Entsoe presents final report for Iberia power outage

24.03.2026

Source: E & M powernews

The cause of the widespread power outage on the Iberian Peninsula in 2025 was not an overload due to too much PV feed-in, but a lack of voltage management.

In a 470-page report, the Association of European Transmission System Operators ("Entso-E") has analyzed the power blackout in Spain and Portugal on April 28, 2025. According to the report, the blackout, which took several hours to resolve, was caused by a combination of several factors.

The report was compiled by 45 experts from European transmission system operators, regulatory authorities and regional coordination centers. The committee was set up by Entsoe to investigate the worst power grid failure in Europe for more than 20 years.

The starting point was an uncontrolled rise in voltage from 12:32 p.m., which triggered a series of shutdowns in Spain, according to the report. As a result, the Iberian grids lost synchronization with the continental European interconnected system.

Cascade of shutdowns

Two oscillation phases had already occurred in the grid before the event, first a localized oscillation at 0.63 Hertz and then a large-scale inter-area oscillation at 0.2 Hertz. However, measures to dampen these oscillations further increased the voltage in the system. A number of conventional and renewable power plants then shut down during the critical time window. This further increased the voltage in the grid, triggered further protective mechanisms and led to a cascade of further shutdowns.

Within a few seconds, the grid collapsed and the systems disconnected from the European grid. According to the report, although the automatic system protection measures worked as intended, they were unable to prevent the collapse.

The effects of the inadequate voltage control in the Spanish power grid were exacerbated by a Spanish peculiarity: the voltage range of the 400 kV grid, at up to 435 kV, was in a significantly wider voltage range than in the rest of Europe. However, generators were already allowed to switch off at 435 or 440 kV. The safety margin between normal operation and shutdown was therefore too small.

Restoring the power supply in Portugal took until 0:22 a.m., i.e. around twelve hours. Spain followed at 4:00 a.m., after almost 16 hours without power supply.

Based on the results of the investigation, the expert panel developed 17 recommendations, including the need for improved voltage regulation, clearer requirements for the provision of reactive power and closer coordination between transmission and distribution system operators.

The full final report "Grid Incident in Spain and Portugal on 28 April 2025. ICS Investigation Expert Panel Final Report" is available on the Entsoe website.

Author: Katia Meyer-Tien