By Zach Dodds-Brown – Development Director
Terra Firma Energy – May 2025

On 28 April 2025, the Iberian Peninsula experienced one of the most severe blackouts in European history. Within seconds, vast areas across Spain and Portugal lost power, and parts of southern France were also impacted. At its peak, tens of millions were without electricity for hours. Public transport systems failed, communication networks collapsed, and emergency services were stretched thin. Tragically, seven deaths have been reported as a result of the outage.

While investigations are still ongoing, the evidence points strongly to an underlying and widely understood issue in modern grid operation: the imbalance between synchronous and inverter-based generation. This article explores how this shift contributed to such a large-scale collapse and why flexible generation assets like ours are essential for building a more resilient energy future.

What Caused the Collapse?

At approximately 12:33 CEST, the Spanish grid operator (Red Eléctrica de España, REE) recorded a sudden loss of 15 GW of generation capacity, equivalent to more than a third of Spain’s peak daytime demand. The precise cause is still being established, but early data suggests a combination of:

• Sudden disconnection at two major substations in southwestern Spain, which triggered cascading failures across the high-voltage network.
• High reliance on inverter-based renewables, including solar PV and wind, which at the time were generating over 56% of Spain’s electricity.
• Low interconnection capacity with France, just ~3% of total generation, limiting Spain and Portugal’s ability to import balancing power when the grid destabilised.

But beneath these events lies a more systemic issue: a lack of grid inertia due to the decreasing share of conventional synchronous generation on the system.

The Role of Synchronous Generation and Grid Inertia

Electrical grids operate at a tightly controlled frequency of 50 Hz in Europe. Small deviations can be tolerated, but larger or prolonged deviations quickly cause equipment failures, blackouts, and damage to infrastructure.

Synchronous generators (e.g. gas turbines, hydro and nuclear) naturally provide inertia, the kinetic energy stored in the spinning mass of turbines and generators. This inertia acts like a shock absorber for the grid, slowing down the rate at which frequency changes following a sudden imbalance between supply and demand.

In contrast, inverter-based resources like solar PV, wind (with asynchronous generators), and battery storage do not provide inertia in the same way. Unless specially equipped with grid-forming inverters, they respond only after frequency has already begun to deviate, often too late to prevent cascading failures.

In the Iberian blackout, the grid’s very low inertia meant that the sudden loss of generation capacity caused frequency to plunge rapidly, beyond the limits of what the remaining inverter-based generators and automated defences could handle. The result: total grid collapse within seconds.

Flexible Generation: A Critical Safeguard

Flexible generation, typically gas reciprocating engine or turbine-based plants designed to respond quickly to market and grid signals, could have significantly mitigated the Iberian blackout.

Here’s how:

• Fast ramping and grid synchronisation: Flexible assets can come online in minutes and provide synchronous support to stabilise frequency in real time.
• Inertia contribution: Unlike inverter-based systems, flexible generation contributes real rotating mass to the grid, enhancing stability during transients.
• Balancing intermittent renewables: When wind and solar drop due to weather changes, flexible generation fills the gap instantly maintaining supply-demand balance.
• Localised stability: Deploying distributed flexible assets across regional substations can help island parts of the grid, preventing nationwide cascading failures.

The lack of adequate standby capacity and grid-forming capability in Spain and Portugal at the time of the incident highlights a clear lesson: renewables need complementary, firm and flexible generation to ensure system resilience.

Planning for a Resilient, Decarbonised Grid

At Terra Firma Energy, our flexible generation plants are designed not only to support the energy market, but also to strengthen the grid itself. We believe a net-zero future must be reliable, resilient, and secure.

While the Iberian blackout has rightly sparked calls for better storage, interconnectors, and smarter grid control, none of these will fully replace the foundational need for stable synchronous support, at least not yet.

Flexible generation isn’t a bridge to the future, it’s a foundation for it. Without it, we risk repeating the events of April 2025 on an even larger scale.

In Summary

The Iberian blackout exposed vulnerabilities that are not unique to Spain or Portugal. As grids across Europe accelerate the transition to renewables, the urgent need for system support, through inertia, ramping capacity, and dispatchable power has never been clearer.

Flexible, engine-based generation is uniquely placed to provide these services today, while technologies like long-duration storage and advanced grid-forming inverters scale up.

We stand ready to support the energy transition with engineering excellence, operational reliability, and a deep understanding of what the grid truly needs.

If you’d like to learn more about how Terra Firma Energy supports grid resilience through flexible generation, contact our team or explore our portfolio of operational assets.