What Caused Spain’s Power Blackout? It is Not Yet Known but It Appears That Loss of Spinning Reserve/Grid Inertia Was a Major Factor

     Spain’s power grid is heavy with solar and wind, both intermittent resources whose power generation is variable. It is second only to Germany in the amount of solar generation. These are also known as inverter-based resources (IBRs) since they require DC to AC conversion via power inverters.  In contrast, so-called thermal resources such as nuclear, coal, and natural gas power turbines that spin and retain spin for a time even as they trip offline, retaining what is known as “spinning reserve,” or “grid inertia.” They are also known as rotational, or synchronous generation. This includes hydropower, which is also turbine-based. The weight of the heavy metal turbines provides the inertia. IBRs are also known as non-rotational, or non-synchronous generation.

“When faults cause a rise or fall in grid frequency, this inertia helps lower the rate of change of frequency, giving system operators more time to respond, noted Adam Bell, director of policy at Stonehaven, in a post on LinkedIn.”

     It has long been known that grids running with a high degree of IBRs are vulnerable to a loss of grid inertia or spinning reserve. Less than two weeks before the blackout of April 28, on April 16, Spain reported a milestone day where they ran on 100% renewable power, with solar providing 78.6% of that power. On April 28, at the time of the blackout, Spain was running on 78% solar and wind, 6% solar, and about 3% powered by natural gas, providing spinning reserve. According to the Daily Mail:

“Spain's state electricity network operator Red Electrica, which is now gradually restoring power to the country and neighbouring Portugal, said a 'very strong oscillation' in the electrical network caused Spain's power system to 'disconnect from the European system'.”

     As shown below, about 15GW of energy dropped suddenly from Spain’s power grid. The blackout lasted about 10-12 hours and disrupted travel and communications.

     Energy writer Javier Blas analyzed the timing of events of the system according to Red Electrica's data and analysis, shown below. (Note that it should read south-west of Spain, not south-east of Spain)

     The blackout is still being investigated, but according to Reuters, too much renewable power on the grid has been ruled out, although I am not exactly sure if that means a lack of grid inertia was ruled out.

“Red Eléctrica, “preliminarily ruled out that the blackout was due to a cyberattack, human error or a meteorological or atmospheric phenomenon”, El País reported the day after the event.”

     Energy researcher Lion Hirth posted on LinkedIn about the two distant ends of the synchronous European power system from Latvia to Spain, and posted the following graph and possible explanation. 

     One commenter compared the blackout to the 2021 winter storm Uri in Texas, with similar causes (although the main issue in Texas was freezing water in natural gas systems):

“…underestimating the role of dispatchable generation and system inertia in maintaining grid stability.”

     It has not been proven that a lack of grid inertia was the root cause of the blackout. The Spanish grid does have synchronous condensers that help to add some grid inertia and balance power. Hirth also wrote:

“[It]seems highly plausible that oscillations like those evident through frequency measurements would have been dampened with more inertia…[Yet] that does not necessarily imply that more inertia would have avoided the blackout. That is a possibility, but not a certainty.”

Thus, more grid inertia would have been helpful, but the lack of it may not have been the cause. He also noted that the issue of grid inertia has long been explored and accounted for, and as Hirth noted, grid inertia has not been ignored or overlooked. It can also be increased by other means than thermal or turbine-based resources, such as flywheels, suggesting that perhaps flywheels can be added to the system.

     Despite many stories, especially by climate skeptics, blaming the blackout on renewables and net-zero goals, that cause has not been proven. The blackout is not a reason to condemn high renewables penetration on power grids. With sufficient engineering and investment, the problem of grid inertia/spinning reserve on such grids can be solved. In any case, grid upgrades to add grid inertia are likely needed to prevent any similar events from occurring in the future or to limit their effects.

 

 

References:

 

Did Over-Reliance On Solar & Lack Of Grid Inertia Cause Spain’s Blackout? Robert Bryce. Substack. April 28, 2025. Did Over-Reliance On Solar & Lack Of Grid Inertia Cause Spain’s Blackout?

Massive power outage strikes Spain and Portugal. Jamie Chisholm. Market Watch. April 28, 2025. Massive power outage strikes Spain and Portugal.

Europe Power Outage Caused by 'Rare Atmospheric Phenomenon,' Company Says. Marni Rose McFall. Newsweek. April 28, 2025. Europe Power Outage Caused by 'Rare Atmospheric Phenomenon,' Company Says

April 16, 2025: Spain Runs 100% on Renewable Power. April 28: Blackouts.David Blackmon. Substack. April 28, 2025. April 16, 2025: Spain Runs 100% on Renewable Power. April 28: Blackouts.

Could renewable energy be to blame for huge Spain blackout? How outage struck days after country's grid ran entirely on green power for the first time. David Averre and James Reynolds. Daily Mail. April 28, 2025. Could renewable energy be to blame for huge Spain blackout? How outage struck days after country's grid ran entirely on green power for the first time | Daily Mail Online

Power is back on in Spain and Portugal, but questions remain about Monday’s blackout. Here’s what we know. Robert Picheta. CNN. April 29, 2025. What caused the power outage in Spain and Portugal? Here’s what we know | CNN

Q&A: What we do – and do not – know about the blackout in Spain and Portugal. Carbon Brief. April 30, 2025. Q&A: What we do – and do not – know about the blackout in Spain and Portugal - Carbon Brief