On April 28, 2025, the Iberian Peninsula experienced an unprecedented electrical blackout, plunging Spain and Portugal into an energy crisis that affected millions of citizens and paralyzed critical infrastructure. The power interruption began at approximately 12:33 PM Central European Time (CET), leaving millions of people without service. The impact was immediate and severe: transport systems halted, traffic lights went dark, banks were inoperative, and communication networks were severely affected. The incident was described as a “total blackout” or a “zero energy” event for the interconnected peninsular system, and its magnitude and simultaneity in Spain and Portugal made it an “exceptional and totally extraordinary” event.
@cloudstudioiot ¿Qué sucedió ayer? 🔍 Ayer 28 de abril, un apagón SIN PRECEDENTES paralizó España y Portugal. 🇪🇸🇵🇹 Caos en transporte, comunicaciones… todo se detuvo. Pero en medio de la oscuridad, algo demostró una resiliencia clave: El Internet de las Cosas. 💡 ¿Cómo y por qué los dispositivos IoT siguieron operativos, almacenando datos cruciales cuando nada más lo hacía? En este Reel, resumimos lo que pasó y te contamos la lección fundamental sobre fiabilidad tecnológica para tu negocio. ¿Quieres saber más? ¡Contáctanos en nuestro perfil! #Apagón #28deAbril #Madrid #España #Portugal #IoT #InternetOfThings #PlataformaIoT #TransformaciónDigital ♬ sonido original – Cloud Studio IoT
Why did the blackout occur?
According to Spanish authorities, the incident was triggered by a sudden and massive loss of power: 15 gigawatts (GW), equivalent to 60% of the peninsular electricity demand at that moment, disappeared from the system in just five seconds. This sudden loss of 15 GW at 12:33h had “never happened before”. Initial investigations point to a “strong oscillation” or “very strong oscillation in power flows” as the key phenomenon that led to the collapse of the peninsular system and its disconnection from Europe. A more specific hypothesis, proposed by the Portuguese operator REN, attributed the event to a “rare atmospheric phenomenon” in inland Spain, characterized by “extreme temperature variations” that caused “anomalous oscillations” or “induced atmospheric vibrations” in very high voltage lines (400 kV). This phenomenon may have caused synchronization failures between electrical systems.
The speed and scale of this power drop (approximately 15 GW in 5 seconds) suggest it was not an isolated failure but a rapid sequence of cascading disconnections. A direct consequence of this internal instability was the disconnection of the Spanish peninsular electrical system from the rest of the interconnected European grid. This separation, while contributing to the isolation and total blackout of the Iberian Peninsula, likely functioned as intended by European network safety protocols (ENTSO-E). The loss of 15 GW represented a significant threat to frequency stability across the continent, and the automatic disconnection of interconnections acted as a firewall, protecting France and the rest of Europe from being dragged into the Iberian disturbance.
Explanation of the cascading loss
Investigations into the exact causes of the systemic failure are ongoing, with technical hypotheses like a strong grid oscillation or an atmospheric phenomenon affecting high-voltage lines being considered, while the possibility of a coordinated cyberattack was initially ruled out by multiple official sources in Spain, Portugal, and Europe. Some external analyses suggested that the high penetration of renewable generation (solar and wind) at that moment could have influenced the system’s dynamics or the severity of the response to the initial disturbance. Before the outage hit, Spain was running its grid with very little dispatchable spinning generation, and therefore not much inertia.
Has something similar happened before?
While Europe has experienced significant regional blackouts before, such as the one in Italy in 2003, the magnitude and duration of the April 28 blackout were particularly concerning. The simultaneous effects in multiple countries at this scale is a rare phenomenon, highlighting an urgent need for modernization in grid infrastructure. The loss of 15 GW in such a short time had not occurred before.
La Castellana, at night
Geographical Scope: Spain, Portugal, France, Andorra, and Other Connections
The blackout comprehensively affected all of peninsular Spain and the entirety of continental Portugal, directly impacting a combined population of approximately 60 million people. It is important to note that the Spanish island electrical systems (Canary Islands, Balearic Islands) and the territories of Ceuta and Melilla, which operate in isolation from the peninsular grid, were not affected by the incident. Gibraltar was also not affected as it is not connected to the European continental power grid.
Beyond the Iberian Peninsula, the direct impact was limited. Areas in southwestern France, specifically in the French Basque Country, experienced brief power cuts lasting only a few minutes before service was restored. In Andorra, the electricity supply was interrupted for mere seconds as an automatic system connected the principality’s grid to the French network to maintain continuity. Indirect incidents were also reported in Morocco, where some internet providers experienced problems due to their dependence on servers located in Spain that went offline due to the power cut.
