The power cuts that swept across Spain, Portugal and parts of southern France plunged the Iberian peninsula into chaos.
But as fresh details emerge, it seems the cause of Europe’s biggest-ever power cut can be traced back to just five crucial seconds.
Red Eléctrica de España, which manages the Spanish national grid, says the crisis erupted owing to a rapid sequence of events that unfolded at Monday lunchtime.
On Tuesday, the company revealed it was “very possible” that the fault which tipped the system over the edge originated from solar farms in the country’s south-west.
It has ruled out the possibility of a cyber attack, although Pedro Sánchez, the Spanish prime minister, appeared to claim that this avenue of investigation had not yet been closed.
Spanish prime minister Pedro Sánchez appeared to claim that investigations into a possible cyber attack had not yet been closed - Burak Akbulut/Anadolu via Getty Images
“There are huge amounts of data that we now have to analyse to understand what happened,” Sánchez told reporters.
Whatever the findings, the crisis is sure to offer lessons for the way grids are operated as countries around the world shift to increasingly “electrified” energy systems that will place more burden on infrastructure and rely more heavily on renewable energy sources.
Seconds from chaos
According to Red Eléctrica, at 12.33pm on Monday, the country’s grid was hit by an event similar in nature to a sudden loss of power generation, seemingly in the south-west of the country.
Such disruptions can be serious because supply and demand must be balanced at all times for electricity grids to function, with the system’s frequency used to measure this.
Following the first event, which would have caused the frequency to drop, the Spanish grid’s computer systems reacted instantly to stabilise the network.
But after just 1.5 seconds, another loss of generation occurred. This was followed, 3.5 seconds later, by the failure of the electricity interconnectors linking Spain and France.
That left Iberia isolated from the rest of Europe, preventing grid operators from importing power to restore balance – and triggered a domino effect whereby solar and wind farms automatically disconnected from the grid en masse to protect themselves.
What followed was a cascading effect across the whole of Spain and Portugal as grid systems and generators shut down to prevent any damage.
At the lowest point, the power being generated fell to zero megawatts – a total blackout, and the first of its kind in Spanish history.
But what was the initial problem that led to these cascading faults?
At Tuesday’s press conference, Eduardo Prieto, director of operational services for Red Eléctrica, told reporters it was “very possible” that the fault had originated from a solar farm in the country’s south-west.
Data published by the company show that about 70pc of Spain’s solar generation is concentrated in the southern provinces of Andalucia (24.3pc), Extremadura (24.3pc) and Castilla La Mancha (22.2pc).
But one industry expert speculates that the fault could just as easily have been caused by an interconnector in the south-west, for example with Portugal or Morocco, given the way Spanish authorities have described the loss of generation-like event.
“They might be worried about p---ing someone off,” the expert adds.
However, the power cuts remain puzzling because modern grid systems should be able to deal with these kinds of disruptions.
“What should happen is that if the losses are within the limits for the system, you should see more power flying across the interconnector from France,” the expert explains.
“But it might be that the second loss is large enough to take you outside the security standards for Spain – in which case they won’t have enough power to compensate, and you might see a much larger inrush from France.
“Perhaps that sudden increase in power flowing across from France contributed to instability.”
The sheer speed at which an electrical event like this spreads – about 1,000 miles a second – means the whole of Spain would have felt the effects within just a few seconds, the expert adds.
Renewable reliance
It is not yet clear whether the two events reported by Red Eléctrica are related, something that will now be a key question for investigators.
If they are linked, it may suggest the system is not working as intended. If their quick succession was a pure coincidence, however, there will still be lessons to learn.
One ongoing question is also whether a low level of “inertia” on the system – the amount of power from generators with spinning parts such as gas, coal and hydro plants – at the time of the problem left the grid more vulnerable.
Inertia acts as a shock absorber, slowing down changes in frequency that may result from drops in generation. However, solar and wind farms do not generate it.
Experts have therefore speculated that the high amounts of solar and wind on the system – which were generating a combined 70pc of power before the power cut – may have left the system more exposed to shocks.
On Tuesday, the Spanish newspaper El Mundo also reported that Red Eléctrica had warned its investors two months previously of the risk of “generation disconnections due to the high penetration of renewables”.
The company also warned that reductions in coal, gas and nuclear capacity would give grid operators less firm power to draw on to balance the system in a pinch, as well as inertia.
“All fingers point to photovoltaic energy, whose massive entry into the system during the middle of the day is causing extremely unstable situations in the grid,” the paper added.
For now, the investigation continues into the power cut’s cause. Sánchez has also announced plans to request a European Union investigation into the crisis.
“The Spanish government will get to the bottom of this matter and will implement the necessary reforms and measures to ensure this doesn’t happen again,” he said.
