Dive Brief:

• Duke Energy Progress, a subsidiary of Duke Energy, on Tuesday filed its updated integrated resource plan (IRP), which calls for natural gas and renewables additions with some coal retirements through 2034.

• The utility projects additional load growth of a little over 2.2 GW in the summer and a little less than that in the winter between 2020 and 2034, the majority of which it plans to meet with new natural gas. Additionally, the utility plans to retire approximately 3.6 GW of coal through 2033.

• Environmental groups were critical of the utility's continued reliance on natural gas and said the utility was not moving fast enough on some of its coal units, three of which aren't retiring until 2024 or later.

Dive Insight:

The growing cost of coal is incentivizing utilities to push older units offline sooner than planned when they see opportunities for customer savings elsewhere. Duke is planning to retire five of its seven coal plants across the Carolinas over the next 15 years, leaving its 2034 base case at 3% coal, down from 12% today.

"Our long-term planning process ensures we serve customers in the most reliable and economic way possible, while using increasingly clean forms of energy," Duke spokesperson Erin Culbert told Utility Dive in an email. "Duke Energy has significantly reduced carbon emissions by retiring coal and adding more renewables and cleaner natural gas resources."

Natural gas additions are expected to meet much of that demand — in its five year plan the utility has a 560 MW combined cycle natural gas plant coming online to meet demand from its retiring 384 MW Asheville plant and its 497 MW Darlington combined turbine gas plant. The utility also plans to meet some of that demand with solar and storage, with plans to add 66 MW of storage over the next five years, paired with its almost 4 GW of solar by that time. By 2025, the utility expects to have a total of 7 GW of solar on its system in the Carolinas.

"Natural gas is a flexible resource that complements and balances the intermittency of our growing renewables portfolio," Duke spokesperson Erin Culbert told Utility Dive in an email. "A dispatchable generation source like natural gas is needed to back up renewables to meet our reliability obligations to our customers and regulators. And when you add in the cost of the storage needed, the actual cost of using renewables in place of gas as baseload generation is much more expensive."

But environmental groups are concerned that the utility is too reliant on natural gas and that some of its coal units are staying online too long — which they say is a burden to customers. 

"Across Duke's coal fleet, the numbers, in terms of capacity factors, are going down notably every single year," David Rogers, southeast campaign director for Sierra Club's Beyond Coal campaign told Utility Dive. "The vast majority of the fleet runs less than 50% of the time. More than half of it runs less than 30% of the time. So these coal plants aren't doing what they were designed to do when they were built in the '60s or '70s. So we're concerned that all of it's uneconomic," he added.

Last week, North Carolina regulators directed the utility to include an economic analysis of potential coal plant retirements, calling its previous resource plan "adequate."

The utility likely didn't have time to incorporate that feedback because it was so soon before its filing, Rogers said. But the commission's ruling was "further evidence that the only way Duke's really gonna change their business model and deliver what customers are asking for is if they're forced to do so from decision-makers, whether that's the commission or the legislature."