Earlier this week, on April 28th 2025, a significant power outage hit the Iberian Peninsula, leaving millions of residents in Spain and Portugal without electricity. The sudden loss of power disrupted daily life on an unprecedented scale: trains were halted, airports suspended operations, and critical infrastructure was forced to rely on emergency backup systems. As one of Europe’s most prominent leaders in renewable energy adoption, Spain now finds itself at the centre of a complex discussion about the resilience and reliability of modern power grids.

Was this event an isolated technical failure, or does it reveal deeper challenges associated with the current integration of renewable energy sources? As investigations continue, the incident has sparked a broader debate about how best to balance the urgent need for decarbonisation with the necessity of maintaining a secure and stable electricity supply. The outcome of this conversation will have important implications not only for Spain but for all countries pursuing a cleaner future.

What Happened?

Timeline of Events

On Monday, at approximately 12:30pm local time, the power outage hit, and within seconds, Spain’s electricity generation plummeted by 15 gigawatts (almost half the peninsula’s load), triggering a widespread grid collapse. The event began with a technical fault, likely involving a high-voltage transmission line between France and Spain, which caused the Iberian grid to disconnect from the rest of the European network. This sudden separation led to a severe imbalance between supply and demand, resulting in a rapid frequency drop and the activation of automated protection systems that ultimately could not prevent the full blackout.

Immediate Effects

The blackout brought daily life to a standstill. All trains across Spain were halted, leaving passengers stranded in stations and tunnels. Airports, including Madrid’s Barajas International, lost power and operated on emergency generators, causing widespread flight delays and cancellations. Telecommunication networks were disrupted, and many residents were left without access to mobile or internet services. Hospitals and critical infrastructure switched to backup power, while emergency services urged citizens to remain indoors to allow for uninterrupted emergency response. Businesses, public offices, and even major events such as the Madrid Open Tennis tournament were suspended or cancelled.

By late afternoon, grid operators began restoring power in phases, with the Basque Country and Barcelona among the first to see electricity return. By Monday night, approximately 61% of Spain’s electricity supply had been restored, while Portugal reported full recovery by the following morning. Despite the rapid response, the disruption’s impact lingered, with ongoing travel delays and continued investigations into the root cause of the blackout.

What Caused the Blackout?

Authorities and grid operators in Spain (Red Eléctrica de España, REE) and Portugal (REN) are still investigating the precise cause, and as of May 2nd, officials have not yet identified a definitive explanation for the blackout and have urged the public and media to avoid speculation until the investigation is complete.

Initial Theories

Several technical factors have been identified as possible contributors. The sudden and dramatic drop of 15 gigawatts destabilised the grid, and experts have pointed to instability and strong oscillations in power flow as key triggers, leading to a cascade failure across the grid.

Some reports suggested that rare atmospheric conditions, such as “induced atmospheric vibration,” may have caused anomalous oscillations in very high voltage lines, further destabilising the system. However, Portuguese grid operator REN later downplayed this theory, emphasising that the investigation is ongoing and that such incidents are rare and not well understood.

Dismissed Causes

Authorities have ruled out certain possibilities. Both Spanish and Portuguese officials have stated there is no evidence of a cyberattack or fire on key transmission lines. The Spanish High Court is also investigating, but so far, has found no indication of malicious activity.

Technical Factors

One theory being mentioned a lot is the role of low grid “inertia” at the time of the incident. Inertia, typically provided by large rotating generators such as those in nuclear or gas plants, helps stabilise the grid against sudden changes. With a high share of renewables and reduced conventional generation, the grid’s inertia was lower than usual, making it more vulnerable to rapid disturbances.

In summary, while the investigation continues, early evidence suggests a complex interplay of grid instability, technical vulnerabilities, and possibly rare atmospheric phenomena, rather than a single, clear-cut cause. Authorities are expected to release more detailed findings as their analysis progresses.

The Renewable Energy Debate

Spain’s energy mix at the time of the blackout was dominated by renewable sources, with solar accounting for 53–59% of generation, wind contributing 11–12%, nuclear 11–15%, and gas 5–15%. Solar and wind now make up nearly 40% of Spain’s annual electricity production, double their share from fifteen years ago, positioning Spain as a leader in Europe’s renewable energy transition.

This rapid growth has fuelled both optimism and controversy. Following the outage, conservative critics and some media outlets were quick to blame the expansion of renewables and the gradual decline of nuclear power for making the grid more fragile. Opposition parties have questioned the government’s ambitious green transition policies, arguing that the country’s push for clean energy may have outpaced investments in grid stability and resilience.

However, grid operator, REE and independent experts have strongly rejected claims that renewables were to blame for the blackout. REE’s leadership called it “misguided” to attribute the outage to renewable energy, emphasising that Spain’s systems are specifically designed to manage the variability of wind and solar generation. Experts also highlighted that modern grid planning already factors in renewable intermittency, and described the blackout as “puzzling” given the sophisticated forecasting and management tools in place.

Looking Ahead

The aftermath of this unprecedented blackout has prompted a formal investigation, with a government commission and parliamentary inquiry established to determine the root causes of the outage and to assess the resilience of Spain’s energy system. There are also growing calls for independent reports to ensure transparency and to provide actionable recommendations for preventing similar incidents in the future.

A central lesson emerging from the crisis is the urgent need for grid modernisation. As Spain accelerates its transition toward renewables, investments in large-scale energy storage, flexible backup generation, and advanced grid management technologies are becoming increasingly critical. Battery storage and pumped hydro projects are being prioritised to help balance the variability of wind and solar power and to provide stability during periods of peak demand or unexpected disruptions. Enhanced digital tools for real-time monitoring and response will also play a key role in supporting a more flexible and resilient grid.

This moment comes as Spain remains committed to phasing out all nuclear power by 2035, with the first reactor scheduled to close in 2027. The government’s strategy is to replace nuclear and coal capacity with renewables, aiming for 81% of electricity to come from clean sources by the end of the decade. However, this ambitious path has generated debate among policymakers, industry leaders, and the public, especially as other European countries reconsider or delay their own nuclear phase-outs in light of grid stability concerns.