On April 28, 2025, Spain and Portugal experienced one of the most significant blackouts in their recent history. Within seconds, the power system of the Iberian Peninsula collapsed, leaving millions of people without electricity, water, and in complete darkness. The Ministries of the Interior declared a state of emergency, and the consequences were visible everywhere: halted metro systems in Madrid, Barcelona, Lisbon, and Porto, grounded flights at major airports, traffic chaos due to inoperative traffic lights, cancelled medical procedures, and disrupted water supply.
Although most services were restored the following day, one critical question remained: how did such a widespread and simultaneous collapse occur in two technically advanced and interconnected systems? And more importantly – what does this incident reveal about the structure of the energy mix and the future of nuclear energy in Spain?
The Structure of Spain’s Energy System
At the end of 2024, Spain’s total net installed generation capacity reached nearly 129,000 MW. Of that, renewable energy sources accounted for 66 percent of the total capacity. Among them, wind power (23.2 percent), solar power (18.6 percent), and hydropower (13.3 percent) dominate, according to data from the grid operator Red Eléctrica. This mix enables a significant reduction in emissions, but also brings new challenges—particularly regarding grid stability.
Renewable sources lack what is known as inertia—the physical resistance to changes in frequency within the power grid. Unlike conventional power plants with large rotating turbines, wind and solar plants rely on inverters that cannot absorb sudden oscillations, making the grid more vulnerable to disturbances. As these plants dropped offline, the next in line were the nuclear units.
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The Role of Nuclear Energy in the Energy Mix
In this context, the debate on the role of nuclear energy is resurfacing. Spain operates seven nuclear reactors, which together produced nearly 20 percent of the country’s total electricity in 2024.
Due to their large rotating turbines, nuclear power plants contribute to grid stability by maintaining constant frequency and providing so-called baseload power. During the incident, four reactors were operational and shut down automatically when the grid collapsed, in accordance with safety protocols. The other three reactors were offline because Red Eléctrica had requested their temporary shutdown due to an oversupply from renewable sources. This decision is now under scrutiny, as the lack of rotating inertia from nuclear and other conventional sources is considered one of the contributing factors to the instability, according to World Nuclear News.
Back in 2019, Spain adopted a plan to gradually phase out all nuclear reactors by 2035. According to that roadmap, four reactors are scheduled to close by the end of 2030, with the remaining three to follow within the next five years. However, the recent events may change the outlook.
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