Published by Global Banking & Finance Review®
Posted on October 3, 2025
3 min readLast updated: January 21, 2026
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The Iberian Peninsula blackout in April was the first known caused by excessive voltage, affecting Spain and Portugal, with no cyber-attack involved.
By Kate Abnett and Pietro Lombardi
BRUSSELS/MADRID (Reuters) -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.
The report, released ahead of an October 28 legal deadline, 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 probes, 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 paralysed cities and stranded people on trains across Portugal and Spain.
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 neither Spain's increasing reliance on renewable energy nor the country's 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.
After 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 power grids respond to disruptions.
The report said that 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 probes.
Redeia, owner of grid operator REE, has blamed the blackout on some power plants' failure to help maintain appropriate voltage while Spanish utilities blamed the Spanish grid operator's poor planning.
ENTSO-E's investigation panel includes representatives from Spanish grid operators - a set-up Spanish utilities have criticised.
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.
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)
Excessive voltage refers to a voltage level that exceeds the normal operating range, potentially causing damage to electrical systems and leading to power outages.
A power outage is a temporary loss of electrical power in a specific area, which can disrupt services and affect daily activities.
Renewable energy sources are energy sources that are replenished naturally, such as solar, wind, and hydroelectric power, and are considered more sustainable than fossil fuels.
A voltage surge is a sudden increase in voltage that can damage electrical equipment and disrupt power supply systems.
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