The Texas grid flirted again with the threat of rolling blackouts on Saturday morning, forcing grid managers to take emergency measures to stabilize the system after a large plant unexpectedly went offline.
The Electric Reliability Council of Texas, which manages most of the state grid, averted possible power disruptions by issuing an alert that required certain large customers to reduce their power use. The reductions are contained in agreements between such customers and the grid operator.
Dan Woodfin, ERCOT’s director of system operations, said in an interview Monday that the council schedules 2,800 megawatts of excess generation capacity in the system to ensure that the grid has enough power even if a plant unexpectedly goes offline. It periodically reviews and adjusts the amount of reserve capacity it tries to maintain during operations, Woodfin said .
Managers are required to issue alerts when reserves dip below 2,300 megawatts, which Woodfin said is still plenty to keep power flowing despite the emergency notice. It’s enough to power more than 1 million Texas homes under normal conditions, according to ERCOT estimates.
The agency tries to protect system reliability without keeping too much extra power online, and that means loss of a large plant may send the system into the reserve margin and require an alert. “We could increase the amount of generation even higher to have more reserves, but that costs money,” he said.
The incident Saturday appeared unrelated to low temperatures or high demand, the ingredients that combined with plant malfunctions on Jan. 6 to send the grid close to sequential regional shutdowns.
Instead, a malfunctioning power plant alone caused the margin of generation capacity above demand to drop below 2,300 megawatts around 9 a.m. Saturday, triggering the alerts. The agency declined to identify the plant involved.
“Additional generation was available, it just took some time to ramp it up,” ERCOT spokeswoman Robbie Searcy said. “At no time did reserves drop to a dangerous level so that reliability was threatened.”
Some of the emailed alerts asked customers to raise thermostat settings to 78 degrees, typically a summer response intended to reduce demand from air conditioners. Searcy said the automated alerts contained a summer message, and that the agency is working to correct its messaging system.
Regulators, industry officials and politicians have been debating whether Texas has sufficient capacity to provide power to its growing population–particularly since air conditioning use during recent summers has pushed demand to record highs.
But overall capacity wasn’t a major factor in the incidents Jan. 6 and Saturday. The grid operator blamed those events on malfunctions of generators that were scheduled to be operating on winter days when many plants were down for scheduled maintenance or mothballed for the season.
Last fall the Reliability Council said the system had plenty of capacity for the winter, even if cold weather boosted demand for home heating.
Warren Lasher, ERCOT’s director of system planning, said in an interview then that 75,000 megawatts of capacity would be available from December through February.
But all available capacity typically isn’t scheduled on a given day. On Saturday morning, the grid went into the emergency situation despite mild temperatures and power demand of less than 40,000 megawatts.
The response system kept power flowing, and grid conditions returned to normal in less than an hour.
But at least one specialist outside of ERCOT says the need for emergency measures to maintain grid stability twice in less than two weeks should raise alarms.
“ERCOT is only going to activate the emergency alerts if it believes there is a significant challenge to reliability,” said Ed Hirs, an energy economic professor at the University of Houston who specializes in electricity markets. “During the emergency a couple of weeks ago, we had to import power from Mexico. Do we really want to have to rely on Mexican power plants to keep our grid reliable?”