Hydropower generates nearly 6 percent of America’s total annual energy output and accounts for over a quarter of our utility-scale renewable energy. However, traditional dams are not the only way to harness water for energy. According to the U.S. Department of Energy, pumped storage hydropower makes up more than 90 percent of the nation’s utility-scale energy storage. Now, the Tennessee Valley Authority is considering expanding pumped storage hydropower capacity. 

The Tennessee Valley Authority (TVA) is the nation’s largest public power provider, keeping the lights on for more than 10 million people across seven states. They operate a diverse portfolio that includes energy sources from nuclear to natural gas. Among its assets is the Raccoon Mountain Pumped-Storage Plant near Chattanooga, Tennessee, which can generate roughly 1,700 megawatts of energy on an average day. TVA is now considering multiple proposals to expand its pumped storage hydropower capacity. 

What is pumped storage hydropower? In simple terms, it is a sort of ‘water battery.’ The system utilizes two reservoirs connected by a tunnel and a turbine pump that is connected to a local energy grid. When the grid has surplus energy, the pump starts and moves water from the lower reservoir to the upper reservoir, storing the energy by using it to power the movement. 

When there is a greater demand for power from the grid, the stored water can be released from the upper reservoir. It functions more like a traditional hydropower project, as it moves downward, generating power that is returned to the grid for use. Pumped storage projects can be open-loop, drawing water from a natural feature and allowing it to be returned, or closed-loop, where two reservoirs are used that do not connect to a natural body of water. 

Pumped storage hydropower offers many benefits. First and foremost, it enhances grid stability by functioning as a battery, helping power grids adapt to the fluctuations in energy supply and demand. It’s a clean power source, is highly efficient and cost-effective, and the plants are long-lasting. 

TVA is publicly examining the future of pumped storage capacity from four different angles. First, they could maintain operations at the Raccoon Mountain plant without expansion. Second, they could expand the existing plant by adding enough capacity to generate an additional 800 megawatts every day. Third, they could build a new plant at Rorex Creek near Pisgah, Alabama, with a daily capacity to generate between 1,200 and 1,600 megawatts. Fourth and finally, they could build a new plant at Widows Creek near Stevenson and Fabius, Alabama, that would have similar generation capacity to the Rorex Creek proposal. 

Of these, the power provider has signaled that it favors the third option—build a new pumped storage hydropower plant at Rorex Creek. However, it is still early in the process; the public comment period won’t close until July, and a final decision will not be announced until the end of 2025. Time will tell whether TVA decides to expand its renewable energy portfolio through adding more pumped storage hydropower or maintain the status quo. 

The views and opinions expressed are those of the author’s and do not necessarily reflect the official policy or position of C3.