Mass April blackout in Spain and Portugal tied to voltage control failures, not cyberattack — government blames grid operator, private firms

A lack of voltage control capacity in the power grid triggered a chain reaction that led to the large-scale blackout in Spain and Portugal on April 28, Spanish Energy Minister Sara Aagesen said Tuesday, citing the findings of an official investigation.

According to the full report, released on June 17, several power plants failed to regulate voltage as required under existing regulations in the moments leading up to the outage. At a press briefing in Madrid, Aagesen said that “the system did not have sufficient voltage control capabilities,” according to a Reuters report.

She added that this had occurred “either because they were not sufficiently programmed, or because those that were programmed did not adequately provide what was required by the standard, or a combination of both.”

While multiple factors contributed to the incident, Aagesen confirmed the blackout was ultimately caused by a voltage surge the grid could not absorb, triggering a cascade of generation shutdowns. Voltage surges can result from lightning strikes, equipment failure, or broader grid instability. The investigation pointed to instability earlier that morning as the likely cause.

National grid operator REE, which is partially state-owned, failed to have enough thermal power stations online when a voltage surge triggered the blackout, Aagesen said. According to her, REE indicated it had calculated that activating additional thermal plants was unnecessary at the time, scheduling them only for the early hours of the day and not during peak midday periods.

She added that many of the power stations responsible for this task failed to manage voltage levels despite being financially compensated to do so. “Generation firms which were supposed to control voltage and which, in addition, were paid to do just that did not absorb all the voltage they were supposed to when tension was high,” the BBC cited her as saying, adding that she did not name any of the companies responsible.

The investigation found no evidence of a cyberattack, the minister stressed.

Utilities lobby Aelec, which represents Spain’s major power companies — including Iberdrola and Endesa — said in a statement that it agreed voltage control failures were the primary cause of the blackout. It added that the responsibility for maintaining such control rests with REE.

In late April, Spain’s Supreme Court launched a probe to determine whether the blackout may have been caused by cyberterrorism. At the time, the court ordered the national cybersecurity agency and the grid operator to submit technical reports and sealed the case due to its sensitive nature.

The blackout affected large portions of the Iberian Peninsula and parts of France. Spanish nuclear power plants were forced offline, and the national railway network was paralyzed. Investment bank RBC has estimated the economic impact of the outage at between €2.25 billion and €4.5 billion.