On April 28, 2025, a massive power outage swept across Spain and Portugal, plunging millions into darkness and chaos. The blackout, which lasted over ten hours, disrupted everything from public transport and internet services to traffic lights and businesses, leaving cities gridlocked and thousands stranded on trains and in elevators. Now, after weeks of investigation, Spanish authorities have revealed the root causes of this unprecedented event, dismissing earlier speculation about cyberattacks or failures due to renewable energy reliance.
According to a comprehensive government report released on June 17, 2025, the blackout was triggered by a surge in voltage—known as "overvoltage"—that sparked a chain reaction of protective shutdowns across the Iberian power grid. Spain's Ecological Transition Minister, Sara Aagesen, explained that the electrical system lacked sufficient dynamic voltage control capacity to manage the surge, leading to cascading failures that ultimately caused the grid to collapse.
"The system did not have sufficient dynamic voltage control capacity," Aagesen said during a press briefing in Madrid. She elaborated that this shortfall was partly due to a miscalculation by the Spanish grid operator, Red Eléctrica de España (REE), which failed to have enough thermal power stations switched on during the peak hours of that day. "REE told us that they made their calculations and estimated that switching on more thermal plants was not necessary at this time. They only set it for the early hours of the day, not the central hours," she noted.
The report also highlighted that several conventional power plants, including nuclear and gas-fired facilities, did not adequately perform their legally mandated role in regulating grid voltage. These plants, many of which are financially compensated for their voltage control services, failed to absorb all the reactive power expected during the high voltage conditions. "Power plants should have controlled voltage and, moreover, many of them were economically remunerated to do so. They did not absorb all the reactive power that was expected," Aagesen added.
Experts described the blackout as a "multifactorial" system failure. It was not a single fault but a convergence of issues, including technical shortcomings, poor planning, and operational mismanagement. The blackout began shortly after 12:30 PM when 15 gigawatts—about 60 percent of Spain's electricity supply—vanished within five seconds. This sudden loss caused a voltage surge that the grid was ill-prepared to handle, triggering a cascade of disconnections that spread rapidly across the network.
"We reached a point of no return with an uncontrollable chain reaction," Aagesen said, emphasizing that the crisis could have been averted had adequate measures been taken in advance to absorb the excess voltage. The report also pointed to "voltage instability" in the hours and days leading up to the blackout, with oscillations detected between noon and 12:30 PM on April 28.
The blackout's impact was vast: approximately 500 flights were cancelled, affecting 80,000 passengers, and public transportation systems came to a halt. Internet and phone connectivity were lost, traffic lights failed, and critical infrastructure like ATMs and metros were paralyzed. Portugal, interconnected with Spain's grid, was similarly affected, while island territories remained untouched.
In the aftermath, speculation ran rampant. Some blamed Spain's increasing dependence on renewable energy, while others suggested a possible cyberattack. However, the government report firmly dismissed these theories. "There were no indications of cyber-sabotage by foreign actors," Aagesen confirmed. She also defended Spain's renewable energy transition, stating that the blackout was not caused by the country's high levels of renewables or the phase-out of nuclear power.
On the day of the outage, Spain's electricity generation was composed of nearly 55 percent solar power, 10 percent wind, 10 percent nuclear, and almost 10 percent hydropower. Aagesen pointed out that similar energy mixes and demand levels had been handled successfully in the past, making it inappropriate to single out renewables as the culprit.
Spanish Prime Minister Pedro Sánchez echoed this defense, stating, "Those who link this incident to the lack of nuclear power are frankly lying or demonstrating their ignorance." He further remarked that nuclear power generation "was no more resilient" than other electricity sources. Sánchez has reaffirmed the government's commitment to its energy transition plans, which aim to generate 81 percent of electricity from renewable sources by 2030.
The report also criticized the planning and operational decisions made by REE and energy companies. Aelec, the utilities lobby representing major electricity companies like Iberdrola and Endesa, agreed that voltage control was the main cause but insisted that REE, as the system operator, bore the responsibility for ensuring grid stability. They asserted that their member companies complied with regulatory voltage control requirements and even operated beyond those obligations.
Pratheeksha Ramdas, Senior New Energies Analyst at Rystad Energy, highlighted the incident's broader implications. "The blackout reflects a critical failure in the Spanish electricity system not due to lack of installed capacity but due to mismanagement of available energy resources and accountability in grid operations," she said, underscoring the essential role of thermal power plants, particularly gas-fired stations, in maintaining grid stability.
To address these shortcomings, the government plans to introduce measures aimed at strengthening grid supervision and compliance, increasing electrical capacity, and enhancing Spain's electricity interconnections with neighboring countries. The blackout exposed the Iberian Peninsula's relative isolation from the wider European grid, making external support from France and Morocco crucial during the crisis. Supporting this effort, the European Investment Bank recently announced 1.6 billion euros in funding for a major electricity interconnection project between France and Spain, which will nearly double power exchange capacity.
The April blackout also unfolded amid political turbulence for Sánchez's administration, which has been grappling with corruption scandals. Despite pressure and calls for a snap election, the prime minister has vowed to continue his political project and energy agenda without deviation.
Ultimately, this massive power failure has laid bare vulnerabilities in Spain's power grid management and underscored the delicate balance required in transitioning to renewable energy. While the government remains steadfast in its commitment to a greener future, the lessons learned from this crisis will undoubtedly shape Spain and Portugal's energy policies and infrastructure resilience for years to come.
