Raccoon Mountain Pumped Storage Facility
A pumped storage facility is used to "store" electricity. The generator/turbine assemblies can be operated in "reverse", becoming giant water pumps. At times of low demand, electricity from the grid is used to power the pumps to fill up a reservior. During peak demands or emergencies, the water is released back through the turbines, producing electricity that is supplied to the grid. Its not 100 percent efficient, of course, but it ain't too bad!
Raccoon Mountain is one of two pumped storage facilities we have bagged. This one is different from Carter's Lake in that the reservoir is not on the main river, but "off line".
Raccoon Mountain is located off of I-24 west of Chattanooga. The Tennessee River runs through some pretty mountanous terrain here...in fact, Nickajack Lake, located in this area, is specified to have "Zero Flood Storage Capacity" because there is no place for the water to spread out. Raccoon mountain is a 1000 foot high peak overlooking the lake. TVA built an impoundment on top of the peak, and drilled two tunnels down to river level. One tunnel was for access, the other for water. The power house was carved out of solid rock about a thousand feet down! Two more tunnels were then drilled sideways out to the river, again one for access and one for water.
TVA still operates a visitors center there, and tours of the powerhouse are available. The visitors center is on top of the mountain, and the tour takes an elevator down to the powerhouse. In case of elevator failure, you hike a half-mile out to the river.
We said "still operates" the center, because, on some of their older literature, you will find references to a visitor's center at Browns's Ferry Nuclear Plant, and the Energy Center in Chattanooga. Don't believe it...they are closed. There was still a sign out on the main drag about the center at Brown's Ferry, and we were momentarily diverted during our Quest to Wilson Dam.
The time we were there, there was a group of Japanese Engineers visiting. They got the grand tour, inside the generator room (we were limited to looking through the glass) but we did get one side benefit that the general public does not. As we rode the elevator back up, they stopped and opened the doors at one of the access points so the engineers could see the construction of the elevator shaft, the emergency access stairway and catwalks, and the cables that conducted power to/from the Power House (the switch yard is on top of the mountain). Since Pat was standing next to the door, he had to step out on the catwalk so the group could peer out the door. Pat: "I was able to rip off a couple of quick shots, which really didn't show any detail because of the low light level. I was also kind of nervous about being that close to (I think) 161 KV conductors!"
The Plant is capable of 1532 Megawatts for about 20 hours. It saved the Chattanooga area's bacon one cold winter night when one of the units at Sequoyah Nuclear Plant scrammed, and the grid suddenly lost about 1100 Megawatts of power. We don't know how long it took them to get the nuke back on line, but Raccoon Mountain was online within 30 minutes, and TVA had about 24 hours of breathing room to make whatever arrangements had to be made.
The resevior takes about 27 hours to completely refill. Like we said, not 100 percent, but not too bad.
If this is one of the "prettier" switchyards you have seen, there is a reason. There are some exclusive neighborhoods in the area, and TVA was very careful to make the plant as palatible as possible for the locals. Notice the white globes inside the yard. They are noise suppressors!
You knew there had to be a dam somewhere! This is part of the largest rockfill dam TVA has done, for the storage impoundment on top of the mountain. (Also notice the self portrait..."closer than it appears!")
Water is taken in or put out through this structure. The design is supposed to reduce vortexing when used as an intake.
This structure on the river helps break up the turbulence from the exiting water when the plant is in production.
If you are interested, here is a view of Chattanooga from one of the overlooks. Be aware that this is a large file. We left it this way so that you can see the cooling towers at Sequoyah in the middle left of the image.