Pumped-storage hydropower plants

Do you know what pumped-storage hydropower stations are used for?

Engenharia Water Hydroelectric power Energy storage

Their main purpose is to store water during off-peak periods, using it to generate energy during peak consumption periods. The largest in Europe is La Muela II, built by Iberdrola on the River Júcar, in the municipality of Cortes de Pallás, Valencia. The company has also inaugurated the ambitious project on the River Támega in northern Portugal.

La Muela II pumped-storage hydropower station.

La Muela II pumped-storage hydropower station.

Hydroelectric pumping technology is the most efficient system that allows to store energy in a large-scale today. It is more cost-effective and provides the electrical system with stability, safety and sustainability, whilst generating large amounts of energy with fast response times without resulting in any type of emission into the atmosphere.

The company is leader in energy storage with a capacity of 4 GW installed using pump technology, the most efficient energy storage method currently available, as it does not release any polluting emissions into the atmosphere and performs much better than the best batteries on the market.

At the end of 2022, Iberdrola reached a total of 101.2 gigawatts per hour (GWh) of storage capacity, exceeding its forecast by more than 10% and with the objective of expanding to 102 GWh by 2025.

How it works a pumped-storage hydropower station

reservoir or river
Intake and
Generator Unit
Surge chamber
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  • 2
  • 3
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  • 5
  • 6
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  • 9
  • 10
  • 11

This kind of electric plant relies on two reservoirs at different altitudes that allow water to be stored when demand is low and then used to generate energy during peak consumption times in order to meet overall electricity demand.

During off-peak hours, typically weekday and weekend nights, excess generation capacity is used — which also has a lower market cost — to pump water from the lower level (1) reservoir to the upper one by means of a hydraulic pump that propels the water through a penstock (2) and conduction tunnel structure. The upper reservoir (3) therefore acts as a storage facility.

During peak hours, i.e. daylight hours, the pumping station functions as a conventional hydroelectric plant: water accumulated in the upper reservoir closed by a dam (4) is sent to the lower reservoir through the conduction tunnel (5). In this step the water passes through the penstock, where it acquires kinetic energy which is transformed into rotational mechanical energy in the hydraulic turbine (6). This is then turned into medium voltage, high intensity electricity in the generator (7). In some cases, a surge tank (8) is built to regulate the water pressure between the intake and discharge tunnels.

The next step sees the transformers (9) transmit the electricity produced in the plant, for consumption by the homes and industries that form part of the grid (10) via high voltage transmission lines.

Once the electricity is generated the water falls through the drainage channel (11) to the lower reservoir, where it is stored again.

Pumped hydroelectric plants thereby bring efficient energy storage, offer a long-term solution and facilitate the integration of renewable energies into the system and bring high returns.

Great examples of pumping hydropowers

La Muela II is the largest pumped-storage hydropower plant in Europe, located on the Cortes de Pallàs reservoir on the right bank of the Júcar river.

Its installed capacity exceeds 880 megawatts (MW) –enough to meet the electricity consumption of nearly 200,000 households– thus doubling the generation capacity of the Cortes-La Muela complex to more than 1,800 MW – equivalent to the annual demand of almost 400,000 families—. The plant features a hall with four groups of reversible turbines, allowing it to take advantage of the 500 metre altitude difference between the artificial La Muela dam and the Cortes de Pallás reservoir to produce electricity.

Another of the Spanish group's major pumping initiatives is the Tâmega hydroelectric complex, whose complex is made up of three new plants on the river of the same name, a tributary of the Douro, located in northern Portugal, near Oporto, and already has the first of the turbines connected to the power grid. The three power plants have a total installed capacity of 1,158 MW, representing an increase of 6 % in the total installed electrical power in the country. The complex is capable of producing 1,766 GWh per year, enough to meet the energy needs of the neighbouring towns and the cities of Braga and Guimarães (440,000 homes). In the same way, it contributes almost 900 MW of pumping capacity to the portugueese electric system, wich implies an increase of 40 % with regard to pumping megawatts that nowadays are provided by the country.