This article has been updated.

Exactly four months after the winter storm in mid-February that crippled the state’s energy systems, left millions without power, and caused more than 150 deaths, Texas’ electrical grid operator again warned of tight conditions on the state’s power grid.

But the calls to conserve power from the Electric Reliability Council of Texas (ERCOT) didn’t come during a period of extreme weather, such as February’s single-digit cold. On Monday, much of the state sweated through hot, humid weather with temperatures in the upper 90s.

ERCOT on Monday called for voluntary conservation measures, including:

  • Setting thermostats to 78 degrees or higher. Every degree of cooling increases energy use by 6%-8%, according to ERCOT.
  • Turning off lights and pool pumps and avoiding using large appliances such as ovens, washing machines, and dryers.
  • Turning off and unplugging any appliances not currently in use.
  • Closing shades and blinds on windows exposed to direct sunlight to reduce indoor heat.
  • Charging electric vehicles after 9 p.m., when energy demand is lower.

Hot, humid weather isn’t unusual for June in Texas. The state has never seen summer blackouts on its electric grid during summer months during ERCOT’s 50-year history, even though Texas electricity use spikes to its highest levels during summer heat. Blackouts have instead come during winter, when cold snaps have caught the power industry off guard.

That’s why Warren Lasher, ERCOT’s senior director of system planning, called it “very concerning” that an unusually high number of power plants — three to four times the normal capacity — were offline for unplanned repairs Monday.

“It is our expectation that generation unit owners would be able to make their plants available under conditions such as this,” Lasher said. “This is not consistent with fleet performance over the past few summers.”

Lasher said ERCOT would study in more detail why so many power generation companies saw outages.

“It’s going to take us some time to start that evaluation plant-by-plant of why these plants are offline and when they’re going to be coming back,” Lasher said, adding that ERCOT officials expect to have more updates on Tuesday.

Voluntary efforts to use less energy appeared to be working, at least. ERCOT first issued its conservation notice around 1 p.m. and began seeing demand for electricity level off, mainly from large industrial sites cutting back their usage.

CPS Energy officials said the San Antonio utility wasn’t among the generators that suffered equipment failures. None of its natural gas, coal, or nuclear plants were offline Monday, multiple spokespersons told the San Antonio Report.

“All of our local plants are up and running, and virtually all of them are at full capacity,” said Rudy Garza, CPS Energy’s chief customer and stakeholder engagement officer, in a prepared statement.

CPS Energy officials also put out calls on its social media pages for customers to cut back on their energy use. More than two-thirds of its roughly 840,000 electrical customers participate in at least one of its programs meant to reduce electricity demand during peak periods.

Even as an unusually large number of power plants remain offline, ERCOT’s forecast called for spikes in energy demand that could beat the previous June record of 69,123 megawatts set between 4 p.m. and 5 p.m. on June 27, 2018.

ERCOT officials didn’t any specific details about which power plants were offline, only broad numbers.

As of 2:30 p.m. Monday, the grid operator counted more than 12,000 megawatts of generation capacity under repair and unavailable to generate electricity. One megawatt is enough to power approximately 200 Texas homes on a hot summer day. Grid operators didn’t plan ahead of time for the vast majority of these plants to be offline Monday, meaning the plants weren’t down for long-planned maintenance.

Traditional power plants — natural gas, coal, and nuclear — made up three-quarters of this lost capacity. Wind, solar, and battery storage accounted for only a quarter of the lost generation, though the electricity flowing from renewables proved to be lower Monday than ERCOT’s forecasts predicted, Lasher said.

Brendan Gibbons is a former senior reporter at the San Antonio Report. He is an environmental journalist for Oil & Gas Watch.