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The Great Hoover Dam, Grand Coolidge Dam, dams in Norway, China, Zaire, Brazil, Japan, and Panama. Almost everywhere you look, people are harvesting energy from moving water. This promising form of energy production has become more popular in recent years as the power of choice in many developing and industrial regions for many reasons. Waterpower is clean, safe, and it reduces the dependence on fossil fuels, thus benefiting the environment. Hydroelectric power has a very promising future as a power source in our modern world.
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The idea of harvesting power from moving water is not a modern idea at all. It has existed in some form since the Greeks and Romans used water-powered mills to grind corn. Modern hydroelectric power plants are much more complex than the original ancient mills, but the same concept that once ground corn is now used to supply electricity to Las Vegas.
Modern hydroelectric power plants are a marvel of human ingenuity. For a power plant to be successful, the entire landscape of an area must be changed. The first step to building a power plant is to build a dam. This is important because the dam creates a huge reservoir from which power can be harvested. This greatly increases the dependability of these power plants. The water behind the dam flows into conduits called penstocks. These penstocks control the flow of water so the correct amount of electricity is generated. The penstocks lead the water to the turbines and out through the tailrace. The swift current spins the turbines at an incredible speed. The spinning generators generate the electricity that is harvested from the moving water. An amazing 25% of the energy on earth is generated in this manner.
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An example of a hydroelectric power plant is the Hoover Dam, located about an hour away from Las Vegas. Within the dam are 17 main turbines used to generate electricity for the nearby cities and two turbines used to generate electricity for the power plant. All 19 of these generators create 2,998,000 horsepower which translates into 4 billion kilowatt hours a year (enough to serve 1.3 million people). It is amazing to know that four billion-Kilowatt hours a year are generated from a stream that would otherwise be nothing more than a trickle of water. Imagine how many other resources remain untapped in the world!
Although there are many benefits to generating electricity with hydroelectric plants, there are two main downsides to the method. The first downside is the huge initial capitol investment required to build a power plant of this type. When the Hoover Dam was built in 1933-35, it cost 165 million dollars, all of which needed to be paid by the customers of the supplier. The second main downside of hydroelectric power plants is the fact that the dam, which is essential to the plant, destroys many habitats. A dam needs to hold a tremendous amount of water, and floods out surrounding forests, deserts, towns and anything else in its way. Lake Mead, supplying the Hoover Dam, has enough water to flood the entire state of Pennsylvania to a depth of 1 foot! Hydroelectric power has many benefits that outweigh the downsides, but improvements are still needed. You must continue the search for others!
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 Lilly from United States contributed:
I'm not so sure you can say that the benefits outweigh the drawbacks. There is a big debate going on about dams being built in various parts of the world -- in many places, archeologists are literally working against the rising tide to salvage what they can of ancient ruins before the floodwaters take them away forever.
However, there are things that can be done to minimize the impact of dams -- for example, we have learned that each year, we need to let different amounts of "flood water" out of the dams to mimic the patterns of floods and drought that are found in nature. This is important because dams not only flood the areas upstream, but create artificial droughts for miles down river!
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