Combination of voltage and oscillation caused Iberian blackout, says ENTSO-E report

The investigation concluded that the blackout was the result of a combination of many interacting factors, including: “Oscillations, gaps in voltage and reactive power control, differences in voltage regulation practices, rapid output reductions and generator disconnections in Spain, and uneven stabilisation capabilities.”

In total, the report highlighted at least 15 different factors that led to the blackout. These combined factors led to a rapid increase in voltage and cascading generation disconnections in Spain, resulting in the Iberian blackout on 28 April 2025. This corroborates ENTSO-E’s previous report released in October, which highlighted the issue of over-voltage as one of the leading causes of the blackout.

During a press briefing on the report’s release, Damián Cortinas, president of ENTSO-E, stated that renewables were not the problem, but voltage control was.

And although renewables were not responsible for the blackout – as was also highlighted last year by the Spanish government’s own report on the incident – the report did mention that rooftop solar units experienced “voltage-related disconnections by activation of inverter protection”.

Following the release of ENTSO-E’s report, the Spanish transmission system operator (TSO) Red Eléctrica – which was involved in the report and was a member of ENTSO-E’s expert panel – denied any wrongdoing on its part during the 28 April 2025 blackout.

In a joint statement, several trade associations – including SolarPower Europe, the Spanish PV Association (UNEF), the Portuguese Renewables Association (APREN), the Global Solar Council and the Global Renewables Alliance – commented on the report the following: “With the right frameworks in place, solar power and battery energy storage systems (BESS) can enhance grid stability. Stronger network resilience helps deliver cleaner, cheaper electricity and reduces Europe’s dependence on imported fossil fuels.

“The Iberian blackout must be a moment of learning. It is a reminder of the importance of transparent information flows between system operators, generators and relevant stakeholders. We stand ready to support TSOs and DSOs and all the relevant stakeholders in resolving this challenge for systems at all scales.”

The full statement can be found here.

Recommendations easily implemented

The report addresses the many factors that led to the incident in April 2025 with recommendations on voltage control and reactive power management, oscillatory stability and generation disconnection behaviour.

The recommendations aim to enhance “the effectiveness of system defence mechanisms and the robustness and preparedness of restoration processes.”

According to the panel experts, these recommendations can be easily implemented as the solutions are already technologically deployable.

In total, the report suggested 23 recommendations, of which 13 are directly linked to the root causes of last year’s blackout. A majority of these recommendations can also be implemented by grid operators.

The Spanish government has already implemented several measures in response to the blackout, aimed at strengthening grid resilience and boosting energy storage growth in Spain.

Another measure that has been adopted – and highlighted in the trade bodies’ joint statement – is the update to Operational Procedure 7.4, which allows renewables to contribute to voltage control.

“The full implementation of this procedure was completed on March 17 2026 and will allow for a more robust system that is better prepared to prevent this type of incident,” wrote the trade associations.