How a lack of power for sale led to Duke Energy's Christmas Eve blackouts
More information is emerging about why Duke Energy couldn't find power to buy as temperatures plunged and demand soared on Christmas Eve — and it's related to the kind of power plant malfunctions Duke was having itself.
Duke had been counting on being able to buy electricity from its northern neighbor, PJM Interconnection, which operates the electrical grid from northeastern North Carolina to Michigan. But PJM reported this week that it lost 23.2% of its power generating capacity due to storms and cold weather. So it had no extra power to sell.
“Quite frankly, while a lot of resources did perform well, generator forced outages were unacceptable,” PJM Senior Vice President of Operations Mike Bryson said at Wednesday's meeting of the company's Market Implementation Committee.
PJM said it expects to levy between $1 billion and $2 billion in fines against plant operators for the shortfalls.
Unlike Duke, JPM does not operate its own power plants. The company manages electricity distribution from independent plant owners. As with Duke, most plant problems came from cold-related malfunctions at coal- and gas-fired power plants. The grid operator also said the cold weather reduced natural gas production and supplies on pipelines.
PJM said in a presentation Wednesday that it lost a total of 46,000 megawatts of generating capacity. About 70% was lost from natural-gas fired plants, and 16% from coal plants. The rest of the outages were listed as "other," which includes nuclear, oil, wind and solar, PJM said in the presentation.
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No power to buy
Duke Energy officials told North Carolina regulators they had firm or tentative agreements to buy 650 megawatts of electricity on Christmas Eve from PJM and elsewhere to supplement their own capacity. But it wasn't there when needed.
"As we moved forward in time, by these prior events, we were out of generation to pick up. There was no purchase power available to us," Duke's Sam Holeman said before the North Carolina Utilities Commission on Jan. 3.
That, along with its own reduced generating capacity due to malfunctions at power plants, forced Duke to begin rolling blackouts early on the morning of Dec. 24. The blackouts affected a half-million customers in the Carolinas. Power cut-offs were expected to last just 15 to 30 minutes, but when an automated system that shuts off and restores power failed, many customers were left without power for hours.
PJM did not specify exactly which plants malfunctioned.
"PJM does not isolate which plants were off line," spokeswoman Susan Buehler said Thursday.
PJM also gets some power from pumped-storage hydroelectric dams. But the electricity shortage "limited our ability to replenish pond levels for pumped storage hydro prior to the morning peak on Dec. 24."
Just as at Duke Energy, PJM forecasters underestimated demand for electricity during the storm and cold by 10%. That came as temperatures plummeted on Christmas Eve and demand for heating rose across PJM's territory.
PJM's shortage of electricity didn't lead to blackouts, but the company did ask users to conserve electricity as power supplies fell.
The reduced performance of gas- and coal-fired power plants during the extreme weather on Christmas Eve has been seized on by environmental groups. Tom Rutigliano of the Natural Resources Defense Council wrote in a post last week: "Once again, we learned that we can’t rely on gas and coal when extreme weather hits. They’re not infallible, and system reliability will continue to suffer if grid operators keep overestimating gas and coal."
PJM said this week's report is preliminary. It is continuing to review performance and forecasting during the holiday period and expects to report results and recommendations in April.
The Federal Energy Regulatory Commission and the National Electric Reliability Council have announced a joint investigation of the power outages and plant malfunctions in December.