The coal-fired power plants of Public Service Co. of Colorado showed a mix of above- or below-expected capacity factors during 2011 and 2012, with the newest, the 783-MW Comanche Unit 3, showing a similar pattern.
That is according to a Sept. 17 report from Colorado Public Utilities Commission staff. The report is the result of a commission concern that the operation of all of this Xcel Energy (NYSE: XEL) subsidiary’s power plants have varied from what was expected.
The concern came out of the company’s 2011 Electric Resource Plan (ERP) case. In the course of the hearings in that case evidence was introduced that indicated that the actual operation of certain plants has deviated far from the expectations set forth in the ERP. In its Phase I decision granting approval of the 2011 ERP, the commission observed that the actual 2011 capacity factor for the then-new Comanche 3 facility was only 52.7%, while the company’s projections and models used a capacity factor of about 85% for most years. The commission also observed that, in 2011, the Blue Spruce combustion turbine units produced more than three times the amount of energy that was projected and modeled for resource planning purposes.
The commission expressed concern that such deviations could have an impact on ratepayers in terms of higher fuel and purchased energy costs. Given these concerns, the commission directed the staff to perform an investigation.
There was in the 2011-2012 period a mix of under- and over-performance of both coal-fired and gas-fired units, the report noted. All of the coal units were utilized noticeably less than would be expected, considering their respective availabilities. Staff noted that in 2011 the actual coal-fired unit production was considerably lower than projected. Staff observed, in 2011, forced outages were the primary driver for reduced production. In addition, staff observed that during four months in 2012, gas prices were sufficiently low enough that combined-cycle gas-fired generation was producing electricity at a lower cost than other baseload coal generation. Therefore, the gas-fired units were dispatched out of traditional economic order.
The commission specifically noted concern with Comanche 3’s lower than average capacity factor (CF), given that Comanche 3 is the largest, newest, and most efficient baseload unit in the Public Service fleet. Comanche 3 was expected to have annual CFs for 2011 and 2012 near 85%, and equivalent availability factors (EAFs) for the same time period near 90%. The 2011 CF (53%) and 2012 CF (68%) fell well below the industry average CF for this type of unit (85%), but also well below what Public Service projected during its modeling for resource acquisition.
Public Service had shakedown issues with Comanche 3
Staff noted that Comanche 3 is new and as a new unit may have experienced higher than average operating risks during its initial shakedown period. Staff compared Comanche 3’s average monthly CF for its first 24 months of operation with the monthly CF’s of nine similar new coal generating units for their first 24 months of operation. That includes the new Trimble County coal unit in Kentucky and the Plum Point plant in Arkansas.
The goal of this comparison was to determine whether the performance during the shakedown period was typical of similar units, and to determine whether the units had achieved their respective maximum capacity factors within the first twenty-four months of operation.
All 10 comparable generation units experienced lower than average CFs during the first 12 months. Other than Comanche 3, the comparable units had an average monthly CF of 72%. Staff concluded that Comanche 3’s performance was typical for the first 12 months with an average monthly CF of roughly 70%. But, Comanche 3’s CFs during months 13 to 24 were considerably lower than those of other generating units of similar size, age and fuel. The investigation also revealed, for months 13 to 24, low unit availabilities due in part to high forced outage rates caused by improper waterwall weld techniques, and tubing leaks caused by slagging in the superheater and reheater pendant sections.
In 2011, Public Service attempted to resolve the issues during eight weeks of planned outages, which further reduced unit usage during the 13- to 24-month operational period. Comanche plant management has stated that while forced outages caused by improper weld techniques have been greatly reduced, the unit experienced at least one such outage in 2013 as a result of this ongoing issue.
Staff also noted that during operating months 13 to 24, Public Service, utilizing economic dispatch, experienced a four-month period of time where gas-fired units were dispatched ahead of Comanche 3 and all other coal units because of low gas prices. This further lowered Comanche 3’s CFs but did not affect the unit’s availability.
The coal units, their sizes, and the actual capacity factors in 2011 and 2012 are:
- Arapahoe 3, 44 MW, 2011-48%, 2012-50%;
- Arapahoe 4, 109 MW, 2011-41%, 2012-63%;
- Cherokee 3, 152 MW, 2011-61%, 2012-62%;
- Cherokee 4, 352 MW, 2011-63%, 2012-65%;
- Comanche 1, 325 MW, 2011-63%, 2012-73%;
- Comanche 2, 335 MW, 2011-65%, 2012-80%;
- Comanche 3, 783 MW, 2011-53%, 2012-68%;
- Hayden 1, 184 MW, 2011-85%, 2012-52%;
- Hayden 2, 267 MW, 2011-64%, 2012-71%;
- Pawnee 1, 505 MW, 2011-66%, 2012-74%; and
- Valmont 5, 184 MW, 2011-63%, 2012-62%.