On April 28 2025, the Iberian power system collapsed. A cascade of generator trips and uncontrolled voltage surges swept across Spain and Portugal, knocking out over 15 gigawatts of load in a matter of seconds. Within moments, automatic defences had exhausted their options, synchronisation with the rest of Europe was lost, and the blackout became continental news.
Initial speculation circled cyberattacks and renewable energy intermittency. However, the truth proved more mundane — and more revealing. Spain’s official post-event report confirmed that the blackout was caused not by frequency instability or renewables, but by a failure of conventional generators to absorb voltage when it surged. Poor coordination, misapplied protection settings, and inadequate dynamic VAR capacity were the root cause.
“This report concludes that the blackout was caused by the failure of nine conventional power plants to do their job,” said Juliet Phillips, energy campaigner at Beyond Fossil Fuels. “This flies in the face of the commentary being pushed by the fossil fuel lobby, who have sought to pin the blame on renewables for causing the blackout.”
El País broke the findings the same morning.
At the centre of the event was a failure to manage reactive power — the push-and-pull component of AC electricity that sustains voltage across lines, transformers and machines. Unlike watts, which are consumed, reactive power (measured in VAR) moves back and forth between the grid and connected equipment, sustaining the system’s electric fields.
If there is too much, voltage spikes. If there is too little, it collapses. Spain’s blackout was triggered by just such a surge. According to Red Eléctrica, multiple thermal units failed to absorb reactive power as required under grid Operating Procedure 7.4, allowing voltage to climb unchecked until protection systems began tripping units offline.
National Grid ESO, which operates Britain’s transmission system, calls reactive power its primary tool for holding the 400 kV grid within ±5% of target voltage — especially overnight, when demand is low and over-voltage risks are highest.
One recent UK project tackling the issue directly is the Mersey Voltage Pathfinder. Here, a 200 MVAr shunt reactor was installed by PeakGen at Frodsham 400 kV substation, under a 10-year reactive power contract. It now quietly absorbs surplus VAR at night, preventing the kind of over-voltage conditions seen in Spain.
Spain’s challenges underscore why paying for flexible VAR is no longer optional. “We urge Spain’s government and Red Eléctrica to work together to build the clean and flexible power system needed to ensure long-term energy security and bring down power bills,” added Phillips.
After the fall: restoring and reacting in real-time
When a blackout occurs, the next challenge is recovery. Black start — the ability to energise the grid from zero — traditionally relies on hydropower or diesel cranking large steam turbines. But as more grids decarbonise, the number of such assets shrinks.
In the Iberian event, Portugal’s Castelo de Bode hydro plant re-energised its network from 12:45, followed by Spanish hydropower stations and power imported through the HVDC links to France and Morocco. Portugal’s system was fully restored by 00:22; Spain followed by 04:00, according to ENTSO-E’s official chronology.
In Britain, the £11.7 million Distributed ReStart project has already demonstrated that battery storage, wind and solar can form ‘islands’ capable of re-energising parts of the transmission grid — using a new Distribution Restoration Zone Controller and updated protocols.
Spain’s blackout wasn’t a bolt from the blue. ENTSO-E confirms that the system exhibited two periods of low-frequency oscillation before the event — from 12:03 to 12:07 and again at 12:16. But without automation in place to isolate or mitigate the fault, the opportunity to intervene slipped away.
This is where wide-area monitoring systems (WAMS) and phasor-measurement units (PMUs) are changing the game. Unlike traditional SCADA tools, PMUs capture voltage and current waveforms 30–60 times per second and timestamp them with GPS accuracy. When analysed across a region, they provide real-time insights into phase shifts, frequency swings and instability risks — and allow for near-instant action.
U.S. Department of Energy documents describe how rising phase-angle separation can trigger automated defence schemes to prevent a cascade (DOE report). NREL field studies have further shown how AI algorithms can categorise disturbances in seconds and enable pre-emptive responses.
“Managing this variability while maintaining reliability and protection is a major engineering challenge of our time,” said Adrian Guggisberg, Division President – Electrical Distribution Solutions at ABB Electrification. He notes that future-ready infrastructure must do more than simply reinforce weak points: “It requires a smarter, more connected approach to electrical infrastructure. This includes everything from substations and feeders to automation systems, protection devices, and yes, medium-voltage switchgear – which plays a key role in controlling power flows and isolating faults.”
True resilience, he adds, comes from system behaviour, not single-point solutions. “It’s about a system that can adapt, isolate faults quickly, recover autonomously, and support real-time decision-making. Upgrading the grid is not just a technical challenge; it’s an economic imperative.”
What resilience means now
Spain’s blackout underscores the new criteria for grid resilience. It’s no longer enough to count on bulk generation and centralised restarts. Operators must be able to dynamically manage reactive power, recover rapidly using diverse sources, and contain faults at speed.
Spain’s regulators have pledged to introduce a new “continuous dynamic voltage-control service,” and a review of all generator protection settings. In the UK, ESO’s Stability and Voltage Pathfinder programmes are already contracting new resources to provide these exact services.
The Iberian collapse was swift, but not unpredictable. And the grid of the future won’t be judged by whether failures occur, but by how fast and how safely it recovers from them.
