Here's why restarting a power grid after massive collapse is so hard

Business Standard

29-04-2025

It's unclear what caused the initial disruption or why it cascaded so dramatically into a widespread failure. But, notably, Spain has been one of the leaders in rolling out wind and solar generation
Bloomberg
It's a worst case scenario that grid operators plan for but hope never to encounter. After one of the worst blackouts in Europe in more than a decade, electricity grid operators in Spain and Portugal are trying to get networks back up and running from the ground up.
The initial estimate from grid operator Red Electrica was that restoring all power supply in Spain may take between six and 10 hours. By Monday evening, that was looking optimistic — at 9pm Madrid time, there was 17.3 gigawatts of demand on the grid, about two thirds the amount seen just before the blackout happened, according to grid data.
It's not clear what caused the initial disruption, or why it cascaded so dramatically into a widespread failure. But it's notable that Spain has been one of the leaders in rolling out wind and solar generation, at a time when governments and grid operators across Europe are grappling with questions about resilience as renewable power takes an ever-larger share of the region's energy mix.
When there has been a failure on the entire grid, a complex process called a 'black start' is needed to restore the network gradually. Smaller, often diesel, generators are used to start bigger ones, in a process that creates 'islands' of power which connect together on the main transmission network to gradually restore the grid.
European rules require grids regularly test their black-start capability, so operators should have a clear plan to follow. But the process is painstaking and complicated.
'These islands of power then need to be all synchronized together,' Simon Gallagher, managing director at UK Network Services, said in a post on LinkedIn. 'Not simple and again, takes time and has to be very controlled.'
Essential services like hospitals will have their own on-site back up generation, usually diesel engines and stores of fuel. Other commercial entities like data centers also pay to have emergency back up generators and batteries to secure supply.
Frequency Factor
So far, the only information about what caused the crisis was a comment from grid operator Red Electrica that the blackout was a result of 'oscillation,' which suggests a disruption in the grid's frequency or voltage — both crucial factors for maintaining stability. The frequency, which normally stays pretty steady around 50 hertz, is the heartbeat of the grid.
Frequency monitoring specialist Gridradar said it identified a rapid movement in frequency just after noon in Spain — right before the blackout hit. Such oscillations can cause chain reactions that ultimately lead to a blackout.
It's not known what caused the initial disturbance. But it's possible it was exacerbated by the large share of energy being generated by renewable sources at the time. To maintain the right frequency and maintain stability, the grid needs kinetic energy, which is created by the spinning turbines of thermal plants. This kinetic energy can't be supplied by wind turbines or solar panels so Spain and Portugal need coal, gas or hydro plants connected.
Loose Ties
Another point of vulnerability for Spain is that it lacks interconnections, meaning it doesn't have many of the huge power cables that connect to neighboring countries. These lines that allow imports and exports are seen within Europe as a way to add energy security.
For Spain, it means that if it has too much power for example on a sunny day, it has only a few routes out of the network. If it doesn't have enough supply, there aren't many options for neighbors to step in and help.
Past Blackouts
Grid collapses are extremely rare and operators will typically do whatever they can to avoid them, including implementing rolling power cuts to protect the system.
The last time there was a blackout on this scale in Europe was in 2006 when there was an outage affecting 15 million homes in Austria, Belgium, France, Germany, Italy, Portugal and Spain.
Since then, renewable energy has been built out at a rapid scale across the region, creating more challenges for grid operators to balance huge swings in supply when it's sunny or windy.
Frequency was a major contributor of blackouts in Texas during an extreme winter storm in February 2021. Freezing weather and ice forced gas plants to trip offline en masse, causing frequency to plunge and other power plants to trip offline, resulting in cascading failures.