Duke Energy to knock down coal plant and build its biggest battery yet

Mega-utility Duke Energy is about to knock down a coal plant that has run west of Charlotte, North Carolina, since 1957. Soon the company will build its largest grid battery on that spot, part of an unprecedented energy-storage construction spree.

The Allen Steam Station used to generate 1,155 megawatts of coal-fired electricity. But four of its five units have been shut down already, leaving just the last 167 megawatts online. Duke plans to shutter that last unit by the end of this month in favor of cleaner, more efficient power sources. At that point, only five coal plants will be left operating in the state, but they’re beefy enough to produce 8,400 megawatts collectively.

The retirement of a coal plant is not, in itself, surprising — that’s been happening across the country since the shale revolution made gas radically cheaper, and this shift has done a lot to clean up the power sector. Almost always, though, fossil gas plants have stepped in to provide on-demand power in place of the outgoing coal. This time, in a first for the region, Duke is investing in batteries to pick up some of the slack.

To begin with, Duke will install a 50 megawatt/​200 megawatt-hour battery on 7.5 acres next to a substation across the street from Allen, with the goal of completing construction by the end of 2025. Once the old coal buildings are demolished, a 167 MW/668 MWh system will spring up where the coal plant flue-gas desulfurization system stands today. That installation, expected by October 2027, will match the instantaneous capacity of Allen Unit 1, though the battery will be able to maintain that power for only four hours straight. Duke could also add more battery storage onsite later.

These plans, which Duke first discussed with local reporters in late November, mean one of the biggest legacy utilities in the country is embracing the large-scale grid battery trend that has already swept through solar-heavy markets like California, Texas, and the desert Southwest. North Carolina, notably, ranks fourth in the nation for installed solar capacity, with nearly 10 gigawatts operating. But Duke dabbled in batteries for years before choosing to deploy them at scale.

The utility’s deregulated subsidiary built a big grid battery in Texas back in 2013 with grant money from the Department of Energy, but the company never pursued other projects like that. Duke engineers tested various battery technologies in their laboratories, and they installed small systems for particular challenges, like an unusual zinc-air battery to power an off-grid station in the Great Smoky Mountains. But while utilities in California and Arizona were signing contracts for 100 MW systems as cost-effective peak power sources, Duke resisted the urge. Last year it touted the start of operations at its biggest North Carolina battery at the time, just 11 MW at Camp Lejeune.

Now, though, big batteries have arrived in North Carolina.

Duke recently asked for and received regulators’ approval to construct 2,700 megawatts of energy storage by 2031. That’s a massive acceleration from basically zero — more capacity than Duke expects to build for any other resources besides solar and combined-cycle gas plants. It’s a big lift, but locating installations at legacy power plants comes with a host of practical benefits.

“Repurposing Allen’s existing transmission system and infrastructure enables a more efficient clean energy transition and lowers the cost for our customers, while maintaining our long-term commitment to Gaston County,” spokesperson Bill Norton told Canary Media.

The Allen site already has a grid hookup, and its other prospects for redevelopment are limited by the large quantities of toxic coal ash present there (Duke is excavating the ash and moving it to double-lined landfills onsite). Plus, Duke could invoke a ​“generator replacement request” to streamline the grid interconnection process for the larger battery, since it exactly matches the last coal unit’s peak capacity.

But this coal-to-battery switch isn’t a clean sweep for clean energy. These batteries are designed to cover four solid hours of peak power delivery, but then they run out, which could be a problem in a heat wave or a winter storm when residents are counting on electricity to keep their homes at a safe temperature.

“For 24/7 reliability, we are also adding Lincoln 17, a natural gas combustion turbine in nearby Denver, N.C., that we take ownership of in December,” Norton noted. That 400 MW unit matches the power from the last two Allen units to retire.

Combustion turbines are designed to fire up quickly when needed for extreme demand — in this case, from 0 to 100 percent in less than 15 minutes, compared with 12 hours for the sexagenarian coal units. That means the turbine probably won’t be running all the time, and the gas it burns will produce fewer carbon emissions than burning coal.

The utility will also build more solar capacity in the region and expects to have surplus solar to charge the new batteries with. But Norton stressed that Duke will not just rely on solar — it will load the batteries up on whatever’s supplying the grid at the time.

In other words, this won’t be a case of renewables and batteries going it alone to meet the needs of the grid. For something like that, you’d need to visit Hawaii, where only new solar and batteries are being built to fill in for a retired coal plant. But the Allen makeover marks a new willingness from one of the country’s biggest utilities to add lithium-ion batteries to the roster of trusted, large-scale tools for reliable power delivery.