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Duke Energy wants to replace two coal plants with natural gas units. What that means.

Raleigh News and Observer
Duke Energy is asking North Carolina regulators to allow it to replace two coal-fired units with a pair of natural gas turbines at its Marshall power plant in Catawba County.

The utility says it needs the project, which was first proposed in its 2023 update to its carbon dioxide reduction plan, to maintain reliability while eliminating coal generation. Critics of the project say that by turning to natural gas, Duke is releasing unnecessary greenhouses gases and imperiling its ability to meet the state’s carbon reduction targets by 2050.

Duke’s plans at the Marshall plant are indicative of a broader shift from coal to natural gas at existing power generation sites, a move company officials say will allow them to meet an anticipated spike in demand and ramp up power generation when necessary while saving on transmission infrastructure and boosting local economies. The utility is also planning to build new natural gas plants to burn a blend of hydrogen and natural gas, with the possibility of future upgrades so they solely burn carbon dioxide-free hydrogen.

“The proposed addition of two hydrogen-capable combustion turbines at Duke Energy’s Marshall Steam Station reflects our focus on delivering a path to cleaner energy that protects grid reliability and affordability while meeting the energy demands of a growing and economically vibrant region,” Bill Norton, a Duke spokesman, said in an email.

The N.C. Utilities Commission regulators would need to approve a certificate of public convenience and necessity for the new Marshall combustion turbines. Duke will also need to obtain an air quality permit from the N.C. Department of Environmental Quality.

What do critics of Duke’s plans say?

Duke’s shift from coal to natural gas, particularly in the short-term, has drawn criticism from many environmental groups. They have argued that Duke is simply swapping out one fossil fuel for another and note that the methane burned at gas plants is a potent greenhouse gas that still generates some carbon dioxide emissions.

“Duke claims that they support an ‘all of the above’ strategy, but actions speak louder than words,” Mikaela Curry, a Sierra Club field manager for the Carolinas and Tennessee, said in a written statement. “Duke’s actions suggest that they are mostly interested in building expensive methane gas infrastructure, as quickly as possible, while dragging their feet on clean, renewable energy.”

Duke has also announced plans to build two new natural gas plants on the site of its Roxboro coal-fired power plant in Person County. Both the Marshall and Roxboro projects were originally announced as part of the update to Duke’s carbon dioxide reduction plan that the utility submitted to the Utilities Commission last year.

How does this project fit with NC’s carbon reduction laws?

In 2021, the N.C. General Assembly passed a bipartisan bill requiring Duke to reduce carbon dioxide emissions 70% from 2005 levels by 2030. It can ask the N.C. Utilities Commission to delay that target if Duke can prove that building an offshore wind farm or small modular nuclear reactor can achieve deeper carbon reductions. Duke must consider affordability and reliability, in addition to carbon dioxide reductions.

The state law also says that Duke must meet carbon neutrality by 2050.

Duke filed an updated version of its resource plan in August 2023, but amended it in January 2024. That amendment came after new demand forecasts found that additional manufacturing facilities and other demand for electricity in the Carolinas mean Duke needs to add 44.5 gigawatts across the Carolinas by 2038, an increase from the 36.5 gigawatts it expected just months before.

In a video posted to Duke’s website, Kendal Bowman, the company’s North Carolina president, said, “This additional growth is unprecedented – historic in both size and speed.. So to meet customers’ needs, we’re proposing to accelerate every resource available to us: solar, storage, natural gas, nuclear and wind as we maintain our diverse, all-of-the-above approach to protect reliability and affordability.”

Coal releases the most carbon dioxide of anything Duke uses to generate power. They also generate significant amounts of nitrous oxides and sulfur dioxide, potent air pollutants.

If Marshall builds the planned natural gas turbines to replace the coal units, they would reduce annual sulfur dioxide emissions by an anticipated 92% and nitrous oxide emissions by 82%, Norton said.

Duke also expects carbon dioxide emissions to decline by about 40%.

But the new plants would come online in late 2028 and are expected to remain operational until 2064, well past the 2050 carbon neutral deadline.

NC told Duke Energy to cut carbon emissions. What’s happened and what’s supposed to.

Could burning hydrogen help?

That’s where Duke’s hydrogen plans come in.

The utility is planning to build the new gas plants so they can burn a blend of hydrogen and natural gas, eventually upgrading them over time to burn 100% hydrogen.

