The Iberian Peninsula Blackout — Causes, Consequences, and Challenges Ahead

The Iberian Peninsula Blackout and Renewable Energy

On April 28, 2025, the entire electrical system of Spain and Portugal shut down. Apart from the islands, which operate on separate grids, both countries — as well as parts of southern France connected to the Iberian network — were plunged into darkness. This was one of the most significant blackouts in the history of the European grid. 

To analyze this widespread power outage and its implications, this commentary examines the following: 

• Sequence of events preceding and during the Iberian Peninsula blackout.
• Potential underlying causes of the blackout.  
• Key lessons for electricity systems undergoing rapid transitions toward high shares of renewable generation, as is the case in the Iberian Peninsula. 
• Challenges ahead for policymakers and energy system planners across the Iberian Peninsula and in other countries pursuing similar energy transitions.

What Happened on April 28 and the Aftermath

At approximately 12:30 pm local time in Spain — just minutes before the grid collapsed — renewable sources accounted for 78% of electricity generation in the Iberian system, with solar alone contributing nearly 60%. By contrast, conventional technologies, such as gas-fired and nuclear power plants, comprised only around 15% of the total generation mix. This configuration is not unusual in Spain or Portugal, where high shares of renewable generation are common, particularly during sunny and windy days.

What sets April 28 apart, however, is that, according to Spain’s national electricity grid operator (Red Eléctrica de España), two consecutive generation loss events occurred in southwestern Spain, likely involving large solar installations. Currently, the exact causes remain under investigation. Given the limited availability of conventional generation, these unexpected losses, combined with reduced support from neighboring systems — the instability triggered a disconnection from the French system — created a “perfect storm” for a massive power outage.

In just five seconds, Spain lost approximately 15 gigawatts of capacity, equivalent to 60% of its national electricity demand. The remaining generation was insufficient to meet demand, thus triggering a cascading failure across the entire grid.  Various generating units were automatically disconnected to protect infrastructure, and nuclear plants were shut down in accordance with safety protocols. 

Within hours, the Iberian Peninsula experienced a complete electrical blackout. Thus, the entire mainland of Spain and Portugal was simultaneously without power, a situation that lasted for several hours.

The system required a black start — meaning a process for restoring power from a total system shutdown — which initially relied on internal generation. Subsequently, the limited interconnections with neighboring countries also played a key role; Morocco supplied up to 900 megawatts through transmission lines across the Strait of Gibraltar, while France contributed up to 2 gigawatts. The recovery was both gradual and uneven across regions. 

That same day, power began returning around 5:00 pm local time and continued progressively into the night and early morning of the next day. By 6:00 am on April 29, 99% of national demand had been restored, an outcome considered a relatively swift and successful black start. However, by that time, the event had caused several casualties, including thousands of individuals being trapped in trains, elevators, and other electrically dependent infrastructure.

Grid Vulnerabilities Exposed

The risk of large-scale blackouts in electricity systems with high shares of renewable energy is well-established. However, the Iberian blackout of April 28 brings these long-recognized vulnerabilities into sharp focus. 

A central issue lies in the lack of ancillary services, in particular frequency regulation and inertia, which are traditionally provided by synchronous generators in conventional power plants, such as nuclear, thermal, and hydroelectric facilities. These generators contribute electrical inertia through their rotating masses, helping to stabilize grid frequency and voltage during sudden fluctuations or imbalances. By contrast, solar and wind installations typically operate with grid-following inverters —devices that synchronize with the grid’s existing frequency and voltage rather than establishing those parameters themselves. These systems depend on a stable grid to function correctly and cannot autonomously support grid stability during disturbances.

As the share of inverter-based renewables increases and the presence of conventional generation declines, the grid becomes more vulnerable to potential disruptions, as was the case on April 28. In the moments leading up to the incident, the generation mix was characterized by a high proportion of solar and limited conventional generation. In turn, this meant that the Iberian system lacked the inertia needed to absorb the initial generation-loss shocks. Automatic protection mechanisms were triggered, including the disconnection of transmission lines and generating units, ultimately resulting in cascading power outages. 

