A 15-gigawatt collapse in generation—60 percent of Spain’s total demand—hit the Iberian grid at 12:33 p.m. on Monday, 28 April, plunging tens of millions of people in Spain and Portugal into darkness, halting high-speed trains, grounding aircraft and silencing mobile networks. Red Eléctrica de España said the loss unfolded in under five seconds, overwhelming safety systems and forcing the disconnection of the interconnector with France.

A rolling blackout measured in gigawatts

Within minutes traffic lights in Madrid and Lisbon went dark, Barcelona’s metro screeched to a halt and hospital back-up generators kicked in across both nations. By mid-afternoon REN, Portugal’s grid operator, reported “very large oscillations” rippling westward from the Spanish network. Initial fears of a cyberattack prompted Prime Minister Pedro Sánchez to convene the National Security Council, but by evening both REE and REN had ruled out malicious interference.

Power companies restored most supply within six hours, yet the scale of disruption was stark:

  • 500 flights cancelled and hundreds more delayed at Madrid-Barajas, Barcelona-El Prat and Lisbon airports
  • 6.2 million of Portugal’s 6.5 million households lost electricity; 99 percent were re-connected by Tuesday morning
  • Spain’s rail manager Adif suspended all AVE and Cercanías services for four hours; road authorities urged drivers to stay home amid traffic signal failures
  • Two oil refineries and at least three data centres executed emergency shutdowns before gradually restarting

Why did the grid fall so fast?

REE’s provisional data show solar provided 59 percent and wind 12 percent of Spain’s electricity at the moment of failure, with nuclear and gas plants at minimal output. Engineers suspect a sudden cloud bank or inverter fault tripped clusters of photovoltaics, erasing gigawatts of supply and triggering a frequency plunge below the safety band. Automatic defences shed load by isolating Spain from France and Morocco, but the imbalance had already propagated into Portugal.

“What failed yesterday was not solar, but the absence of enough inertia and flexible reserve.”

Grid experts stress that renewables are not inherently unreliable; they require fast-response backup—hydro, battery or gas peakers—to ride through large swings. “It’s not the energy source that failed, but the lack of flexible reserves,” said Ana Fontes, power-systems lecturer at the Technical University of Lisbon.

Politics, infrastructure and the path forward

Sánchez called the event “unprecedented” and promised a public report within 30 days. Opposition leader Alberto Feijóo blamed plans to phase out nuclear reactors by 2030. In Portugal, Environment Minister Duarte Cordeiro noted REN had stabilised voltage in Porto within two hours and Lisbon within six.

Both grid operators are urging Brussels to accelerate new cross-border links. REE’s operations chief Eduardo Prieto said the 2-GW Bay of Biscay cable to France, due in 2028, “must become a national-security priority.” Analysts warn that as Spain aims for 81 percent renewables by 2030, storage and interconnection aren’t keeping pace, leaving the peninsula vulnerable to extreme swings.

For now, lights are back on and trains are moving, but Monday’s five-second voltage dive has reignited the debate: how to decarbonise at speed without sacrificing resilience. The solutions—batteries, gas peakers, smarter demand response, thicker cables—will demand billions and take years. Yesterday’s blackout showed how little time the Iberian grid now has to spare.