What the 28 April 2025 Iberian Blackout Teaches a Zero-Carbon-Ready UK Grid

At midday on 28 April 2025, a massive power outage blacked out most of Spain and all of Portugal.

In just minutes, lights went out for tens of millions, halting transport, communications, and daily life.

This 90-minute Iberian blackout – one of Europe’s worst in decades – raises urgent questions and lessons for the UK as it races toward a zero-carbon grid.

The Iberian Blackout

A routine day turns dark

What began as a normal Monday lunchtime in Iberia quickly unravelled into a full-scale power collapse.

At around 12:30 p.m. local time, the electricity supply across mainland Spain and Portugal plummeted from about 26,695 MW to 15,970 MW – a drop of over 10,700 MW in minutes​.

For context, that’s roughly a 40% loss of demand, equivalent to cutting power to a country the size of Greece.

By 12:33 p.m., lights flickered out from Lisbon to Madrid in an unprecedented simultaneous blackout across the entire peninsula.

Never in Spain’s modern history had an outage of this magnitude occurred.

Instant impacts everywhere

The effect was immediate and indiscriminate.

Office buildings fell into darkness and evacuated en masse, while hospitals switched to emergency generators​.

Metro trains halted mid-journey, stranding thousands of passengers underground​.

Traffic lights failed at once, turning city intersections into mayhem.

In Madrid, the metro closed all stations, and on the streets the failure of traffic signals caused huge jams.

Across Iberia, mobile phone and internet networks began collapsing within minutes as cell towers and broadband equipment lost power.

Even airport operations were disrupted, with flights delayed and some terminals running on backup power.

Scramble to respond

By 1:00 p.m., about half an hour into the crisis, grid operators had mobilised emergency procedures.

Spain’s grid operator Red Eléctrica (Redeia) reported that it had begun to “recover power” in parts of the north and south of the country as of 1 p.m., initiating a black start – the gradual re-energisation of the network by coupling generation units step by step​.

Portugal’s operator, REN, undertook similar measures, and the Spanish government convened an emergency cabinet chaired by Prime Minister Pedro Sánchez to coordinate the response.

In the absence of central communications, local police and transit authorities used loudspeakers and social media to instruct the public.

The Mayor of Madrid urged residents to ‘absolutely minimize movement’ because “the traffic lights are down…and it’s essential that emergency services can circulate”​insurancejournal.com.

Power returns, questions remain

By around 1:45 p.m., a slow recovery was underway as electricity supply was incrementally restored in many areas​.

Critical infrastructure began coming back online: lights blinked on in some neighbourhoods and trapped metro passengers were evacuated.

Within roughly 90 minutes, the worst of the outage had passed, though full normalisation took longer in some pockets.

By mid-afternoon, power had returned to major cities and transport services started resuming on a limited schedule.

However, even as the lights came back on, a larger shadow loomed: what exactly caused this grid meltdown and could it happen again?

Investigations were only just beginning, and for now answers were as scarce as electricity had been an hour before.

Timeline of Key Events (28 April 2025, Iberian Peninsula):

A 90-minute timeline of the April 28, 2025 Iberian blackout and its immediate impacts.

Why did the lights go out?

With the crisis contained, attention turned to how a whole region could plunge into darkness so abruptly.

The exact trigger remained under investigation in the immediate aftermath.

Spain’s Department of Homeland Security cautioned that “it is still too early to know what has happened”, refusing to jump to conclusions.

Early clues, however, pointed to a confluence of factors – both structural and potentially external – that exposed the grid’s vulnerabilities.

A single point of failure – The Perpignan Incident

Initial probes suggested the outage might have originated in the south of France, near Perpignan.

This region is where key cross-border transmission lines connect France and Spain.

A failure there (whether due to equipment fault or mis-operation) could have suddenly severed the Iberian grid from the rest of continental Europe.

In essence, Spain and Portugal became an electrical island without warning. Ironically, being cut off from France meant Iberia lost not import capacity but its export outlet – Spain had been exporting power (250–1700 MW) to France in the late morning.

When the link tripped, all that surplus supply had nowhere to go.

The abrupt imbalance (excess generation vs. demand) would have sent the grid frequency surging above safe limits in seconds.

Protections then kicked in, tripping generation plants offline to protect equipment, which in turn caused a rapid collapse of supply.

This domino effect likely explains how a local fault cascaded into a peninsula-wide blackout.

