Comanche 3, Xcel Energy’s troubled $1.3 billion, coal-fired power plant in Pueblo, is in trouble again — shut down for repairs to a damaged turbine that are expected to take eight months.
Since the plant opened in 2010 it has been plagued by breakdowns for more than 900 days offline, according to a Colorado Public Utilities Commission report. It was shut for repairs almost all of 2020 and part of 2021.
On Aug. 12, the 750-megawatt plant experienced “elevated vibrations” that tripped the turbine offline and led to “notable damage to the unit,” according to a notice letter filed with the PUC and the Colorado Office of Utility Consumer Advocate.
“The first question is reliability,” said Cindy Schonhaut, UCA director. “Is this plant going to be able to operate? The second is, who is going to pay for the cost of repairs and replacement power?”
“We are concerned about how much this is going to cost consumers,” Schonhaut said.
When it went online in 2010, Xcel Energy said in a PUC filing that the unit would add about $3 a month to the average bill. Between 2025 and 2029 the operating and maintenance costs for the plant are estimated by the company at $34.5 million a year.
Xcel Energy, Colorado’s largest electricity provider with 1.6 million customers, said it is investigating the “root causes” of the Aug.12 incident with the aid of a structural consultant and the turbine maker, and that the estimated date for return to service is June 2026.
“Power plants are complex machines with many moving pieces of equipment that can cause a unit to come offline,” Xcel Energy said in a statement to The Colorado Sun.
“We are working with external steam turbine experts on a detailed analysis of the cause of this outage and are waiting until the analysis is complete before providing further comment,” the company said.
The Comanche 3 plant was bedeviled with problems even before it opened in 2010, after six years of construction.
The opening was delayed due to leaking steam tubes in the boiler. The plant’s builder, Alstom Power, welded the tubes in its shop in the Czech Republic. Alstom Power was bought by GE Vernova in 2015.
In a 2009 report to the PUC, Xcel Energy said that it had been told by Alstom that the same problem had occurred on five boilers Alstom supplied in China and Taiwan in the 1990s and at an 850-megawatt power plant being built for Kansas City Power and Light.
For the next 15 years leaks plagued Comanche 3.
The plant was equipped with advanced supercritical pulverized coal technology and top-of-the-line pollution controls and was projected to operate until 2070. It is now slated to close by 2031 as part of the state’s mandate to reduce greenhouse gas emissions.
When the power plant opened, it emitted a high-pitch whine that could be heard in homes 3 miles away. After five months it was closed to add baffles to dampen the sound and to replace some steam tubes.
It wasn’t the last time the plant was shut for repairs.
A 2021 PUC staff report found that the unit had 700 days of shutdowns since it was opened. Since the report it has been down at least another 293 days, according to data from the UCA.
The biggest outage, which began in January 2020, started with a loud noise and vibrations from a low-pressure turbine. The plant was down until June 2, 2020, for repairs, costing $4.2 million.
When it was started up there was a failure in a valve that led to a loss of lubricating oil and the turbine overheating. It was not until 2021 that Comanche 3 was online again. The cost for the second set of repairs was $20.4 million.
Since then, the plant has been shut at least 17 times for a total of 293 days, according to notice letters filed by Xcel Energy with the UCA and the PUC.
“The cause of the leak was determined to be porosity in the initial weld, an original construction weld defect,” a September 2023 letter said. “The leak was fully repaired and should not require additional repairs.”
On Sept. 28, 2024, Comanche 3 was shut due to another leak, this one in the lower waterwall tube. The unit was closed for four days “to avoid collateral damage” while the leak was repaired.
This year has been a particularly difficult one for Comanche 3. In March the plant was closed for 10 days due to leaks from ruptured tubes and collateral damage.
Then it was out of service for eight days in July, according to a company report filed with the PUC, including July 27 and July 28 when the temperature reached 97 degrees, spurring a jump in electricity demand.
On Aug. 7, with temperatures pushing toward 100 degrees and Xcel Energy projecting a gap in generation capacity, an Orange Alert was issued urging customers to reduce their use between 3 p.m. and 10 p.m.
Orange Alerts are rare, with the utility issuing 13 in the past nine years. The alert was in part the result of the high temperatures, but a big part of it was due to outages from fossil-fuel plants, according to a PUC analysis.
The Fort Lupton and Valmont gas-fired units were out and the three coal-fired units, Hayden, Comanche 2 and Comanche 3, were running below capacity. The coal units accounted for 80% of the capacity lost.
The reason for Comanche 3’s low output, or its being “derated,” is not listed, but when it was derated in July 2024 it was due to a leak in one of the unit’s coal mills.
The situation in August was exacerbated by wind and solar generating about a third less electricity that day than average, although they still produced more than their targeted levels. In all, Xcel Energy projected that it could be about 643 megawatts of generation short for the day.
“The reliability was much more on the fossil side than the renewable side,” Erin O’Neill, a PUC deputy director, told the commission during Sept. 23 review of the incident.
The utility managed to get through the day with no disruption of service and from 3 p.m. to 10 p.m. wind generation increased about 80% to 1,800 MW. “What really saved us was the wind,” PUC Chairman Eric Blank said.
Customers — through programs such as switch savers and smart thermostats and energy credits to businesses — cut their usage by 525 MW off the project peak demand of about 7,000 MW.
“Was this a one-time oops, so many coal units went, or is there a more chronic problem with reliability?” Commissioner Megan Gilman asked.
Part of the issue is that with all coal-fired plants to close by 2031, Xcel Energy is “managing down the units,” but there have also been continuing issues of chronic reliability, O’Neill said.
“People hear, certainly in this political environment, that coal is going to give us more reliability and lower costs,” Commissioner Tom Plant said, “but what we’re seeing here is exactly the opposite. It’s less reliable, it’s more expensive.”
The day after the Orange Alert, Aug. 8, Comanche 3 was again shut down to repair an external water wall tube leak. It went back online Aug. 11. The following day vibrations damaged the turbine, shutting the unit perhaps until next summer.