How giant ‘water batteries’ could make green power reliable

The machines that turn Tennessee’s Raccoon Mountain into one of the world’s largest energy storage devices—in effect, a battery that can power a medium-size city—are hidden in a cathedral-size cavern deep inside the mountain. But what enables the mountain to store all that energy is plain in an aerial photo. The summit plateau is occupied by a large lake that hangs high above the Tennessee River, so close it looks like it might fall in. Almost half a century ago, the Tennessee Valley Authority (TVA), the region’s federally owned electric utility, built the lake and blasted out the cavern as well as a 329-meter-tall shaft that links the two. “It was quite an effort to drill down into this mountain, because of the amount of rock that’s here,” senior manager Holli Hess says dryly. The cavern holds a candy-colored powerhouse, filled with cherry-red electrical ducts and vents and beams in a pale grape. Four giant cylinders, painted bright green and yellow, are the key machines: Each one houses a turbine that becomes a pump when it spins the other way, and a generator that is also an electric motor. At night, when demand for electricity is low but TVA’s nuclear reactors are still humming, TVA banks the excess, storing it as gravitational potential energy in the summit lake. The pumps draw water from the Tennessee and shoot it straight up the 10-meter-wide shaft at a rate that would fill an Olympic pool in less than 6 seconds. During the day, when deman...
Source: Science of Aging Knowledge Environment - Category: Geriatrics Source Type: research