Aldeadávila, the spark that started Spain

On the natural border between Spain and Portugal, drawn by the Arribes del Duero River in Salamanca, stands one of Spain's most impressive civil infrastructure projects: the Aldeadávila hydroelectric power plant, which takes advantage of one of the largest natural slopes of the Duero River. At the top, a 386-hectare dam with a capacity to store 114 hectometres of water. Two plants, Aldeadávila I (1962) and Aldeadávila II (1986), and 140 metres below, a second dam, Saucelle.

In between, a complex network of tunnels dug into granite reminiscent of the most legendary James Bond film sets of the 1970s, housing the tool that was key to Spain's electricity recovery after the blackout of April 28.

“Aldeadávila II is a black-start power plant. Using autonomous batteries and generators or using water from its own reservoirs, it's capable of producing energy even during periods of zero energy, like the one that occurred on April 28. And that's what was done. Voltage was injected into the grid so that Red Eléctrica could begin connecting demand and recover the system,” explains Ramón Delpuy, head of generation for the Duero basin at Iberdrola, the company that owns the Salamanca power plant.

Ninety-nine percent of power plants, whether thermal, gas, nuclear, solar, or wind, require external energy to start up; however, Aldeadávila started up its generators and began supplying the first spark of energy, allowing the gradual reactivation of other plants and substations.

The plant is part of the Douro-France axis, vital to the stability of the national electricity system.

It is the hydroelectric plant with the highest production in Spain. It accounts for 8% of the country's total hydroelectric production and is designed with a power modulation system, making it strategic. At its maximum capacity, it can supply 733,000 homes. It is part of the Duero-France axis, which is strategic for boosting all the system's replacement connections.

In addition to its operational appeal, it also has a visual appeal. It has been the setting for blockbuster films such as Doctor Zhivago , Terminator 6 , the latest Fast & Furious film, and the Spanish film The Cabin , as well as countless commercials. The location of its two turbines, with moving elements weighing over 500 tons, 140 meters beneath the waters of the Duero River inside the granite rock, creates a visual impact similar to that of a great cathedral. But even more astonishing is its versatility to act as turbines (they drop water from the top and produce electricity) and as pumps (they use excess renewable energy in the grid to pump water up from the lower Saucelle dam), making it one of the largest natural energy batteries in Spain.

On April 28, while most Spaniards were torn between astonishment, disbelief, and speculation about the blackout, in Aldeadávila there wasn't even a moment of doubt.

The 22 workers who work at this plant every day were much more familiar with the situation than the rest of Spain. The so-called zero-start drills are common. They had already experienced the last one last December. “We all knew where we had to go and what to do at each moment,” says Clodoaldo Rodríguez, head of the plant, acknowledging that the real situation was slightly different. “It was inevitable to feel some nerves in our stomachs, although they passed as soon as we started applying the protocol,” Rodriguez explains.

The technicians executed the start-up protocol after years of planned drills, the last one in December

From pumping to turbine operation in just minutes, Rodríguez and his team were at the foot of the dam for the next 24 hours, ensuring that power was injected into the Spanish electricity system. "That's our mission. To make the outlets work. Then REE is responsible for gradually connecting demand to ensure stability," he explains. In this way, "islands of light" are created, which gradually connect until normality is restored to the national electricity system.

On April 28, that capacity was combined with the help of interconnections with France and Morocco. Other hydroelectric plants with zero start-up, such as the one Endesa has in Catalonia, also started up, but in this case, the protocol mandates another priority objective: providing energy and ensuring the safety of other critical infrastructures such as nuclear plants.