I've been inviting my students to submit links and articles for this blog. Last Thursday, one of them submitted not just one, but two links on the same subject... pumped hydro-storage.
To tell the truth, I've never considered a resevoir to be a storage battery, but that's exactly what my student discovered. It makes lots of sense. Take excess power available during periods of low demand to pump water up-hill for storage. When customer demand is high, this energy is available for use.
The first article is from the Tennessee Valley Authority (TVA). Here is the text of the article found at http://www.tva.gov/sites/raccoonmt.htm:
Raccoon Mountain Pumped-Storage Plant is located in southeast Tennessee on a site that overlooks the Tennessee River near Chattanooga.
The plant works like a large storage battery. During periods of low demand, water is pumped from 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 plant works like a large storage battery. During periods of low demand, water is pumped from 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 area around Raccoon Mountain is a state-designated Wildlife Observation Area. The mountaintop is home to whitetail deer, woodchucks, gray foxes, and, of course, raccoons. The most compelling wildlife attraction of the area is a large wintering population of bald eagles, which can be sighted from the overlook as they hunt in the woods and waters.
The Raccoon Mountain Visitor Center is open from 9 a.m. to 5 p.m. daily except major holidays and during the winter months, when it closes at 4 p.m. Tours of the power plant itself are no longer available, but the center has photographs, models, and knowledgeable staff to discuss plant operations and TVA. TVA closes all visitor centers when the homeland security alert level is orange (high) or red (severe).
Racoom Mountain may be the largest pumped storage station that TVA has, but Bath County has the most powerful one in the world. Here's what Dominion Virginia Power has to say about it at http://www.dom.com/about/stations/hydro/bath-county-pumped-storage-station.jsp:
Cradled in Virginia's rugged Allegheny Mountains, the world's most powerful pumped storage generating station quietly balances the electricity needs of millions of homes and businesses across six states.
The Bath County Pumped Storage Station, which went into operation in 1985, is jointly owned by Dominion and the operating companies of the Allegheny Power System, and managed by Dominion Generation. This mammoth station was cited as one of the nation's most outstanding 1985 engineering achievements. The earth and rock fill moved to construct the dams and other project facilities, if piled up, would create a mountain 1,000 feet (305 meters) high. Enough concrete was poured to build 200 miles (322 kilometers) of interstate highway.
The station consists of two large reservoirs — one 1,262 feet (385 meters) higher than the other, a massive power house and the huge tunnels that connect them. When demand is low, water is pumped from the lower reservoir to the upper one.
When demand is high, valves permit water to run through the tunnels to the lower reservoir at a rate as high as 13.5 million gallons (852 cubic meters/second) per minute, turning six 462-megawatt turbine generators. The water level in the 265-acre upper reservoir can fluctuate as much as 106 feet when the unit is operated.
About the Environment
The Bath County Pumped Storage Station is nearly surrounded by the George Washington National Forest and was built in cooperation with the U.S. Forest Service. Occupying a relatively small amount of land, it has had minimal adverse effect on the environment. Flows to both streams, Back Creek and Little Back Creek, are supplemented by storage from the station reservoirs. This significantly improves stream flow during periods of drought and enhances the environment for fish and other aquatic life.
The extreme fluctuations in water levels in the two reservoirs make them unsuitable for recreation. However, a separate 325-acre (1.32 sq. kilometers) public recreation area containing two lakes is located just downstream from the lower dam. The area has facilities for fishing, non-power boating, picnicking, swimming, hiking and camping. The recreation area is open on a seasonal basis only.
All that power, and fishing too!
This may be a stupid question, but are these pumped storage plants remotely close to being closed, self-sufficient systems? I know that's a dodgy question because it hints at the impossible perpetual motion concept, but it seems logical that (whether formally isolated within the system or driven via shared electrical power from other facilities) if the plants produce more energy than they consume -- that's perpetual energy production. Or, does it in fact consume more energy pumping the water back up to the reservoir than it generates?
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