El power outage that left Spain and Portugal without electricity on April 28, 2025 It wasn't a simple, isolated failure, but rather the most obvious symptom of underlying weaknesses in the Iberian electrical system. What began as a very localized problem in southern Spain ended, in a matter of seconds, in the biggest energy meltdown seen in Europe in decades.
After months of analysis, a panel of 49 European experts coordinated by ENTSO-EThe association representing electricity transmission network operators across the continent has published its final report. The conclusion is clear: there was a “perfect storm” of technical, operational and regulatory factors which led the system to a point of no return, where not even properly activated defense plans could stop the electrical zero.
An unprecedented blackout in the Iberian Peninsula
On April 28, 2025, at noon, the The electrical system of Spain and Portugal completely collapsedIn just a few seconds, the Iberian grid lost synchronization with the continental European grid, leaving millions of users without power. France, interconnected with Spain, only experienced minor disruptions, highlighting that the epicenter of the problem was on the Iberian Peninsula.
The report places the origin of the incident in a initially a local problem in southern Spain which “escalated very rapidly,” affecting first the Spanish grid and then immediately the Portuguese system. By 12:32, very high levels of voltage were already being observed; at 12:33:23, the interconnections with France were disconnected and the Iberian system went into total blackout.
ENTSO-E experts describe the event as a a blackout of unprecedented magnitude in Europe in the last two decadesIt was not an isolated failure or a single human error, but a succession of oscillations, automatic disconnections and decisions conditioned by a technical and regulatory framework that was not prepared to manage a network with so much renewable generation based on power electronics.
In this context, the panel insists that There is no single identifiable culprit.The system, as it was configured and regulated, allowed a set of factors relatively well known in electrical engineering to combine until the network reached a critical situation from which it was no longer possible to escape without collapse.
What happened minute by minute: from fluctuations to collapse
The ENTSO-E document details a complex sequence of events In the half hour prior to the blackout, between 12:03 and 12:08, a first oscillation was recorded, associated with instabilities linked to equipment based on power inverters. Later, between 12:19 and 12:22, a second inter-area oscillation appeared, typical of energy exchanges between large areas of the European system.
These oscillations were a sign of “dynamic weakness” in the systemThe behavior of the network became very sensitive to small changes, and some generators did not have well-adjusted or even installed power system stabilizers (PSS), which limited the ability to dampen these disturbances.
Given these indications, the Spanish operator, Red Eléctrica, adopted measures such as reduce exports to France and reconfigure domestic linesOn paper, these were reasonable actions to contain the fluctuations, but some of these decisions indirectly contributed to further increasing the tension at certain points in the network.
From 12:32 onwards, the situation accelerated. A widespread increase in voltage was recorded at multiple nodes, while A significant portion of renewable energy generation was reducing its output. or it was automatically disconnected. According to estimates, around 500 MW of renewable generation were lost, in addition to more than 200 MW from other disconnections, while net demand increased due to the drop in distributed generation.
Within seconds, the Iberian system was operating virtually in “island mode” with respect to the rest of Europewith a delicate balance between generation and consumption. That balance could not be maintained: the frequency began to drop, the voltage remained uncontrolled, and finally, the interconnections with France were disconnected, and there was a total blackout in Spain and Portugal.
Voltage control and reactive power failures
If there is one element that appears repeatedly in the report, it is the poor voltage and reactive power managementThe investigation concludes that the determining factor in the collapse was the system's inability to maintain voltage within safe limits when disturbances were chained together.
On one hand, several conventional synchronous generatorsThe units theoretically responsible for providing voltage support failed to supply the expected reactive power. The analysis shows that, during critical hours, some units did not even meet 75% of the operator's reactive power requests. The report does not delve into the specific technical reasons for this at each plant, but it does emphasize that the regulations did not establish clear incentives or penalties for this non-compliance.
On the other hand, a large part of the renewable generation operated with a fixed power factorThis means that their ability to modulate reactive power exchange was tied to active power, so they could barely contribute dynamically to voltage regulation. Furthermore, the operating framework did not impose strict limits on the rate of change of active power, which can exacerbate transients and their interaction with voltage control systems.
The ENTSO-E panel also draws attention to certain network compensation equipment, such as shunt reactors, which required manual operationIn a crisis that unfolds in milliseconds, relying on human decisions and physical actions on the ground is simply too slow. This dependence on manual intervention is one of the points experts identify as incompatible with the dynamics of such a complex system.
