A year ago, during a Christmas Eve cold snap, a half-million electricity customers across the Carolinas had their power cut off for hours in a series of rolling blackouts. Could that happen again?
Last Dec. 24, temperatures dipped into the single digits in the Carolinas — colder than forecast. Demand for electricity spiked higher than Duke Energy expected as people cranked up their heat.
The frigid temperatures froze equipment at Duke's coal and gas plants, reducing generating capacity by 10%. And when Duke went to buy power from neighboring states, it wasn't available as other utilities faced their own demands. Suddenly there wasn't enough power to go around.
"At that time, we made the only decision that we could. This was the first time in our company's history, we began rolling service disruptions," Kendal Bowman, Duke Energy's North Carolina president, said as she testified before state regulators on Jan. 3 to explain what happened.
Those automated outages were supposed to last 15 to 30 minutes. But problems with the software controlling them caused some to last for hours.
About 6.3 million customers across the East lost power during that stretch of winter weather a year ago. The power disruptions in North Carolina and elsewhere also brought inquiries from federal energy regulators and the North American Electric Reliability Corporation, or NERC, which monitors the grid. In September, they called for new federal and state rules to improve reliability and said power grid operators needed to improve communication.
Last month, NERC came out with its annual Winter Reliability Assessment. It warned of similar risks again this year, possibly affecting more people.
"The areas that we've identified as being at risk extend over much of the eastern two-thirds of the continent, so it's a much bigger area than we've seen in the past," said NERC's Mark Olson, who helped prepare the report. He spoke during a recent briefing hosted by the American Council on Renewable Energy.
"We found that even though nearly all of the areas we assess have adequate resources for a normal winter peak demand, the risk from a prolonged wide area cold snap is very challenging," Olson said.
To avoid power shortages, electric companies are required to set aside reserves. That means planning for increases in power generation or buying power from other companies to cover forecast demand.
Olson said as NERC developed the report, it looked at companies' reserve margins, potential risks such as weather, and demand forecasts.
After last year's power shortage, Duke Energy pledged to do better this year. Spokesman Jeff Brooks said the company has improved processes and updated its models for predicting power demand.
"We use a forecast model that learns from every event that it experiences. And so even right after the events last year, on Dec. 24, we gave it new data, and that helped it perform much better even on Dec. 25," Brooks said.
He said Duke also updated the software that controls rotating outages. And he said Duke has adjusted power plant maintenance schedules "so that we complete that work around the first week of December. That way, we've got all the available resources possible to serve our customers."
The biggest risk again this year could be low temperatures that freeze instruments and sensors and cause other mechanical problems at older plants.
"We've gone back and looked at those instances and added corrective measures, including insulation and heating elements - things that we can keep that instrumentation giving the proper measurements so that we can operate our plants at the best during these extreme conditions," Brooks said.
Brooks said Duke is also boosting its reserve margins to account for the risk that there won't be any power available from neighboring states. It's also working with customers who have agreed to voluntarily cut their power use in exchange for lower rates.
Meanwhile, Duke doesn't have any new generating plants to count on this year, but it's considering all these risks as it plans new plants.
Environmental groups see last year's outages as both a warning sign and an opportunity.
"The weather extremes we're experiencing are what scientists have told us we are going to experience due to climate change," said David Neal, a lawyer with the Southern Environmental Law Center.
Neal pointed out that most of last year's equipment failures were at coal and gas plants, while solar and hydroelectric plants continued generating electricity. To him, that's an argument for more renewable energy.
"We've long had a concern that Duke over-relies on its fossil resources," Neal said this week. "And given the state law that requires Duke to move towards cleaning up the electricity grid, it's also an opportunity to think about reliability in a different way. And think about resilience in a different way."
But Duke's long-range plans rely on more gas-fired plants. State regulators will consider those plans in the new year.
