The Spanish national grid operator has dismissed the possibility of a cyber attack as the catalyst for the widespread power outage that disrupted Spain, Portugal, and areas of France on Monday.
Eduardo Prieto, operations director of Red Eléctrica, reported that initial assessments indicate “no evidence of interference within control systems” that would suggest a cyber incident, echoing statements made earlier by Portuguese Prime Minister Luís Montenegro.
Nonetheless, the precise cause of the outage remains undetermined.
The grid operator said on Tuesday that they are unable to issue definitive conclusions until comprehensive data becomes available. Spanish Prime Minister Pedro Sánchez noted that investigators are working to establish the origin of the disruption and will implement measures to prevent similar incidents in the future.
As more details emerge, various theories have been proposed regarding the sequence of events. Experts consulted by the BBC suggest the blackout likely stemmed from multiple system failures.
This is what is currently known and which questions are yet to be answered.
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On Monday evening, Prime Minister Sánchez detailed that 15GW of power—roughly 60% of demand at the time—was “instantaneously removed from the system… within just five seconds.”
Mr Prieto stated at a Tuesday press conference that two “disconnection events” occurred almost simultaneously, within a second of each other, in southwestern Spain, an area with significant solar generation capacity.
A potential factor mentioned by the Spanish grid operator involves utilities identifying imbalances in supply and demand which create instability, prompting temporary disconnections to secure their networks.
Despite this, Sánchez clarified that the outage was “not a problem of excessive renewables.” He clarified there was no supply shortage and electricity demand was relatively typical in the days leading up to the incident.
So what precisely occurred? This remains uncertain, especially as various failure modes impact electricity networks frequently—including, but not limited to, renewables. Outages of this scale are rare but do occur on a global basis, about once a year.
A mismatch between electricity supply and demand may alter the grid’s frequency—50Hz in both Europe and the UK.
Departures from this narrow frequency range can result in equipment damage.
“When a large utility observes frequency deviations outside of tolerance, it may disconnect to safeguard its assets,” explained Prof Hannah Christensen at the University of Oxford.
If multiple utilities take such action consecutively, “cascading effects” can occur, resulting in widespread blackout, she added.
However, operators of renewable energy facilities use sophisticated short-term weather forecasting to anticipate surpluses in wind or solar output, allowing them to fine-tune supplies accordingly, according to Prof Christensen.
While renewable sources present unique challenges due to their intermittency, she noted, these are established and planned for within the industry.
“It is somewhat surprising that this was not predicted,” Prof Christensen observed.
Prof Keith Bell from the University of Strathclyde added that system design reflects reliance on renewables, implying that increased renewable supply would not be an unexpected variable for the grid operators.
“Spain boasts considerable experience managing wind and solar energy, supported by a longstanding forecasting infrastructure,” he said.
He added, “Failures affect all kinds of systems: renewables, fossil fuels, or nuclear. This could be a case of the ‘Swiss cheese model’, where vulnerabilities align by coincidence.”
Red Eléctrica also indicated that the sharp loss in supply caused a transmission link between Spain and France to trip.
There are two principal technologies for cross-border or grid interconnections: conventional alternating current transmission lines and—more recently—high-voltage direct current lines.
According to Prof Bell, Spain’s high-voltage link, operational for seven years, is a tested component of the network.
Due to its limited connections through the Pyrenees to France, the Iberian Peninsula is sometimes described as an “electricity island,” which can potentiate vulnerability during failures.
Sánchez noted that power was restored using connections with France and Morocco, as well as via gas and hydropower resources.
Portugal’s grid operator REN has rejected early reports—attributed to the agency—that the outage was the result of an unusual atmospheric phenomenon.
One message cited “extreme temperature variations in Spain’s interior” leading to atypical oscillations on high-voltage lines—a phenomenon described as ‘induced atmospheric vibration.’
“These oscillations triggered synchronization failures across electrical systems, cascading disturbances throughout Europe’s interconnected network,” the message stated.
However, REN spokesman Bruno Silva informed AFP on Tuesday that the grid operator “did not issue this statement,” declining to elaborate further.
Spaniards in Madrid applauded as electricity was restored following a blackout that brought the city to a halt.
Passengers remained stranded on trains, telecommunications were down, and retail operations were disrupted as the blackout unfolded.
Spain declared a national emergency as scenes of confusion erupted, leaving millions without power.
So far, 96 outbound flights from Portuguese airports were grounded, alongside 45 cancellations from Spain.
Photographs highlight the extensive disruption caused by the power outages across Spain and Portugal.