The Lights Went Out in Spain and Portugal – Are Renewables to Blame?
by Bob Shively, Enerdynamics President and Lead Facilitator
At midday April 28, 2025, the entire Spanish and Portuguese mainland grid experienced a complete blackout—the largest in European history. This catastrophic event offers critical lessons for energy professionals regarding the importance of voltage control in modern power systems, particularly as the integration of renewable energy accelerates. However, it does not indicate that renewable generation was to blame. Let’s explore why.
Region of outage is shown in dark pink; the blue shows a region in France that was affected but not part of the full outage.
What Occurred: A Cascading System Failure
The blackout unfolded rapidly over just 33 seconds. Starting at 12:32:57, voltage levels began climbing dangerously across central and southern Spain, surging well above the regulatory maximum of 435 kV on the 400 kV transmission system. Multiple generators responded by disconnecting to protect themselves, causing the frequency to plummet from the target 50 Hz to just over 46.1 Hz. The cascading failure isolated the Iberian Peninsula from the European grid and triggered all six stages of emergency load shedding in less than 1.5 seconds—but it was too late for corrective measures to save the system. By 12:33:30, the entire system collapsed.
Remarkably, restoration began immediately, with 99.95% of power restored by 7:00 AM the following day, demonstrating the grid's recovery capabilities even after total system failure.
Understanding Voltage and Reactive Power Management
To understand why this happened, you must grasp the relationship between voltage control and reactive power. To do so, you must understand that there are two types of power required to run a grid – active power and reactive power. Unlike active power (measured in watts), which performs actual work, reactive power (measured in volt-amperes reactive, or VAR) is essential for maintaining proper voltage levels across the transmission system. Think of voltage as the "pressure" in the electrical system. Just as water pressure must be maintained within specific ranges in a plumbing system, electrical voltage must stay within tight bands—typically between 380 kV and 435 kV on Spain's main transmission network. Reactive power acts like a regulator valve, allowing generators and other equipment to either inject or absorb reactive power to maintain voltage within acceptable limits.
Traditional synchronous generators (nuclear, gas, coal, and hydro) provide both active and reactive power through their rotating machinery. They can quickly be adjusted to either inject or absorb reactive power, acting as the system's voltage regulators. This function can also be performed by power electronics associated with batteries, inverters on wind and solar generation, and other equipment such as synchronous condensors, static VAR compensators, and capacitors.
The Root Cause of the Outage: Insufficient Voltage Control
Spain's government investigation, issued June 17, 2025, identified multiple contributing factors with the primary cause being insufficient dynamic voltage control capacity. On April 28, only 11 thermal power plants were connected with voltage control obligations, the lowest number recorded that year. Several critical failures compounded the problem:
- Planning Errors: Grid operator Red Eléctrica de España (REE) miscalculated the energy mix and didn't activate sufficient thermal plants for voltage control
- Equipment Failures: Some connected thermal generators failed to respond properly, with one unit injecting reactive power when absorption was needed
- Premature Disconnections: Multiple generators disconnected before voltage thresholds were exceeded, accelerating the cascade
- System Stress: Voltage instability episodes had been building for days, with overvoltages recorded on April 22 and undervoltages on April 24
Renewables: Scapegoat or System Challenge?
Initial commentary blamed the high renewable penetration—82% of generation was from renewables at the time of failure. However, the official investigation decisively rejected this narrative. The system had adequate rotational inertia and frequency control capabilities before the incident. The real issue wasn't too much renewable energy, but rather the lack of voltage control services from non-synchronous sources. While solar and wind technologies can provide reactive power for voltage regulation, Spanish regulations didn't require or compensate them for this service. This created an over-reliance on the shrinking fleet of thermal generators for voltage control duties.
Generation mix and consumption in Spain prior to and after the outage (Source: entsoe.eu)
Building Resilient Systems for the Future
The investigation's recommendations provide a roadmap for preventing similar failures:
Immediate Measures
- Stricter enforcement of voltage control obligations for existing thermal generators
- Fast-tracking of procedures enabling power electronics solutions for voltage control
- Enhanced oversight of all grid participants' technical compliance
Long-term Solutions
- Create technology-neutral markets for voltage control services, allowing renewables and batteries to participate
- Deploy synchronous compensators and FACTS (Flexible AC Transmission Systems) across the peninsula
- Strengthen interconnections with France beyond the current 3% of capacity
- Implement grid-forming inverters and hybrid storage systems
Regulatory Evolution
- The incident highlights the urgent need to update grid rules that were designed for conventional power systems.
- Future regulations must recognize that renewable generators and storage assets can and should contribute to system stability services, including voltage control.
Conclusion
The April 28 blackout wasn't a failure of renewable energy—it was a failure to adapt grid management practices to a changing energy mix. As the energy transition accelerates globally, this incident serves as a crucial reminder that technical regulations, market structures, and operational procedures must evolve alongside the physical infrastructure. The future grid will be more renewable, but it must also be more resilient, with all participants contributing to system stability regardless of their technology type.
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