Pumped Storage Hydropower
The process is simple:
Pumped storage stores energy by using water as the storage medium, transferring it between two reservoirs located at different elevations. The system stores energy by pumping water from a lower reservoir to an upper reservoir during periods of surplus electricity generation. When electricity demand increases, the stored water is released through hydraulic turbines to generate electricity.
Depending on the size of the reservoirs, PSH can provide electricity for several hours and, in some cases, multiple days.
Main configurations:
Open-loop pumped storage: In an open-loop system, at least one reservoir is connected to a naturally flowing water body, such as a river or lake. During charging, electricity powers pumps that transfer water from the lower reservoir to the upper reservoir. During discharge, the water flows back through hydraulic turbines to generate electricity.
Closed-loop pumped storage: A closed-loop system uses two reservoirs that are not continuously connected to a naturally flowing water body. Water circulates between the upper and lower reservoirs as the facility charges and discharges. After the reservoirs have been filled, the plant mainly reuses the same water, although additional water may be required to compensate for evaporation and other losses. Closed-loop systems may offer greater flexibility in site selection and potentially reduce some impacts on rivers, but they still require suitable terrain, sufficient elevation difference and careful environmental assessment.
Binary configuration with reversible pump-turbines: one reversible hydraulic machine performs both functions. During charging, the pump-turbine operates as a pump and moves water to the upper reservoir. During discharge, the direction of operation is reversed and the same machine acts as a turbine, converting the water’s gravitational potential energy into mechanical power.
Ternary configuration with separate pumps and turbines: A ternary unit combines a separate pump, a separate turbine and a motor-generator on the same shaft line, generally with a hydraulic coupling between the pump and turbine. Because pumping and generating are carried out by different hydraulic machines, each machine can be optimised for its own operating mode.
Why is PSH important to support the Energy Transition?
Pumped Storage Hydropower is the most established form of large-scale electricity storage in Europe and currently provides the vast majority of the EU’s energy storage capacity.
Pumped Storage Hydropower offers:
- Large power and energy storage capacities.
- Storage durations ranging from several hours to longer periods, depending on reservoir size.
- Fast and flexible electricity generation.
- Frequency regulation, voltage support, operating reserves and other grid-stability services.
- Potential applications in renewable energy shifting, balancing, congestion management and security of supply.