The massive power outage that hit the Iberian Peninsula in April is the first known blackout caused by excessive voltage, the European network of electricity transmission system operators said in a report on Friday [October 3] .
Released ahead of an October 28 legal deadline, the report focused on the power systems’ condition on the day of the outage and the sequence of events, and did not look into what acted as its trigger.
The report, like previous inquiries, pointed to a surge in voltage as the immediate cause of the April 28 outage – Europe’s most significant blackout in more than two decades, which paralyzed cities and stranded people on trains across Portugal and Spain.
Read more: Spain Reveals Details of Chain Reaction That Caused Outage
A final report, due in the first quarter of 2026, will investigate the root causes and steps taken to control voltage in the system.
Missing Data and Unexplained Power Generation Losses
Damian Cortinas, chair of ENTSO-E’s board, said nothing in its findings had indicated a cyber-attack was involved.
He also said that neither Spain’s increasing reliance on renewable energy nor its limited power interconnections with other countries had played a role.
“If there had been double the interconnection capacity, this would not have stopped the blackout, and this would not have accelerated the recovery,” Cortinas told Reuters.
Since the blackout, the Spanish and Portuguese governments have urged the EU to help them develop new power links with other countries, which they say would help their electricity grids respond to disruptions.
The report said the reasons for some initial power generation losses were still unknown and that some power plant operators in Spain said they lacked this data.
“Collecting complete, high-quality data proved very challenging for this investigation,” ENTSO-E said.
Its report follows several others by the Spanish government and power and grid companies. The national energy watchdog and Spanish lawmakers are also conducting separate investigations.
Redeia, owner of grid operator REE, has blamed the blackout on some power plants’ failure to help maintain appropriate voltage, while Spanish utilities blamed what they called poor planning by the Spanish grid operator.
ENTSO-E’s investigation panel includes representatives from Spanish grid operators – a set-up Spanish utilities have criticized.
Cortinas said their expertise was needed for the investigation, and the 45-member panel included representatives from across Europe, ensuring no individual operator had undue influence.
Spanish Energy Minister Sara Aagesen welcomed the report, saying it was fully in line with the findings of a government investigation.
“The report shows that the voltage control systems in the conventional power plants in Portugal operated as expected,” she said. “But this was not the case in Spain.”
Redeia said on Friday that the report confirmed the sequence of events described in its own findings.
Spanish power utility lobby Aelec declined to comment.
(Reporting by Kate Abnett and Pietro Lombardi, editing by Inti Landauro and Tomasz Janowski)
Photograph: People gather outside Atocha train station during a major power outage in Madrid, Monday, April 28, 2025. (AP Photo/Manu Fernandez)
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