Hydroelectric Projects: Pumped Storage Projects in the News

A recent New York Times ("N.Y.T.") article focuses on the ongoing Tâmega project in rural Portugal.  See: "Is a Dam in Rural Portugal a Key to Our Alternative Energy Future?" by Stanley Reed and Matilde Viegas, January 3, 2023. Its authors point to "a kind of global renaissance in the technology, known as pumped storage, " as currently taking place. 

In reading and considering this article, it is worth recalling that pumped storage projects for hydroelectric power are not new technologies.

One leading example that may be  known to many is Tennessee Valley Authority's (TVA's) Raccoon Mountain pumped storage unit. Located outside Chattanooga, Tennessee, Raccoon Mountain’s four Allis-Chalmers pump-driven generating units have a combined installed capacity of 1,652 megawatts and a summer net dependable capacity of 1,616 megawatts. Its reservoir, located at the top of the mountain, contains approximately 107 billion gallons of water covering 528 acres of water surface, drawn from the adjacent Tennessee River.  As TVA reports: "With its 1.6 million kilowatts of capacity, the Raccoon Mountain Pumped Storage Plant generates 14 times more power than nearby Chickamauga Dam."

Raccoon Mountain is not a new facility. Its construction started in 1970, and Raccoon Mountain has been in safe and reliable operation since 1978.   In TVA's description: "The plant works like a large storage battery. During periods of low demand, water is pumped from [the Tennessee River's] Nickajack Reservoir at the base of the mountain to the reservoir built at the top. It takes 28 hours to fill the upper reservoir. When demand is high, water is released via a tunnel drilled through the center of the mountain to drive generators in the mountain’s underground power plant."

The N.Y.T. article notes that Iberdrola plans to install a large wind farm near the Tâmega pumped-storage project. The piece further speaks to how pumped storage units can fit in with wind and solar energy: "Pumped storage plants can also provide, in essence, energy insurance to install even more sources of clean power generation, aiding the effort to tackle climate change, analysts say. " The article's authors note the following among the downsides of such projects: "In Europe, the scope for building such huge facilities may be limited by high costs, long lead times and opposition from environmentalists and local residents objecting to flooding river valleys. And the flooding from dams can hurt the riverine habitats of fish, birds and plants and inundate antiquities."

Lead time is, of course, a highly significant consideration in scoping and building any pumped storage site.  The scope of earth and water displacement required can equally be considerable.  (For informational purposes: TVA's construction of Raccoon Mountain displaced some 10 million cubic yards of earth to build the reservoir. 12,000 feet of subterranean tunnels were constructed, and the plant's central hall is described as being "a space the size of a football field [carved] out of solid limestone.")  Naturally,  these projects are subject to geographic considerations and limitations. Obviously, to maximize the gravity-related effects vital to a pumped storage unit's operations, such a plant's reservoir requires siting on a suitable height adjacent to an ample water supply.  Droughts, of course, can exert a limiting effect on being able to maximize draws from nearby water sources, much as they can on other hydroelectric facilities.  

While environmental concerns arise in connection with the initial construction and operation of such facilities, it may be worth noting here that the lakes resulting from pumped storage projects can, in time, became a haven for many animal and bird species. The area around TVA's Raccoon Mountain facility is a State of Tennessee-designated wildlife observation area. The mountaintop is home to raccoons, whitetail deer, woodchucks, gray foxes and, moreover, a large wintertime population of bald eagles.

Finally, for existing hydroelectric plants looking into hydro-modernization opportunities and the possibility of expanding capacity, the N.Y.T. article raises the potential of using pumped storage as a useful expansion option for certain strategically sited dams: "[E]nergy companies may focus on upgrading existing hydroelectric facilities with pumps and other equipment so that they can keep reusing water that is lost when it flows through a conventional hydroelectric dam."

Not only worldwide, but equally in the U.S., the day of new pumped storage projects may have returned after a thirty-year hiatus. Such plants can offer some unique synergies for hydroelectric operators to consider and investigate.