Many of the traffic lights were turning from red to green again. The trains in Madrid’s subway system were rolling on all but one line. And baristas at cafes in the Spanish capital were serving café con leche to the few clients out on the quiet streets Tuesday morning.
By that time, electricity had returned to almost all of Spain and Portugal, nearly 18 hours after both countries were hit by extensive blackouts. The return of power left many relieved, though questions about what had happened were growing sharper.
A spokesperson for the electricity and gas supplier in Portugal, REN, said Tuesday that power had been restored to all the substations of the country’s grid and that everything was “100 percent operational.” All 6.4 million electricity users in Portugal were getting power, the Portuguese news agency Lusa reported.
The cause of the blackout, which stranded tens of millions of people on the Iberian Peninsula, remained unknown early Tuesday.
Eduardo Prieto, the director of services for Spain’s national power company, Red Eléctrica, told journalists on Tuesday morning that there were no “definitive conclusions” as to the reasons for the outage.
He joined a chorus of officials who declared that there had been no cybersecurity attack. But he also ruled out human error and meteorological causes.
He said that the Spanish electricity system had shut down after being hit by two separate power outages, just a second and a half apart.
“This may seem like a small amount,” he said, “but in the electrical world, it’s a significant amount.” He said that the shutdowns had occurred in southwestern Spain.
Kristian Ruby, secretary general of Eurelectric, a trade body that represents the European electricity industry, said it could take weeks or even months to complete the technical analysis required to fully understand the outage.
But some initial information has already emerged, he said. Around noon on Monday, a high-voltage connection line between France and Spain was interrupted. The power outage occurred just over 30 minutes later.
While that interruption would have been disruptive, it would not normally lead to a “system collapse” like that seen on Monday, Mr. Ruby said. Something more would typically need to happen, “like a sudden outage at a power plant, a sudden development on the demand side,” he said. “Then you can have an incident like this.”
Mr. Ruby said the outages were “somewhere on the scale between a 50- to 100-year event.”
Both Spain and Portugal shut down on Monday afternoon. Traffic lights across both countries went dark, trains and subways halted, elevators stopped — often with people stuck inside.
Businesses, factories and schools shut down, and airports delayed and canceled flights.
There were also widespread problems connecting to the internet and to phone networks, leaving many bewildered and unable to access information.
When the power turned on again Monday evening, and the lights suddenly turned back on, cheers erupted across Madrid.
In cities across the two countries, life was returning to normal on Tuesday.
“It seems like everything is better today, but I don’t understand how something like this is possible with all the technology we have today,” said Doroteo García, an 87-year-old retiree, walking with difficulty near a Madrid train station. He had spent the day before trapped in his apartment, he added, because the elevator was not working.
“I lived off canned sardines all day because I couldn’t cook,” he said.
Though the power was back on, the Spanish capital was not quite back to its bustling self. Many people stayed home. Schools were open, but few with regular classes.
María del Carmen Sánchez, a school assistant at Cervantes Secondary School in the Lavapiés neighborhood of Madrid, said, “barely 5 percent of the students came” on Tuesday.
The blackout “was very confusing because we had no communication with the outside world,” she said. Some parents arrived very late to get their children. “Within the chaos of the situation, I think everything went quite well,” she said. “People were very patient, although there was some nerves and concern at first.”
In downtown Lisbon, parents dropped off their children at school on Tuesday morning, gyms had opened their doors again, and the sound of power drills filled the air.
In Murcia, a city in southeastern Spain, police officers who had been stationed at intersections to direct traffic were gone, and the traffic lights were working normally again.
María José Egea, 71, said she had gone to her regular Pilates class with a friend. She described the evening she spent in her seventh-floor apartment on Monday as “terrible.” But she said that her neighbors had come to check in on her.
“At first, we heard a lot of stories about the origin, and people were coming and telling me nonsense,” she said, standing out on a street in front of a busy coffee shop. “Everyone had a theory. The worst was the lack of communication.”
Azam Ahmed contributed reporting from Lisbon.
