By Tuesday, officials in both nations reported that power had been almost fully restored. Attention then shifted to investigating how such a far-reaching and unprecedented failure could have occurred.
Solar power accounted for more than 70% of Spain’s energy mix when the cut hit on Monday, with some 59% from solar and 12% more from wind.
Authorities in both countries have yet to give a definitive cause for the outage, though they have they do not suspect a cyber attack.
Even the strongest critics of renewable energy haven’t said that solar panels or wind turbines were directly responsible for taking out the power.
People buy groceries in a store during a shutdown of electricity in Lisbon, Portugal on April 28, 2025 (Photo: Adri Salido/Getty Images)But, the heavy reliance on those sources did make the outage harder to deal with, experts said.
Multiple points of failure
“The cause is not due to a single failure, but to a concatenation of events that led to the blackout,” said Manuel Alcazar Ortega, an electrical engineering professor at the University of Valencia.
In comments shared by the Science Media Centre Spain, he said the country’s high reliance on solar on Monday was one factor, as was its limited connection to the broader energy network in Europe.
Fossil-fuel generators can absorb power surges as movement in their vast, spinning turbines, a capacity renewable systems lack.
Spain and Portugal’s unit together “functions almost like an energy island,” said Alvaro De La Puente Gil, a lecturer in electrical engineering at the University of León.
A subway station in Lisbon, lying in darkness (Photo: Adri Salido/Getty Images)
“This makes it more vulnerable to internal disturbances: if a major failure occurs within the peninsular system, it cannot receive sufficient external support to stabilise itself.”
How to prevent another massive failure?
Ortega, the electrical engineering professor, had two suggestions for reducing the likelihood of another catastrophic power failure.
square SPAIN The biggest questions on Iberia's mass blackout answered by experts
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He also recommended strengthening its connections to France, which would enable the much bigger Europe-wide electricity network to take some strain.
“So if you have renewable energy from Norway, nuclear from France, that can be much better distributed across the whole wider European member countries rather than just consumed locally,” she pointed out.
“It’s really a far more efficient way to share the resources because different countries would have different types of resources. If one country has a problem, you can draw support from other countries.”
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