Duke Energy proposes a second underground Bad Creek powerhouse with four reversible turbines, using reservoirs already in place
Beneath the Blue Ridge foothills of South Carolina, Lake Jocassee sits deep and still — a 7,980-acre reservoir that has quietly served as the lower half of one of the country’s most powerful underground power plants for decades. Buried inside the surrounding mountains, four reversible turbines already generate up to 1,400 megawatts by shuttling water between Jocassee and a smaller upper reservoir perched 1,200 feet above.
Now Duke Energy wants to do it again — right alongside the first. The company has proposed a second underground powerhouse at the same site, with four additional turbines, and without altering either existing reservoir.
A mountain that stores electricity
The existing Bad Creek Pumped Storage Project is, at its core, a giant rechargeable battery — one made of rock, water, and elevation. When electricity demand is low, the plant pumps water from Lake Jocassee up to a 363-acre upper reservoir sitting at roughly 2,310 feet above sea level. When demand peaks, that water rushes back down through a 5,026-foot power tunnel, spinning four reversible pump-turbine units rated at 350 MW each — a combined 1,400 MW of generating capacity.
Pumped storage absorbs surplus generation and holds it until demand calls — a role that no battery chemistry has yet replicated at this scale.
The numbers deserve a moment. The project produces an average of about 1.88 million MWh of electricity per year, and the powerhouse itself is carved into bedrock, connected to the surface through steel-lined penstocks and a network of tunnels that most people driving through Oconee County will never see.
The proposal: A second powerhouse, same lakes
Duke Energy filed a new major license application with the Federal Energy Regulatory Commission on July 14, 2025, proposing to build what it calls the Bad Creek II Complex — a second underground powerhouse at the same site.
The central engineering insight is straightforward: the reservoirs are already there. No modifications to the existing upper or lower reservoirs would be required. The new facility would tap the same two water bodies, adding a new upper reservoir inlet/outlet structure, a water conveyance system, underground powerhouse, access tunnels, a lower reservoir inlet/outlet structure, a switchyard, a transformer yard, and a new transmission line.
The new powerhouse would contain four reversible pump-turbine units with installed generating and pumping capacity ranging from 106 MW to 425 MW each — a range that reflects the flexibility still being designed into the project at this stage.
What the numbers mean for the grid
Adding the second powerhouse would increase average annual generation by up to 25,856 MWh. Meaningful, though modest relative to the existing plant’s output. The bigger value isn’t in the kilowatt-hours alone — it’s in the balancing act that pumped storage makes possible.
The existing plant already illustrates the trade-off clearly. It consumes about 2.4 million MWh per year for pumping while generating roughly 1.88 million MWh, a net consumption of about 513,000 MWh. That gap isn’t waste. It’s the cost of storing energy when it’s cheap and releasing it when the grid needs it most.
Solar and wind capacity keeps growing across the Southeast, which makes that balancing function increasingly critical. Renewables generate power on the sun’s and wind’s schedule, not the grid’s. Pumped storage absorbs surplus generation and holds it until demand calls — a role that no battery chemistry has yet replicated at this scale.
The regulatory road ahead
FERC accepted Duke Energy’s application and declared it ready for environmental analysis, as reflected in the March 4, 2026 Federal Register – Bad Creek II licensing proposal. That acceptance marks the beginning of a lengthy public process, not the end of one.
Motions to intervene, protests, and comments are due by April 28, 2026, at 5:00 p.m. Eastern Time, with reply comments following on June 12, 2026. Duke Energy must also submit water quality certification — or evidence of a waiver — by that same April deadline. Environmental review, agency coordination, and commission deliberation all lie ahead before any construction could begin. Licensing processes for major hydroelectric projects typically unfold over several years.
Why Bad Creek, and why now
Reusing existing reservoirs isn’t just convenient — it’s strategically significant. Building a new pumped-storage site from scratch requires finding the right geology, the right elevation difference, and a viable water source, then navigating years of environmental permitting. Bad Creek already solved all of those problems decades ago.
The nearly 1,000-foot elevation difference creates exceptional hydraulic head, which translates directly to efficiency. Few sites in the eastern US combine that kind of head with infrastructure already in place.
Utilities across the country are racing to add long-duration storage as coal plants retire and variable renewables scale up. Duke Energy’s proposal points to one underappreciated answer: look at what’s already built. The mountain has been quietly doing its job since the 1990s. Whether it has room for more is now a question for regulators to weigh.
Kelly is an experienced writer with 15 years of experience exploring the big stories that shape our world, from tech breakthroughs and space exploration to climate, energy, and the fascinating quirks of science. She has a talent for turning complex ideas into sharp, memorable insights that stay with readers long after they’ve finished reading.
