Explainer: Spain and Portugal's historic power failure

A rare and widespread blackout struck Spain and Portugal on Monday, affecting millions.

The power failure began at 12:33 p.m. local time and caused Spain's electricity demand to drop by 15 gigawatts in just five seconds – roughly 60 percent of national consumption.

Rail services were halted, airports faced disruptions, and many cities experienced full outages.

Cause of the blackout

Investigations are ongoing, but early assessments from Portugal's grid operator REN suggest that high-voltage line oscillations in Spain triggered the event.

These oscillations may have stemmed from sharp temperature variations, which can stress overhead lines and destabilize transmission. REN clarified it never used the term "induced atmospheric vibration," correcting earlier media interpretations.

Spain's national court also opened a preliminary investigation into whether sabotage or terrorism might be involved, but as of now, cyberattack has been officially ruled out.

The role of renewables and grid complexity

Spain's grid now relies heavily on solar and wind power, which – while clean – are less predictable than conventional sources.

Experts say this reduces "system inertia," making the grid more vulnerable to sudden disruptions. With fewer rotating generators like gas or hydro plants online, voltage and frequency can fluctuate more easily during stress events.

Although renewable integration itself isn't to blame, managing stability in such a system is more complex.

Sudden disconnection of a solar-heavy region could have triggered a chain reaction across the interconnected European grid.

Operators have since highlighted the need for updated stabilization mechanisms, including better real-time monitoring and battery-based buffering.

Restoration efforts

The blackout lasted several hours, with electricity gradually returning through a controlled "black start" process.

Grid operators restarted local gas and hydro plants and temporarily imported power from France and Morocco to re-synchronize the system.

(With input from agencies)

(Cover: The streets of Ciudad Real without lighting at night due to the blackout in Ciudad Real, Spain, April 28, 2025. /VCG)