Spain and Portugal were plunged into darkness on April 28 in what experts now call Europe’s worst power blackout in two decades. The cause wasn’t wind or solar energy, as some feared, but a rare “surge cascade” — a runaway chain reaction of rising voltage that overwhelmed the Iberian grid in seconds.
The findings were published by the European Network of Transmission System Operators for Electricity (Entso-E), which represents grid operators across Europe. Its first report describes the blackout as “a unique event in the world” and the first time such a cascading surge has ever been recorded on the continent.
“This has never happened before in Europe,” said Entso-E president Damián Cortinas. “A total blackout in two countries has huge consequences for citizens and society. We must understand it and make sure it never happens again.”
Renewables Not to Blame
The report is clear: renewable generation was not the culprit. Instead, the crisis exposed the need for all types of power — including solar and wind — to provide voltage control, the basic ability to keep the grid’s “electrical pressure” stable.
“The problem is not that there were renewables, but that we need generation with voltage control,” Cortinas said. “The good news is that it can be done, just as with traditional plants.”
Voltage imbalances are a classic cause of blackouts, usually because of sudden drops. This time, however, voltage spiked. Several renewable units disconnected automatically, interconnections with Morocco and France shut down, and defense systems failed to contain the surge.
A Chain Reaction in Seconds
The morning of April 28 looked normal enough: renewable generation was rising, prices were falling, and Spain was exporting a hefty 5 gigawatts of electricity. But by mid-morning, the system showed signs of strain.
At 12:03 p.m., the grid came under stress. Operators tried to ease the pressure by cutting exports to France and reconfiguring power flows. The tweaks calmed fluctuations but left the Iberian system with dangerously high voltage.
At 12:32 p.m., the collapse began:
- 12:32:00 – 208 megawatts of wind and solar went offline, along with 317 MW of rooftop solar demand.
- 12:32:57 – A transformer in Granada tripped, cutting supply to solar and wind plants. Seconds later, 725 MW of solar power disappeared in Badajoz.
- Moments later – Another 950 MW of wind generation dropped out in Segovia, Huelva, Seville, and Cáceres.
In just 20 seconds, 2.5 gigawatts of renewable power vanished. Much of it had been providing “reactive power” to help keep voltage in check. Without it, voltage surged uncontrollably, the grid lost synchronization, and automatic protections could not save the system.
Five seconds later, Spain and Portugal went dark.
Portugal restored its grid by 12:22 a.m. the next day; Spain followed at around 4:00 a.m.
No Finger-Pointing — Yet
Entso-E insists its role is to explain, not to assign blame. Liability questions, it says, belong to national authorities. The investigation involved 45 experts from across Europe and relied heavily on Spain’s transmission operator, Red Eléctrica de España (REE).
REE welcomed the findings, saying they confirm its own analysis. The company stressed that the transmission grid was within safe operating limits and that the first disconnections happened in distribution networks, outside its control.
Still, the analysis was incomplete. While 33 companies agreed to share data, eight refused, limiting the investigation.
What’s Next
This first report is labeled “factual” and focuses on the sequence of events. A final report, with a deeper root-cause analysis and recommendations for how to prevent similar disasters, will be published in early 2026.
For now, the April 28 blackout stands as a warning of how quickly Europe’s electricity system can unravel.
“This was new. This was different,” Cortinas said. “And we must learn from it.”
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