ERCOT report confirms gas- and coal-fired plant outages played big role in June grid woes

AUSTIN — New data from ERCOT confirms that issues with thermal energy sources, including coal and natural gas, were largely responsible for the smaller-than-expected generation capacity on the grid that led to supply concerns in June.

Information about which power plants had unplanned outages in June, rattling public confidence in the Texas power grid, was released Wednesday by the Electric Reliability Council of Texas. There were more than 1,200 unplanned outages at generation facilities during the month, including 224 June 14-18, when the grid operator urged Texans to conserve energy because of higher demand and less available power than expected.

The report came a week after the Public Utility Commission of Texas ordered ERCOT to post information about maintenance-level outages and forced outages within three days after they happen. Previously, the grid operator had 60 days to post those reports.

Many Texans worry that the mid-June conservation period may be a warning for what’s to come later in the summer as temperatures rise.

The mid-June conservation notice was issued because of a combination of unplanned outages, low wind and a heat wave with temperatures in the high 90s that led to more air conditioner use and a greater draw of electricity.

ERCOT reported unplanned, or “forced,” outages on June 14 of about 12,000 megawatts at generating plants, enough to power more than 2 million homes. About 9,000 of those lost megawatts were from thermal power sources fueled by natural gas, coal or nuclear power.

Daniel Cohan, an associate professor of civil and environmental engineering at Rice University, said many of the plants that had issues during the February winter storm also had outages in April, when ERCOT said grid conditions were tight, and again in mid-June. Cohan said thermal generation has been the primary source of unplanned outages.

“I think this really brings into question the assumption that we can count on 95% output from these aging gas, coal and nuclear plants,” Cohan said. “Of the thermal capacity in ERCOT, 30% of it is more than 40 years old.”

Cohan explained that with age comes an increased need for maintenance and a higher likelihood that a plant will be down for repair at any given moment, reducing reliability.

Beyond greater-than-usual outages the week of the conservation notice in June, Cohan said, the new ERCOT data shows that thermal plants were consistently down more often than the grid operator says they should be.

In its summer assessment of resource adequacy, ERCOT said it’s 64,000-megawatt thermal fleet should be operating at 95% of capacity at any given moment. Cohan said the data shows it’s usually operating at 85% to 90%.

A late-June report by Wood Mackenzie, a global energy consulting firm, identified four of the major generation outages that led to that month’s conservation notice, including the fire-caused shutdown of one of the Comanche Peak nuclear power plant’s two units, which removed about 1,200 megawatts. When both units are operating under normal conditions, they produce enough energy to power 1.15 million homes.

The report also correctly identified outages at two large coal-fired power plants.

During the conservation period, there were outages at the Limestone coal-fired generation facility in Jewett. That plant, owned by Houston-based NRG Energy, has a capacity of 1,660 megawatts. Another NRG-owned coal-fired facility, the W.A. Parish plant in Thompsons, near Houston, also had outages in mid-June. It has a capacity of 1,120 megawatts.

Talen’s Barney Davis natural gas-fired facility in the refining and chemical hub of Corpus Christi was transmitting just a fraction of its 933-megawatt capacity in the days leading up to the heat wave.

The ERCOT data also revealed several significant outages not identified in the Wood Mackenzie report. Martin Lake, a coal plant in Tatum owned by Luminant, a Vistra subsidiary, appeared to have outages during the week of tight grid conditions. Sandy Creek, a McLennan County coal plant, also had outages.

Built in 2013, Sandy Creek is Texas’ newest coal-fired power plant. Cohan said the outages there and at W.A. Parish are interesting because they don’t fit his theory about older plants that need maintenance being the source of the unplanned outages.

“With coal, most of the units were built in the 1970s and early ’80s,” Cohan said. “But even the few that were built in the 2010s were having outages.”

Although Cohan blames thermal resources, which make up the bulk of Texas’ installed generating capacity, for most of the unplanned outages, he acknowledged the role of wind in mid-June’s tight grid conditions. At the lowest output during that week, only 179 megawatts — out of 25,121 megawatts of installed wind capacity — were being produced.

Cohan said one other thing the data makes clear is that “solar kept the lights on.”

Bob Whittmeyer, a consultant for ReSolved Energy, has another theory about why the unplanned outages are happening now. He said unplanned outages are typical after the planned outages generation facilities undergo in the spring.

“It’s been my experience that forced outages are often a direct function of coming back from a planned outage, where something was missed — like if somebody left a rag in an oil cooler,” Whittmeyer said. “They took the equipment apart, they put it back together, and something got missed that will lead to a forced outage, and they’re generally short.”

What was different this spring, Whittmeyer said, was the probably higher-than-usual number of planned outages happening at once after delayed maintenance during the pandemic.

“So you would have seen, in my opinion, a likely higher number of planned outages in the spring of 2021, which would naturally lead to a higher number of forced outages immediately following,” he said.

Whittmeyer said unplanned outages that follow planned outages usually don’t happen long after maintenance. If his theory holds up, he’s hopeful that unplanned maintenance will taper off as the summer continues.