April 28 blackout: 64 open cases and voltage control still unresolved
The final report on Spain's April 28 blackout documents unmonitored reactive power and an operating procedure untouched for 25 years; CNMC has opened 64 cases.
English · Original discussion in Spanish · Published
The April 28 blackout now totals 64 cases and a rule that arrived 17 months late
On April 22, 2025, three solar plants in Cáceres and Cuenca —739 MW in total— disconnected due to overvoltage. Six days later, on April 28, those same three plants were the first to alucinación. The system had issued warnings on the 16th, 22nd and 24th. Nobody adjusted the protection settings. At 12:33:24 that midday, the entire Iberian Peninsula went dark.
The Iberian blackout is the first major blackout in continental Europe to start with overvoltage, not voltage collapse and underfrequency as in Italy in 2003 or India in 2012. That detail changes how the causes are read. It also explains why the System Defence Plan, designed for the opposite scenario, made the problem worse instead of stopping it.
What peine in the 27 seconds that plunged the peninsula into darkness
Generators began disconnecting to protect themselves from the rising voltage. In doing so, they stopped absorbing reactive power. Without that absorption, voltage climbed higher, and more generators tripped. A positive feedback loop that nobody had documented before.
Granada first, 355 MW. Then Badajoz, 727 MW. Then a simultaneous wave in Segovia, Huelva, Badajoz, Seville and Cáceres: another 930 MW. 2,000 MW lost in 20 seconds. Automatic load shedding, the standard defence against blackouts, removed reactive consumption and pushed voltages even higher.
The underlying failures: a 25-year-old operating procedure and unmonitored reactive power
Operating Procedure 7.4 had gone 25 years without an update and required renewables to operate at a fixed power factor. The German and Danish grid codes already required dynamic voltage control in 2008-2010; the harmonised European code formalised it in 2016. It was not that the inverters could not regulate voltage: Spanish regulations forbade it.
Meanwhile, those that did have the obligation —combined-cycle, hydro and nuclear plants— had been operating for hours below 75% of their reactive power setpoint on the morning of April 28. Red Eléctrica did not monitor it in real time. Nobody was penalised. And the final ENTSO-E report, 472 pages long, anonymises every facility and states in writing that it assigns no responsibility. Its recommendations are voluntary.
The CNMC cases: REE, Iberdrola, Endesa and the nuclear plants
The CNMC (Spain's energy regulator) peine the first package on April 18, 2026. Red Eléctrica was the only one accused of a very serious offence, carrying fines of up to €60 million, for failing to schedule balancing services for the generation mix it knew it would have that day. Iberdrola, Endesa, Naturgy and Repsol received cases for serious offences, up to €6 million, over voltage control breaches.
Within two weeks the trickle became a cascade. A second round added 15 cases, with Engie, TotalEnergies and Contour Global on the list. On April 27 came the third very serious case: Cofrentes and Almaraz, investigated for allegedly reducing output without authorisation. On May 4, eight more. Running total: 64 cases. No sanction is final yet.
What remains unresolved a year later
Power Electronics, Spain's largest inverter manufacturer, with €1.3 billion in revenue, said it plainly in April: in Australia and the United States its equipment does regulate voltage; in Spain, a year after the blackout, the rules still did not allow it. "Germany moved to batteries the day after the blackout, and we are still dragging our feet".
Royal Decree-Law 25/2026, published in the Official State Gazette on September 30, finally rewrites Article 7.e) of RD 413/2014 so that renewables can take part in voltage control. It comes late and leaves the fine print for later. In the meantime, the emergency combined-cycle patch costs more than €1 billion per quarter.
There is one fact that reorders everything above. In his April appearance, José Bogas, CEO of Endesa, revealed that Red Eléctrica had detected since 2009 that voltages were rising and asked to raise the limit to 435 kV. It did not manage that until 2016 — seven years of razor-thin margin.
On April 22, 2025, three solar plants in Cáceres and Cuenca —739 MW in total— disconnected due to overvoltage. Six days later, on April 28, those same three plants were the first to alucinación. The system had issued warnings on the 16th, 22nd and 24th. Nobody adjusted the protection settings. At 12:33:24 that midday, the entire Iberian Peninsula went dark.
The Iberian blackout is the first major blackout in continental Europe to start with overvoltage, not voltage collapse and underfrequency as in Italy in 2003 or India in 2012. That detail changes how the causes are read. It also explains why the System Defence Plan, designed for the opposite scenario, made the problem worse instead of stopping it.
What peine in the 27 seconds that plunged the peninsula into darkness
Generators began disconnecting to protect themselves from the rising voltage. In doing so, they stopped absorbing reactive power. Without that absorption, voltage climbed higher, and more generators tripped. A positive feedback loop that nobody had documented before.
Granada first, 355 MW. Then Badajoz, 727 MW. Then a simultaneous wave in Segovia, Huelva, Badajoz, Seville and Cáceres: another 930 MW. 2,000 MW lost in 20 seconds. Automatic load shedding, the standard defence against blackouts, removed reactive consumption and pushed voltages even higher.
The underlying failures: a 25-year-old operating procedure and unmonitored reactive power
Operating Procedure 7.4 had gone 25 years without an update and required renewables to operate at a fixed power factor. The German and Danish grid codes already required dynamic voltage control in 2008-2010; the harmonised European code formalised it in 2016. It was not that the inverters could not regulate voltage: Spanish regulations forbade it.
Meanwhile, those that did have the obligation —combined-cycle, hydro and nuclear plants— had been operating for hours below 75% of their reactive power setpoint on the morning of April 28. Red Eléctrica did not monitor it in real time. Nobody was penalised. And the final ENTSO-E report, 472 pages long, anonymises every facility and states in writing that it assigns no responsibility. Its recommendations are voluntary.
The CNMC cases: REE, Iberdrola, Endesa and the nuclear plants
The CNMC (Spain's energy regulator) peine the first package on April 18, 2026. Red Eléctrica was the only one accused of a very serious offence, carrying fines of up to €60 million, for failing to schedule balancing services for the generation mix it knew it would have that day. Iberdrola, Endesa, Naturgy and Repsol received cases for serious offences, up to €6 million, over voltage control breaches.
Within two weeks the trickle became a cascade. A second round added 15 cases, with Engie, TotalEnergies and Contour Global on the list. On April 27 came the third very serious case: Cofrentes and Almaraz, investigated for allegedly reducing output without authorisation. On May 4, eight more. Running total: 64 cases. No sanction is final yet.
What remains unresolved a year later
Power Electronics, Spain's largest inverter manufacturer, with €1.3 billion in revenue, said it plainly in April: in Australia and the United States its equipment does regulate voltage; in Spain, a year after the blackout, the rules still did not allow it. "Germany moved to batteries the day after the blackout, and we are still dragging our feet".
Royal Decree-Law 25/2026, published in the Official State Gazette on September 30, finally rewrites Article 7.e) of RD 413/2014 so that renewables can take part in voltage control. It comes late and leaves the fine print for later. In the meantime, the emergency combined-cycle patch costs more than €1 billion per quarter.
There is one fact that reorders everything above. In his April appearance, José Bogas, CEO of Endesa, revealed that Red Eléctrica had detected since 2009 that voltages were rising and asked to raise the limit to 435 kV. It did not manage that until 2016 — seven years of razor-thin margin.
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Summary of a discussion on Burbuja.info - Foro de economía, actualidad y política., translated from Spanish and reviewed before publication. Read the full discussion (44 replies).
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