Impact in Spain: Chaos and Disruption
Blackout in a neighborhood greengrocer
The blackout on April 28, 2025, plunged peninsular Spain into a situation of chaos and widespread disruption, profoundly and simultaneously affecting all aspects of modern life dependent on electricity supply.
Transportation Collapse
The transportation sector was one of the most immediate and severely affected. The Spanish railway network was completely paralyzed. Renfe suspended all its Medium and Long Distance services, as well as commuter trains throughout the peninsular territory, leaving thousands of passengers stranded. An estimated 30,000 to 35,000 people had to be evacuated from over 100 trains stopped on the tracks. Metro systems in major cities also collapsed, with the Metro de Madrid and Metro de Barcelona suspending service. Numerous passengers were trapped inside trains, some in tunnels, and had to be evacuated by emergency services. Air traffic, while not completely stopped, suffered significant effects. Major Spanish airports operated on backup power systems (generators) to maintain minimum operations, but delays were reported, and air traffic capacity was reduced by 20-30% as a safety measure. On the roads, the lack of electricity caused traffic lights to go out in numerous cities, generating chaotic traffic situations. Critical road infrastructures, such as the M-30 tunnels in Madrid, also had to be closed. Citizens and police officers had to manually direct traffic at some major intersections.
Blackout in the Madrid Metro
Communication Interruption
Communication networks, both mobile and fixed, suffered a massive interruption. One of the most immediate and widespread consequences was the inability to make voice calls through mobile phone networks in much of the country. While some data services and messaging applications worked intermittently in certain areas, communication was severely limited. Internet connectivity was also drastically affected. Data from Cloudflare indicated that national internet traffic in Spain plummeted by approximately 60% immediately after the blackout, falling up to 80% below normal levels in the following hours. Fixed communications were also affected, and congestion on the networks that were still functioning exacerbated the problems. This widespread failure of communications highlights a critical dependence of modern telecommunications infrastructure on continuous electricity supply. The extent of the failure suggests that backup power systems for this essential infrastructure were insufficient, overwhelmed by the duration of the blackout, or simply non-existent in many parts of the network. The drop in announced IP address blocks is technical proof that crucial network equipment went offline, demonstrating a vulnerability in the energy resilience of the communication network itself.
Essential Services Under Pressure
Essential services were under enormous pressure. Hospitals across Spain immediately activated their backup power systems, mainly diesel generators, to maintain critical operations, and these systems functioned correctly, ensuring energy flow in vital areas and preventing serious incidents. However, some incidents were reported, such as the cancellation of non-urgent surgeries in some centers. In terms of nuclear safety, Spanish nuclear power plants responded according to established protocols, automatically disconnecting from the grid safely and activating emergency diesel generators to maintain safe reactor conditions. This successful automatic response demonstrates the effectiveness of the rigorous safety protocols required for these high-risk facilities in the face of contingencies like the loss of external power. Emergency services were overwhelmed by incidents resulting from the blackout, notably the high number of rescues of people trapped in elevators, with 286 interventions in the Community of Madrid alone. Firefighters had frantic activity, and a significant police deployment was made to manage traffic and ensure public order. Other public services were also affected; gas stations without their own generators had to close, most ATMs were inoperative, and the possibility of affecting water supply in some areas was mentioned. Government offices and Parliament closed their doors.
Socioeconomic and Daily Life Impact
The interruption of electricity supply completely disrupted daily life and economic activity. Numerous offices and businesses were forced to close their doors. With the failure of electronic payment systems and inoperative ATMs, commercial transactions reverted to cash payment, limiting activity for those who did not have it or for unprepared businesses. Supermarkets reported problems, and there were reports of panic buying of basic products. Industry also suffered shutdowns; major car manufacturers like Seat and Ford stopped their production lines due to lack of supply. In the financial sector, stock exchanges could continue operating thanks to their own backup systems. The citizen experience was marked by confusion, initial chaos, and the alteration of routines. Thousands of people were stranded in train stations, bus stations, or airports. The search for reliable information became a priority. Scenes of anxiety and fear were reported, but also of adaptation and social resilience. Citizens spontaneously collaborated in directing traffic. Important events were affected, such as the Mutua Madrid Open tennis tournament, which had to suspend and postpone matches.
