For the first time in the company's history, Duke Energy enacted rolling blackouts on Christmas Eve amid freezing temperatures. The move left half a million customers without power. And on Tuesday, the company issued an apology, attributing several compounding factors as its reasoning.
"I want to express how sorry we are for what our customers experienced. We own what happened," said Julie Janson, executive vice president and CEO for Duke Energy Carolinas. "Making rotating outages [was] necessary to protect the integrity of the grid and mitigate the risk of serious failure affecting a far greater number of customers for longer time frames."
The North Carolina Utilities Commission questioned Duke Energy about the situation during a public briefing Tuesday.
Equipment failure due to severe cold and inaccurate modeling contributed to the outages. Duke said there was extremely high demand and not enough supply of power.
Three of Duke's power plants — Dan River, Mayo and Roxboro — had to cut its operations in half because instrumentation lines froze, causing Duke to lose 1,300 megawatts of power. This happened despite these lines having weatherization measures.
"That equipment had functioning insulation and operating heat freeze, and yet the weather was able to overcome those circuits," said Preston Gillespie, the company's chief generation officer. "We have some evaluation work to go do to figure out why that happened on those particular pieces of instrumentation and didn't happen on others."
Duke tried to increase its supply by buying power from nearby utility providers, like PJM Interconnection. However, PJM and other companies were having similar problems because of the cold, so that power never came through.
Finally, Duke was relying on a modeling system that is used to predict customer demand.
On the evening of Dec. 23, this model projected having enough energy production reserves to meet peak demand the next morning.
That estimate turned out to be wrong. This model operates based off of past events, and as Nelson Peeler, Duke's chief transmission officer, pointed out, this was an unprecedented weather event.
"It was a very cold day in December...with very high winds. The holiday makes it more complicated," said Peeler. "The model is trying to determine how the load will behave. So, for example, what industrial or commercial loads are there on a Saturday [on] Christmas Eve? That's a challenge to predict without history."
Officials said the weather over the holiday weekend brought the coldest temperatures in a December in North Carolina since the 1980s.
Once the model had the data from Christmas Eve, it was able to accurately predict demand for Christmas Day and the following days.
Yet another system failed after operators started the rolling outages. This system is supposed to automatically take power away from customers, then automatically bring customers back online. However, this system failed around 7 a.m. on Christmas Eve. It's still unclear why.
This forced operators to manually take power away and manually bring power back. Operators worked to restore power until about 4 p.m. on Christmas Eve.
This system failure caused outages to go on much longer than anticipated.
"We do deeply regret that some of our customers were without power for an extended amount of time on Christmas Eve, but given the challenging situations our operators faced, they took the proper actions," said Scott Batson, chief distribution officer at Duke Energy.
Duke told the utilities commission that it's investigating why it's automatic system failed and why it's weatherized equipment froze.
Duke also intends to evaluate how it communicates with its customers. The company faced some criticism for not telling customers about the outages ahead of time.
State utilities Commissioner Floyd McKissick said Duke's customer notification system should be upgraded as soon as possible so people can be prepared.
Additionally, the Federal Energy Regulatory Commission has launched an investigation into the rolling blackouts. Duke said it will fully engage and comply with that inquiry.
This comes shortly after two electrical substations operated by Duke Energy in Moore County were shot and damaged by gunfire, causing widespread outages for several days. There is no evidence at this time that these two events are connected.
The Associated Press contributed to this report.
