The Calaveras Power Plant.
CPS Energy's Sommers natural gas units at the Calaveras Power Plant are performing "very well," say utility officials. Credit: Scott Ball / San Antonio Report

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Every type of power generator suffered problems as a winter storm gripped Texas this week, with state and local power officials saying their industry was caught off guard by an unprecedented deep freeze.

“I don’t know of one technology in producing power that has not been affected by these freezing cold temperatures,” CPS Energy President and CEO Paula Gold-Williams told reporters Tuesday. “It is very hard to start a plant and keep it going at these temperatures.”

The Electric Reliability Council of Texas (ERCOT), the state’s grid operator, reported similar issues. Speaking to reporters Tuesday, ERCOT Senior Director Dan Woodfin gave a breakdown of all types of generators that went offline during the freeze.

ERCOT logged 16,000 megawatts of wind and solar generation that was unavailable, Woodfin said, along with 28,000 to 29,000 megawatts of “thermal generation” – natural gas, coal, and nuclear. One megawatt can power roughly 200 Texas homes on an extremely hot or cold day.

As of late Tuesday, the lost generation capacity was “primarily due to issues on the natural gas system,” Woodfin said.

“And I mean the system at large, from getting the gas from the frozen wellheads through the pipes to the generators and to [meet] consumer demand for heating,” Woodfin said.

CPS Energy, one of the biggest power companies on the ERCOT system, suffered problems with every type of power plant it uses to generate electricity, Gold-Williams told reporters Tuesday. San Antonio’s municipally owned utility has seen natural gas, coal, and nuclear plants stop generating at various times since temperatures began dropping Sunday.

“For the most part, most of our plants did function, but we did run into problems,” Gold-Williams said.

At the South Texas Project, a nuclear plant on Matagorda Bay that CPS Energy shares with Austin Energy and NRG, one of its plants performed “well,” but another had to be taken offline temporarily Tuesday “to keep it very, very safe,” Gold-Williams said.

Other natural gas plants suffered largely as a result of a lack of fuel supply, Gold-Williams said. Many power generators reported difficulty acquiring enough natural gas, which has been in high demand as a heating fuel.

“When we had the supply not come through, we had to dial back the performance and the capacity output of one of our best natural gas systems,” Gold-Williams said.

Ironically, CPS Energy’s oldest generators – O.W. Sommers and V.H. Braunig, both gas steam plants built in the 1960s and 1970s – performed “very well,” Gold-Williams said.

“They’re about 50 years old, though, and they’re both nearing end-of-life,” she said. “So I think we were fortunate that those units did perform well.”

CPS Energy also has a significant share of wind and solar generation in its portfolio. Renewables account for 22 percent of its generation capacity, with another 45 percent from natural gas, 18 percent coal, and 14 percent nucelar.

Gold-Williams described CPS Energy’s wind energy output as “spotty at best” due to mostly to frozen turbines. But the utility reported modest solar production on Tuesday, though energy producers don’t expect to get much out of solar during the winter.

“We got some pretty good sunshine yesterday and that was helpful, but there were days … where it was cloudy and we got very little solar over the entire event,” she said.

CPS Energy and ERCOT officials largely blamed single-digit temperatures, colder than most of Texas has ever faced before. Most power plants here can function at around freezing temperatures or even into the high 20s, Gold-Williams said.

“When we’re in the single digits – and that’s without wind chill factor – and then when you add that and you’re in negative temperatures, that’s what’s making it hard for every single technology to function.”

Sometimes, the problem came in the form of support systems for the plant that failed in the cold. In one case, CPS Energy converted one of its Spruce coal units to run on natural gas, Gold-Williams said.

“That took us a couple days,” she said. “It’s functioning today but it’s going to have to come back down. You can’t do it with a minor repair for a very long period of time.”

Crippling cold and winter storms were the cause of Texas’ last bout with rolling blackouts in February 2011, when ERCOT reported an unexpectedly high number of plants going offline. Following that, power companies began submitting winter weatherization reports to ERCOT and the state Public Utility Commission, which oversees the power industry and the Texas grid.

But as Woodfin said Tuesday, those measures proved too little to cope with this week’s cold.

“I think if we had had typical extreme weather like a 2011, those would have worked,” Woodfin said. “The issue is this is an unprecedented weather event.”

CPS Energy is a financial supporter of the San Antonio Report. For a full list of business members, click here.

Brendan Gibbons

Brendan Gibbons is the San Antonio Report's environment and energy reporter.