The simulations carried out by the working group indicate that, with a greater available reactive power margin With more robust voltage regulation, the system would have been more likely to withstand the stress without collapsing. However, the existing design made the grid extremely sensitive to any disturbance when operating near its limits.
An outdated and undemanding regulatory framework
Beyond the purely technical aspects, the report focuses on the role of the Spanish regulatory framework at the time of the incident. Experts point out that the rules governing the provision of the voltage control service were incomplete: basic requirements were defined, but not clearly defined. dynamic response criteria or effective sanctioning regimes in case of non-compliance with reactive power support.
In practice, this meant that the system It did not internalize the true economic or operational value of reactive powerThe generators had a certain degree of freedom to not adjust their behavior to what the system needed at any given time without facing significant economic consequences, something the panel identifies as a structural weakness.
Another aspect criticized is the wide range of permissible voltages in the 400 kV network in SpainThis was more lax than in other European countries. This flexibility allowed the system to operate at relatively high voltages for extended periods, reducing the margin for error in the event of overvoltages. When the escalation of events occurred, this narrow margin between “normal” operation and automatic tripping of protective devices left very little room for corrective action.
The report also highlights the lack of clear incentives and sanctions linked to the dynamic behavior of conventional power plants. Compliance with certain static requirements was mandatory, but no maximum response times or penalties were established for failing to act quickly enough during critical moments. Following the blackout, the State Secretariat for Energy has implemented a specific sanctions regime, and the National Commission for Markets and Competition (CNMC) has drafted proposals to strengthen these requirements.
According to experts, the incident demonstrates that the regulatory design had not been adapted to the new energy transition scenario: a system with high penetration of renewables and power electronics It requires more detailed rules, economic mechanisms aligned with security of supply, and clear demands for dynamic behavior from all agents.
Renewables, self-consumption and distributed resources: part of the problem, part of the solution
The Iberian blackout has reignited the debate about the role of renewable energies in the stability of the system. The ENTSO-E report clarifies this discussion: clean technologies They are not the sole cause of the collapsebut their behavior in the current context contributed to worsening the situation.
First, the high penetration of inverter-based renewable generation This made the network more sensitive to certain dynamic phenomena. The forced instability observed in one of the previous oscillations is linked precisely to electronic conversion systems, revealing the need for more careful design and coordination of this equipment.
Secondly, many The renewable energy plants were configured to automatically shut down. Faced with certain overvoltage conditions, and even before reaching the permitted limits at the connection points, this massive generation shutdown at such a critical time increased the net demand that the rest of the system had to cover, accelerating the deterioration of stability.
The report also dedicates a significant section to self-consumption and small power generation connected to distribution networksA significant number of photovoltaic installations of less than 1 MW were disconnected in reaction to the overvoltage, which triggered a domino effect: with part of the distributed generation suddenly disappearing, the apparent load seen by the system increased, further complicating the task of the operators.
In terms of global control, experts conclude that The effective contribution of these small generators to voltage regulation was limited and poorly coordinated. with the system's needs. Furthermore, the lack of visibility and management capacity over these resources during the supply restoration process made it difficult to start up certain areas and keep them stable.
Red Eléctrica, European operators and the division of responsibilities
One of the most delicate issues in the report is to what extent Red Eléctrica and the other Spanish agents They are responsible for the event. The ENTSO-E investigation acknowledges significant deficiencies in the operation and monitoring of the network, but avoids pointing to a single culprit and emphasizes the systemic nature of the problem.
In the case of Red Eléctrica, experts point out that The connection and disconnection of critical elements for voltage control was performed manually.This form of operation introduces unavoidable delays in decision-making and in the execution of necessary actions, a serious handicap when the system enters a phase of rapid oscillations and chained events.
Furthermore, the study highlights that There was no sufficiently detailed real-time monitoring of the reactive power supplied by the power plantsThe operator needed that information to assess the risk when the voltage approached dangerous levels, but the lack of fine monitoring prevented anticipating the critical point.
Red Eléctrica, for its part, has stated in a press release that the report confirms its own internal analysis, published in June of the year of the incident, and maintains that It complied with regulations before, during and after the blackoutAccording to the company, the factors that triggered the power outage were multiple and not solely attributable to its actions.
The ENTSO-E panel agrees that responsibility is shared among transmission operators, distributors, large generators, and regulators. In their view, the incident is a manifestation of a structural problem in the provision and control of auxiliary services —especially voltage regulation— in an environment where converter-based generation is rapidly gaining ground.