Blackout at Mercadona on April 28, 2025
Governmental and Institutional Response
The Spanish government activated a coordinated institutional response to manage the crisis. A national State of Emergency (level 3) was declared after receiving formal requests from several autonomous communities. The National Security Council met in extraordinary session multiple times to monitor the situation and coordinate actions. Public communication was a key element, with President Sánchez appearing on several occasions to inform about the situation, the progress of service restoration, and the measures taken, calling for calm and citizen responsibility. A significant security deployment was carried out, with 30,000 members of the National Police and Guardia Civil mobilized. The Military Emergency Unit (UME) was also prepared for possible intervention. Other measures included actively managing energy import from France and Morocco through interconnections and increasing national hydroelectric and combined cycle plant production.
The Portuguese Experience: Shared Crisis on the Peninsula
Portugal, intrinsically connected to the Spanish electrical system, suffered equally severe and widespread consequences from the blackout. Life in Portugal was paralyzed in a similar way to Spain. Public transport stopped, including the Lisbon Metro and national rail services. Mobile communications were severely limited. Hospitals resorted to their backup generators. Airports were affected, with Lisbon’s Humberto Delgado airport closing its terminals for hours. ATMs and electronic payment systems stopped working. Numerous rescues of people trapped in elevators were reported. Judicial activity stopped, and many businesses closed their doors. Testimonies from residents and tourists described scenes of chaos, confusion, and a general paralysis of activity.
The Portuguese government reacted by convening an emergency meeting of the Council of Ministers. Prime Minister Luís Montenegro held several conversations with his Spanish counterpart, Pedro Sánchez. Montenegro described the situation as “serious and unprecedented”. The Portuguese transmission system operator, REN, immediately activated restoration procedures, using the black start capability of hydroelectric and thermal power plants. The Portuguese police reinforced their presence in the streets. The Portuguese National Cybersecurity Center actively ruled out the cyberattack hypothesis.
The restoration process in Portugal progressed significantly during the afternoon and evening. REN reported restoring supply to hundreds of thousands and then millions of customers throughout the night. By the morning of Tuesday, April 29th, REN reported that electricity supply had been restored to 6.2 million of the country’s 6.5 million total users, representing over 95% recovery.
Secondary Effects: France, Andorra, and Additional Connections
Outside the Iberian Peninsula, the direct effects of the blackout were minimal and short-lived. In France, the incident was limited to some power cuts of a few minutes in areas of the French Basque Country near the Spanish border. The French transmission system operator, RTE, confirmed the rapid restoration of service and assured there was no risk of “contagion” to the French grid. In Andorra, the electricity supply was affected for just a few seconds before an automatic system switched the power to the interconnection with France. Internet connections in the principality also suffered a brief interruption. Gibraltar was not affected as it is not connected to the continental European power grid.
Despite the limited impact on its own territory, France played a crucial role in assisting the recovery of the Iberian system. RTE quickly mobilized to provide assistance to REE, initially providing energy support and offering to increase this aid as soon as the Iberian network was technically ready. Subsequently, as restoration progressed, France significantly increased its contribution, exporting up to 2,000 MW (2 GW) to Spain through the interconnections. This aid was explicitly acknowledged by the Spanish authorities.
Morocco also played a role in managing the crisis. Spain used the interconnection with Morocco to import electricity and help stabilize and restore supply in the south of the peninsula. On the other hand, the blackout in Spain had an unexpected collateral effect in Morocco: some Moroccan internet service providers reported service interruptions due to their dependence on computer servers physically located in Spain that went offline due to the power outage. This reveals the existence of hidden transnational digital dependencies.
Service Restoration: The Path to Normalcy
The process to restore electricity supply throughout the Iberian Peninsula was a complex and meticulous operation, coordinated by REE and REN following established protocols. The restoration strategy was based on the immediate activation of “restoration plans” designed for this type of contingency. A key element was the use of power plants with “black start” capability, able to start without external power supply, acting as initial nuclei to create energized network “islands”. From these islands, the gradual and controlled re-energization of the transmission network proceeded, sequentially connecting substations and progressively coupling other generation units as different areas stabilized. International interconnections with France and Morocco played a fundamental role in this process, allowing energy import to stabilize sections of the network and accelerate recovery. Simultaneously, production from available national thermal and hydroelectric plants was increased.
Initial estimates for full restoration varied, with REE initially calculating 6 to 10 hours, while REN was more cautious, suggesting total normalization could take up to a week. The actual restoration progress in Spain was remarkably fast, though with significant geographical variations. Shortly after the blackout, REE reported the start of voltage recovery in northern and southern areas. By 2:09 PM CET, approximately 20% of demand had been restored, and by 2:39 PM CET, 35% was reached. By mid-afternoon (around 7:20 PM CET), 45% of the transmission network substation parks were energized. Recovery continued at a good pace during the night. President Sánchez reported around 10:30-11:00 PM CET that almost 50% of the national supply had been restored, with 70% of substations operational. By midnight, 61.35% of demand had been recovered. Figures continued to improve during the early morning, with near full recovery by the morning of Tuesday, April 29th. By 6:00 AM on Tuesday, REE and the Ministry for Ecological Transition confirmed that 99.16% of peninsular demand had been recovered and 100% of transmission network substations were in service. At 7:00 AM, recovered demand reached 99.95%.
