Hydroelectric Power Generation
How the Potential Energy of Water is Used to Generate Electricity
May 6, 2008
Hydroelectricity is power generated by capturing energy from flowing water. According to REN21’s 2006 Renewables Status Report, hydroelectric power contributed 19% of the world’s power in 2006, and is the most widely used renewable energy source in the world. Hydroelectric power requires no fuel and produces no direct emissions or by-products.
History of Hydroelectric Power
The energy of moving water has been used by humans for thousands of years to power flour mills and irrigation systems. Water wheels were placed within a flowing stream of water, and the rotation generated in the wheel was used to perform work. Water powered the textile and industrial mills of the 19th century, and mill buildings dot the edges of rivers throughout the United States and Europe.
The first commercial hydroelectric project in the United States was built in Appleton, WI, in 1882. This plant used a water wheel to power a generator, which delivered power to two area paper mills.
Hydroelectric Power from Dams
Today, most hydroelectric power is generated from dams. Dams build up reservoirs behind them and allow for large potential energy to be developed. The reservoir water is sent through the turbines at the bottom of the dam, maximizing the energy that can be harvested from the water.
The potential power from a dam is based on the formula P = hrk, where P is the theoretical power generation, h is the maximum water height behind the dam, r is the flow rate of water into the turbines, and k is a conversion factor that takes into account system efficiency, acceleration due to gravity, and the density of the water.
World Hydroelectric Power Generation
China is the leader in worldwide hydroelectric power production, with 486.7 TWh of production in 2007, according to the China Electricity Council. Other countries with significant hydroelectric power production include Canada, Brazil, and the United States. China also has the largest capacity of hydroelectric power in the planning and construction stages, ensuring that it will be the world leader in hydroelectric power generation for the forseeable future.
Controversies with Hydroelectric Power Systems
When a dam is built, a location is selected where a large reservoir can be collected behind the dam, maximizing the potential energy that the water can provide. In order to create a significant depth, often large tracts of land must be flooded to create the reservoir. The Three Gorges Dam project in China has generated significant controversy for the number of people that have been displaced in order to create the reservoir. In 2007, the BBC reported that as many as 4 million people would have to be relocated over the course of development of the Three Gorges Dam. In addition, many historical and archeological sites have been flooded as the water level has risen.
Another issue associated with hydroelectric dams is the inability of fish to navigate the dammed river. This issue has led to the severe reduction of population of salmon in the Pacific Northwest region of North America, who rely on swimming upstream to spawning grounds in order to reproduce. The introduction of fish ladders has reduced population declines in recent years.
Hydroelectric power is one of the oldest power generation methods. It is a critical part of world power generation, and will continue to expand due to its non-reliance on fossil fuels.
Sources
REN21 Renewables Global Status Report, 2007
IEEE History Center
China Electricity Council website
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