How did Spain’s electricity grid collapse

On April 28, 2025, Spain experienced one of the most severe electrical failures in modern European history, with effects cascading across the Iberian Peninsula.

Within mere seconds, the Spanish electrical grid went from normal operations to complete collapse, triggering a peninsula-wide blackout that affected more than 50 million people and lasted nearly ten hours in most areas. This report examines the sequence of events, potential causes, and factors that contributed to this unprecedented grid failure.

The Cascading Failure Sequence
The collapse of Spain's electrical grid unfolded with remarkable speed. At 12:33 CEST, a series of rapid events destabilized the entire system within just five seconds. According to Red Eléctrica de España (REE), Spain's grid operator, the failure occurred in distinct stages:

First, REE systems detected "an element compatible with a loss of generation" in the southwestern peninsular region. While the grid's automatic protection systems successfully managed this initial disruption, approximately 1.5 seconds later, a second generation loss occurred. This second event proved catastrophic, as it triggered massive disconnections across the system. Within five seconds, approximately 15 gigawatts of electricity generation-representing about 60% of Spain's demand at that moment-vanished from the system.

The sudden, dramatic imbalance between generation and demand caused severe frequency fluctuations, with the grid frequency dropping from the standard 50 hertz to 49 hertz. This destabilization triggered automatic disconnection protocols in power plants across the peninsula, designed to protect equipment from damage. As Eduardo Prieto, Services Director at REE, explained: "A second and a half may not seem like much, it's nothing for human action. In the electrical world, it is a very long time".

Cascade of Protective Disconnections
The grid destabilization set off a chain reaction of protective measures that ultimately exacerbated the crisis:

The French electrical system detected the frequency anomalies in the Spanish grid and automatically disconnected to protect its own system and the rest of Europe's integrated grid. This disconnection proved particularly problematic as it removed a potential external stabilizing force for the Spanish system. Nuclear power plants throughout Spain triggered emergency SCRAM procedures, automatically shutting down reactors to prevent overheating during the supply disruption. This further reduced available generation capacity at a critical moment.

As Álvar de la Fuente Gil, professor of electrical engineering at the University of León, explained: "This widespread blackout happened because, within a mere five seconds, more than half of the electricity generation capacity was lost". The grid simply could not manage such a severe mismatch between generation and demand, forcing it to disconnect both internally and from the broader European grid.

Grid Conditions at the Time of Failure
At the moment of the blackout, Spain's electrical grid was operating under specific conditions that may have influenced its vulnerability:

Generation Mix and System Load
At 12:30 CEST on April 28, just before the blackout:

• Solar photovoltaic generation dominated the mix at 54.86% of total generation
• Wind power contributed 10.87%
• Nuclear provided 10.52%
• Hydroelectric supplied 9.86%
• The remainder came from various sources including solar thermal (4.65%), combined cycle gas (3.05%), and other minor sources
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According to Red Eléctrica's data, the grid was producing approximately 32 gigawatts to meet 25 gigawatts of demand, with surplus power being exported to France (0.87 GW), Morocco (0.78 GW), and Portugal (2.6 GW), plus 3 GW dedicated to hydropumping. This indicates the system had sufficient generation capacity prior to the failure.

Critical Grid Vulnerability Factors
Several technical factors may have increased the grid's susceptibility to cascading failure:

Low System Inertia: Industry experts noted that at the time of the outage, the Spanish grid was operating with minimal "inertia"-the stabilizing energy stored in large rotating masses of traditional generators. With high solar penetration (primarily inverter-based technology that provides no natural inertia), the system had less inherent ability to resist frequency changes during disturbances.

Limited International Interconnections: Professor Miguel de Simón Martín highlighted that while Spain's grid has historically been reliable due to its extensive high-voltage transmission network, its geographical isolation by the Pyrenees has always limited its international connections. These connections could otherwise provide stability during crises.

Rapid Solar Production Changes: Red Eléctrica's figures show that within just five minutes (12:30-12:35), solar PV generation plummeted from over 18 GW to just 8 GW. While not necessarily the initiating cause, such volatility could have contributed to system instability.

Warning Signs and Prior Incidents
The April 28 blackout did not occur without warning. Multiple incidents and concerns had been documented in the preceding months:

Previous System Warnings
Red Eléctrica had issued several warnings about potential vulnerabilities in the system:

In January 2025, REE warned the government about possible system failures due to the increasing penetration of renewable energy sources. In March 2025, REE's parent company Redeia specifically warned of the risk of "severe disconnections" as renewable energy percentage increased, and cited the closure of conventional coal, nuclear, and gas plants as additional factors creating uncertainty for grid stability.

Recent Near-Miss Incidents
Just six days before the nationwide blackout, Red Eléctrica documented two similar but less severe incidents that nearly destabilized the system:

On April 22, 2025, a combination of changing power exchanges with Portugal, reduced photovoltaic production, and rainfall in central Spain caused voltage oscillations in the system. Engineers managed to stabilize the grid within five minutes. On April 24, 2025, another incident involving sudden increases in exports to France combined with fluctuating photovoltaic generation created transient voltage problems that were successfully controlled.

Red Eléctrica acknowledged in an internal report that on April 22, they experienced a combination of incidents that, while "relatively frequent in operation," had "never all coincided at the same time". The system withstood these challenges on April 22 and 24 but ultimately failed when facing similar conditions on April 28.

Ongoing Investigation
As of early May 2025, the definitive cause of the blackout remained under investigation. Several important developments in the investigation include:

Red Eléctrica has provided its complete system logs-described as the grid's "black box"-to government investigators, including millions of data points recording system operations during the incident. The European Commission has required the Spanish government to submit a comprehensive investigation report within three months, and is conducting its own independent technical analysis to be completed within six months.

Additional analysis has identified a third incident that preceded the major failure, occurring 19 seconds before the blackout in southern Spain, followed by two more incidents in the southwest region. According to Environment Minister Sara Aagesen, the system successfully managed the first incident but could not recover from the subsequent disruptions.

Disputed Factors and Political Debate
The blackout has ignited significant debate regarding the role of renewable energy in grid stability:

Some industry sources have pointed to the volatility of photovoltaic technology in terms of frequency stability as a potential contributing factor. However, Spanish President Pedro Sánchez has forcefully rejected claims that excessive renewable energy caused the outage, stating that those linking the blackout to insufficient nuclear power "are lying or demonstrating their ignorance". Minister Aagesen similarly called blaming renewables "irresponsible and simplistic," while acknowledging that the increasing complexity of modern electrical systems presents new technical challenges.

Both Spanish and Portuguese authorities have ruled out cyberattack as a cause of the blackout.

Conclusion
The collapse of Spain's electrical grid on April 28, 2025, resulted from a complex sequence of events that unfolded with extraordinary speed. While the exact triggering events remain under investigation, it's clear that within just five seconds, cascading failures led to the loss of 60% of Spain's electricity generation, creating an insurmountable imbalance between supply and demand.

The incident highlights several potential vulnerabilities in modern electrical grids with high renewable penetration, particularly regarding system inertia and frequency stability during disruptions. However, it also demonstrates how quickly even robust systems can fail when multiple adverse conditions coincide. The ongoing technical investigations will likely yield important lessons for grid operators worldwide as they navigate the transition to renewable-dominated power systems while maintaining essential reliability.

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