Five seconds in April: anatomy of the Iberian blackout

Twelve Thirty-Three

At 12:33 on Monday 28 April 2025 (11:33 in Lisbon, a warm, cloudless spring midday across the whole peninsula) the electricity systems of mainland Spain and Portugal ceased to exist. Not partially, not regionally: entirely. In the space of about twenty-seven seconds, roughly 31 gigawatts of load, 25.2 GW in Spain and 5.9 GW in Portugal, was disconnected, and the grid that serves nearly 60 million people went to what system operators call, with clinical understatement, "zero". Inside that window, in a span the Spanish prime minister would later put at five seconds, about 15 GW of generation (some 60% of Spanish demand at that moment) vanished from the system.

Metro trains stopped in tunnels under Madrid and Barcelona and were evacuated on foot. Traffic lights went dark in every city on the peninsula at once. The Madrid Open tennis tournament was suspended mid-match. Hospitals switched to diesel. Mobile networks degraded and then, as base-station batteries drained through the afternoon, largely failed. High-speed trains stranded between stations were still being reached by rescue crews after nightfall. It was the largest loss of load in modern European history, bigger than the Italian blackout of September 2003. Unlike Italy's, which began prosaically with a tree flashover on a Swiss transmission line, this one began with something the investigators would later say had no known precedent: not a shortage of power, but a surplus of voltage.

This editorial tells the story of those twenty-seven seconds, the ten hours that followed, and the fourteen months of investigation, blame and rewiring that followed those. It is worth telling in full, because almost everything that matters about how an alternating-current power system actually stays alive (frequency, inertia, voltage, reactive power, interconnection, black start) turns up in this one event, behaving exactly as the textbooks say it should. The Iberian blackout is the most expensive physics lesson Europe has ever been given. The least we can do is learn it.