Many of the projects' developers have only started in earnest overthe past few years, as the economics have been made attractive toinvestors by state renewable energy standards, the decision to lethydropower plants get a federal tax credit that previously wasgeared toward wind and solar, and the expectation that clean energywill pay off in the long run. Ciocci's group is lobbying to extendthe 1.1-cent credit per kilowatt-hour of hydropower generated,which was approved by Congress in 2005 and expires at year's end. She doesn't necessarily expect the full 80,000 MW to be built. That is almost the total production of the United States' existinghydropower dams, which generate about 7 percent of U.S.electricity. Some will be derailed by environmental concerns orpoor economics. So far, few projects besides AMP's have startedconstruction. Still, Ciocci said, "it's a huge insight into the industry thatthere is that much interest right now." River flow times drop equals hydropower Hydropower developers' push into the Midwest provokes a question:If the dams on the Ohio River have such potential, why didAmerica's first big wave of hydroelectric dams pass them by? The remaking of the river started all the way back in 1820, whenCongress provided $5,000 to study ways to ease the navigation ofthe Ohio and Mississippi rivers. Four years later, another $75,000came from Washington, this time with directions to remove the"planters, sawyers, and snags" that were blocking boats and barges.A century later, the Ohio was where the Army Corps of Engineersbuilt its first dams, hoping to prevent flooding and allow for easynavigation. Hydropower was an afterthought, said Donald Jackson, a historyprofessor at Lafayette College in Pennsylvania and co-author of ahistory of American dam building. When the Army Corps built up theOhio River's system of navigational locks in the 1930s, it was waryof electric power, only adding turbines to a couple of dams on theupper reaches of the Mississippi River. "Overall, the corps was not interested," Jackson said. Between 1939 and 1976, when the agency built many of these dams,the amount of goods barged down the Ohio multiplied more than 28times over. In 2008, the river carried about 259 million tons ofcommodities worth about $30 billion, 58 percent of it coal, andthat number is still increasing; the Army Corps predicts it willrise to 370 million tons by 2030. The main reason hydropower skipped the Ohio during that period wasgeography, Jackson said. Over the 981-mile span of the Ohio River,from Pittsburgh to the confluence with the Mississippi at Cairo,Ill., the water level drops less than 6 inches per mile. That is smooth and reliable, perfect for shipping, but without anyof the major drops that the turbines of the big dam era needed. The gorges of the mountainous West and the hill country of theTennessee Valley had better sites for dams to back up the flow ofrivers, making hydroelectric power so cheap that it overcame anypolitical obstacles, such as resistance from the owners ofcompeting power plants. "Your power, in the end, is just flow times drop," Jackson said."On the Ohio and the Mississippi, you have a really high flow, butyou don't have much of a drop, and there's no place I'm aware ofwhere you can create a large storage dam. ... They're just notamenable to anything other than a really low-head power plant, sothe political factors and the traditions of the corps probablymitigated against any real serious interest in trying to developthem as multipurpose dams." Still, the Army Corps had the foresight to build some of its damswith temporary "coffer cells" -- steel cylinders filed with sandand capped with concrete -- in anticipation that the dams mightsomeday be expanded and electrified, Meier said. That was able tohappen once the new technology in the light-bulb-shaped turbinesmade it easier to get electricity without a big drop. Stephen Little, president of the Paducah barge company CrounseCorp., said he is glad the dams are finding a new use. "What you're seeing at Meldahl is another one of the beneficiaries,and that's good," he said. His company operates 35 towboats and 1,100 barges, which todaymostly carry coal from mines to power plants. Little said he is notworried that the hydroelectric dams will compete with his customerswhen it comes to selling power to the electric grid. "We don't view it as being competition or taking away from ourelectric utility customers, because if the economy grows and we getthrough this recession ... it's not a matter of picking one energysource over the other," he added. "We will need all of them. Wewill need hydroelectric, coal, natural gas, nuclear, conservation." Some areas along the Ohio River that get most of their power fromcoal will see their energy mix transformed. The city of Hamilton,Ohio, which owns a large share of the electricity from AMP'sproject, will meet 70 percent of its power needs with renewablesources once the project is complete. Up and down the river, a fewmore workers will make a living in renewable energy. But combined, the 10 dams that the Oak Ridge researchers deemedmost promising would be able to provide about 3 gigawatts ofelectricity, less than 1 percent of U.S. coal-burning capacity andenough to power a few million U.S. homes. That means developerswould have a hard time making existing dams more than just aboutique source of new electricity. "In the end of the day, 3 gigawatts is a lot, but boy -- in termsof our energy demand?" Jackson said. "That saves a couple of bigcoal-burning plants, but it isn't going to transform the world." Want to read more stories like this? 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