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Duke Energy recently celebrated a big birthday for one of its oldest workhorses — Mountain Island Hydroelectric Station in Gaston County, northwest of Charlotte. The dam and power station were built 100 years ago. But don't call it a historical relic. It was renewable energy before electricity's fossil-fuel era and it's expected to keep generating long after Duke closes its last coal-fired power plant in 2035.
The plant's four giant industrial-green turbines stand in a row, facing a brick wall of massive windows that let in natural light. Those turbines were silent when I visited the other day, because of planned maintenance. That's how Duke and its predecessors have kept it going for so long, said Ellen Morton, a Duke Energy communications manager.
"When we're doing scheduled maintenance outages, we totally shut down the units, one or all of them, to be able to perform the work safely, to be able to make these units operate for another 100 years hopefully," Morton said.
A long history
The Mountain Island station is steeped in history, not only of the power industry but of the Charlotte region. It was one of a series of hydroelectric projects built on the Catawba River in the early 20th century to fuel economic development.
The dam and powerhouse were built by Southern Power Company to supply the growing number of textile mills that were popping up around the Charlotte area. Construction started in 1921, and the plant began generating electricity in 1923.
Mountain Island Dam is about 100 feet tall and stretches across the Catawba River near Mount Holly. It holds back Mountain Island Lake, which is the eighth lake in Duke Energy's 11-lake system along the Catawba and Wateree rivers in the Carolinas.
The project has endured storms, high winds and floods. In 1938, a storm destroyed the transmission station on top of the powerhouse. Duke Power rebuilt it below. Today, the textile mills are mostly gone, but Mountain Island hydro still produces enough electricity to power 7,600 homes.
And here's another big change: It only takes two employees at a time to run the station. Since 2005, it has been managed remotely from Duke Energy's renewable energy operations center in uptown Charlotte. Before that, 15 operators in shifts had to be at the station 24 hours a day, ready to start or stop the flow whenever the phone rang from power dispatchers.
Meanwhile, the Mountain Island project is more than just a power station, Morton said.
"Over a million households get their drinking water from Mountain Island Lake. And it also provides a lot of recreation opportunities. Last year, we saw 16 million visits to the lake," Morton said.
Hydropower for the future
Hydroelectric power is green energy. When operators release water from the lake, that causes the turbine blades to spin and turn shafts that go into generators, producing electricity. The Mountain Island plant runs when power demand starts to peak. Hydropower is critical on hot summer afternoons and cold winter mornings, Morton said.
The Mountain Island station can generate up to 65 megawatts of electricity. By comparison, the nearby McGuire Nuclear Station and Marshall plant on Lake Norman both have generating capacities of more than 2,000 megawatts.
Duke Energy's long-range "Carbon Plan" calls for increasing the use of hydroelectric power, alongside nuclear stations, wind and solar farms, and gas-fired power plants.
"In 2022, hydro energy accounted for 2.5% of our total generation for Duke Energy. And we continue to look forward to more ways that that can be used. It is one of our oldest forms of electrical or electric generation. And it's pretty cost effective," Morton said.
Overall, renewable energy including hydropower accounted for about 8% of Duke's company-wide generating capacity at the end of 2022, and Duke says that will rise to 18% by 2030.
A key advantage of hydroelectric power is that it's available on demand, at the flip of a switch. That makes hydropower and a newer kind of on-demand power source — battery storage — good complements to intermittent solar and wind energy, said Glen Snider, Duke Energy's head of long-term planning.
"As you increase renewables … it's ever more important to have the hydro and the battery storage to help move (the energy from) those renewables to periods of the day or week to balance that customer demand," Snider said in a recent interview.
For example, Duke can use hydroelectric power to fill in when the sun isn't shining and solar farms aren't producing.
Besides keeping the Mountain Island hydro station operating, Duke also has other long-range plans for hydroelectric power. It's completing an upgrade to its Bad Creek hydroelectric plant in South Carolina this year. And officials have told regulators they want another upgrade that will double the peak capacity of that plant in the coming years.
By the way, there's a difference between Mountain Island Hydroelectric Station and Bad Creek. While Mountain Island relies on natural water flows, Bad Creek is what's called a "pumped storage" hydroelectric — a sort of natural battery. Water is pumped up into the lake when electricity demand is low, such as overnight, then released when demand picks up.
