Hydroelectricity: Difference between revisions

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	].The power station at the lower reservoir has four water turbines which can generate 360 megawatts of electricity within 60 seconds of the need arising. The water of the upper reservoir (Llyn Stylan) can just be glimpsed on the right.]]

	'''Hydroelectricity ''' is ] obtained from ''']'''. Most hydroelectric power comes from the ] of ]med water driving a ] and ]. Less common variations make use of water's ] or undammed sources such as ]. Hydroelectricity is a ] source.

	The energy extracted from water depends not only on the volume but on the difference in height between the source and the water's outflow. This height difference is called the ]. The amount of ] in water is ] to the head. To obtain very high head, water for a hydraulic turbine may be run through a large pipe called a ].

	While many supply public electricity networks, some projects were created for private commercial purposes. For example, ] processing requires substantial amounts of electricity, and in ]'s ] there are examples at ] and ], designed and constructed during the early years of the 20th century. Similarly, the ] were constructed in ] to provide electricity for the ] aluminium industry.
	In many parts of ] (the provinces of ], ], ], ] and ]) hydroelectricity is used so extensively that the word "hydro" is used to refer to any ] delivered by a power utility. The government-run power utilities in these provinces are called ], ], ] (formerly "Ontario Hydro"), ] and ] respectively. Hydro-Québec is the world's largest hydroelectric generating company, with a total installed capacity (]) of 31,512 MW.

	==Importance==

	Hydroelectric power supplies 20% of world electricity. ] produces virtually all of its electricity from hydro, while ] produces 83% of its requirements (]), ] produces 67 % of all electricity generated in the country from hydro (over 70 % of its requirements). ] is the world's largest producer of hydro power and produces over 70% of its electricity from hydroelectric sources.

	Apart from a few countries with an abundance of it, hydro capacity is normally applied to peak-load demand, because it can be readily stored during off-peak hours (in fact, ] are sometimes used to store electricity produced by thermal plants for use during peak hours). It is not a major option for the future in the developed countries because most major sites in these countries having potential for harnessing gravity in this way are either being exploited already or are unavailable for other reasons such as environmental considerations.

	==Advantages and disadvantages==

	]
	], ] (tower)]]
	], ]]]

	The chief advantage of hydro systems is elimination of the cost of fuel. Hydroelectric plants are immune to price increases for fossil fuels such as ], ] or ], and do not require imported fuel. Hydroelectric plants tend to have longer lives than fuel-fired generation, with some plants now in service having been built 50 to 100 years ago. Labor cost also tends to be low since plants are generally heavily automated and have few personnel on site during normal operation.

	] currently provide the most significant means of storage of energy on a scale useful for a utility, allowing low-value generation in off-peak times (which occurs because fossil-fuel plants cannot be entirely shut down on a daily basis) to be used to store water that can be released during high load daily peaks. Operation of pumped-storage plants improves the daily ] of the generation system.

	Reservoirs created by hydroelectric schemes often provide excellent leisure facilities for ], and become tourist attractions in themselves. Multi-use dams installed for irrigation, flood control, or recreation, may have a hydroelectric plant added with relatively low construction cost, providing a useful revenue stream to offset the cost of dam operation.

	In practice, the utilization of stored water is sometimes complicated by demand for ] which may occur out of phase with peak electricity demand. Times of drought can cause severe problems, since water replenishment rates may not keep up with desired usage rates. Minimum discharge requirements represent an efficiency loss for the station if it is uneconomic to install a small turbine unit for that flow.

	Concerns have been raised by ]s that large hydroelectric projects might be disruptive to surrounding aquatic ]s. For instance, studies have shown that dams along the ] and ] coasts of ] have reduced ] populations by preventing access to ] grounds upstream, even though most dams in salmon habitat have ]s installed. Salmon ] are also harmed on their migration to sea when they must pass through ]. This has led to some areas ]ing smolt downstream during parts of the year. Turbine and power-plant designs that are easier on aquatic life are an active area of research.

	Generation of hydroelectric power can also have an impact on the downstream river environment. First, water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks. Second, since turbines are often opened intermittently, rapid or even daily fluctuations in river flow are observed. In the ], the daily cyclic flow variation caused by ] was found to be contributing to erosion of sand bars. Dissolved ] content of the water may change from preceding conditions. Finally, water exiting from turbines is typically much colder than the pre-dam water, which can change aquatic faunal populations, including ].

