An unexpected power failure in southern Spain set off a chain reaction that left the Iberian Peninsula in darkness, with authorities still searching for answers.

An abrupt loss of power generation at a substation in Granada, followed by additional failures seconds later in Badajoz and Seville, caused a massive blackout across Spain and Portugal on 28 April, Spain’s Energy Minister Sara Aagesen told lawmakers on Wednesday.

The cascading failures resulted in a 2.2-gigawatt loss of electricity generation, which triggered multiple grid disconnections. Aagesen noted that while the root cause of the incidents remains unclear, this is the first time Spanish authorities have publicly identified the origin of the blackout.

“We are analysing millions of pieces of data. We also continue to make progress in identifying where these generation losses occurred and we already know that they started in Granada, Badajoz and Seville,” she said.

Grid operator REE stated that Spain’s main transmission network showed no faults on the day of the incident and suggested the problem may have originated outside the main grid—potentially at generation plants or smaller local grids.

The investigation is also considering high voltage fluctuations observed in the days preceding the outage as a possible factor. However, Aagesen ruled out cyberattacks, grid capacity issues, or imbalances in supply and demand.

She also rejected claims by opposition lawmakers that the government had ignored expert warnings. “There was no alert, no warning,” she asserted.

In the aftermath, scrutiny has fallen on Spain’s increasing reliance on renewable energy and its strategy to phase out nuclear power by 2035. Critics argue that the reduced share of nuclear and fossil fuel sources may have weakened grid stability due to a lack of "grid inertia."

Aagesen defended the current energy mix, stating that renewables have brought down consumer costs and improved energy independence amid geopolitical uncertainty. Spain continues to use the same level of renewables as before the blackout.

She left the door open to extending the life of nuclear power plants, provided that safety, affordability, and supply security could be ensured.

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