Within a couple of miles of downtown Chattanooga, a man-made lake carved atop Elder Mountain helps supply TVA’s biggest hydroelectric plant and one of the most unique power plants in the South.
The Raccoon Mountain Pumped Storage plant, a mountaintop facility just west of Chattanooga that opened in 1978, works like a giant battery. TVA fills the 528-acre reservoir atop Raccoon Mountain at night by pumping Tennessee River water upward through a vertical tunnel drilled through the mountain. It flows into the reservoir through a reinforced concrete water intake structure that sticks up 220 feet from the reservoir bottom — taller than the Statue of Liberty.
Doing so burns electricity that TVA has to spare, since its nuclear and coal power plants generally run at full tilt around the clock and demand is down when people are asleep.
When TVA needs a lot of power in a hurry — for example on a 95-degree day when people crank up the air-conditioning — it pulls the reservoir’s plug.
Water gets sucked through the intake structure, which is designed to prevent whirlpools, and it blasts back down the vertical tunnel. The release spins turbines that power four generators before it floods out into the Tennessee River. Massive concrete baffles prevent turbulence in the river as water is released from the reservoir.
It takes 28 hours to fill the upper reservoir and Racoon Mountain is capable of generating a net dependable capacity of 1,652 megawatts, or enough power to temporarily supply about three cities the size of Chattanooga.
TVA shut the Raccoon Mountain plant down in March 2012 as a precaution because of cracks in the rotors that spin inside the generators’ magnetic field, creating electricity. Because similar rotor cracks caused a catastrophic failure in 2009 at a pumped storage plant in Austria, TVA opted to replace and repair all the rotors.
It took about three years to get the plant fully back online in 2015 with all four generators working.
The area around Raccoon Mountain is a state-designated Wildlife Observation Area.