ENTSO-E publishes preliminary report on power outage in Spain and Portugal

On October 3, the European Network of Transmission System Operators for Electricity (ENTSO-E) published a preliminary report on the power outage that interrupted the electricity supply in Spain and Portugal for 12 to 16 hours on April 28 (250402). “This unprecedented incident, which led to a complete power outage on the Spanish mainland and in Portugal, is the most significant event in the European power grid in over two decades and had a major impact on the Spanish and Portuguese populations and society,” it stated.

Final report with detailed cause analysis and recommendations to follow in the first quarter of 2026

The report (PDF) now published contains a detailed description of the system conditions on April 28 that led to the power outage, as well as the sequence of events from the gradually escalating crisis situation to the restoration of power. It is based on the findings of an investigation conducted by a panel of 45 experts from transmission system operators and regulatory authorities across Europe. The findings are largely consistent with the reports presented on June 17 by the Spanish government (PDF) and the following day by the Spanish transmission system operator REE (PDF), and supplement them with further details. Work is already underway on the final report, which is expected to be published in the first quarter of 2026. It will contain a detailed analysis of the causes and recommendations on how similar events can be prevented in the European power grid in the future.

The Spanish electricity system appears to be in need of reform in a number of areas

It is likely that this final report will also be unable to identify a single, clear cause for the power outage. Rather, the impression is growing that there were a whole series of factors in the Iberian electricity system that were not strictly adhered to and therefore, through an unfortunate combination of circumstances, caused the cascading collapse of the power supply. The lack of reactive power compensation is likely to have played a particularly important role in this, leading to high overvoltages and preventing the voltage and frequency from being stabilized by shifting the phase angle.

In this context, a press release issued by the Austrian transmission system operator Austrian Power Grid (PWG) on October 3 is noteworthy, in which some of the weaknesses of the Iberian grid are outlined as follows:

• At the beginning of the relatively early expansion of renewable electricity generation (especially wind and PV) in Spain, simplified grid connection conditions were granted to these generation technologies. This led to a very limited ability of these plants to actively regulate the voltage in the grid.

• t the same time, it was assumed that active dynamic voltage control would be provided to a sufficient extent by conventional power plants. The analysis of the blackout shows that some of the regulations for conventional power plants are also outdated.

• The grid connection conditions regarding voltage control/maintenance, which are formulated in very general terms, have not been updated for many years and are not geared to the current dynamics and volatility of the electricity system with its high share of renewables.

• Another specific feature of Spain is the increased permitted operating voltage of 435 kV instead of the 420 kV otherwise applicable in Europe at the 400 kV level, which equates to a reduced “safety reserve” with regard to voltage fluctuations.
  
  

Links (internal)

• Power outage in Spain and Portugal had several causes (250601)
• Hours-long power outage in Spain and Portugal (250402)

• List of links to power supply disruptions (international)

Link (external, no guarantee)

• PDF ENTSO-E: Grid Incident in Spain and Portugal on April 28, 2025 – ICS Investigation Expert Panel Factual Report, October 3, 2025 (264 pages)