水力發電的優點和缺點 ( USE ENGLISH)

圖片參考：http://upload.wikimedia.org/wikipedia/commons/d/de/Stwlan.dam.jpg

優點Advantages
Economics
The major advantage of hydroelectricity is elimination of the cost of fuel. The cost of operating a hydroelectric plant is nearly immune to increases in the cost of fossil fuels such as oil, natural gas or coal. Fuel is not required and so it need not be imported. Hydroelectric plants tend to have longer economic lives than fuel-fired generation, with some plants now in service having been built 50 to 100 years ago. Operating labor cost is usually low since plants are automated and have few personnel on site during normal operation.
Where a dam serves multiple purposes, a hydroelectric plant may be added with relatively low construction cost, providing a useful revenue stream to offset the costs of dam operation. It has been calculated that the sale of electricity from the Three Gorges Dam will cover the construction costs after 5 to 8 years of full generation.[3]

Greenhouse gas emissions
Since no fossil fuel is consumed, emission of carbon dioxide (a greenhouse gas) from burning fuel is eliminated. While some carbon dioxide is produced during manufacture and construction of the project, this is a tiny fraction of the operating emissions of equivalent fossil-fuel electricity generation. However, there may be other sources of emissions as discussed below.

Related activities
Reservoirs created by hydroelectric schemes often provide facilities for water sports, and become tourist attractions in themselves. In some countries, farming fish in the reservoirs is common. Multi-use dams installed for irrigation can support the fish farm with relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project. When dams create large reservoirs and eliminate rapids, boats may be used to improve transportation.

圖片參考：http://upload.wikimedia.org/wikipedia/commons/thumb/a/a4/Water_turbine.jpg/230px-Water_turbine.jpg


Hydraulic turbine and electrical generator.



Hydroelectric dam in cross section


Main article: Electricity generation

缺點Disadvantages
Environmental damage
Greenhouse gas emissions
Population relocation

Dam failures


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