Information gaps: the problem of missing data
One striking aspect of the experts' work is the difficulty accessing all the necessary data to accurately reconstruct the incident. The report dedicates a specific section to the limitations imposed by the absence of certain records, especially in the case of Spain.
The researchers explain that They were unable to obtain complete information about some generation disconnections prior to the blackout.Facility owners claimed that records were lost as a result of the disconnections themselves, leaving undocumented events that could prove relevant to understanding the exact origin of some shootings.
A significant example is the loss of approximately 725 MW of photovoltaic and solar thermal generation connected to two 400 kV substations in the Badajoz area. The lack of detailed records on these partial outages complicates the fine analysis of the failure sequence and the behavior of certain equipment.
To try to complete the picture, the ENTSO-E panel and the operators involved exchanged over 240 emails and letters between the end of May 2025 and February 2026, in addition to organizing meetings with distributors, generators, and other affected stakeholders. Even so, experts acknowledge that some information gaps have not been filled.
In contrast, the report highlights that in Portugal and France Transport operators provided the requested data more quickly and completely. This difference has led the panel to emphasize the need to strengthen obligations regarding the recording, retention, and provision of information critical to the investigation of serious incidents.
A system pushed to its limits: “point of no return” and service restoration
A detailed reading of the report reveals that, although The system's defense plans were activated correctly.The system was already in such an extreme condition that, once the cascade of events was triggered, total collapse was virtually inevitable. Experts speak of a true "point of no return."
The sequence of overvoltage disconnections, the loss of renewable and distributed generation, poorly damped oscillations, and insufficient available reactive power gradually pushed the system towards an unstable state from which it could no longer be recovered with the existing protection mechanisms.
Despite this, the panel positively assesses the supply replenishment processIn Portugal, the restoration was completed in about 12 hours; in Spain, around 16 hours. Experts emphasize that thorough restoration procedures were followed, well-defined contingency strategies were implemented, and there was active commitment from operators, generators, and other stakeholders.
However, during that phase, the following were also identified: relevant operational problemsThese include the difficulty in starting up certain generating units and the complexity of maintaining stability in specific areas of the grid. One of the cited causes is the limited information available on the status and performance of generators connected to the distribution networks, an increasingly important segment of the electricity mix.
Overall, the report insists that this blackout demonstrates that, in such an interconnected system with so much distributed generation, Local incidents can have regional consequences in a matter of seconds if safety margins have been narrowing over time.
Lessons for the future: coordination, monitoring, and new rules
Faced with an event of this magnitude, the ENTSO-E experts have focused less on assigning blame and more on extract practical lessonsThe final report includes 22 recommendations, grouped into blocks such as voltage control, oscillation management, disconnection criteria, contingency plans, and restoration procedures.
One of the most repeated ideas is the need to Strengthen coordination among all actors in the electricity systemTransmission operators, distributors, large generators, significant network users, and regulatory authorities are all involved. Managing complex events requires real-time information flow and a clear understanding of each stakeholder's role in stressful situations.
Another key line of work involves improve real-time monitoring of system behaviorThis is particularly important regarding reactive power, the status of voltage control equipment, and the response of distributed generation. Without a complete and up-to-date picture of what is happening on the grid, detecting instability risks in a timely manner is very difficult.
The panel also insists that the Regulatory frameworks need to be updated to support the transformation of the electricity system. This includes everything from reviewing operating procedures—such as PO 7.4 in Spain, relating to voltage regulation—to establishing stricter dynamic behavior requirements for renewables and distributed resources, including their active participation in voltage support services.
According to ENTSO-E officials, the proposed measures are technologically viable with current toolsIt is not about inventing futuristic solutions, but about coherently applying established electrical engineering knowledge to an environment where power electronics and distributed generation play a leading role.
The massive Iberian blackout has exposed the weaknesses of an electrical system that was rapidly moving towards the energy transition without having fully adapted its rules, control tools, or operational culture to a context dominated by power electronics and distributed resources. The ENTSO-E research describes a scenario in which technical deficiencies, regulatory gaps, lack of data, and conditional operational decisions These factors combined to cause a historic collapse. How the recommendations are implemented now—more coordination, better monitoring, new obligations for renewables and self-consumption, and much stricter voltage control—will determine whether that April 28, 2025, remains an isolated incident or the first warning sign of an electricity model that needs to adapt to the new European reality.
