YOUR TURN, TVA: Apologies and acceptance from Duke Energy over recent rolling blackouts.

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.

At least they apologized. But actually, so did TVA, though I didn’t see it until I searched: Tennessee Valley Authority apologizes for rolling blackouts, vows investigation.

With much of Tennessee seeing low temperatures over the weekend, TVA had power issues that led it to demand local power companies reduce electricity load by 5% for two hours and 15 minutes on Friday and then 5% to 10% reductions on Saturday for five hours and 40 minutes.

Those mandatory rolling blackouts came as many Tennessee residents lost power for extended periods during the winter storm. . . .

TVA said in its statement that it takes full responsibility for the power loss. The company did not say what the issues were that led to the need for the blackouts, but the Memphis Commercial Appeal reported that TVA said during a weekend call with local power companies that it had issues with electricity supply, including losing natural gas plants, at least two coal power plants and issues with third-party plants scheduled to be available for additional supply when necessary.

The Tennessee Valley Authority is the largest public power corporation in the country, generating 90% of the state’s electric generating capacity and three-fifth of its power plants. It is federally owned and serves 10 million by providing electricity to 153 local power companies.

The top source of electricity generation in Tennessee is nuclear power plants, which provide 47% of the state’s electricity while 20% comes from natural gas and 18% from coal. All three of the TVA nuclear plants — Brown’s Ferry (Alabama) and Sequoyah and Watts Bar (Tennessee) — were generating power at 100% capacity during the cold snap, according to data from the U.S. Nuclear Regulatory Commission.

Clearly we need more of those.