The massive blackout in Spain and Portugal. An analysis of possible causes

On April 28, 2025, at 12:33 PM, the Iberian Peninsula was plunged into darkness due to an unprecedented power outage that affected Spain and Portugal, with brief incidents in southern France and Andorra. This collapse, which paralyzed transportation, communications, and economic activities, left millions without electricity for hours. Despite the efforts of authorities and grid operators, the exact causes of the incident remain under investigation. Below, we analyze the potential reasons behind this historic "zero energy" event, based on available information and critical reasoning.
 
Context of the Incident
According to Red Eléctrica de España (REE), the blackout was triggered by the sudden loss of 15 gigawatts (GW) from the grid, equivalent to 60% of the demand at that moment. This collapse stemmed from a "strong power flow oscillation" that caused the automatic disconnection of the Iberian grid from the European electricity system. Recovery began progressively hours later, reaching 99.95% of the peninsula’s electricity demand by 7:00 AM on April 29. However, uncertainty about the origin of the failure persists, with hypotheses ranging from technical malfunctions to speculation about cyberattacks.
 
Possible Causes of the Blackout
Grid Oscillations: A Technical Issue in System Control
The most supported hypothesis by REE and experts points to a technical problem related to an anomalous oscillation in high-voltage lines (400 kV). These oscillations, defined as significant variations in frequency, power flows, or grid voltages, destabilized the Iberian system, leading to its collapse. Eduardo Prieto, Director of Operations Services at REE, noted that this oscillation caused the automatic disconnection of the Iberian grid from the European system, leaving Spain and Portugal as an "electrical island" unable to balance its loads.
 
An initial theory proposed by Portugal’s grid operator, Redes Energéticas Nacionais (REN), suggested that these oscillations might be linked to a phenomenon known as "atmospheric vibration-induced," attributed to sudden temperature changes. However, this hypothesis was debunked by the Portuguese operator and Spain’s State Meteorological Agency, which confirmed the absence of unusual atmospheric phenomena on April 28. This suggests that the oscillation likely had a technical origin, such as a failure in grid control systems or a coordination error in network management.
 
From a technical perspective, the Iberian grid operates as an interconnected system that relies on a constant balance between supply and demand. Any significant disturbance, such as the sudden loss of a transmission line or generation group, can trigger a chain reaction. The likelihood of a failure in control software or grid protection systems, which failed to compensate for the oscillation, seems high, though the specific triggers remain unidentified.
 
Cyberattack: A Hypothesis Under Investigation
Amid rising geopolitical tensions, the possibility of a cyberattack has gained traction, particularly following statements by Juanma Moreno, president of the Andalusian Regional Government, who mentioned this hypothesis based on information from the Andalusian Cryptologic Center. The National Cryptologic Center (CCN), part of Spain’s National Intelligence Center (CNI), is investigating whether the blackout could result from malicious action. Spain, due to its stance in conflicts such as those in Ukraine and Gaza, has been a target of cyberattacks in recent months, adding plausibility to this theory.
 
A cyberattack could have compromised grid control systems, manipulating power flows or disabling protection mechanisms. However, both REE and the Vice-President of the European Commission, Teresa Ribera, have emphasized that there are no clear indications of sabotage. France’s Industry Minister, Marc Ferracci, also ruled out a cyberattack as the primary hypothesis. While it cannot be entirely dismissed, the lack of concrete evidence suggests this possibility is less likely than a technical failure, at least until investigations progress.
 
Failure in Critical Infrastructure
Another hypothesis considers a physical failure in critical infrastructure, such as the severing of a transmission cable or a malfunction in a key substation. Some reports speculated about a possible cut in an underwater cable, fueled by sightings of Russian ships in international waters near the Iberian Peninsula. However, experts have dismissed this theory, as a failure in a substation or transmission line is typically mitigated by isolating the affected node, preventing a total collapse.
 
Similarly, the notion of a fire in the grid, as rumored and denied by the French operator RTE regarding an alleged blaze between Perpignan and Narbonne, has been debunked. The robustness of the Iberian grid, designed to handle localized failures, makes it unlikely that an isolated physical failure caused a blackout of this magnitude without an aggravating factor, such as an error in control systems or a chain reaction.
 
Excess Demand or Insufficient Generation: A Discarded Possibility
Some experts have considered whether a demand spike or insufficient generation could have overwhelmed the system. However, this hypothesis has been ruled out by REE and analysts, as the forecasted demand for April 28 (26,837 MW) was covered by the available generation capacity (26,144 MW managed by the Iberian Energy Market Operator). Spain has surplus generation capacity and mechanisms like interruptibility, which disconnects large industrial consumers during stress periods, to prevent collapses. The absence of a significant supply-demand imbalance reinforces the idea that the issue lies in grid management, not energy availability.

Contextual Factors and System Vulnerabilities
The blackout has highlighted the vulnerability of the Iberian grid, which operates as an "electrical island" with limited interconnection to the rest of Europe, primarily through the Pyrenees. This reliance on a weak connection with France may have amplified the consequences of the initial oscillation, as the Iberian grid could not stabilize after disconnecting from the European system. Additionally, the growing integration of intermittent renewable sources, such as solar and wind, poses challenges to grid stability, though there is no evidence that these were the direct cause of the incident.
 
Moreover, the scale of the blackout, which simultaneously affected Spain and Portugal, suggests a failure at a critical point in the high-voltage grid, possibly in shared infrastructure or coordination systems between the two countries. France’s rapid recovery, restoring its system in minutes, contrasts with the prolonged Iberian outage, pointing to a structural weakness in the peninsula’s grid resilience.
 
Conclusion: A Technical Failure as the Primary Hypothesis
While investigations are ongoing, the available information points to a technical failure in grid control systems as the most likely cause of the blackout. The anomalous oscillation in high-voltage lines, which triggered the disconnection of the Iberian grid from the European system, appears to be the primary catalyst, possibly exacerbated by an error in protection systems or operational coordination. Hypotheses of a cyberattack or physical infrastructure failure, while not ruled out, lack solid evidence at this stage.
 
This incident, described by REE as "absolutely exceptional," underscores the need to strengthen the resilience of the Iberian grid, enhance interconnections with Europe, and modernize control systems to prevent future collapses. As authorities and operators continue to analyze data, the public awaits clear answers about an event that, in mere seconds, exposed the fragility of a system critical to modern life.
 
Final Note: As investigations are ongoing, this analysis is based on data available as of April 29, 2025. New evidence may alter the conclusions presented here.
 

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