To meet demand on hot days, Duke Energy and other utilities turn to fossil fuels
When North and South Carolinians turn up the air conditioning to stave off high temperatures this summer, the state’s utilities burn more fossil fuels.
That’s according to data from the International Energy Agency, which reported that utilities in the two states started burning more coal and natural gas as temperatures started rising in late June.
As temperatures soared last week, utilities in the Carolinas burned more fossil fuels to keep up with demand than they had at any other point this year. The turn toward fossil fuels illustrates a key challenge of the energy transition: keeping lights on and HVAC systems running when temperatures are very high or very low while engineering a shift to carbon-free resources.
“The key really is, Which resources are dispatchable? So which forms of power generation can be quickly turned on to meet a surge in demand from extreme heat events or extreme cold events,” Brian Murray told The News & Observer.
Murray, an energy economist, is the interim director of Duke University’s Nicholas Institute for Energy, Environment and Sustainability.
The Carolinas’ energy mix
Nuclear was the main source of electricity over the past year in the Carolinas, according to the Paris-based IEA, generating nearly 11 gigawatts of power daily. That’s followed by natural gas with 6.69 gigawatts, coal at 4.48 gigawatts, other combustibles at 1.08 gigawatts, solar at 1.05 gigawatts and hydropower at 0.45 gigawatts.
Jeff Brooks, a Duke Energy spokesman, said North Carolina’s largest utility will add large-scale solar and other carbon-free resources over the next 10 to 15 years as it works to eliminate coal from its portfolio. But pushing coal off the grid and adding other generation sources can be tricky, especially on extreme temperature days.
For now, natural gas — whose methane emissions are drawing increased attention from climate scientists and activists — is a major part of the answer.
“You can’t take coal out of the equation and not have an equally reliable resource to compensate for it, so certainly natural gas plays a big part in that because of its ability to be flexibly adjusted and deployed when needed,” Brooks told The News & Observer.
Duke’s six remaining North Carolina coal plants regain importance when demand is high, like during July’s heat spell.
Last Friday, for example, nuclear remained the largest source of energy in region with 11.78 gigawatts of power. But natural gas were virtually tied, with 9.5 and 9.48 gigawatts of generation.
Over the weekend and on Monday, coal plants generated more power than natural gas plants.
“Coal is still very important to our diverse energy mix, it’s just playing a different role than it did perhaps a decade or more ago,” Brooks said.
When plants powered by fossil fuels are used, they add emissions to the atmosphere. Coal plants emit carbon dioxide, a key pollutant in global warming, and natural gas plants release methane, a short-lived but potent greenhouse gas.
Murray likened the new emissions to turning on the faucet in a bathtub that already has water in it.
“It’s not as if the surge in emissions last week is going to cause a surge in warming this week. That’s not the effect we’re talking about,” Murray said. “We’re talking about the constant contribution of emissions into the atmosphere leading to higher levels.”
Battery storage potential
Resources that prevent adding to that concentration like solar and wind aren’t yet at a point where their carbon-free energy can be called upon quickly. That will take battery storage, something Duke is working on but that has not yet achieved widespread adoption in the Carolinas.
Solar typically provides the most energy around midday, Brooks said. That’s doesn’t align with the periods of highest energy usage, which are typically summer evenings and winter mornings.
Battery storage would allow Duke and other utilities to store the solar energy, helping to keep a coal or natural gas plant from firing up to meet that peak demand.
Duke Energy operates at least three battery storage sites in North Carolina, including an 11-megawatt facility at Camp Lejeune, a nine-megawatt battery system in Asheville and a four-megawatt system that is part of a Hot Springs microgrid.
The Utilities Commission’s Carbon Plan order directed the utility to purchase a gigawatt of battery storage, as well as 600 megawatts of battery storage connected to solar generation.
“In the next 10 to 15 years you’re going to see significant quantities of that being added to the grid,” Brooks said. “It’s just not there today.”
Murray, the Duke University professor, outlined a potential future where solar and battery storage could effectively push natural gas into the role coal has now. That would see the renewables generating more power than gas-fired power plants, with utilities largely turning to those facilities when demand spikes.
“As more and and more of the base load is met with solar, that will probably relegate gas to playing more of this peaking role in the future until that is overtaken by battery storage,” Murray said.
This story was produced with financial support from the Hartfield Foundation and 1Earth Fund, in partnership with Journalism Funding Partners, as part of an independent journalism fellowship program. The N&O maintains full editorial control of the work.
This story was originally published August 3, 2023 at 8:00 AM.