Photo: Dierk Gut from Pixabay
The European Network of Transmission System Operators for Electricity has published the final report of its expert panel on the April 28, 2025, blackout in continental Spain and Portugal. The report identifies the causes of the blackout and outlines recommendations to strengthen the resilience of Europe’s interconnected electricity system.
The report on the grid incident in Spain and Portugal on April 28 was produced by a technical expert panel of 49 members, including representatives from transmission system operators (TSOs), regional coordination centres (RCCs), the Agency for Cooperation of Energy Regulators (ACER), and national regulatory authorities (NRAs).
“The investigation concludes that the blackout resulted from a combination of many interacting factors, including oscillations, gaps in voltage and reactive power control, differences in voltage regulation practices, rapid output reductions and generator disconnections in Spain, and uneven stabilization capabilities. These factors led to fast increases of voltage and cascading generation disconnections in Spain, resulting in the blackout in continental Spain and Portugal,” the European Network of Transmission System Operators for Electricity (ENTSO-E) said.
The incident occurred on a typical spring day in Spain
The expert panel noted that the day of the incident was a typical spring day in Spain, with mild temperatures and mostly sunny weather. Photovoltaic generation was similar to previous days, while wind generation was more variable but within the ranges observed in previous days, it added.
The technical analyses indicate that the voltage surge was driven by a combination of interacting factors identified in the root cause tree, which unfolded over very short timescales, leaving limited time for effective operational response, according to the report.
These include limitations in the availability and effectiveness of voltage control resources, the reactive power behaviour of connected assets, the protection settings of connected generators and the behaviour of small-embedded generation, compounded by limited observability, the report reads.
Expert panel sets out recommendations
Based on these findings, the expert panel set out recommendations addressing each of the factors identified in the report to help prevent similar events in the future.
“These include strengthened operational practices, improved monitoring of system behaviour and closer coordination and data exchange among power system actors. The findings of the investigation also underscore the need for regulatory frameworks to adapt in order to support the evolving nature of the power system,” the report underscores.
The experts stressed this blackout was the first of its kind and that the recommendations aim to strengthen system resilience with solutions that are already technologically deployable.
Of note, in June last year the Government of Spain said the blackout was caused by overvoltage, with several factors contributing to the crash.
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