It’s a stark reminder that even a “small” bottleneck (a few GW line) can destabilise a 50 GW system if it’s a critical artery.

Low inertia at midday

The timing of the blackout was no coincidence.

Midday on a sunny, breezy spring day means lots of solar generation and moderate wind, but relatively low demand.

Under these conditions, fewer big conventional power plants were online, so the system inertia was lower than at an evening peak.

Inertia – the stabilising weight of spinning turbines – is what keeps frequency steady when disturbances occur.

Grid experts noted that an “undue reliance on solar power” made the Iberian grid less resilient to shocks than if more gas or coal units had been running​.

In the minutes before the outage, solar farms and wind parks were supplying a significant share of power.

When the frequency spike hit, many of these inverter-based sources would have swiftly curtailed or tripped to protect themselves.

Meanwhile, several large nuclear, hydro, and fossil-fired plants automatically went offline as well during the frequency excursion.

Essentially, the grid had plenty of megawatts, but not enough momentum to ride through the disturbance.

This lack of inertia turned a single fault into a system-wide failure.

Cyberattack or sabotage?

Given the scale of disruption, authorities did not rule out malicious causes either.

Within hours, Spain’s National Cybersecurity Institute (INCIBE) and National Cryptologic Centre were mobilised to investigate the possibility of a cyber-attack behind the blackout​.

However, as of the day of the event, there was no hard evidence of a cyber intrusion.

Rumours of an attack were officially discounted by experts soon after, who leaned more toward a technical root cause in the grid’s dynamics.

The lesson here is that, in an age of heightened cyber warfare, even if this blackout wasn’t caused by hackers, the fear of cyber vulnerability hung over the response.

Ensuring strong cyber defences for critical grid controls is now as essential as guarding against physical failures.

Weather and renewable surplus

Some observers pointed to an interesting contributing factor: an oversupply of renewable power earlier that day.

Spain has seen an unprecedented number of hours with negative power prices in recent months due to abundant solar and wind output.

Going into midday, Iberia likely had very high renewable generation relative to demand, forcing exports to France and even curtailment of excess.

While an oversupply situation hadn’t caused blackouts in the past, it could amplify vulnerability.

If a grid is already curtailing power to keep balance, the margin for error is thin.

Grid frequency can swing faster when the only generation online are power-electronics-based sources or small gas turbines on low load.

The events of April 28 suggest that the combination of high renewables, low inertia, and a sudden grid split created a “perfect storm”.

As one analyst summarized: this was a stress-test of the green energy transition, and it exposed where the system is not yet as robust as it needs to be.

In short, the Iberian blackout appears to stem from a cascading technical failure initiated by a grid separation at the French border, exacerbated by low system inertia and excess renewable generation. Investigations are ongoing, but the incident already offers a trove of insights for other nations pushing toward renewable-heavy grids.

Could a similar blackout happen in the UK?

As Britain pursues its own green energy goals, the obvious question is: Could the UK face a similar blackout?

The Iberian event is a wake-up call, highlighting both unique regional issues and shared challenges of a decarbonising grid.

Great Britain’s electricity system in 2025 has some important differences from Iberia’s – but also some striking similarities in terms of risk profile. Below, we compare the two:

Table: Iberia’s vulnerabilities versus Great Britain’s 2025 grid outlook. RE = renewable energy; OCGT = open-cycle gas turbine.

Different grids, similar challenges

Great Britain’s grid is not identical to Spain’s, but the blackout triggers seen in Iberia have echoes in the UK.

One key difference: Britain is already an island grid, used to balancing itself independently from moment to moment.

The Iberian grid, by contrast, normally operates as part of the vast Continental Europe synchronous area, and only became isolated by accident.

UK grid operators (National Grid ESO) have deep experience handling sudden imbalances – for instance, if a big power station or interconnector trips, the UK can’t lean on a larger neighbour to absorb the shock.

This inherent self-reliance is a strength, and it’s backed by defensive measures like automatic load shedding and frequency containment reserves.

Indeed, during the August 2019 UK outage, the system contained the issue within seconds (albeit after 1 GW of demand was disconnected)​.

In Iberia’s case, it appears the protective systems couldn’t halt a cascading failure fast enough, perhaps due to the scale of the event and lower inertia available.

However, Britain in 2025 also has much higher renewable penetration than a decade ago, and it’s only growing.

