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Spain’s national grid operator, Red Eléctrica (REE), has sounded the alarm after recording sudden voltage fluctuations in October that could threaten the country’s power stability. The company said these sharp swings pose a risk to the electricity supply.
The warning comes just months after a massive blackout in April left parts of Spain and Portugal without power. Officials are now calling for urgent measures to prevent a repeat, as the nation’s energy system faces growing pressure amid its transition toward renewable sources.
EU’s worst power outage in 20 years
A recent report by Europe’s grid operators confirmed that the massive April 28 outage across Spain and Portugal was the continent’s “most severe” in two decades. The blackout, which crippled transport and power networks, was traced to an unprecedented surge in voltage—the first known case of its kind in Europe.
The blackout left around 60 million people across Spain and Portugal without electricity for over 10 hours, briefly extending into parts of southwestern France. The sudden loss of power crippled transport systems, shut down mobile and internet networks, and interrupted vital services across the Iberian Peninsula.
Cities were plunged into darkness as traffic lights failed, ATMs stopped working, and commuters were stranded when metro lines and air traffic systems came to a standstill. In Madrid alone, emergency crews rescued hundreds trapped in elevators, while hospitals activated contingency plans and suspended routine procedures.
Speaking to reporters, Damian Cortinas, chairman of the European Network of Transmission System Operators for Electricity (ENTSO-E), said, “It has never happened before in Europe, this is new territory, the first of its kind.”
EU energy experts found that the blackout was triggered by overvoltage after the grid failed to absorb a sudden loss of power, causing cascading disruptions across the network.
With the recent voltage fluctuations across Spain’s electricity grid, the National Commission on Markets and Competition (CNMC) urged rapid technical adjustments to prevent potential disruptions. The regulator announced a public consultation to consider urgent temporary measures aimed at stabilizing the system while longer-term solutions are developed.
In a statement, the CNMC noted that although voltage levels remained within established limits, the recent rapid swings “can potentially trigger demand and/or generation disconnections that end up destabilizing the electrical system.”
Meanwhile, REE called for immediate operational adjustments to better handle sudden swings in solar power. The operator cautioned that without rapid improvements in voltage management, the reliability of Spain’s electricity supply could be seriously threatened.
(Also read: Why Rushing the Energy Transition Could Backfire)
Renewables linked to grid instability
Spain, a European leader in renewable energy (RE), generates roughly 46% of its electricity from solar and wind sources, and at times this share exceeds 70%, according to the think tank Ember.
Experts said Spain’s heavy reliance on solar power increased the risk of blackouts, noting that renewable generators operate differently from traditional power plants. Additionally, declining nuclear capacity reduced backup options.
Meanwhile, the ENTSO-E report found that the mass blackout began after several solar and wind farms in southern Spain abruptly went offline. Echoing these findings, the CNMC warned that the growing number of solar farms has made the grid less stable. Unlike traditional plants, these installations adjust voltage in abrupt steps, while rooftop panels reduce demand from the national grid on sunny days, causing sudden voltage swings when sunlight is interrupted.
Some observers also cited inertia as the cause. The shortage of “grid inertia,” stemming from Spain’s reduced reliance on nuclear and fossil fuel generation, may have amplified the system’s vulnerability.
Michael Shellenberger, a prominent nuclear advocate and long-time RE critic with over a million followers on X, commented on the blackout the same day, “Renewables don’t risk blackouts, said the media. But they did and they do… it’s clear that too little ‘inertia’ due to excess solar resulted in system collapse.”
Inertia, generated by spinning turbines, provides temporary energy to stabilize the grid during sudden power losses. Modern sources like wind, solar, and batteries lack this physical rotation, offering no built-in shock absorption. At the time of Spain’s blackout, inverter-based renewables accounted for nearly 70% of electricity, leaving the grid without sufficient inertia to buffer the disruption.
However, REE clarified that inertia was not the cause of the outage.
Rana Adib, executive director of the Renewable Energy Policy Network for the 21st Century (REN21), described the Iberian blackout as a wake-up call to accelerate grid modernization. She emphasized, “As renewable energy grows, system resilience must grow with it. This means planning holistically: for supply, infrastructure, flexibility, and demand — and ensuring strong multi-stakeholder collaboration from the start.”
The European Commission is set to unveil legislation on November 25 aimed at modernizing and strengthening the bloc’s power network.
At the same time, Madrid’s government has consistently rejected claims that RE triggered the outages, attributing the disruptions instead to poor planning by REE.
(Also read: Powering the Future: A Diverse Energy Mix for a Strong Green Transition)
Exploring measures to stabilize the grid
To help operators manage sudden fluctuations, the CNMC proposed tighter temporary controls on voltage and more precise scheduling of power output. The regulator said it will hold a five-day public consultation before implementing the measures, which are expected to remain in effect for an initial 30-day period.
Additionally, REE has sought immediate approval for technical adjustments and temporary operational measures covering scheduling, voltage management, secondary regulation, and other restrictions to prevent the grid from being overloaded again.
Cortinas stressed that all power generation sources need voltage control, highlighting that the current grid lacks automatic regulation. “It can be done in the same way as in classical generation, it’s not complicated, but needs to be required. We will advocate clearly for changes in future regulation,” he noted.
Ahead of the April blackout, the EU encouraged member states to create optional 72-hour emergency kits to help citizens cope during crises. These kits proved valuable for residents in Spain and Portugal, providing essential support in the blackout’s immediate aftermath.
With the risk of another blackout looming, experts are urging residents to keep a basic emergency kit at home. Recommended items include drinking water, non-perishable food, a first aid kit, a flashlight, a battery-powered radio, a mobile phone power bank, cash, warm clothing, and candles.
Sources:
https://www.telegraph.co.uk/business/2025/10/09/spain-at-risk-of-fresh-net-zero-blackouts/
https://www.bbc.com/news/articles/cg7d4vjdlrmo
https://www.npr.org/2025/10/08/nx-s1-5534949/spain-blackout-misinformation-renewable-energy
https://www.reuters.com/business/energy/dont-blame-renewables-spains-power-outage-bousso-2025-04-30/