How much more? In New York City, weekday electricity use by Manhattan apartment dwellers has increased by 7 percent compared with pre-lockdown days. Much of the increase is from 9 a.m. to 5 p.m., when in normal times most people would be at work or school. Locked-down New Yorkers are using about 25 percent more power during the daytime.
“You can actually see in the electricity data that people are home much more,” said Christoph Meinrenken, a physicist and associate research scientist at the Earth Institute at Columbia University.
The data comes from a study set up two years ago by Dr. Meinrenken and his colleagues that uses special electric meters installed in about 400 Manhattan apartments to provide information on energy use every few seconds. When the coronavirus lockdowns began in New York in late March, the researchers realized they could easily track shifting usage patterns.
Utilities across the country have also noted a general increase in residential consumption. But they say that overall electricity use has declined, in some cases by 10 percent or more, because the drop in commercial and industrial demand more than offsets residential increases.
Those figures are certain to change as the weather warms and if the lockdowns continue, or if some restrictions are lifted and more businesses reopen. And even in a full lockdown, commercial buildings still use power, said Michael Tobias, founding principal partner of Nearby Engineers, which designs building mechanical systems.
“If there’s still one tenant in a 50-story building, they have to operate their systems,” Mr. Tobias said, although building managers can adjust temperatures or turn off some air-handling equipment to save energy.
The Columbia researchers noted that there is little demand for cooling in April and consequently little stress on the power distribution grid. But in warmer months, as more stuck-at-home apartment dwellers run air-conditioners longer, energy use will climb even more.
“If you extrapolate to May, June, July, that could you get you into territory where you won’t be able to say anymore, well the grid, no problem,” Dr. Meinrenken said.
“The challenge of this stuff is it could occur, but locally,” potentially straining transformers and other equipment in areas that are mostly residential, said Vijay Modi, a professor of mechanical engineering at Columbia who is involved in the study. “A weekday peak is what the utility has to worry about.”
Anne Marie Cobalis, a spokeswoman for Con Edison, the utility that supplies power to the city, said crews were working to harden the grid for peak summer demand, replacing and upgrading transformers, cables and other infrastructure.
“If things stay as they are into the summer months, we anticipate seeing a rise in residential usage and some additional commercial usage for air conditioning,” she said. Should any part of the grid become stressed, she added, the utility is ready to provide temporary equipment like mobile generators.
Nationally, reduced overall demand should continue into the summer even if more of the economy reopens, said Adam Jordan, an analyst with Genscape, which provides pricing and other forecasts to the electricity industry. He pointed to the oil industry in Texas, which has been shutting down production amid the pandemic and the resulting worldwide glut of oil.
“That’s going to have a big impact in Texas no matter if we’re locked down or not,” he said. “We’re talking about gigawatts of demand for power from the oil industry, and who knows when it’s coming back.”
The reduction in demand makes it unlikely that broader grid reliability problems will appear this summer even if residential consumption rises, Mr. Jordan said. “In terms of keeping the lights on, this isn’t really a big threat.”
But Mr. Jordan said there eventually could be some distribution bottlenecks, because many utilities are putting off scheduled power plant shutdowns for maintenance work to reduce employees’ risk of becoming infected with the coronavirus.
Rescheduling that work for the fall or next year, when other shutdowns are scheduled as well, could result in reductions in generating capacity, forcing grid operators to juggle power from different sources, including wind and solar generation that is farther from population centers, he said.
The New York apartment study — which was financed by the federal Department of Energy with the goal of developing ways to help apartment dwellers reduce energy use — found other shifts in consumption patterns, especially on weekday mornings.
“There’s usually a quick ramp-up from 6 a.m. to 7:30,” Dr. Meinrenken said, as people start the workday and turn on lights and appliances. Now, he said, with no commute to work and no need to get children ready for school, “people just seem to get up later,” he said. On weekends the morning ramp-up is similar to that of pre-lockdown days.
But where before the lockdown weekday consumption would drop off sharply after 9 a.m. as apartments became vacant, now electricity use just keeps climbing throughout the day, with computers and other electronic devices in use. (It keeps climbing on weekends, too, although the increase from before the lockdown is only about 10 percent, the researchers said.)
Because more people are at home all day, the evening ramp-up, when people typically come home and turn on lights and appliances, is less abrupt. But the data showed that in the lockdown, people are using more energy at night, and usage remains slightly higher even as midnight approaches.
In addition to waking up later, Dr. Meinrenken said, “people also seem to be going to bed a little later.”