Spain, Portugal switch back on, seek answers after biggest ever blackout

MADRID (Reuters) -Spain and Portugal switched their power back on after the worst blackout in their history, though authorities offered little explanation for what had caused it or how they would prevent it from happening again.

Traffic lights were back on, train and metro services slowly returned and schools reopened. Commuters battled with delays to get back to work after an outage that had left people stranded in lifts and cut off from phone contact with their families.

The sudden outage had seen the equivalent of 60% of demand in Spain drop in five seconds around midday on Monday.

While Spanish grid operator REE on Tuesday ruled out a cyber attack as the cause, Spain's High Court said it would investigate whether the country's energy infrastructure had suffered a terrorist strike and Prime Minister Pedro Sanchez said his government had not ruled out any hypothesis.

"We must not rush to (conclusions) and (commit) errors through haste," Sanchez said on Tuesday. "We will find out what happened in those five seconds."

REE said it had identified two incidents of power generation loss, probably from solar plants, in Spain’s southwest that caused instability in the electric system and led to a breakdown of its interconnection with France.

Spain is one of Europe's biggest producers of renewable energy, and the blackout sparked debate about whether the volatility of supply from solar or wind made its power systems more vulnerable.

Investment bank RBC said the economic cost of the blackout could range between 2.25 billion and 4.5 billion euros, blaming the Spanish government for being too complacent about infrastructure in a system dependent on solar power with little battery storage.

STATE OF EMERGENCY

Javier Diaz, a 24-year-old student, was forced to sleep in Madrid's Movistar Arena, a music venue, after finding himself stranded in the capital. Luckily, he had just finished walking the Camino de Santiago, a Christian pilgrimage route in northern Spain, and had a sleeping bag, "so we had quite a good night".

Madrid authorities put on free buses to get people to work on Tuesday and the metro and some trains resumed operating, although with delays. Construction worker William Galicia, 39, had seen three buses pass by completely full.

"We'll have to be lucky for one with a bit more space inside so we can get in," he said.

A state of emergency was declared across many Spanish regions on Monday, with the deployment of 30,000 police. In Atocha station in Madrid, police and Red Cross workers handed out blankets and bottles of water.

Bars and restaurants counted the cost of lost produce after fridges and freezers were switched off for more than eight hours.

"(We’re) scared it will go bad, that we have to throw everything away. We don’t know if the insurance will cover it," said Maria Luisa Pinol, 63, owner of the Granja Isabel bar in Barcelona, which had to shut on Monday night.

In Portugal, the government said hospitals were back up and running, airports were operational albeit with delays in Lisbon, while the capital's metro was restarting operations and trains were running.

Energy systems can be vulnerable when combining intermittent renewable power such as wind and solar with traditional sources such as gas and nuclear plants, said Victor Becerra, a professor of power systems engineering at the University of Portsmouth.

"Whatever the cause, a major failure in one area can place sudden pressure on neighbouring systems, causing protective shutdowns to prevent further damage," Becerra said.

More than 75% of the electricity Spain was using at the time of the outage came from renewable sources, according to Red Electrica data.

Sanchez on Tuesday ruled out an excess of renewable energy as a cause of the network's collapse. He said Spain's nuclear power stations still hadn't resumed operating on Tuesday, which he said showed they were no more resilient than renewables.

He said demand at the time of the blackout was relatively low and that there was ample supply.

"What happened yesterday was an exceptional event in normal, everyday circumstances," Sanchez said.

($1 = 0.8787 euros)

(Reporting by Inti Landauro and Pietro Lombardi in Madrid, America Hernandez in Paris; writing by Aislinn Laing and Charlie Devereux; editing by Susan Fenton, Peter Graff and Mark Heinrich)