The blackout in Portugal and Spain: Summary for EU Energy Industry

On April 28, 2025, a widespread power outage plunged mainland Spain and Portugal into darkness, marking one of the most significant blackouts in the history of the European grid.

Even if the real satellite imagery of luminosity changes isn't as dramatic as the widespread edit of the Iberian peninsula from space, a blackout of this caliber is no walk in the park.

Affecting millions, disrupting transport, communications, and daily life, this event served as a stark "wake-up call" regarding the urgent need to modernize and reinforce Europe’s electricity grid, particularly as it integrates increasing amounts of renewable energy.

Wide-spread edited image of the Iberian peninsula during the blackout.

However to give credit where credit is due, if nothing else, this contrast can be illustrative of how much worse such an event could be.

As an energy software development focused company, Wirtek understands the critical importance of grid stability and resilience, especially during this period of rapid energy transition.

This article delves into the available information about the Iberian blackout, distinguishing between official statements, ongoing investigations, technical analyses and speculative theories.

We explore the crucial steps needed for prevention, mitigation, and faster service resumption.

What Happened on April 28, 2025?

Spectators roam inside the Madrid Open tennis tournament venue during a general blackout in Madrid. (Source: AP Photo, Manu Fernandez)

The blackout occurred around 12:30 pm local time in Spain. At that moment, the Iberian system was characterized by a very high share of renewable generation, with renewables accounting for 78% of the power mix and solar alone contributing nearly 60%. Conventional sources like gas and nuclear comprised only about 15%. Negative electricity prices were observed, Spain was exporting power, and hydroelectric facilities were operating at their regulatory limits.

According to Spain’s national electricity grid operator, Red Eléctrica de España (REE), the blackout was triggered by two consecutive generation loss events in southwestern Spain. The grid reportedly stabilized after the first event but could not cope with the second. Approximately 1.5 seconds after the first event, a second one occurred, followed about 3.5 seconds later by a disconnection from the French system due to instability. This led to a massive loss of capacity – around 15 gigawatts (GW) in Spain (60% of demand) and 5 GW in Portugal – within just five seconds, triggering a cascading failure across the entire grid. Automatic protection mechanisms caused generating units and nuclear plants to shut down. The system experienced a complete electrical blackout across the mainland.

Restoring power required a "black start" process. Recovery was gradual, initially relying on internal generation and later utilizing limited interconnections with Morocco and France. Power began returning within hours and was largely restored by the morning of April 29. Grid operators in Spain and Portugal were congratulated for the "rapid recovery".

Official Statements & Ongoing Investigations

Immediately following the event, official statements confirmed the massive scale of the outage and its impact across both countries. Spanish Prime Minister Pedro Sánchez initially stated that the causes were unknown and had not yet been established by experts. Portugal's Prime Minister, Luís Montenegro, confirmed the problem originated in Spain.

REE initially ruled out a cyberattack, human error, or a meteorological/atmospheric phenomenon as the cause, although reports citing the Portuguese grid operator about an "induced atmospheric vibration" were later denied by the source. REE did state that it was "very possible that the affected generation [in the initial events] could be solar". The president of Redeia, REE's parent company, stated the fault was not REE's and it would be wrong to blame renewables. Spain's environment minister also pushed back on blaming solar, citing past system performance under similar conditions.

Crucially, the exact causes remain under investigation. Multiple investigations are currently underway:

• Spain has asked its own investigators and EU regulators to investigate.
• Spain’s Prime Minister launched an inquiry involving cybersecurity and intelligence services (INCIBE, CNI).
• Spain’s High Court will investigate whether the event was a result of a cyberattack.
• Portugal is setting up an independent technical commission.
• The EU Energy Commissioner will open a “thorough investigation”.

Despite initial preliminary statements ruling out cyberattacks, the fact that it is still under investigation by high-level bodies highlights the need for a comprehensive examination of all possibilities.

Technical Analysis and Emerging Theories

While the official investigations are ongoing, technical analysis and theories drawing on the known grid conditions at the time have emerged:

• The Role of Renewables and Grid Stability: A widely discussed issue is the inherent vulnerability of grids with high shares of renewable energy like solar and wind. These sources typically use grid-following inverters that synchronize with the existing grid frequency but do not autonomously support stability during disturbances. In contrast, traditional synchronous generators in conventional power plants provide electrical inertia, which helps stabilize grid frequency and voltage during sudden fluctuations. With high renewable penetration and declining conventional generation, the grid has less inertia to absorb shocks. Experts point out that the Iberian system likely lacked the necessary inertia to absorb the initial generation-loss shocks on April 28, leading to the cascading failure. This aligns with the observation that few stable base-load sources were active at the time.
  
  
• Frequency Issues: The theory that a divergence from the standard 50 Hertz (Hz) frequency caused parts of the system to shut down to protect equipment is plausible. Oscillations in grid frequency shortly before the event have been noted.
  
  
• Interconnection Limitations: The instability triggered a disconnection from the French system. The Iberian Peninsula's power systems are known to lack sufficient connections to other grids for backup. Spain has only about 5% interconnection capacity outside the Iberian Peninsula. This lack of robust interconnections meant limited external support was available to help stabilize the grid after the initial failures and played a role in the slower recovery.
  
