Lisbon, Oct. 3, 2025 (Lusa) — The Iberian blackout on 28 April was caused by a succession of sudden shutdowns of renewable production and subsequent loss of synchronisation with the continental European grid, according to the panel of experts investigating the incident.
The report published on Friday, drawn up by 45 experts from network operators and regulators from 12 countries, classifies the incident as "scale 3", the most serious level provided for in European legislation, and describes it as "the most significant to have occurred in the European electricity system in more than 20 years", affecting millions of citizens and causing serious disruption to essential services.
According to the analysis by the European Network of Transmission System Operators for Electricity (ENTSO-E), the sequence of failures began at 12:32 p.m. (Brussels time), when several solar and wind power plants in southern Spain suddenly disconnected from the grid, followed by additional losses in regions such as Granada, Badajoz, Seville and Cáceres. In under a minute, more than 2.5 gigawatts of production capacity were eliminated. This shortfall reduced the available reactive compensation, resulting in a surge in electrical voltage and triggering a cascading effect throughout the Iberian Peninsula.
At 12:33 p.m., the Iberian system began to lose synchronisation with the continental grid, registering frequency and voltage oscillations that could not be stabilised by Portugal and Spain's automatic defence plans. Shortly afterwards, the interconnections with France and Morocco were also disconnected, completing the electrical separation of the Peninsula and the total collapse of the Portuguese and Spanish systems.
REN - Redes Energéticas Nacionais was one of the key players in the immediate response. In coordination with Red Eléctrica de España (REE), it immediately activated the defence and restoration plans provided for in European regulations, as well as operating the connection with France and managing the start-up of autonomous power stations. In Portugal, two "black-starts" were successful, speeding up the restoration of voltage and frequency.
Despite occasional difficulties, such as failed starts and the need to rebuild power islands, the grid was restored quickly. At 6.36 p.m., Portugal once again received voltage through the interconnector with Spain and, by midnight, the national transmission network had been completely restored. In Spain, the process lasted until 04:00 on 29 April.
The report also notes that the analyses carried out by the regional coordination centres the day before the incident had not identified any significant risks, concluding that the Iberian network was "N-1 safe". This finding raises additional questions about the behaviour of the grid under conditions of high renewable production, which will be the subject of an in-depth study in the coming months.
Among the aspects to be clarified in the final report are the technical causes of the initial disconnections, the effectiveness of the voltage control mechanisms, and the performance of operators, producers, and protection equipment. Measures to strengthen the resilience of networks in the face of unprecedented phenomena such as those recorded in April will also be evaluated.
The conclusions released today are factual and based on data collected up to 22 August.
The final report, initially scheduled for October 2026, has since been brought forward to the first quarter of 2026 and will include concrete recommendations aimed at preventing similar incidents not only on the Iberian Peninsula but throughout the European electricity grid.
SCR/ADB // ADB.
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