By Rod Walton, Power Engineering and POWERGEN+ Content Director
It didn’t experience the full-on disaster that befell the Texas grid during February’s historic Winter Storm Uri, but the Southwest Power Pool (SPP) had its hands full and much of its capacity empty when the lengthy sub-zero temperatures, snow and ice hit the U.S. region.
The grid system operator responsible for 14 states–including those to the north, east and west of the Electric Reliability Council of Texas territory—survived a worst case scenario, but still suffered up to 35 GW in generating capacity outages and had to shed about 3.2 GW of total load over several hours during the worst periods of Feb. 15 and 16.
“That’s not what we want to do, but we had to prevent uncontrolled outages which could have lasted much longer,” Lanny Nickell, executive vice president and chief operating officer for SPP, told the Oklahoma Corporation Commission during a recent presentation on the impact of the winter storm to that state and others in the SPP territory.
“This was unprecedented for us,” he pointed out.
Numerous southern states were hit by lingering freezing and icy weather which was resource agnostic in how it damaged power generation and grid performance during that frigid February storm. Gas plants failed, gas pipelines failed, coal plants and wind farms failed. Everything failed on some level for some time.
In Texas, 52 GW of outage forced load sheds impacting millions of customers and may have led to as many as 80 deaths, according to reports. ERCOT has reported that the loss of generation threatened frequency on the grid system and almost caused a complete blackout which might have taken weeks or months to repair.
SPP’s drama was only slightly less intense, Nickell noted. In his talk with the Oklahoma Corporation Commission – which oversees the regulated utility operations in that state—he underlined that blame, if any was going to be assigned, could be pointed in every direction.
“This is a very complicated machine,” he told the regulators. “When it changes, sometimes it changes very fast.”
The impact of Winter Storm Uri, as some have called it, is actually less of a grid event and more about loss of generation. Close to 40 percent of nameplate capacity within the SPP was unavailable during the most extreme periods of the freezing stretch—and that included gas-fired, wind and coal-fired generation.
In fact, generation supply could not meet demand in the mornings of Feb. 15-16, when it was coldest and customers were trying to keep their homes warm. The SPP was forced to import significant amounts of energy from the Eastern Interconnection, while also appeal publicly for customers to lower their thermostats and weather the storm without further interruption.
Natural gas makes up the predominant generation resource in the SPP, and it also failed on a larger level than coal and nuclear. At one of the worst periods, only half of the accredited gas capacity was available, Nickell pointed out. Among the reasons for this unavailability was heightened use of gas for home heating, as well as pipeline supply disruptions.
“The majority of unavailability was driven by lack of fuel,” he said to the Oklahoma Corporation Commissioner, adding moments later, “Gas generation contributed 60 percent of the unavailable generation problem.”
Utility-scale wind power capacity was also hobbled by freezing temperatures shutting down turbines and generators. Overall in the SPP, however, wind did pretty well, with close to 95 percent of its accredited supply available to dispatch into the grid.
Coal provided a bigger overall percentage of the generation mix during the worst periods, but actually delivered a lower percent of its capacity than wind. Overall, SPP records show that coal delivered 41 percent, gas 27.7 percent, wind 10.5 percent, nuclear 5 percent and hydro 4.7 percent during the controlled service interruptions (load shedding events) on Feb. 16.
Normally, that SPP accredited capacity mix is 45 percent gas-fired, 38.5 percent coal, 5.6 percent wind, 3 percent nuclear and 4.4 percent hydro. Fuel oil and solar deliver much smaller contributions to the capacity in the regional grid.
In other words, wind nearly doubled its position in generation mix during the worst period, while coal and nuclear performed above their usual positions compared with gas-fired power—and that’s only because so much gas supply and generation capacity was out.
Yet SPP’s Nickell continued to point out that this was an unprecedented event which gives all involved something upon which to learn and improve.
“There’s no room to blame anyone,” Nickell pointed out. “We all worked together.”
The Southwest Power Pool leadership is working on a more comprehensive report detailing the events leading up to, during and after the winter storm. It may be completed by July.
(Rod Walton is content director for Power Engineering, POWERGEN International and the online POWERGEN+ series. He is a 13-year veteran of covering the energy industry both as a longtime newspaper journalist and trade publication editor. Walton can be reached at 918-831-9177 and email@example.com).