Massive power outage in Spain and Portugal: surge at the center of the investigation

"This is the most serious power outage Europe has experienced in the last 20 years, and most importantly, it is the first of its kind" linked to a phenomenon of "cascading surges," said Damian Cortinas, chairman of the board of ENTSO-E, the European network of electricity transmission system operators, during the presentation to the press of this preliminary report on Friday.

"This has never happened before in Europe, we are sure of it," he said in Brussels. And probably "in the whole world," he added.

Electrical voltage can be compared to the "pressure" of water in a pipe: when applied to electricity, it sets the electrons in motion. In the event of a "power surge," the electrical system must protect itself.

The blackout in question occurred on April 28 at 12:33 PM Spanish time and affected the entire peninsula. It caused chaos in both Portugal and Spain, where residents were left without power, internet, and mobile phone service.

This "factual" report, conducted by a panel of 45 European experts mandated to carry out technical investigations and describing the chronological sequence that led to the widespread and uncontrolled breakdown, does not yet provide the primary causes of the first incidents.

The expert group will release its final report in the first quarter of 2026, which "will include a detailed root cause analysis and recommendations on how to prevent similar events in the European electricity system in the future," according to the press release.

Mitigation measures

The preparation of this progress report relied on a colossal amount of data. It took "a long time" to gather them, particularly because some "third parties" "had not given their consent to the Spanish transmission system operator to transmit the data," stressed Klaus Kaschnitz, the number two on the expert panel. Some data remains missing.

According to the report, the half-hour preceding the outage was marked by two episodes of "power, voltage and frequency fluctuations" that mainly affected the Spanish and Portuguese electrical systems.

The network managers then "took several mitigating measures, such as reducing exports from Spain to France" which "helped limit fluctuations" but "led to an increase in voltage in the Iberian electricity system."

This phenomenon preceded a series of production losses from wind and solar installations, followed by chain disconnections of several power generation centers. "Without adequate compensation from other system resources," these disconnections in turn led to voltage surges, the report states.

But it remains to be established why the mechanisms implemented to mitigate this surge did not work.

The supposed instability of renewable energy sources had been singled out by nuclear power supporters. Beatriz Corredor, president of the Spanish electricity grid operator REE, had instead pointed to the role of certain producers of "conventional energy," from gas, nuclear, or hydroelectric power plants, with voltage control thresholds set too low.

In June, the Spanish Minister for Ecological Transition, Sara Aagesen, also questioned the role of the REE manager, explaining that "the system did not have sufficient capacity to control the voltage" on that day.

The ENTSO-E report confirms that the widespread blackout "was not caused by an over-reliance on renewable energy, but by a series of cascading events aggravated by several failures in the system," commented the think tank Ember.