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AGUAYO II

Reversible Pumped-Storage Hydroelectric Power Plant

The AGUAYO II pumping plant expansion project is one of the initiatives set out in the Strategic Plan in our commitment to low-carbon energies, bringing us closer to the goal of 9-10 GW of generation capacity by 2027.

Vista aérea panorámica del embalse de Alsa

The AGUAYO II project consists of the expansion of the current AGUAYO I Pumping Plant, combining greater efficiency in energy generation from renewable sources with an underground installation and without the need to expand existing resevoirs and, therefore, without impact to the environment in line with environmental conservation. 

This project, which is in the processing phase, is expected to be launched by the end of 2030 and together with the large portfolio of services that we have developed in renewable energy, sustainability, and the circular economy, will help us reach our goal of net zero emissions by 2050 in compliance with the Paris Agreement.

Project figures

1.4

GW

of total installed capacity with the foreseen increase of 1 GW.

2,000

GWh/year

of total energy production.

~€900M

investment

representing an important economic boost for the area.

2nd

biggest

hydroelectric power plant in Spain and the 3rd in Europe.

Seal PCI: 1-18 - Electricity Storage

The AGUAYO II project has obtained this seal within the 1st List of Projects of Common Interest and Projects of Mutual Interest, thus demonstrating that its contribution is key for the EU's energy grid.

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Aguayo II, energy to reach everyone
An efficient and viable solution for generating and storing electricity.
Aguayo Hydroelectric Power Plant illustration
Video

How does Aguayo II work?

How would the expansion be?

New underground water pipes and 4 groups of 250-MW reversible turbines would be installed.

In hours of low demand or high renewable production:

  • Surplus electrical energy in the system is used to pump large amounts of water to an upper reservoir, called Mediajo reservoir (upper 10 hm3 reservoir).

At times of high demand or low renewable production:

  • Additional electrical energy is required, water is dropped in the lower reservoir, the Alsa reservoir (lower 22.9 hm3 reservoir), to move the turbines, which generate electricity again.

This differential advantage allows its use within the electricity system to compensate for times when there is excess renewable production, accumulating energy, and times of excess demand, generating energy.

In addition to being a cavern power plant inside a mountain and making the most of existing reservoirs, Aguayo II stands out for its compatibility with the conservation of the environment in other aspects.

The expansion will involve improvements in the surroundings of the power plant during its construction such as:

  • The improvement of paths in the area.
  • The construction of 2 new roads to avoid heavy traffic through the surrounding municipalities.
  • The creation of additional landfills.
  • Compaction of the power transmission line.

As the project progresses, we will bear in mind the importance of conservation and lower environmental impact through:

  • Reforestation of nearby natural areas.
  • Habitat recovery.

Advantages of pumped-storage hydroelectric power plants

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Mature technology and high efficiency

Its pumped hydro storage is extremely effective in converting the kinetic energy of water into electricity.

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High flexibility and availability

It adjusts quickly amidst fluctuating electricity demand or when intermittent renewable energy sources are integrated.

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Long lifespan

They last for several decades reducing the need for frequent investments in new infrastructure, thus amortizing the initial investment over a long period.

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Operational synergies

Leveraging existing infrastructure leads to cost savings, operational efficiencies, greater integration, and operation of the new facility.

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Favorable environmental indicators

It has the lowest impact on the ozone layer, the highest Energy Returned on Energy Invested ratio, the lowest pressure on mineral resources, and one of the lowest water footprints during construction and manufacturing.

Progress of the project

    • Execution of the preliminary study
    • Preparation of feasibility study
    • MayObtaining the Environmental Impact Statement +
    • NovemberAAP submission to public information +
    • Conceptual engineering closure
    • AprilInclusion in the 1st PCI/PMI list +
    • Basic engineering development
    • AugustDissemination of public information on the hydraulic concession +
    • Execution of optimization engineering
    • Detailed engineering completion
    • DecemberEntry into operation
    • Milestones
  • 2010
  • 2012
  • 2020
  • 2021
  • 2022
  • 2024
  • 2025
  • 2026
  • 2027
  • 2030
    • Development phase
    • Construction phase
    • Operation phase
    • Phases

News

Aguayo Hydroelectric Power Plant

Closer to obtaining the hydraulic concession!

On September 25, 2025, the confrontation process was successfully carried out through a visit with the stakeholders, which brings us closer to the objective of achieving the hydraulic concession, an essential aspect for the viability of the project.

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Still have questions about the project?

If you are curious, please contact us through our email. We will be happy to assist you.

Ask us!

Updated as of October 2025.