Grid Stability Solutions and Concerns for High-Renewable Systems

One of the most widely recognized and urgent recommendations for mitigating the risk of grid destabilization is to invest in grid-forming inverters. These inverters enable renewable resources to mimic the behavior of conventional power plants by establishing a stable voltage and frequency reference, thereby helping to maintain grid stability during disturbances. For system operators such as the one in Spain, these investments are increasingly viewed as a key measure to mitigate grid instability and are expected to garner more attention in the aftermath of the April 28 blackout. In fact, much of the current energy system debate in Spain centers around the deployment of grid-forming technologies.

However, while grid-forming inverters represent a promising step toward improving system stability in high-renewable scenarios, significant challenges remain. First, although grid-forming inverters have been successfully deployed in microgrids and isolated systems, such as in parts of Australia and Hawaii, they have not yet been widely tested in large, interconnected grids. Second, these inverters are typically designed to set the grid’s frequency reference. Most systems rely on a single inverter to perform this role. Attempting to operate multiple inverters in this mode simultaneously can lead to conflicting frequency signals. Current research is exploring new approaches that involve coordinating multiple grid-forming inverters to work together to maintain grid stability.

Pumped-storage hydropower plants and battery systems are also seen as key elements for managing energy surpluses and ensuring supply during critical moments. Batteries, in particular, can potentially support grid stability by rapidly injecting or absorbing power. However, since they are also inverter-based technologies, the core challenge remains: designing and programming their inverters to respond effectively as grid conditions fluctuate. Electricity systems, such as Electric Reliability Council of Texas (ERCOT) in Texas, are actively exploring these possibilities with batteries through simulations and controlled testing environments. However, as of now, there are no proven models for large-scale deployment of battery-based grid stabilization in complex, interconnected systems, in which a large amount of storage capacity will be needed.

Finally, another key area of concern is the flexibility and capacity of grid interconnections, particularly between Spain and France. Infrastructure proposals aimed at increasing interconnection capacity have gone unfulfilled, but should be urgently reprioritized, both to prevent the Iberian Peninsula from continuing to operate as an electrical island and to enhance its overall resilience.

Rethinking Costs and Responsibilities in the Renewable Transition

One of the immediate risks following the Iberian blackout is a potential public backlash against renewable energy. However, renewables themselves were not the root cause of these sweeping outages. The key lesson is that ensuring the stability, reliability, and resilience of a grid dominated by variable renewable energy sources requires more than simply increasing the number of solar panels and wind turbines. These technologies should be supported by a grid specifically designed to accommodate their characteristics and variability. 

Put simply, an upgraded grid is essential for the energy transition to succeed. This leads to a critical and often overlooked question: Who should pay for it?

Renewables often displace conventional generation, which then remain idle for extended periods. This makes it more difficult for coal, gas-fired, and nuclear operators to recover their fixed costs and can discourage future investment. As a result, the availability of conventional resources tends to decline as renewable penetration increases. This displacement brings notable environmental benefits, as it reduces well-known environmental externalities, such as CO2 emissions and other pollutants that are associated with conventional generators. These benefits have long justified the provision of subsidies and tax incentives to support renewable deployment. 

However, as the events of April 28 illustrate, renewables also introduce new system-level requirements — such as frequency control and inertia, typically provided by conventional generators — that, if not adequately addressed, can undermine grid stability and potentially lead to blackouts. By the same logic that has justified financial support for renewables’ environmental benefits, renewable producers should also contribute to the cost of maintaining grid stability that is required as their integration increases within the system.

This logic, though, is potentially politically sensitive. In the past, policies requiring that solar and wind project expenses contribute to grid costs were met with public resistance in Spain. As a result, the extra costs of maintaining stability in high-renewable systems are often passed on to consumers — or simply postponed, potentially contributing to future issues. 

As the need for strategic grid investment becomes increasingly recognized, the debate over who should fund it will only grow louder — unless political forces attempt to reverse the energy transition altogether.

This publication was produced on behalf of Rice University’s Baker Institute for Public Policy. Wherever feasible, the material was reviewed by external experts prior to its release. Any errors are the responsibility of the author(s) alone. 

This material may be quoted or reproduced without prior permission, provided appropriate credit is given to the author(s) and Rice University’s Baker Institute for Public Policy. The views expressed herein are those of the individual author(s) and do not necessarily represent the views of Rice University’s Baker Institute for Public Policy.