Spain’s national electricity grid has experienced significant voltage swings over the past two weeks, the country’s competition watchdog said on Wednesday – fuelling fears of another mass power failure like the one that paralysed the Iberian Peninsula in late April.
The 28 April outage – described as Europe’s most severe blackout in two decades – shut down transport systems, disrupted internet and telephone networks, and left large areas of mainland Spain and Portugal without power. Click here to read all our reports related to Spain’s blackout.
A European expert panel reported last week that ‘cascading overvoltages’ were to blame for the April incident. Its conclusions matched those of a Spanish government report released in June, which also identified ‘overvoltage’ as the cause. ALSO READ: Spain’s grid operator and electricity providers exchange accusations over blackout.
Overvoltage occurs when excessive electrical current runs through the grid, overwhelming equipment. It can result from oversupply surges, lightning strikes, or failures in protective systems.
Spanish investigators also found that large power swings had been detected moments before the April blackout, triggering a domino effect of shutdowns across the grid. ALSO READ: Reasons for Spain’s April power blackout: ‘overvoltage’ & ‘poor planning’.
In a document published on Wednesday, the CNMC watchdog said grid operator Red Eléctrica (REE) had notified it of ‘sudden voltage variations’ detected recently.
‘Although the voltages always remained within the established margins, they can potentially trigger disconnections of demand and/or generation that end up destabilising the electrical system,’ the CNMC quoted REE as saying.
The April crisis reignited debate about Spain’s reliance on renewable energy and its plan to phase out nuclear power, but the government and several experts have dismissed claims that the energy transition made the grid more vulnerable. ALSO READ: Spain’s opposition parties blame PM’s renewable energy policies for blackout.
According to the CNMC, REE linked the recent disturbances to ‘sudden changes in programming, in particular of renewable generation, as well as the response time of generation supplying dynamic voltage control’.
Because renewable sources ‘do not regulate voltage continuously’, their growing role in the system ‘increases the probability that increasingly large variations in their production happen’, REE noted.
The operator warned that such swings ‘can have an impact in the security of the supply’ unless urgent corrective measures are adopted.
In a post on social media platform X on Thursday (see below), REE issued a ‘message of reassurance’, stating: ‘We have not spoken of any risk of a blackout, neither imminent nor widespread. We have recently observed voltage variations that must be avoided, but which have not posed a risk to supply, as they have remained within acceptable limits’.
REE has proposed technical rule changes to allow better real-time management of power imbalances and to curb sudden voltage spikes. The CNMC said it will open a public consultation on these operational adjustments until 15 October to evaluate their potential effects, noting that the measures would be temporary.
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Ante las informaciones publicadas, lanzamos un mensaje de tranquilidad:
▶️Desde Red Eléctrica no hemos hablado de riesgo de apagón ni inminente ni generalizado.
▶️Hemos observado recientemente variaciones de tensión que deben evitarse pero que no han supuesto riesgo de… pic.twitter.com/BGy00S0t7P— Red Eléctrica (@RedElectricaREE) October 9, 2025
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