  
• Specific Generator Trips: REE's statement about the possibility of the initial affected generation being solar and analysis suggesting a sudden drop from solar photovoltaic sources points towards potential issues with how specific renewable facilities responded to initial fluctuations or specific faults. However, experts note that generator trips happen frequently across all types, and a robust grid should be designed to withstand multiple losses. The scale of the loss (15GW) suggests thousands of facilities or a few very large ones were involved.
  
  
• Potential Grid Management/Software Issues: One theory suggests the event points to a potential problem in grid synchronization and that computer programs managing systems may not have been prepared for this kind of situation.
  
  
• Economic and Policy Influences: Analysis suggests that low or negative electricity prices, driven by high renewable output, made it economically unviable for nuclear plants to operate due to taxes, leading to reduced conventional capacity availability. This economic pressure on conventional sources could indirectly contribute to grid instability if insufficient backup or stability services are procured or available.

It's important to reiterate that many of these points are technical analyses and theories explaining how the grid failed given the initial triggers, rather than confirmed root causes. The precise trigger(s) and sequence of events leading to the massive capacity loss are still under investigation. Most experts agree that the blackout was likely the result of a cluster of factors—a "perfect storm"—rather than a single failure.

Lessons Learned: Strengthening the Grid

The Iberian blackout underscores that successfully transitioning to a grid dominated by variable renewable energy requires significant investment and technical advancements beyond simply installing more wind and solar capacity. The event highlights several key areas for action:

1. Massive Infrastructure Investment: Europe's ageing grid infrastructure, much of it dating back to the last century, needs a trillion-dollar upgrade to cope with rising green energy, increasing demand (from data centres, EVs), and to avoid blackouts. This includes rebuilding and adding more power lines over long distances. The International Energy Agency estimates annual global grid investment needs to double by 2030. The European Commission estimates Europe needs $2.0-2.3 trillion in grids by 2050.
2. Enhanced Energy Storage: More storage capacity is essential for grid stability. Technologies like battery systems and pumped-storage hydropower can manage energy surpluses and provide rapid power injection or absorption. While Europe plans to increase battery storage capacity, the required 200 GW needed by 2030 is significantly higher than current levels.
3. Improved Interconnections: Increasing cross-border grid connections enhances resilience by allowing neighboring systems to provide backup and helps stabilize frequency. Reprioritizing infrastructure proposals, like Spain's links to France and Morocco, is crucial to prevent regions from operating as electrical islands.
4. Advanced Grid Stabilization Technologies: As conventional sources decline, grids need new ways to provide stability services.
   • Grid-Forming Inverters: Investing in and deploying grid-forming inverters for renewable sources is a widely recognized recommendation. These devices can mimic conventional generators, establishing stable voltage and frequency references and supporting grid stability. While promising, they need further testing and development for large, interconnected grids.
   • Sophisticated Inverter Control: For existing inverter-based resources like batteries, developing and programming their inverters to respond effectively to grid condition fluctuations is key.
   • Alternative Inertia Sources: Deploying technologies like flywheels can also help stabilize the grid.
5. Maintaining Essential Backup Capacity: Ensuring the availability of synchronous backup power (hydro, gas, nuclear where applicable) remains critical for moments when variable renewables are insufficient or disturbances occur. Policies need to address how these essential services are compensated, particularly when market prices are low due to high renewable output.
6. Modernizing Grid Management Systems: The potential role of computer programs suggests a need for sophisticated grid management systems prepared to handle complex, high-renewable scenarios, including issues like synchronization and cascading failures.
7. Clear Policies and Cost Allocation: The blackout raises the question of who should pay for necessary grid upgrades and stability services. Some argue that renewable producers should contribute to the costs of maintaining stability services required by their integration. Clear, technically informed policies are needed to ensure grid stability costs are addressed and not simply postponed. Decision-making on energy infrastructure should be guided by independent technical expertise.

Conclusion

The Iberian Peninsula blackout of April 28, 2025, serves as a critical learning event. While the exact root causes are still under investigation, it starkly highlighted the technical challenges associated with integrating high levels of variable renewable energy into aging grid infrastructure. The event underscored the need for adequate inertia, improved interconnections, sophisticated control systems, and sufficient backup capacity.

Moving forward with the energy transition requires a holistic approach that prioritizes grid resilience and stability alongside renewable deployment. Significant investments in infrastructure upgrades, energy storage, advanced grid technologies, and potentially revised market/policy frameworks are essential steps to prevent similar widespread outages and ensure a reliable, secure, and sustainable energy future. The ongoing investigations will provide crucial data, but the technical pathways to a more resilient grid are already becoming clear.

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About Wirtek

We are a Danish IT Services and Solutions company that provides software development, embedded engineering, R&D, Quality Assurance, and testing services to help clients worldwide.

We specialise in Energy, Wireless Communication, Automation & IoT, as well as helping clients within X-Tech. We also offer our own product solution portfolio for the energy and IoT sector.

At Wirtek, we prioritise building long-term client relationships, with some lasting over a decade. We believe that quality partnerships are just as important as software quality in achieving our clients’ goals.

Established in 2001 as a spin-off from NOKIA, we have offices in Denmark, Romania, and Portugal, and have been listed on Nasdaq First North Copenhagen since 2006. 

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