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The environmental impact of electricity generation is significant because modern society uses large amounts of electrical power. This power is normally generated at power plants that convert some other kind of energy into electrical power. Each system has advantages and disadvantages, but many of them pose environmental concerns. ==Water usage== The amount of water usage is often of great concern for electricity generating systems as populations increase and droughts become a concern. Still, according to the U.S. Geological Survey, thermoelectric power generation accounts for only 3.3 percent of net freshwater consumption with over 80 percent going to irrigation. Likely future trends in water consumption are covered here.〔AAAS Annual Meeting 17–21 February 2011, Washington DC. Sustainable or Not? Impacts and Uncertainties of Low-Carbon Energy Technologies on Water. Dr Evangelos Tzimas, European Commission, JRC Institute for Energy, Petten, Netherlands〕 General numbers for fresh water usage of different power sources are shown below. Steam-cycle plants (nuclear, coal, NG, solar thermal) require a great deal of water for cooling, to remove the heat at the steam condensors. The amount of water needed relative to plant output will be reduced with increasing boiler temperatures. Coal- and gas-fired boilers can produce high steam temperatures and so are more efficient, and require less cooling water relative to output. Nuclear boilers are limited in steam temperature by material constraints, and solar is limited by concentration of the energy source. Thermal cycle plants near the ocean have the option of using seawater. Such a site will not have cooling towers and will be much less limited by environmental concerns of the discharge temperature since dumping heat will have very little effect on water temperatures. This will also not deplete the water available for other uses. Nuclear power in Japan for instance, uses no cooling towers at all because all plants are located on the coast. If dry cooling systems are used, significant water from the water table will not be used. Other, more novel, cooling solutions exist, such as sewage cooling at the Palo Verde Nuclear Generating Station. Hydroelectricity's main cause of water usage is both evaporation and seepage into the water table. Reference: Nuclear Energy Institute (factsheet ) using EPRI data and other sources.hOE Source(s): Adapted from US Department Of Energy, Energy Demand on Water Resources. Report to Congress on the Interdependence of Energy and Water, December 2006 (except where noted). *Cambridge Energy Research Associates (CERA) estimate. #Educated estimate. Water Requirements for Existing and Emerging Thermoelectric Plant Technologies. US Department Of Energy, National Energy Technology Laboratory, August 2008. Note(s): 3.6 GJ = gigajoule(s) == 1 MW·h = megawatt-hour(s), thus 1 L/GJ = 3.6 L/MW·h. B = Black coal (supercritical)-(new subcritical), Br = Brown coal (new subcritical), H = Hard coal, L = Lignite, cc = combined cycle, oc = open cycle, TL = low-temperature/closed-circuit (geothermal doublet), TH = high-temperature/open-circuit. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Environmental impact of electricity generation」の詳細全文を読む スポンサード リンク
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