	The reservoirs of hydroelectric power plants in tropical regions may produce substantial amounts of ] and ]. This is due to plant material in newly flooded and re-flooded areas being inundated with water, decaying in an anaerobic environment, and forming methane, a very potent ]. The methane is released into the atmosphere once the water is discharged from the dam and turns the turbines. According to the World Commission on Dams report, where the reservoir is large compared to the generating capacity (less than 100 watts per square metre of surface area) and no clearing of the forests in the area was undertaken prior to impoundment of the reservoir, greenhouse gas emissions from the reservoir may be higher than those of a conventional oil-fired thermal generation plant . In ] reservoirs of Canada and Northern Europe, however, greenhouse gas emissions are typically only 2 to 8% of any kind of conventional thermal generation.

	Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In many cases, no amount of compensation can replace ancestral and cultural attachments to places that have spiritual value to the displaced population. Additionally, historically and culturally important sites can be flooded and lost. Such problems have arisen at the ] project in China, the ] in New Zealand and the ] in Southeastern Turkey.

	Some hydroelectric projects also utilize ], typically to divert a river at a shallower gradient to increase the head of the scheme. In some cases, the entire river may be diverted leaving a dry riverbed. Examples include the ] and ].

	==Hydro-electric facts==
	===Oldest===
	*], ], ] completed ].

	*], ], ] completed ], A waterwheel on the ] supplied the first commercial hydroelectric power for lighting to two paper mills and a house, two years after ] demonstrated ] to the public. Within a matter of weeks of this installation, a power plant was also put into commercial service at ].

	*], Launceston, Tasmania. Completed 1895. The first publicly-owned hydro-electric plant in the Southern Hemisphere. Supplied power to the city of Launceston for street lighting.

	* Decew Falls 1, ], ], ] completed 25 August 1898. Owned by ]. Four units are still operational. Recognised as an IEEE Milestone in Electrical Engineering & Computing by the ] Executive Committee in 2002.

	===Largest hydro-electric power stations===
	]
	The ] Complex in ], ], is the world's largest hydroelectric generating system. The eight generating stations of the complex have a total generating capacity of 16,021 MW. The ] station alone has a capacity of 5,616 MW. A ninth station (Eastmain-1) is currently under construction and will add 480 MW to the total. An additional project on the Rupert River, currently undergoing environmental assessments, would add two stations with a combined capacity of 888 MW.



	<td>]</td><td>Brazil/Paraguay</td><td>1984/1991</td><td align="right">12,666 MW</td><td align="right">93.4 TW-hours</td>
	</tr><tr>
	<td>]</td><td>Venezuela</td><td>1986</td><td align="right">10,200 MW</td><td align="right">46 TW-hours</td>
	</tr><tr>
	<td>]</td><td>United States</td><td>1942/1980</td><td align="right">6,809 MW</td><td align="right">22.6 TW-hours</td>
	</tr><tr>
	<td>]</td><td>Russia</td><td>1983</td><td align="right">6,400 MW</td>
	</tr><tr>
	<td>]</td><td>Canada</td><td>1981</td><td align="right">5,616 MW</td>
	</tr><tr>
	<td>]</td><td>Canada</td><td>1971</td><td align="right">5,429 MW</td><td align="right">35 TW-hours</td>
	</tr><tr>
	<td>]</td><td>Romania/Serbia</td><td>1970</td><td align="right">2,280 MW</td><td align="right">11.3 TW-hours</td>
	</table>

	These are ranked by maximum power.

	====In progress====
	*], ]. First power in July ], scheduled completion ], 18,200 MW

	===Countries with the most hydro-electric capacity===
	*], 341,312 GWh (66,954 MW installed)
	*], 319,484 GWh (79,511 MW installed)
	*], 285,603 GWh (57,517 MW installed)
	*], 204,300 GWh (65,000 MW installed)
	*], 173,500 GWh (44,700 MW installed)
	*], 121,824 GWh (27,528 MW installed)
	*], 84,500 GWh (27,229 MW installed)
	*], 82,237 GWh (22,083 MW installed)
	*], 77,500 GWh (25,335 MW installed)

	These are 1999 figures and include ] schemes.

	== References ==
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	==See also==
	{{Commons\|Category:Hydroelectric_power}}
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	*] an early private hydro-electric station

	==External links==
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	{{Sustainability and energy development group}}

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Revision as of 16:46, 25 May 2006

RICKY + HAROLD = FAMILY