What Caused the Massive Blackout That Left Spain and Portugal in the Dark?

The massive blackout that plunged much of Spain and Portugal into darkness—and briefly affected southern France—remains a mystery. However, authorities have ruled out a cyberattack.

Eduardo Prieto, Chief Operating Officer of Red Eléctrica, confirmed that "there was no intrusion into the control systems" to suggest a cyberattack. His statement echoed that of Portuguese Prime Minister Luís Montenegro.

Still, the exact cause has yet to be determined.

Thousands of people were stranded at train and bus stations on Monday, April 28, when the power outage occurred. Red Eléctrica has described the data released so far as preliminary and stated that final conclusions are still in progress.

Spanish Prime Minister Pedro Sánchez said a thorough investigation is underway and emphasized, “This must never happen again.”

Was Renewable Energy to Blame fot the Blackout?

Sánchez explained that within seconds, the power system lost 15 gigawatts of electricity, which accounted for 60% of the demand at that time.

According to Red Eléctrica, two nearly simultaneous disconnections were detected in the southwest of the country, a region with significant solar power generation. In situations like this, energy companies may disconnect their systems if they detect imbalances between supply and demand to prevent damage.

However, Sánchez ruled out the idea that the blackout was caused by excess renewable energy. He also stated that electricity demand at the time was low and there were no coverage failures.

Europe’s power grid frequency is 50 Hz, and any significant deviation can lead to disruptions. If multiple operators disconnect their systems in quick succession after detecting imbalances, it can lead to a cascading blackout.

Hannah Christensen, from the Department of Physics at the University of Oxford, explained that operators typically use accurate short-term weather forecasting to predict surges in wind or solar power generation—making this situation surprising.

Keith Bell, a researcher at the University of Strathclyde in Scotland, added that power systems are designed to handle the variability of renewable sources. “Spain has extensive experience with wind and solar energy,” he said. “All types of systems can fail: renewable, fossil-fuel-based, or nuclear. Sometimes, multiple failures align—like the Swiss cheese model.”

Did the Connection With France Play a Role?

Red Eléctrica also pointed to a possible disruption in the electric interconnection between Spain and France as one of the contributing factors.

Spain is connected to France via a high-voltage direct current (HVDC) line that was commissioned seven years ago. While this is a proven and robust technology, the Iberian Peninsula is often referred to as an "electric island" due to its limited connections to mainland Europe—making it more vulnerable to disruptions.

Sánchez highlighted that the power supply was restored thanks to support from interconnections with France and Morocco, along with gas and hydroelectric energy reserves.

An Unusual Atmospheric Phenomenon?

Initial speculation suggested the blackout may have been triggered by an extreme atmospheric event. According to an early report attributed to the Portuguese grid operator REN, large temperature swings in inland Spain allegedly caused vibrations in very high-voltage lines—a phenomenon known as "induced atmospheric vibration."

These oscillations could have led to synchronization issues within the interconnected European grid.

However, REN denied issuing that report. Its spokesperson, Bruno Silva, told AFP on Tuesday that the grid operator “did not release such a statement,” without providing further details.