Gencos selling into the wholesale market in Texas are no longer primarily responsible for the reliability of supply. In that deregulated market, responsibility for reliability has been largely transferred to the Electric Reliability Council of Texas (ERCOT), an independent system operator regulated by the state Public Utility Commission. Gencos are, however, given financial incentives to provide services and products to the market, and they respond to these incentives in the same way that they respond to a need to maintain a reserve margin or another reliability-related parameter. One of the incentives is ERCOT's award of daily contracts to plants to quickly ramp up or down in response to overall system demand.
The amount and type of power supply capacity in ERCOT has changed dramatically over the past eight years for two main reasons: deregulation and the commissioning of over 20,000 MW of high-efficiency, natural gas–fired combined-cycle plants. Power producers responded to these two events by mothballing or decommissioning around 10,000 MW of older gas-fired steam plants whose marginal operating costs could not compete with those of the combined-cycle plants. Every owner of an older gas-fired steam plant had to decide whether to throw in the towel or find something other than capacity that the plant could sell profitably.
Adding support to supply
Lower Colorado River Authority (LCRA) began operating the first 150-MW unit of the Sim Gideon Power Plant (see cover photo) in 1965. Another 150-MW unit was commissioned in 1968, and a third, rated at 350 MW, went commercial in 1972. The old plant shares its site with the Lost Pines 1 Power Project, a gas-fired combined-cycle plant that came on-line in May 2001 (Figure 1). At the time, Lost Pines was owned by GenTex Power Corp., a nonprofit subsidiary of LCRA. In 2006, when the facility became wholly owned by LCRA, it was renamed the Lost Pines Power Park and the staffs of both plants were combined.
1. Shared site and staff. The Lost Pines Power Park includes the three gas-fired steam units of the Sim Gideon Power Plant (shown on the cover) and the six-year-old Lost Pines Power Project combined-cycle plant shown here. A single plant staff operates both facilities. Courtesy: LCRA
LCRA had long been proactive about upgrading the Sim Gideon plant's controls, but the opportunity to sell ancillary services provided an additional incentive for investment. Any plant owner willing to spend a little to configure his asset to operate in load-following mode may be richly rewarded. LCRA realized this, and its modest investment in Sim Gideon has given the 42-year-old facility a new mission: to be a strong competitor in ERCOT's ancillary services niche market while continuing to supply reliable, low-cost power to the utility's customers in central Texas.
In the ancillary services market, generators are paid to provide load regulation services. The market places a high value on a plant's ability to change load rapidly. For example, a genco wishing to provide load regulation services to ERCOT will bid, on a day-ahead basis, how much he requires to be paid to provide a fixed megawatt change over any 10-minute period. ERCOT will award a contract to the low bidder and pay his bid price whether the ramping capability is called for or not.
When the Sim Gideon plant began its life in 1970, it was hardly the nimble operator it is today. Over the years, it was retrofitted with state-of-the-art distributed controls and, more recently, with a plant optimization system capable of maximizing unit ramp rate—the Holy Grail of ancillary services provision. A new set of operational challenges arose with the shift in plant operation from baseload mode to load-following mode and unit cycling. One of those challenges was to optimize unit ramp rate while minimizing the negative impact on steam turbine longevity of rotor bore stresses caused by rapid metal temperature excursions.
Email
Comments
Print
Reuse
