The Iberian Blackout of April 28, 2025: What really happened — and how Europe can avoid the next one

Enerdealers Editorial

On Monday, April 28, 2025, at exactly 12:33 pm (CEST), daily life across the Iberian Peninsula came to an abrupt halt.

In just a few seconds, mainland Spain and Portugal — nearly 60 million people — lost electricity almost entirely. Trains stopped, traffic lights went dark, mobile networks became unreliable and hospitals switched to emergency generators. For many citizens, it was the first time they had experienced a blackout of such magnitude.

What initially looked like a technical accident quickly became something much bigger: the most severe power system failure in Europe in more than two decades.

Months later, after extensive investigations, one conclusion stands out clearly:this blackout was not an anomaly — it was a warning.

A blackout measured in seconds, not hours

Shortly before midday, Spain’s power system appeared to be operating normally.

• Electricity demand was moderate

• Solar generation was exceptionally strong

• Spain was exporting electricity to neighbouring countries

Then, within less than five seconds, the system collapsed.

According to data published by Red Eléctrica de España (REE) and European grid operators, total generation plunged from roughly 32 GW to almost zero. Automatic protection systems disconnected large parts of the grid to avoid physical damage, but in doing so, they accelerated the collapse.

The blackout affected:

• All of mainland Spain

• Continental Portugal

• Parts of southern France and Andorra

Power restoration took between 6 and 12 hours, depending on location, with full normalisation only achieved in the early hours of April 29.

Why this blackout was different

Blackouts happen. Europe has seen them before, usually caused by:

• Severe weather events

• Equipment failures

• Human or operational errors

But the Iberian blackout of 2025 was fundamentally different. It was not caused by:

• A storm or heatwave.

• A single line or substation failure.

• Cyberattacks or sabotage.

Instead, investigations confirmed something far more complex: a system-wide instability, linked to how the grid was operating in a context of very high renewable penetration and low synchronous support.

The system had enough energy — but not enough stability.

The fragile conditions before the collapse

Several factors combined to create a highly sensitive system on April 28.

Exceptionally high solar generation

Spain was experiencing one of its strongest solar days on record. At midday, photovoltaic generation represented a dominant share of total electricity production.

This is a success story for decarbonization — but it also means:

• Fewer conventional power plants online

• Lower system inertia

• Reduced voltage control capability

Low levels of synchronous generation

Gas-fired plants, hydro units and other synchronous generators — essential for voltage regulation and frequency stability — were operating at relatively low levels.

This reduced the grid’s ability to absorb sudden disturbances.

Early warning signals

Post-event analysis revealed abnormal voltage oscillations minutes before the blackout. The system was already under stress — even if the collapse had not yet begun.

What the investigations uncovered

Following the blackout, multiple investigations were launched at national and European levels. Despite being conducted independently, their conclusions converged.

No cyberattack, no sabotage

Speculation about cyber warfare was quickly ruled out.

Spain’s cybersecurity and intelligence bodies — including INCIBE and the CNI — found no evidence of malicious interference. The Spanish High Court later formally closed its investigation.

The blackout was a technical failure, not a security incident.

The real technical causes

1. Loss of voltage control

The main trigger was a progressive voltage instability in the transmission network.

Overvoltages developed in different areas. Protection systems reacted by disconnecting equipment — which unintentionally worsened the problem, triggering further disconnections in a cascading process.

2. Insufficient system inertia

Modern power systems rely on inertia — the physical resistance of spinning machines — to slow down sudden changes.

With much of the system supplied by inverter-based renewables, inertia levels were historically low. When disturbances occurred, the system could not stabilize fast enough.

3. Renewable disconnection dynamics

Some renewable installations disconnected automatically when voltage limits were exceeded. While compliant with existing grid codes, this behaviour contributed to the rapid loss of generation.

Importantly, experts stress that renewables were not the root cause, but rather how the system was designed to manage them.

4. Thin operational security margins

Perhaps the most important lesson:there was enough capacity — but not enough stability-oriented capacity.

The system was operating too close to its technical limits.

The future power system must be not only green — but resilient.

A European wake-up call

The ENTSO-E expert panel, representing Europe’s transmission system operators, described the event as the most serious grid failure in over 20 years.

Although the blackout occurred in a relatively weakly interconnected region, its implications extend far beyond Iberia. Europe’s power systems are evolving faster than the operational rules designed to manage them.

How the grid was restored

Restoring a collapsed system is one of the most complex tasks in power engineering.

Operators relied on:

• Hydropower plants and gas turbines capable of “black start”

• Emergency interconnections with France and Morocco

• Step-by-step re-energisation of the network

By the early hours of April 29, most of the system was back online.

What experts say must change

The blackout has triggered intense debate across the energy sector. While no grid can be made perfectly risk-free, experts broadly agree on a set of critical actions.

Key recommendations to avoid future blackouts

1. Redefine grid stability standards

Capacity alone is no longer enough. Experts call for:

• Minimum inertia requirements.

• Explicit voltage stability criteria.

• New reliability metrics for high-renewable systems.

2. Guarantee synchronous support

Even in a decarbonized future, synchronous resources remain essential. Proposals include:

• Keeping a minimum number of synchronous units online.

• Deploying synchronous condensers.

• Properly remunerating stability services through markets.

3. Upgrade grid codes for renewables

Renewables must increasingly support the grid, not just inject energy. This means:

• Advanced voltage control.

• Stronger fault-ride-through requirements.

• Faster dynamic response.

4. Invest in digitalisation and forecasting

Modern grids need modern tools. Experts recommend:

• Real-time dynamic stability monitoring.

• Predictive analytics and AI-based tools.

• Enhanced operator training for rare, extreme events.

5. Strengthen European coordination

Extreme events require coordinated responses. ENTSO-E proposes:

• Harmonised emergency protocols.

• Faster cross-border support.

• Shared learning across TSOs.

Conclusion: a turning point for the energy transition

The Iberian blackout of April 28, 2025, was not a failure of renewable energy — but a stress test for the energy transition.

As electricity systems become cleaner and more decentralised, stability must become a first-class priority.

For regulators, operators, investors and policymakers, the message is clear: For regulators, operators, investors and policymakers, the message is clear: The future power system must be not only green — but resilient.