In Spain, hydropower has been a key element in the country's industrial and social development for over a century. Harnessing the power of water in complex terrains like the Pyrenees has provided access to manageable and renewable electricity. Today, although other sources such as wind and solar have gained ground, hydroelectric plants continue to play an essential role as a strategic support in the transition to a decarbonized energy system.
Much of the historical success of hydroelectric power lies in pioneering installations like the Seira power plant in the Aragonese Pyrenees. Built over 100 years ago, it was the result of a remarkable technical and human feat: more than 2.000 workers were needed to install its tunnels, dams, and turbines, bringing in components from various countries. The result was a veritable industrial marvel, which even today maintains several of its original turbines in operation and continues to supply electricity to thousands of homes. The plant combines heritage value with innovation , having been modernized in the 1990s and now boasting an installed capacity of 37 MW, with an annual production that can supply 20.000 homes.
In the same region, examples like the Eriste power plant reveal the potential of modern hydroelectric plants: water, stored in high-mountain reservoirs, flows down tunnels to turbines capable of powering an entire medium-sized city. Thanks to automation and remote monitoring from specialized control centers, these facilities can now be started up and regulated in minutes, facilitating a rapid response to the demands of the electrical grid and guaranteeing the stability of supply even in critical situations.
Hydropower allows for the operation of both conventional power plants —which use stored water for turbines—and pumped-storage hydroelectric plants . The latter have gained prominence in new energy plans, as their function as "natural batteries" makes it possible to store surplus renewable electricity (for example, photovoltaic generation during midday overproduction) and release it when demand requires it. This process is achieved by pumping water to an upper reservoir and then generating turbines in the reverse direction.
Currently, Spain has over 6 GW of pumped storage capacity , and dozens of projects are underway to significantly increase this capacity in the coming years, particularly in the Ebro and Miño-Sil river basins. The goal is to bolster storage capacity and reduce dependence on fossil fuels and external energy imports.
Hydropower is important not only for the volume of energy it generates, but also for the management capacity it brings to the electrical grid. Unlike other renewable energy sources dependent on weather, hydroelectric plants can adjust their production according to demand, helping to maintain the stability and security of the grid. Furthermore, these plants help regulate river flows, facilitate irrigation and water supply, and minimize environmental impact because much of their infrastructure—such as pipelines and power plants—is built underground.
Another key aspect is the technological modernization of the infrastructure. From turbine replacement and complete automation of operations to the incorporation of advanced monitoring systems—including drones and predictive software—technology has improved the efficiency, safety, and oversight of dams and equipment. Continuous monitoring allows for the detection of anomalies and optimizes maintenance, extending the lifespan of the facilities and preventing more serious incidents.
The role of hydroelectric power plants was particularly highlighted during the major blackout that affected Spain and Portugal. Thanks to their autonomous start-up systems ('black start'), it was possible to quickly restore power to many areas, demonstrating their strategic importance in emergencies. The very process of restoring power after a blackout requires systems capable of operating without external support, and hydroelectric plants fulfill this role effectively, facilitating the gradual reconnection of the national electricity grid.
Major Spanish electricity companies , such as Endesa and Iberdrola, are reinforcing their commitment to traditional hydropower and the development of new pumped storage facilities, recognizing the need for flexible energy storage and the feasibility of transforming the Iberian Peninsula into a "large hydroelectric battery." These investments are accompanied by environmental impact studies that aim to minimize visual and ecological impacts, thanks to the underground design of many installations and the reuse of existing reservoirs.
The role of hydroelectric power plants remains central to Spain's current energy mix, and their contribution is expected to be even more crucial in the future. Capable of responding quickly and efficiently to demand, facilitating the integration of other renewable energy sources, and providing security and autonomy to the system, hydropower—in both its conventional and pumped-storage versions—is proving to be an irreplaceable resource in Spain's energy mix and a guarantee for the energy transition and resilience in the face of crises.