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Hydroelectricity

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Definitions
Waterwheels capture the energy of falling water
Hydroelectricity
is the result of converting the kinetic energy of flowing water into electricity. The amount of electricity produced is contingent both on the volume of water and amount of head created by a dam. Head refers to the actual height of the turbines in a power plant in correlation to the surface of the water. The greater the water flow and head, the more electricity can be generated.[1] Hydroelectricity uses large hydraulic turbines connected to generators to produce electricity.

Some advantages of hydroelectricity compared to other electrical power sources such as nuclear power or fossil fuel are that it is available in vast supply, is relatively cost-effective, and is both a renewable and what can be considered environmentally friendly, or "green,” electrical energy source.[2]

Contents

[edit] History

The use of water flow to produce power has occurred since the 1700s and was widely exploited as early as the 1850s, first with the use of water wheels and then eventually with turbines ranging up to 1,000 horsepower. These turbines began to be manufactured more readily in the U.S. and Canada in the early 1870s. One Canadian company was producing up to 20 turbine machines annually during this period.

[edit] The Role of DC Generators

Hydroelectricity was first used in both the U.S. and Canada during the 1880s upon the invention of the direct current (DC)electric generator. One of the primary manufacturers of the direct current electrical generators was Thomas Edison, inventor of the light bulb.[3]

Direct current systems did not use transformers to increase the voltage leaving the power plant. With DC, the voltage of electrical current dropped as it traveled further and further away from the generator. Power plants had to therefore be built in close proximity to the power plant or station.

The first direct current generators were nothing more than belt-driven steam engines. Eventually, the use of 10 to 12-kilowatt generators using belt drives from existing mill turbines surpassed that of belt-driven steam engines.[4]

The advent of electrical lighting easily perpetuated a market demand for such service. Turbines eventually came into play and were used to drive direct current generators to provide lighting in evening hours only.[5] In the U.S. from 1880 to 1895, direct current hydro-based power stations were primarily built to arc power and provide incandescent lighting.[6]

[edit] The Role of Alternating-current Transmission

In the 1890s, the development of commercially viable transformers made high-voltage alternating current (AC) transmission feasible; this allowed the delivery of electrical power over longer distances. In an alternating current system, the transformers are used to increase the voltage leaving the power plant, enabling it to travel over greater distances. Another transformer located near the end destination is then used to step down the voltage before use.[7] Upon the invention of AC systems, hydropower became more widely used in both Canada and the U.S. By the 1900s, up to 5,000 horsepower directly coupled turbine-generator sets were being manufactured for use in hydropower plants. All these developments sparked the building of hydroelectric sites in remote areas as well as led to the transmission of higher-voltage levels. From 1920 to 1950, hydroelectric power stations accounted for over 90 percent of Canada’s total electrical power generating capacity.[8] By the early 1900s in the U.S., hydroelectric power accounted for more than 40 percent of the supply of that country’s electricity.[9] Today, hydropower projects still account for 60 percent of power within Canada.[10]

[edit] How it Works

Hydroelectricity works by capturing the energy of moving water in rivers or man-made installations where it flows from a high-level reservoir down through a tunnel or penstock and away from the dam. Hydraulic turbines are directly placed in the path of the water as it falls, causing them to rotate at very high speeds. The turbines are used to drive a generator that then converts the kinetic energy of the moving water into mechanical energy. These hydroelectric systems vary from heads of only a few meters to larger, more complex systems that feature massive turbines housed in power stations situated hundreds of meters below a reservoir. Hydroelectric systems can also be connected to a large power grid or operate as part of a stand-alone unit or system. There are currently three main types of hydroelectric schemes or systems in use.[11]

[edit] Storage Scheme

In a storage scheme, a dam impounds a reservoir that feeds turbines and a generator. Both the generator and turbine are usually located in the dam itself. This kind of system can also feature a diversion tunnel that channels water from a lake or reservoir to a remote power station that contains the turbine and generator. After passing through the turbines, the water is directed back into the river or into an alternate water way.[12]

[edit] Run-of-river Scheme

A run-of-river scheme uses the natural flow of a river. The continuity of the river's flow can be enhanced with a weir. A run-of-river scheme can also feature a diversion tunnel to channel water.[13]

[edit] Pumped Storage Scheme

The pumped storage scheme usually incorporates two reservoirs, with the release of water to generate power controlled entirely on a basis of supply and demand. When demand is low, electricity is used to pump water from an upper basin reservoir to a lower basin reservoir. Water is only released to generate power when necessitated by demand.[14]

[edit] References

  1. Bellis, Mary. Lester Allan Pelton - Water Turbines and the Beginnings of Hydroelectricity. About.com, 2008-09-30.
  2. Hydroelectric Power. Expert-Eyes.org, 2008-09-30.
  3. History of the Electric Power Industry. Edison Electric Institute, 2008-09-30.
  4. Hydroelectricity. The Canadian Encyclopedia, 2008-09-30.
  5. Hydroelectricity. The Canadian Encyclopedia, 2008-09-30.
  6. Bellis, Mary. Lester Allan Pelton - Water Turbines and the Beginnings of Hydroelectricity. About.com, 2008-09-30.
  7. History of the Electric Power Industry. Edison Electric Institute, 2008-09-30.
  8. Hydroelectricity. The Canadian Encyclopedia, 2008-09-30.
  9. Bellis, Mary. Lester Allan Pelton - Water Turbines and the Beginnings of Hydroelectricity. About.com, 2008-09-30.
  10. Hydroelectricity. The Canadian Encyclopedia, 2008-09-30.
  11. Hydroelectric: How it Works. BERR, 2008-09-30.
  12. Hydroelectric: How it Works. BERR, 2008-09-30.
  13. Hydroelectric: How it Works. BERR, 2008-09-30.
  14. Hydroelectric: How it Works. BERR, 2008-09-30.