There are times of day, or certain weather conditions, where the UK grid closely resembles Spain’s in terms of stress factors: e.g. a summer noon with 10+ GW of solar output and low demand, or a windy night with 80% of power from wind farms.

During such periods, the effective inertia of the GB system drops, because fewer gas/nuclear units are on.

National Grid ESO has recognised this and begun deploying solutions (such as synchronous compensators – essentially spinning flywheels – in Scotland and Wales to boost inertia).

Battery energy storage systems are also contracted to inject rapid bursts of power to steady frequency.

These efforts are part of making the grid “zero-carbon ready,” so it can run with 100% renewable generation without falling over.

Interconnection: Both a blessing and a risk

The comparison also highlights the double-edged nature of interconnectors.

Iberia’s physical links to the European grid are relatively small (only ~5–7% of its demand).

In this incident, that meant losing the link to France had an outsized impact, as the peninsula couldn’t import help quickly nor export its surplus – it was truly on its own.

Great Britain, while an island, has more interconnector capacity (over 10% of demand) spread across multiple routes. In a crunch, the UK can draw on Norway’s hydropower, French nuclear, or other neighbours.

But relying on imports is risky if those links fail.

A failure on a major connector (as happened on one UK-France cable in 2021 due to a fire) can suddenly remove a lifeline and force rapid domestic balancing.

In summary, a Spain-style blackout is not far-fetched for the UK, unless we heed the warnings and shore up our defences. The following are five technical lessons Britain (and any grid moving towards net-zero) should take away from the Iberian experience.

Five technical lessons for a resilient zero-carbon grid

1. Invest in Grid Inertia
Iberia’s blackout showed how quickly a system can unravel without enough inertia.

As renewables replace spinning turbines, the UK must invest in stability tools like synchronous condensers and grid-forming inverters.

National Grid ESO is on the right path, but more scale is needed. Inertia isn’t optional – it’s what keeps the system steady when things go wrong.

2. Flexibility Beats Curtailment
Excess renewables can be a risk if the system isn’t ready to absorb them.

Iberia had surplus solar and nowhere to send it once the France link failed.

The UK needs to scale up battery storage, demand response, and other flexible tools to capture rather than curtail green energy. It’s not just good economics – it’s a grid safeguard.

3. Interconnect, but Plan for Isolation
Interconnectors are vital for balancing supply, but they can also be a point of failure.

If links go down, like they did in Iberia, we need to be ready to operate in “island mode.”

The UK should strengthen its ability to split the grid into self-sufficient regions in a crisis and not assume Europe will always be able to help.

4. Cybersecurity is Grid Security
Spain’s outage sparked cyber-attack fears, even though none were found.

The UK must treat cyber and physical security as grid-critical.

That means red-teaming SCADA systems, securing substations, and training operators for digital fallbacks.

A zero-carbon grid is a digital grid – and needs defending like one.

5. Be Ready to Restart
Iberia recovered quickly thanks to prepared black start sites.

The UK must maintain and expand its own – from hydropower to batteries – and rehearse restoration plans regularly.

Rapid recovery isn’t just a technical need, it’s a public expectation. If things go dark, we need to bring them back fast.

Aftermath: Human and commercial impacts of blackouts

The Iberian blackout lasted just 90 minutes, but the impact was huge. Trains stopped mid-journey, tills failed, offices emptied, and mobile networks dropped out.

For businesses, the hit ran into millions in lost output.

For the public, it meant confusion, stalled lifts, and medical worries for those reliant on home equipment.

The psychological toll was real too – no power and no information led to panic. With few official updates, rumours spread fast.

In any country, a blackout becomes a test of public trust. The UK must be ready not just to restore power, but to communicate clearly if things go wrong.

Power cuts don’t just threaten productivity, they threaten confidence. And in an electrified economy, outages feel like national emergencies.

That’s why preparation, resilience, and fast recovery aren’t luxuries – they’re essentials.

Final Thoughts

The Iberian Blackout serves as a stark reminder that building a zero-carbon grid demands more than just clean generation, it demands resilience, flexibility and foresight. For the UK, the time to act is now.

At Astute, we work closely with energy businesses to secure the specialist talent needed to deliver stability projects, resilience upgrades and innovation across the sector.

If you would like to discuss how we can support your business with technical advice or recruitment solutions, get in touch today.