Some environmental advocates question that plan. They wonder if planning for a hydrogen infrastructure that doesn’t yet exist in North Carolina to materialize is more affordable than switching over to solar and wind energy now.

Will Scott, the Environmental Defense Fund’s Southeast climate and clean energy director, is among those critics.

“If you can’t convert to hydrogen, then you’re only going to get half of the anticipated lifetime out of these plants but you’re still going to be paying for them the entire time,” Scott said, referencing the 2050 deadline for Duke to reach carbon neutrality.

In its August 2023 resource plan filing, Duke officials said they are planning for new combustion turbines like those proposed at Marshall to burn a blend containing 1% hydrogen by 2035, 2% by 2038 and 3% by 2041. Duke could convert the units to operate solely on hydrogen by 2050 in order to meet the carbon neutrality requirement

Duke is planning to build new combustion turbines with piping inlets and a combustion system that can support a blend containing up to 30% hydrogen, with other upgrades including room for equipment that injects hydrogen into natural gas, an ammonia control system and a fire suppression system designed for hydrogen. The utility expects to be able to further modify those turbines to operate on 100% hydrogen.

Would solar, battery storage work instead?

Scott suggested that Duke could have better taken advantage of existing power lines, transformers and other transmission infrastructure that exist at Marshall by putting batteries on the site and charging them via solar or on-shore wind.

Planning to switch the plants from a blend of natural gas and hydrogen to solely hydrogen, Scott said, leaves Duke dependent on an industry that doesn’t yet exist at scale quickly emerging.

Generating green hydrogen would require Duke to build solar or wind to generate power, electrolyzers to convert the raw energy into hydrogen, storage capacity to store the hydrogen and transmission pipes to transport it. Duke has announced a green hydrogen pilot at one of its Florida plants.

“It’s making a bet that a whole hydrogen infrastructure is going to materialize in a cost-effective way and the counterpoint to that would be we have existing clean technologies and storage now,” Scott said.

Scott also warned that higher levels of hydrogen could leave pipes brittle, a challenge Duke acknowledges in its 2023 resource plan.

Duke officials maintain that building natural gas now actually helps it add renewables to the grid, maintaining reliability when cloud cover limits energy from solar panels or batteries are emptied. At the same time, Norton wrote, the manufacturing projects and technological users coming to the Carolinas need energy about 90% of the time.

That’s where Duke sees a technology like the combustion turbine, which they can turn on or off more quickly than the existing coal fleet, playing a role.

“While renewables have a key role to play, they are insufficient to power our region’s economy alone, without the addition of more 24/7 natural gas and nuclear. A diverse resource mix is absolutely critical to maintaining North Carolina’s competitive edge,” Norton wrote in an email.

When would the Marshall construction happen and what would it cost?

If the N.C. Utilities Commission approves the project, Duke would start construction in 2026 and start operating the new combustion turbines in late 2028, before retiring two of the four coal units at the facility. The cost of the project is confidential because Duke plans to take bids for the construction.

The company anticipates that the project will cost customers $104 million in 2029, the first full year they are operational, resulting in a 2.2% rate increase for Duke Energy Carolinas customers that would decline over time. The Utilities Commission would need to approve any such increase in a future rate case.

the new natural gas facilities would be built on Duke’s existing Marshall Steam Station property. Their footprint will be on 20 acres, about a mile northeast of the coal-fired plants they’re replacing, Norton, the Duke spokesman, wrote in an email.

“Dispatchable and flexible generation is increasingly critical to maintain reliability and energy adequacy as the Companies’ fleet transitions toward more variable energy and energy-limited resources,” Norton wrote.

How much power would these generate and when would they be used?

The new units are what are known as “peakers” because they are ramped up and used when demand is the highest.

The new plants will be capable of generating 850 megawatts of power, more than the 760 megawatts the two coal units they are replacing are capable of.

What about Marshall’s remaining coal plants?

Duke expects to continue operating two additional plants that co-fire coal and natural gas at the Marshall site until 2031, when it plans to retire them, as well.

The utility has said it plans to fully exit coal by 2035.

NC Reality Check is an N&O series holding those in power accountable and shining a light on public issues that affect the Triangle or North Carolina. Have a suggestion for a future story? Email

This story was produced with financial support from the Hartfield Foundation and Green South Foundation, in partnership with Journalism Funding Partners, as part of an independent journalism fellowship program. The N&O maintains full editorial control of the work. If you would like to help support local journalism, please consider signing up for a digital subscription, which you can do here.

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