the generated power from the plant into the grid.

Components are often housed underground.