ESLA RIVER BASIN: OUR HYDROELECTRIC POWER PLANTS

Ricobayo, a key dam on the Esla, part of Spain's largest hydroelectric complex

Iberdrola España has a presence in two hydroelectric plants and two mini-hydroelectric plants in the basin of the river Esla, the largest tributary of the Duero. The prominent Ricobayo hydro complex, together with the smaller Santa Eulalia and El Hoyo plants, have a combined installed capacity of 341,77 MW. They all form part of the Duero System: the largest hydroelectric complex in Spain.

HYDROELECTRIC PLANTS IN THE ESLA BASIN

Number of hydroelectric plants

Total installed capacity

341,77 MW

Number of households benefited

238.000

Year of first installation

1935

The Esla is one of the most important rivers in northwest Spain. It rises in the Cantabrian Mountain Range, crosses the provinces of León and Zamora from north to south, flows into the Duero river - being its largest tributary, carrying more water than the Duero itself at its mouth -, has a length of 286 km and drains a catchment area of 16,163 km². Iberdrola España uses this water resource through the reservoirs of the Esla, its dams and power stations, distributed along the course of the river through Zamora. The Ricobayo hydroelectric complex is the most important, as well as the oldest, and we also have the Santa Eulalia and El Hoyo mini-power stations, with a combined installed capacity of 341,77 MW. The energy generated by this set of infrastructures directly benefits approximately 238,000 homes in Spain.

Esla Reservoirs

The great water potential of the river Esla makes it an ideal scenario for the creation of reservoirs and waterfalls and dams, which help to regulate the flow and optimise the uses of water, including its use for the generation of hydroelectric energy: cheap, clean and renewable. Iberdrola is present at the Ricobayo reservoir.

Ricobayo Reservoir

The Ricobayo Reservoir is located on the lower course of the Esla, near the Zamora town of Ricobayo de Alba, in the municipality of Muelas del Pan. This reservoir, whose construction began in 1929 and was completed in 1933, is considered one of the largest in Europe with a total capacity of 1,145 hm³ of water and a surface area of 5,725 hectares (ha), according to data obtained from Embalses.net.

The reservoir supplies the local population and is used for recreational activities such as sailing, fishing and bathing. In addition, Ricobayo has an impressive gravity dam, with a height of almost 100 metres, one of the most impressive engineering works of its kind to be seen in Europe.

Hydroelectric Power Plants in the Esla River Basinla Reservoirs

Iberdrola España has a presence in four hydroelectric plants located in the Esla basin, taking advantage of the waterfalls of the Ricobayo, Santa Eulalia and El Hoyo dams. Our commitment to sustainability and the promotion of renewable energies is reflected in this commitment to hydroelectric generation on the Esla River as it flows through Zamora: a clean, renewable and environmentally safe source, with which we contribute to the reduction of greenhouse gas emissions and compliance with the energy transition objectives.

The construction, management and maintenance of the Ricobayo I, Ricobayo II, Santa Eulalia and El Hoyo power plants have a major positive impact on the area: generating local jobs, stimulating the economy, strengthening infrastructure and promoting sustainable development in the community.

Ricobayo I and Ricobayo II

With almost a century of history, the Ricobayo complex consists of two hydroelectric power stations: one at the foot of the dam, Ricobayo I, with a waterfall of 83 metres, and one underground, Ricobayo II, with a waterfall of 75 metres. Commissioned in 1935 and 1999, respectively, both plants were pioneers in electricity production in Europe and form part of the hydroelectric system known as Saltos del Duero, the largest Spanish hydroelectric complex.

The installed capacity at Ricobayo I is 174,53 MW and at Ricobayo II 153,56 MW, giving a total installed capacity of 328,09 MW.

The hydroelectric power station of Ricobayo, located in the Esla basin, key to the recovery of the blackout in Spain

The hydroelectric power station of Ricobayo played a key role in restoring electricity supply in Spain following the blackout on 28th April 2025. Situated in the Esla basin, its unique large-scale storage system through pumped hydro and operational flexibility enabled the rapid restoration of power to the most affected areas, particularly for the replenishment of the electricity grid that connects with the French energy system.

This was only made possible because this hydroelectric power station has an autonomous start-up system — known as "black start" — which allows it to restart without any external support. This process can be carried out through a battery system, autonomous generators, or by using the water flow from its own dams.

Thus, in situations where external power is disconnected, these facilities are capable of producing the initial energy needed to progressively restart other generation plants, in a coordinated manner with the protocols established with the state operator, Red Eléctrica Española (REE). In this way, without the hydroelectric energy produced by the Ricobayo power station, the restoration of electricity supply on 28th April would not have been possible within the same timeframe.

Santa Eulalia

The Santa Eulalia gravity dam, located in Santa Eulalia de Tábara, at the tail of the Ricobayo reservoir, has an 8.3-metre waterfall and an external mini-hydroelectric power station of the same name, which has been in service since 2005. The installed capacity of the Santa Eulalia plant is 9,74 MW.

El Hoyo

The El Hoyo dam, a masonry dam with a height of almost 4 metres, located in the municipality of Breto in the province of Zamora, has had an external mini-hydroelectric power station of the same name in operation since 1995. The installed capacity of the El Hoyo plant is 3,94 MW.