Apologies and acceptance from Duke Energy over recent rolling blackouts

Duke Energy officials speak at North Carolina Utilities Commission, Jan. 3, 2022

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  • A series of systemic failures in Duke Energy's two utilities triggered outages over Christmas across North Carolina and South Carolina.
  • Duke Energy's “nuclear fleet” was reliable, but solar generation was unable to meet peak demand because it occurred before sunrise.

Duke Energy executives repeatedly apologized and owned up to the situation that caused thousands in North and South Carolina to be without power during a bitter cold snap leading up to the Christmas holiday weekend. The admissions came during a hearing Tuesday before the North Carolina Utilities Commission

According to testimony before the NCUC, high winds had already left 300,000 without power during the day of Dec. 23 before a severe cold snap later that night and into Dec. 24. Company officials called the weather combination “unique,” saying they used rolling blackouts for the first time in the utility company’s history. 

“I want to express how sorry we are for what our customers experienced,” said Julie Janson, executive vice president, and CEO, of Duke Energy Carolinas. “Winter storm Elliott was an extremely powerful event with a unique confluence of high winds, extreme temperature drops, and other conditions that forced us to curtail power as a last resort. We regret not being able to provide customers as much advance notice of the outages as we would have liked, and we acknowledge that the outages themselves lasted far longer than we expected.”

Janson said the rotating outages were necessary to protect the integrity of the grid and mitigate the risk of serious failure affecting a more significant number of customers for more extended time frames. However, she said, they own what had happened and have launched internal reviews of their systems and procedures. They will also examine how other providers responded to the regional event for any best practices they can learn.

Kendal Bowman, Duke Energy’s North Carolina president, said they monitored the weather the week before and thought they had enough power to meet the demand that was projected, even though temperatures were much lower than typical and dropped much faster than normal for the region. 

But a first in a series of failures for Duke had arisen. Peak demand increased far more than a model had predicted during the early morning hours of Dec. 24, leading to reduced generating capacity. 

Duke operates two different energy utilities: Duke Energy Carolinas (DEC) and Duke Energy Progress (DEP).

Bowman said they began to see a divergence between actual power demand and their forecast on the evening of Dec. 23, alerting them that their reserves would be tighter than expected on the DEC system, and saw the same divergence on the DEP system at 4 am on Dec. 24. The model was 10% below what the company actually needed. Between midnight and early Saturday morning, they lost around 1300 megawatts of power-generating capability due to equipment malfunction, a second failure.

Third, the purchase of power from out-of-state entities never materialized. 

“The power that we purchased did not show up, therefore, we were confronted with the hard truth that our energy demand would soon be eclipsed by our capacity,” stated Bowman. “At that time, we made the only decision that we could. For the first time in our company’s history, we began rolling service disruptions.” 

Sam Holeman, Duke Energy’s vice president of system planning and operations, said the Carolinas had experienced some of the coldest temperatures since the 1980s. He also stated that between midnight on Dec. 23 to 6 am on Dec. 24, Duke Energy’s operating reserves had been depleted and that load forecasting and predicting operational conditions in that run-up will be a central part of an inquiry by both the Federal Energy Regulatory Commission (FERC) and North American Electric Reliability Corporation (NERC).

He said there wasn’t any more power to purchase at that point, and surrounding areas were faced with the same situation. 

Company officials also say that the holidays did make the situation more complicated, and divergence would have been less if the cold weather did not occur during the holidays.

Duke Energy’s “nuclear fleet” was reliable during the storm, according to Preston Gillespie, Duke Energy’s executive vice president and chief generation officer. Still, he said, in a few cases, insulation and heat tracing did not prevent instrumentation lines from freezing which caused a reduction in generation. 

He also said that solar generation performed as expected but was not available to meet the peak demand since the peak occurred before sunrise. This problem is concerning if another outage occurs during high demand periods that include several cloudy days.

The load reduction shedding tool, the automated system geared toward controlling the rolling blackouts, also failed, leaving customers in the dark for hours instead of 15-30 minutes, according to Scott Batson, senior vice president and chief distribution officer for Duke Energy. As a result, workers had to run the outages manually. He said they began to use the tool in 2017 and last tested it on Dec. 12. He said they would investigate what happened with the malfunction.

Batson also noted that the messaging that some customers received about the length of the power outages were also inaccurate and was actually longer in duration. As a result, the company has developed automated messages to use for customers for another similar event. 

Company officials also defended staffing, saying it was increased during the situation and not decreased because of the holiday. They also thanked the public for the increased conservation efforts during the period and thanked the commission for letting them give a timeline of the events. 

Power was restored to all customers on Dec. 24, and the company increased their load forecasts by adding new generating resources and was able to purchase power from out of state on Dec. 25.

NC Utilities Commissioner Floyd McKissick Jr., appointed by Gov. Roy Cooper in 2020, recommended that the utility upgrade its customer notification system and prediction model before another similar event occurred.

The NCUC also asked Duke Energy to submit a report documenting how accurate the peak load forecast had been for the past three winter peaks.