Lisbon, Oct. 3, 2025 (Lusa) — The experts investigating the Iberian blackout emphasised the difficulty of collecting data and refused to assign blame, stressing that the factual report focuses on the technical analysis of the incident and serves as a basis for future recommendations.
During the presentation of the factual report on the 28 April blackout, the most serious in more than 20 years in the European electricity system, Klaus Kaschnitz, from APG (Austrian Power Grid) and co-leader of the expert panel of the European Network of Transmission System Managers for Electricity (ENTSO-E), explained that the investigation faced a "very challenging" process due to the difficulty of obtaining complete information from operators and generators, including third parties who did not consent to sending the data.
"Some data simply doesn't exist," he said, referring above all to small units such as domestic solar panels. The collection of information took five months and required the submission of around 150 formal requests, allowing the incident to be accurately reconstructed only in August.
Klaus Kaschnitz and Damian Cortinas, chairman of the ENTSO-E Board, stressed that the report is not intended to pinpoint those responsible, but to analyse the incident technically. "Our focus is to understand the facts and use that information to prevent something similar from happening again, not to apportion blame," explained Damian Cortinas.
According to Klaus Kaschnitz, the investigation identified multiple voltage oscillations and atypical frequencies before the blackout, culminating in three main events that led to the loss of synchronisation with the European grid.
Despite the unprecedented nature of the collapse, the restoration of the grid was swift, with Portugal fully recovering its high-voltage connection shortly after midnight and Spain at 04:00 the following day.
The chairman of the ENTSO-E board explained the role of international interconnectors, particularly the link between Portugal and France. "The size of the interconnector had no impact on the blackout, either at the beginning or at the end. The problem was local, in southern Spain. The existence of interconnectors in general only helped in the system's recovery, allowing voltage to be restored in a coordinated manner. Still, it could not have prevented the incident," he said.
Klaus Kaschnitz emphasised that the blackout highlighted a new phenomenon: cascading overvoltages that require local voltage control. "Voltage needs to be managed locally, close to the problem. All units, renewable or conventional, can contribute to voltage control, as long as they fulfil the technical requirements," he explained.
The ENTSO-E report emphasises that strengthening voltage control capacity throughout the grid is essential to prevent similar incidents. The investigation will continue with a detailed analysis of local oscillations, the interaction between generators and consumers, and the effectiveness of system defence plans, to increase the resilience of the European electricity system.
Damian Cortinas emphasised that the factual report serves as the basis for the final report, scheduled for the first quarter of 2026, which will include technical and regulatory recommendations aimed at preventing similar incidents on the Iberian Peninsula and in Europe.
"We aim to prevent it from happening again, not just in Spain and Portugal, but throughout Europe," said Damian Cortinas, pointing out that the incident revealed a new phenomenon: blackouts caused by cascading overvoltages, which require local voltage control, a function that can be fulfilled by all forms of generation, renewable or conventional, as long as the appropriate technical requirements are in place.
Klaus Kaschnitz added that the research will further study local oscillations, the interaction between generators and consumers and how the grid responds in extreme situations, to increase the resilience of the European electricity system.
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