SOCOTEC towards Spain's energy future: Reversible Hydroelectric Power Plants

Among the different variants of this technology, reversible hydropower plants represent a key innovation that promises a crucial role in the future of energy supply. In this article, we will explore what a reversible hydroelectric power plant is, highlight some of the most important in Spain and discuss the relevance of adapting to this model those traditional hydroelectric plants whose configuration allows it, taking into account the opportunities provided by state aid through the Next Generation EU funds  and highlighting the experience of SOCOTEC's team of engineering experts in this field.

What kind of energy transformation do hydropower plants perform?

Hydroelectric power plants perform a transformation from hydropower to electric power. This process is carried out by using the potential energy of water stored at height, which when it falls under the effect of gravity and passes through the turbines, is converted into mechanical energy. The turbines are connected to a generator that transforms this mechanical energy into electrical energy, which can be distributed to the power grid.

In the case of reversible hydroelectric power plants, this process can be reversed. In other words, at times of low electricity demand, these plants use surplus electricity to pump water from a lower reservoir to a higher one, storing it and thus increasing its potential energy. In this way, the plant acts as a huge energy storage system, which can be released again in the form of electricity when demand requires it.

What is a pumped hydroelectric power plant?

A reversible hydropower plant is an infrastructure that can not only generate electricity from water energy, but can also store it and, when necessary, return it to the system. Reversible power plants always have two reservoirs, one downstream and the other upstream. The water available in the upper reservoir is nothing more than a store of energy, which can be used when it is convenient. Turbopumps make it possible to lift water from the lower reservoir when the demand for electricity is low and the surplus energy allows it. Subsequently, during peak demand, water from the upper reservoir is turbinated to the lower reservoir, thereby generating energy.

In addition, this type of power plant provides the grid with the capacity to regulate frequency and voltage, as well as being able to compensate for reactive energy, so in systems in which renewable generation is predominant, they are essential. Operationally, they provide great flexibility, since it can reach full load in a few minutes, and can also quickly switch from turbine to pumping.

What are the main reversible hydroelectric power plants in Spain today?

Spain has a rich tradition in the use of hydroelectric energy, and also has a fleet of reversible power plants that, between pure and mixed, add up to just over 6 GW of installed power. More than 20 reversible power plant projects are currently being processed, with a total capacity of more than 19 GW.

Among the most prominent are:

1. Cortes-La Muela Hydroelectric Power Plant (Valencia): This plant located on the Júcar River, is currently the largest reversible hydroelectric plant in Europe, with a turbine capacity of 1,762 MW and 1,293 MW of pumping capacity. Its ability to efficiently store and release energy is essential for maintaining the stability of the electrical system. 

2. Estany Gento-Sallente Hydroelectric Power Plant (Catalonia): Reversible pure pumped power plant, located on the Flamisell River, in the Catalan Pyrenees. It has a generating capacity of 468 MW and a pumping capacity of 400 MW. It was put into operation in 1985, being a technological milestone at the time.  

3. Villarino Hydroelectric Power Plant (Salamanca): Inaugurated in 1970, this mixed reversible power plant has six generator sets with a total capacity of 810 MW, with a reservoir capacity of 2,475 Hm³. The Almendra dam, a key element of this infrastructure, is the highest in Spain, at 202 m high.  

The Importance of Adapting Hydropower Plants to Reversible Models

The transition to a more sustainable energy system requires innovative solutions. The construction of new reversibles and the adaptation of traditional hydropower plants to reversible models is essential for several reasons:

In terms of efficiency, reversible hydropower plants stand out for their energy storage capacity. In situations of low electricity demand, these plants can use the surplus energy to pump water from a lower reservoir to an upper one, storing it for later use. This pumped storage process can achieve energy efficiency between 70% and 80%. 

Why will reversible hydroelectric power plants become the energy vector of the future?

In the coming years, an increase in the implementation and development of Reversible Hydroelectric Power Plants (CHR) is expected. As we approach the European Union's 2050 goal of a 100% renewable electricity grid, CHRs will play a crucial role due to their high energy storage capacity.

The need for an electricity system capable of managing non-dispatchable renewable sources (such as wind, sun or water) makes reversible hydropower plants a viable and sustainable solution. Especially those with pure pumping are expected to be key to the operation of an electricity system based on renewable production.

The additional renewable energy storage potential in hydropower plants is an opportunity for CHR investment and development. "Alternative" energies have overtaken thermal sources, becoming the most installed source of electricity in the world.  Operating on the basis of two reservoirs at different levels, these plants are a sleeping giant in today's energy landscape. We'll find out how they work, their advantages and why they could be key to Spain's energy future.

What is a reversible hydroelectric power plant and how does it work?

1. Energy Flexibility: Reversible hydroelectric power plants provide unprecedented flexibility to the electricity system, allowing energy to be stored when demand is low and released when it is high and collaborating in the stability of the grid based on its ability to regulate voltage, frequency and reactive energy, essential to compensate for the fluctuations that other intermittent renewable sources have.  like solar and wind, they generate. 
2. Large-Scale Storage: Today, the reservoir of a reversible power plant is the most efficient and sustainable battery that exists. It does not lose capacity, is not a potentially polluting element and does not require the extraction of scarce minerals. Nowadays, innovative configurations are being proposed that facilitate the sustainability of these facilities, such as pumping with seawater in coastal areas where the orography allows it, or storage outside rivers, with upper reservoirs outside and lower underground reservoirs, so that the design is independent of the topography.  or even the use of old open-pit mines or underground mines as reservoirs, and finally their hybridization with wind and photovoltaics.  
3. Emission reduction: By enabling more efficient energy management, reversible power plants become a key element in reducing the need for carbon-linked energy sources, which translates into a significant reduction in greenhouse gas emissions, capable of enabling ambitious decarbonization targets.  

Regulatory framework for the conversion of hydroelectric power plants to reversible power plants:

The regulatory framework for the conversion of hydroelectric power plants to reversible power plants is a key aspect to facilitate this transition. Within the framework of Order TED/807/2023, the regulatory bases for the granting of aid to innovative energy storage projects within the framework of  the Recovery, Transformation and Resilience Plan, financed by the European Union, are approved. This includes the conversion of hydropower plants to reversible models.

In addition to financial support, it is crucial to take into account regulatory and normative aspects of each country. For example, consideration should be given to countries' regulations regarding the potential development of reversible hydroelectric power plants and the possible identification of areas of opportunity.

It is crucial to address and resolve barriers to hydropower plant modernization, which may include outdated regulatory frameworks, inadequate institutional capacity, hydropower concession terms and timing, and conflicts between competing uses of water resources.

SOCOTEC's Experience in Reversible Hydroelectric Power Plants

SOCOTEC has proven to be a leader in the field of reversible hydropower plant engineering. Their team of experts combines state-of-the-art technical knowledge with a deep understanding of the specific needs of each project. Its contribution to projects such as the Cortes-La Muela Hydroelectric Power Plant, or the intervention of our experts in the design of other reversible plants, such as Matalavilla or Girabolhos, is a testament to its ability to carry out innovative and sustainable transformations in the energy industry.

Reversible hydropower plants represent a key piece in the transition to a decarbonized energy future. Adapting existing facilities to this model, or building new plants, is a key strategy, supported by Next Generation EU state aid. With engineering leaders such as SOCOTEC at the forefront, Spain is well positioned to lead this movement towards cleaner and more efficient energy.