What Caused the Spanish Energy Supply Outage?

On 28 April, Spain and Portugal both experienced widespread power outages  that brought daily life and critical industries to a standstill. 

With energy cut for hours in Lisbon, Madrid and Barcelona, industrial activity halted and the energy sector was left searching for answers.

At the heart of it all lay a fragile energy infrastructure and a network of supply chains deeply exposed to disruption.

Now, rumours about the underlying cause have been put to rest with the release of an official report into the circumstances of the outage.

Operators and generators clash over responsibility

Rumours ranged from a surge in renewables due to fast-changing weather to the possibility of a cyber attack.

But as the investigation progressed, the cause of the blackout proved far more complex, and deeply rooted in the structure and operation of the electricity supply chain.

Now, the official version of events has been published in The Report of the Committee for the Analysis of the Circumstances Surrounding the Electricity Crisis of 28 April 2025.

According to Spain’s Minister for Ecological Transition, Sara Aagesen, the event — described as an “electrical zero” — had a “multifactorial origin.”

While the report lists several contributing factors, it places most of the blame on the shoulders of the national grid operator, Redeia (formerly Red Eléctrica), and private power generation companies.

Sara Aagesen states that Redeia failed to properly calculate power capacity needs for the day in question.

“The system did not have enough dynamic voltage capacity,” she says, adding that the regulator should have brought another thermal plant online.

She also criticised generation companies for not managing the grid’s voltage levels.

“Generation firms which were supposed to control voltage and which, in addition, were paid to do just that did not absorb all the voltage they were supposed to when tension was high,” she says

As the blackout disrupted industries reliant on continuous electricity, the event revealed the fragility of the energy supply chain in moments of stress.

With factories halted and transport disrupted, the effects spread well beyond the electricity sector.

Spain’s Prime Minister Pedro Sánchez pointed towards private electricity firms, while Redeia rejected the claim that its planning had failed.

Concha Sanchez, the grid’s operations chief, says: “Had conventional power plants done their job in controlling the voltage there would have been no blackout.”

Renewables, cyber attacks ruled out — but tensions remain

The report makes clear that neither renewable energy sources nor cyber attacks were to blame.

Sara comments: “It can be determined that no indications or evidence have been found that point to a cyber attack or cyber incident as the cause of the energy crisis.”

Still, she acknowledged the presence of vulnerabilities and configuration weaknesses in the system, pointing to longer-term risk in the infrastructure.

Critics of Spain’s energy strategy had argued that a growing reliance on renewables, combined with a rejection of nuclear energy, might have been a factor.

But the government has consistently denied this, and the report reiterates that position.

Meanwhile, Redeia pushed back firmly, blaming conventional energy producers — those operating coal, gas and nuclear plants — for failing to maintain voltage stability.

Concha said at a news briefing: “Based on our calculation, there were enough voltage control capabilities planned.”

She added that the system was operating under “absolutely normal conditions” just before the failure, and insisted that activating another gas plant would not have prevented the outage.

Aelec, the industry group representing major electricity companies such as Iberdrola and Endesa, also responded. “Claiming everything was done correctly while blaming some power plants for the blackout was damaging to the sector's reputation,” it said.

“The operator failed to safely cover all the system's needs.”

In an effort to protect its position, Redeia released its own technical report.

But with both government and grid operator assigning blame elsewhere, the event underscores how fragmented responsibility across the energy supply chain can hinder crisis response.

Experts call for stronger enforcement and smarter systems

Jan Rosenow, Energy Programme Leader at Oxford University, offered his view on LinkedIn.

He wrote: “‘It was renewables that did it!’ That was the headline of a lot of media commentary when the Spanish blackout happened back on 28 April this year.

“Not so fast tiger – the reality is (as so often) much more complex. It is a combination of several factors with human error playing a significant role.”

Jan pointed to failure across multiple parts of the supply chain.

Gas, nuclear and hydro generators underperformed and the grid operator failed to manage the unfolding conditions. Jan argues this points to structural weaknesses in the way supply obligations are enforced.

“What’s clear is that we need stronger enforcement to ensure all generators meet their obligations, as well as more interconnections to boost system resilience,” he says.

He also called for greater access to real-time information: “Better access to real-time information is also essential for operators to make informed decisions in critical moments.

“Grid reliability isn’t about pointing fingers at one technology – it’s about building a smarter, more robust system for the future.”

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