CPS Energy overrode its automatic rotating outage system Monday evening to help stabilize the state’s electrical grid, at one point shutting off roughly two-thirds of its system to help meet steep cutback requirements from the Texas grid operator.

With Texas in its third day of a power crisis wrought by a record deep freeze, the Electric Reliability Council of Texas (ERCOT) issued calls for transmission companies to cut demand by 20,000 megawatts statewide, said Rudy Garza, CPS Energy’s chief customer engagement officer. ERCOT’s demand cuts had already reached record highs the day before.

To meet these cuts, CPS Energy, which serves more than 860,000 electric customers in the San Antonio area, had been using an automated system of rotating outages for most of Monday. The utility has since switched to a manual system to give it more control, Garza said.

“We wanted a little bit more control over being able to leave customers on for a longer period of time [with power],” Garza said. “Our automated system was not allowing use the kind of flexibility we were trying to get, so we moved to a manual system.”

As of 3 p.m. Tuesday, more than 253,000 customers were still without power, according to CPS Energy’s outage map.

Making matters worse is a forecast ahead for more cold and freezing rain across Texas. Outages could last through Wednesday or longer as power suppliers and transmission operators struggle to get equipment back online.

“This condition is going to persist until we get back above freezing temperatures, not just in San Antonio but across the state,” Garza said.

The rotation blackouts affect roughly 250 circuits in CPS Energy’s system, with another 125 circuits not eligible for power cuts because they connect to a site considered critical, such as a hospital or medical research facility.

Many of those served by the 250-or-so eligible circuits saw their allotment of electricity shrink throughout the day. Reports poured in Monday of people with less than 5 minutes of power per hour.

Around 7 p.m. Monday evening, CPS Energy stopped the rotation system and shut off all of the eligible 250 circuits, Garza told the San Antonio Report in a Tuesday morning phone interview.

“We were stressed to give ERCOT what they were asking for, and people were complaining that the one-minute-on-and-an-hour-off was worse, so we stopped the rotation,” Garza said.

Doing this helped stabilize the overall system, Garza said around 11 a.m. Tuesday.

As of 12:30 p.m., ERCOT officials said they had worked with local utilities to restore power to 400,000 households across Texas, but the grid operator’s forecasts for Tuesday afternoon and evening show demand vastly exceeding supply, likely signaling the need for continued blackouts.

During a phone hearing with Texas legislators Tuesday, Dan Woodfin, ERCOT senior director of system operations, said the best-case scenario is “we’ll get more generation online this afternoon and be able to restore a large amount of the generation this afternoon.”

“I don’t think given the forecast that we have of generation availability that even the best case would result in us having everybody back online today,” Woodfin said. “What we’d like to get back to is an amount that we’re reducing is enough that we could get back on a cycle of rotation outages rather than keeping all loads out constantly.”

A worst-case scenario involves “having to leave people out for more days as opposed to getting people up rotating again,” Woodfin said.

ERCOT’s calls to shed 20,000 megawatts of demand from the state grid exceed all previous records. This week marks the fourth time Texas has faced such rolling outages since the advent of the modern electrical grid.

CPS Energy accounts for approximately 7% of the demand on the state grid and thus must shed 7 percent of that 20,000 megawatts. That means CPS Energy needed to drop its demand by 1,400 megawatts, enough to power approximately 280,000 Texas homes on a sweltering or frigid day.

“Believe me, I get it,” Garza said. “I empathize with every customer in our system who’s out. This is not a condition we ever want to be in, but when ERCOT tells us we have to get rid of a certain amount of load in our system to stabilize the entirety of the grid, we’re obligated to do it.”

Disclosure: CPS Energy is a San Antonio Report business member. For a full list of donors, click here.

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