Report: Blackout in Spain and Portugal followed unusual fluctuations

The European Network of Transmission System Operators for Electricity (ENTSO-E) has published a comprehensive report on the large-scale blackout in Spain and Portugal on 28 April 2025. The report documents in detail the system conditions, the sequence of events and the restoration process of the blackout, which began at 12:33 pm and lasted several hours.

The report, which was compiled by a panel of experts including specialists from the Federal Network Agency, is based on the analysis of over 300 gigabytes of data from transmission system operators, distribution system operators and electricity producers. More than 75 experts were involved in the investigation. ENTSO-E describes the event as the most significant European power system event of the past two decades – around 60 million people on the Iberian Peninsula were affected.

The current report focuses on collecting and documenting the facts. A final analysis with an assessment of the causes and specific recommendations for improving grid resilience is due to follow at the beginning of 2026. As initial findings in May showed, the chain of disruptions began with three consecutive power outages in substations in Granada, Badajoz and Seville within just 20 seconds.

The report also documents the complex restoration process: it was not until 10 p.m. that almost half of the supply area was connected again, and some sub-grids were not even connected until the next morning. At least seven people died as a result of the indirect consequences of the blackout, three of them from carbon monoxide poisoning caused by emergency generators.

Voltage cascades as a critical factor

A central aspect of the investigation is the voltage cascades that led to the collapse of the entire system. As a detailed analysis in July revealed, the three incidents resulted in a loss of 2.2 gigawatts of electricity within 20 seconds. Immediately afterwards, the cascading overvoltage shutdown phase began, bringing the entire Iberian power grid to a standstill.

At the time of the blackout, around 69% of the electricity generated in Spain came from renewable energies – around 59 per cent from solar energy and 10 per cent from wind power. However, early speculation that the high proportion of renewable energy favoured the outage was refuted. According to the working group, the solar modules and wind turbines connected via inverters did not play a causal role in the power outage.

Differences to other European grids

The study also reveals structural peculiarities of the Iberian electricity grid. As a comparison with Germany makes clear, the electricity grids in Spain and Germany have very different structures. These differences influence the likelihood of certain problems occurring and the options for solving them.

Experts see battery storage systems as an important component for future grid stability. They can increasingly replace conventional power plants in the provision of reserve capacity and help to stabilise the grid.

The full fact sheet is available for download on the ENTSO-E website. The recommendations announced for the first quarter of 2026 will contain concrete measures to improve grid resilience in Europe and identify lessons learnt from the Iberian blackout for other European power grids.

(mki)