Five seconds to failure: Iberia’s blackout and grid resilience in a high-renewables future

Paddy Finn of VIOTAS writes on the grid failure that plunged the Iberian Peninsula into darkness and what is says about grid resilience for European operators looking to accelerate the uptake of renewables into the energy system.

On 28 April 2025, at precisely 12:33:20, the Iberian Peninsula plunged into blackout. Within just five seconds, a cascading failure triggered by the near-simultaneous disconnection of two solar farms in southwestern Spain resulted in the loss of 15 GW of generation capacity. It ultimately islanded Spain and Portugal from the Continental European Grid, leaving operators across the region scrambling to understand how an apparently minor disturbance could evolve so rapidly into a regional blackout.

Initial speculation pointed to cyberattacks or rare atmospheric conditions, but both were swiftly ruled out. The root cause, while still under formal investigation, appears to stem from a combination of factors that are becoming increasingly familiar to utilities worldwide: high renewable penetration, low inertia, insufficient fast-response reserves, and a planning framework built around outdated assumptions.

This wasn’t just a Spanish or Portuguese problem. It was a warning signal for every grid in Europe that is accelerating its decarbonisation journey.

For decades, utilities have designed their systems around the loss of the single largest infeed — typically a nuclear or gas plant — as the most credible contingency event. Contingency reserves have been sized accordingly, and in that context, this approach has served grids well.

However, the Iberian blackout illustrates how risk is evolving. The greatest threat may no longer come from a single, large failure but from multiple, smaller disturbances that escalate rapidly. These challenges are becoming more likely as systems shift to higher shares of inverter-based renewables like wind and solar.

These technologies, while essential to achieving climate goals, do not inherently provide inertia — the stabilising force of traditional rotating generators. Without inertia, frequency changes can occur almost instantaneously, leaving very little time for operators or automated systems to respond.

In Spain’s case, contingency reserves were designed to respond within 15 seconds. But the system destabilised in just 5 seconds. Currently, it appears that this was not a result of defined operational procedures not being followed, but a reflection of how quickly system needs are evolving — and how essential it is to continue adapting operational standards.

More insights into the Iberian blackout:
Spain and Portugal recover from massive power outage
Jolt to the system: What the Iberian blackout says about grid investment

At the time of the event, nearly 70% of Spain’s electricity was being generated by wind and solar. The system was exporting power to Portugal, France, and Morocco, while also storing excess generation via pumped hydro. On paper, everything looked stable.

But beneath the surface, a convergence of technical factors created a system vulnerable to rapid disruption. The near-simultaneous tripping of two large solar farms triggered sympathetic tripping from other nearby assets. Within moments, the system faced a 15 GW shortfall — far greater than the scale most contingency reserves are designed to manage.

Portugal, which was importing roughly 30% of its electricity from Spain, experienced similar impacts. France temporarily supported the Iberian grid until the interconnectors disconnected to protect system stability, effectively isolating the region.

In the first chart below, we can see the frequency on the French grid drop as it swings from being a consumer to being a supportive provider to Spain, followed by a rapid increase in frequency, like a spring releasing as the interconnector disconnects and the load drops. Fortunately, this is quickly arrested, presumably due to the activation of automatic protection measures, with the frequency resynchronising to the wider grid. Thanks to the speed at which this oscillation was brought under control, France emerged largely unscathed, with the French Basque Country, in the southwest, experiencing relatively minor power outages lasting only a few minutes.

Sympathetic tripping, once considered rare, is increasingly observed in grids with lower inertia. As renewables rise and rotating mass declines, small disturbances can travel farther and faster — a dynamic now prompting system operators to re-examine assumptions around fault containment and recovery.

Utilities around the world a have made tremendous progress integrating renewable energy. From Great Britain, Germany and Ireland to Australia and the US, decarbonisation efforts are reshaping generation portfolios and system behaviour. The Iberian event offers a valuable opportunity to reflect on emerging challenges and resilience strategies. Here are four key questions system operators might now consider:

• Are contingency reserves scaled for today’s most likely scenarios? Systems may benefit from reviewing whether current reserve volumes are sufficient to address potential cascading losses, not just single largest events.
• How fast does response need to be? Sub-second responses are becoming increasingly important. Ireland’s system, for example, includes services that activate in under 150 milliseconds — a speed that proved valuable in recent near-miss incidents.
• Are all available resources being used effectively? Technologies like synchronous condensers can help restore inertia, while Virtual Power Plants and demand-side response offer ultra-fast, decentralised flexibility. Many of these tools are in place but remain underutilised.
• Is cross-border coordination robust enough? Interconnected systems bring efficiency and security but also require shared contingency planning and harmonised operational responses.

Grid resilience today is as much about speed and coordination as it is about supply and demand. The Iberian event highlighted how quickly conditions can change — and how quickly responses must follow.

High-speed grid monitoring in France showed how the system adapted within moments as it shifted from exporter to emergency support. In systems like Ireland’s, where high-resolution monitoring and ultra-fast services are already deployed, the foundational tools to manage such risks are in place.

But tools alone are not enough. Operational strategies, planning criteria, and procurement practices all need to reflect the evolving nature of system risk. The Iberian blackout presents an opportunity to revisit assumptions, update standards, and invest in the speed and diversity of response mechanisms.

One of the most important takeaways is that stability models must now consider the possibility of rapid, compounding failures — not just isolated disturbances. This shift in perspective can guide more resilient design, ensuring that clean energy growth is matched by equally robust safeguards.

Prof. Paddy Finn is the CEO & CTO of VIOTAS, an international smart grid technologies and services company, headquartered in Limerick, Ireland.

Since entering the electricity market in 2014, the company’s Irish portfolio has grown to be capable of offering similar grid balancing capability at some of the country’s largest power plants, while avoiding the cost and carbon emissions associated with building new grid infrastructure.

Finn is responsible for the strategic direction of VIOTAS, including the company’s research and development activities, and international expansion.