On the 28th of April 2025, at 12:33 CEST, the power systems in Spain and Portugal crashed, plunging the two countries into a total blackout. As a result, millions of people were left without power or communications. The incident demonstrated our absolute dependence on power-reliant technology in every aspect of our lives.
Mobile phone lines were patchy depending on the availability of back-up generators at the local antenna towers. People struggled to buy their necessities in dark shops, and with payment systems disabled had to resort to cash. Others roamed the streets trying to get home from closed offices and had to rely on the old, rusty skill of asking for directions. Those who dared to get in a car had to dodge others without the assistance of traffic lights.
Everyone went out to the streets and local parks to chat with one another and huddled around old-style radio sets retrieved from lofts and dusty drawers trying to find out what was going on. Broadcasters were relying on diesel generators and news relayed from servers elsewhere in Europe. As systems came back online, emergency systems reported rescuing hundreds of people trapped in elevators. Others who relied on healthcare such as powered oxygen dispensers had to be helped by taxi drivers to reach those hospitals with enough back up power to operate.
The event was the worst power outage in over 20 years, and soon many hypotheses about its cause began circulating. Was it a cyberattack from Russia? Was it a terrorist attack? An unexplainable weather event?
The power was restored around 4am the next day, but the impacts would be felt for many months after as everyone came to terms with what it meant and the kind of vulnerability it had uncovered.
The issue soon became politicised. The Spanish government was quick to blame the management of the electric infrastructure and the private companies that produce energy. The opposition however, sustained that it was the heavy reliance on renewable energy production and the decrease in nuclear power spearheaded by the left-leaning Socialist Party government that were at fault.
Months later, at the beginning of June, the Spanish government released the results of its own in-depth investigation into what happened that day. In an “unprecedented” analysis of Spanish power infrastructure, they again pointed the finger at the power and grid companies as the ones to blame for the event. The government did not however, seem keen to assign any guilt to itself, even if the Spanish electric system is highly regulated, including its ownership of 20% of Red Electrica Espanola, the Spanish grid operator.
The story has come back to the news with the release last month of a new report by ENTSO-E, the association of European electricity grid operators. The report, created by an Expert Panel according to the European Commission’s protocols, is meant to investigate the root causes of the incident, produce a comprehensive analysis, and make recommendations.
The report is only the first output of the Expert Panel and is intended as a “statement of facts”. It points towards a series of cascading overvoltages, an increase in the electrical supplied voltage above the norm.
This is what the report shows:
- Before the event: The morning of the 28th of April 2025 was characterised by an increasing, but not unusual, generation of renewables. From approximately 09:00, the variability of the voltage in Spain started increasing, albeit without significant variations. However, half an hour before the event there were two main periods of oscillations (power, voltage, and frequency swings). The operators in the control rooms of the electric network took several measures which mitigated the oscillations but led to an increase of voltage in the power system.
- Phase 1 (12:32:00.-12:32:57): There was a loss of 208MW identified distributed wind and solar generators in northern and southern Spain as well as an increase in net load in the grids of approximately 317MW. This could be due to the disconnection of small embedded generators <1MW (mainly rooftop PV) or to an actual increase in load or to a combination of both. The reasons for these events are not known.
- Phase 2 (12:32:57 – 12:33:18): Major disconnection events occurred which resulted in an additional loss of generation of at least 2GW. Some of these trips occurred due to overvoltage protection, but the reason for most of the trips are not known.
- Phase 3 (12:33:18 and 12:33:21): The voltage of the South area of Spain sharply increased, and consequently also in Portugal. The over-voltage triggered a cascade of generation losses (trips for high voltage of generation plants) that caused the frequency of the Spanish and Portuguese power system to decline and thus losing synchronism with the rest of Europe forcing France and Morocco to disconnect their lines. After this AC separation of the Iberian Peninsula, the power imbalance continued to increase, causing the frequency to further decline.
The report, however, does not yet determine the root causes of the incident and the Expert Panel’s investigations are still ongoing. Their final analysis will be presented in a final report to be published next year.
The Expert Panel did highlight the difficulty of getting data from certain players (8 out of the 41 involved in the event) in the industry.
The Spanish government believes this latest report completely aligns with its own conclusions. In the document released in June, it had already pointed out some of the causes of the failure. This was done in an anonymised manner in a heavily redacted report in accordance with the legal agreements reached between the government and the various agents of the network.
The main areas of failure according to them, were:
- REE, the network operator, did not program enough synchronous generation (gas/petrol, nuclear, hydroelectric and even thermo-solar) to control reactive power. Reactive power is the energy that moves back and forth in an AC electrical system to create and sustain magnetic fields in devices like motors and transformers, but it is not converted to do useful work. This power is vital to provide stability in the network but its excess tends to raise its voltage.
- The synchronous power plants that had been scheduled and were actually operating absorbed less reactive power than they were meant to. These power plants receive payment to be online when they do so for the network’s own technical needs.
- Some of the trips (cases where power stations became disconnected due to overvoltage protection) happened incorrectly with voltages that didn’t reach 435kV (the usual level in a 400kV network).
We will need to wait until next year to read the final conclusions from the Expert Panel, but ENTSO-E has characterised this event as “the first of its kind” and their work analysing it as a dive into “new territory”.
The Spanish government has rushed forward a series of measures that are meant to bring more stability to the network and avoid any such event happening again. For Spain, and the rest of the world, it brings to the forefront a worst-case scenario that we all have to prepare against and for, especially in the current changing geopolitical and technological climate.
