'First of its kind' power surge behind Iberia blackout: experts

A power surge that caused a paralysing blackout across all of Spain and Portugal in April was an unprecedented event in Europe and possibly the world, but the root cause remains unknown, an expert panel said Friday.

"This was the most severe blackout incident in Europe in the last 20 years," Damian Cortinas, president of the association of electricity grid operators ENTSO-E, said during a presentation of the panel's preliminary report into the incident.

He said "cascading overvoltages" were behind the blackout, which he called a "first of its kind" on the continent.

Cortinas added that "we think (it is unprecedented) in the world as well", but cautioned that the experts did not have information from every country.

The April 28 outage cut internet and telephone connections, halted trains, shut businesses and plunged cities into darkness across Spain and Portugal. It also briefly affected southwestern France.

A Spanish government report had previously blamed the massive outage on overvoltage in June.

Overvoltage occurs when there is too much electrical voltage in a network, overloading equipment. It can be caused by surges in networks due to oversupply or lightning strikes, or when protective equipment is insufficient or fails.

'New territory'

Friday's "factual" report, produced by a panel of 45 European experts mandated to carry out technical investigations, describes the sequence of events that led to the uncontrolled, widespread outage.

But it does not yet provide the primary causes of the initial incidents.

"This is new territory. This is also why we need a bit of time to be sure that we analyse what's going on and what would happen," Cortinas said.

The expert group will publish its final report in the first quarter of 2026, ENTSO-E said in a statement

"It will include a detailed root cause analysis and recommendations on how to prevent similar events happening across the European power system in the future," it added.