The Iberian Blackout Report Points to Voltage Control, Not Renewables as Such. Grid Rules Must Catch Up
On 3 October 2025 the expert panel set up by ENTSO-E to investigate the blackout of 28 April published its factual report. At 12:33 CEST that day continental Spain and Portugal lost all power. A small area of southern France was briefly affected, but the rest of the European system saw no disturbance. ENTSO-E called it the most severe blackout on the European power system in more than 20 years and the first of its kind, caused by overvoltage.
The panel of 45 experts from transmission operators and regulators across Europe gathered data from generators, grid users and network operators to reconstruct the sequence. It noted significant difficulties obtaining high-quality data from several Spanish distribution operators and generation companies. A final report with root causes and recommendations is due in the first quarter of 2026. The factual report does not assign blame or reach conclusions on root causes. But the sequence it describes is already clear enough to draw lessons.
The morning of 28 April looked like a typical spring day in Spain, with a high concentration of solar and wind output in the south-west at midday. Before the collapse, the system experienced oscillations: a local oscillation at 0.63 Hz and an inter-area oscillation at 0.21 Hz. Voltage on a transmission grid is managed by injecting or absorbing reactive power. Many solar and wind plants are connected through inverters and, under the rules in force in Spain, operated with a fixed power factor rather than actively controlling voltage.
Our view is that three lessons are already clear, even before the final report. Second, system operators need enough voltage control resources online at all times, which means scheduling synchronous plants or equivalent devices based on voltage needs and not only on energy and reserve needs. The Iberian peninsula is weakly connected to the rest of Europe through France. The Iberian blackout was a warning to every European system with fast-growing inverter-based generation.