Restoration in Portugal also progressed significantly during the night. By the morning of Tuesday, April 29th, over 95% of users had their power restored. However, President Sánchez highlighted the “asymmetry” in recovery within Spain, with some autonomous communities reaching 97% restoration while others remained below 15% at certain times during the night. Progressive recovery was reported in specific areas like Catalonia, Aragon, Basque Country, Galicia, Asturias, Navarre, Castile and Leon, Extremadura, and Andalusia.
The restoration process, while fast compared to other major blackouts, was not without challenges. The operation’s very nature is complex, requiring precise coordination to avoid new instabilities when reconnecting network sections and synchronizing generators. Aftermath in the transport sector persisted, with long and medium-distance trains not resuming normal service until Tuesday, and commuter services planned with reduced capacity. Assistance to passengers on the last stranded trains extended well into Monday night. Recovery of communication networks also directly depended on restoring power to antennas and network equipment.
By the morning of Tuesday, April 29th, the energy situation had drastically improved. Electricity supply was practically restored throughout Spain (>99%) and Portugal (>95%). Transportation services began to resume, although with significant residual disruptions, especially in the railway sector. Air traffic control centers had recovered 100% capacity, and the Metro de Madrid resumed service. Most educational centers reopened, except in regions where the suspension was maintained. Infrastructures like the M-30 tunnels in Madrid also reopened. The main focus shifted from emergency restoration to full service normalization and the start of a detailed investigation into the causes of the blackout.
The Resilient Role of IoT During the Blackout
One of the more optimistic lessons from this event was the resilience shown by the Internet of Things (IoT). While traditional infrastructure collapsed, numerous IoT devices equipped with batteries or solar panels continued to function.
These devices not only continued operating but also securely stored data and waited for any minimal connection signal to transmit the accumulated information. Thanks to their reliability-based design, IoT solutions demonstrated their value in crisis situations, maintaining the traceability of essential data in sectors like logistics, renewable energy, and precision agriculture.
Indeed, IoT was fundamental in minimizing losses: refrigeration sensors reported real-time temperatures once the connection was restored, environmental monitoring systems continued recording vital data, and platforms like Cloud Studio showed their resilience capacity, collecting and processing data autonomously with no significant losses. Do you want to learn more about IoT? Explore our dedicated article.
Conclusion: Lessons Learned and the Path Forward
The blackout that paralyzed the Iberian Peninsula on April 28, 2025, is a milestone in the energy history of Spain and Portugal, not only for its unprecedented scale but also for the critical lessons it offers. The incident, triggered by a sudden and massive loss of power in the Spanish grid, likely due to a strong oscillation whose ultimate origin is still under investigation, demonstrated the deep interconnectedness and dependence of modern society on electricity supply. The consequences were immediate and widespread, severely affecting transportation, communications, essential services, and economic and social activity.
The coordinated response of network operators, governments, and international partners allowed for a relatively rapid restoration of supply, highlighting the importance of emergency protocols, the black start capability of certain power plants, and, crucially, the role of electrical interconnections with France and Morocco. However, the event also exposed significant vulnerabilities in the resilience of critical infrastructure, especially in communication networks and the capacity to maintain all services during a prolonged outage.
The lessons learned are clear and urgent. It is imperative to strengthen the resilience of electricity grids, not only by reinforcing physical infrastructure and interconnections but also by adapting operation and planning to the challenges posed by the transition to a system with high penetration of variable renewable energies. This involves investing in modernization, flexibility, and advanced control systems. Equally crucial is improving preparedness and contingency plans in all electricity-dependent sectors, adopting a cross-cutting approach that recognizes systemic interdependencies. Crisis communication and citizen education are also fundamental elements to mitigate the social impact of future events.
Ultimately, the Iberian blackout of 2025, although managed and overcome, serves as a powerful reminder that the security and reliability of our energy infrastructures cannot be taken for granted. They require constant vigilance, continuous investment, and proactive and adaptive planning to ensure that the foundations upon which our society rests are robust enough to face the uncertainties and challenges of the future. The resilience demonstrated by IoT devices during this event, continuing to collect and store data and being ready to transmit information upon connection, highlights the potential of such technologies as strategic allies in emergency scenarios and underscores the need to integrate resilient and connected technologies in critical infrastructure.
