Energy efficiency
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224535566
2008-07-09T08:29:56Z
Guenter Sonnenschein
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/* See also */
{{About|energy efficiency as a ratio|the term as used in energy economics|Efficient energy use}}
{{seealso | Energy conversion efficiency}}
In [[physics]] and [[engineering]], including [[mechanical engineering|mechanical]] and [[electrical engineering]], '''energy efficiency''' is a [[dimensionless]] number, with a value between [[0 (number)|0]] and [[1 (number)|1]] or, when multiplied by 100, is given as a percentage. The energy efficiency of a process, denoted by [[Eta (letter)| eta]], is defined as
:<math>
\mathrm{efficiency} \ \eta = \mathrm{{output} \over \mathrm{input}}
</math>
where ''output'' is the amount of <!--''useful'': if the definition of "useful" work is "mechanical" work just refer to the latter to avoid confusion --> [[mechanical work]] (in [[watt]]s) or energy released <!-- what [[type of energy]]; heat, biomass, UV? or doesn't it matter??--> by the process (in [[joule]]s), and ''input'' is the quantity of work or energy used as input to run the process.
Due to the principle of [[conservation of energy]], energy efficiency within a closed system can never exceed 100%.
==Energy efficiency and global warming==
{{Main|Global warming}}
Making homes, vehicles, and businesses more energy efficient is seen as a largely untapped solution to addressing [[global warming]], [[energy security]], and [[peak oil|fossil fuel depletion]]. Many of these ideas have been discussed for years, since the [[1973 oil crisis]] brought energy issues to the forefront. In the late 1970s, physicist [[Amory Lovins]] popularized the notion of a "soft path" on energy, with a strong focus on energy efficiency. Among other things, Lovins popularized the notion of [[negawatts]] -- the idea of meeting energy needs by increasing efficiency instead of increasing energy production.
Energy efficiency has proved to be a cost-effective strategy for building economies without necessarily growing [[energy consumption]], as environmental business strategist [[Joel Makower]] has noted. For example, the state of [[California]] began implementing energy-efficiency measures in the mid-1970s, including building code and appliance standards with strict efficiency requirements. During the following years, California's energy consumption has remained approximately flat on a per capita basis while national U.S. consumption doubled. As part of its strategy, California implemented a three-step plan for new energy resources that puts energy efficiency first, renewable electricity supplies second, and new fossil-fired power plants last.
Still, efficiency often has taken a secondary position to new power generation as a solution to [[global warming]] in creating national [[energy policy]]. Some companies also have been reluctant to engage in efficiency measures, despite the often favorable returns on investments that can result. Lovins' [[Rocky Mountain Institute]] points out that in industrial settings, "there are abundant opportunities to save 70% to 90% of the energy and cost for lighting, fan, and pump systems; 50% for electric motors; and 60% in areas such as heating, cooling, office equipment, and appliances." In general, up to 75% of the electricity used in the U.S. today could be saved with efficiency measures that cost less than the electricity itself.
Other studies have emphasized this. A report published in 2006 by the McKinsey Global Institute, asserted that "there are sufficient economically viable opportunities for energy-productivity improvements that could keep global energy-demand growth at less than 1 percent per annum" -- less than half of the 2.2 percent average growth anticipated through 2020 in a business-as-usual scenario. Energy productivity -- which measures the output and quality of goods and services per unit of energy input -- can come from either reducing the amount of energy required to produce something, or from increasing the quantity or quality of goods and services from the same amount of energy.
The [[Vienna Climate Change Talks 2007]] Report, under the auspices of the [[United Nations Framework Convention on Climate Change]] (UNFCCC), clearly shows "that energy efficiency can achieve real emission reductions at low cost" <ref>[http://unfccc.int/files/press/news_room/press_releases_and_advisories/application/pdf/20070831_vienna_closing_press_release.pdf Microsoft Word - 20070831_vienna_closing_press_release.doc<!-- Bot generated title -->]</ref>
== Energy efficiency and peak oil ==
[[Image:PU200611 Fig1.png|thumb|250px|right|Peak oil depletion scenarios graph which depicts cumulative published depletion studies by [[Association for the Study of Peak Oil and Gas|ASPO]] and other depletion analysts.]]
{{main article|Peak oil}}
In addition to concerns over [[global warming]], a potentially more immediate problem drew increasing attention during the mid-2000s: the possibly imminent [[peak oil|peaking of world production of petroleum]], natural gas, and (eventually) coal. Because [[petroleum]] is critical to vital sectors of industrial economies (especially [[transportation]], [[industrial agriculture]], and [[petrochemical]]s), and replacing petroleum in these applications takes time, an unexpected decline in the world production of petroleum could result in drastic increases in petroleum prices, leading to economic hardship which may range from moderate to catastrophic, depending on how rapidly oil production declines after the peak. The [[Hirsch report]] recommended several [[Mitigation of peak oil|mitigation strategies]], which will necessarily involve reducing the demand for petroleum through increasing the efficiency of use, as well as expanding the supply of alternatives.
== Energy efficiency in power supplies ==
{{main | Computer power supply }}
Computer power supplies are generally about 70–75% efficient;<ref>[http://www.tomshardware.com/2005/02/28/strong_showing/page38.html Strong Showing: High-Performance Power Supply Units | Tom's Hardware<!-- Bot generated title -->]</ref> to produce 75 W of DC output they require 100 W of AC input and dissipate the remaining 25 W in heat. Higher-efficiency power supplies can be over [[80 PLUS | 80% efficient]]; higher energy efficiency uses less power directly, and requires less power to cool as well.
==See also==
{{commons|:Category:Energy efficiency|Energy efficiency}}
*[[Domotics]] for energy efficiency.
*[[Earth's energy budget]]
*[[Energy conservation]].
*[[Energy conversion]].
*[[Energy efficiency in British housing]]
*[[Energy Policy Act of 1992]] (EPACT92).
*[[EROEI]].
*[[Exergy efficiency]].
*[[Figure of merit]].
*[[Fuel efficiency]].
*[[High temperature insulation wool]].
*[[Hybrid vehicle|Hybrid]] and [[plug-in hybrid vehicle]]s.
*[[International Electrotechnical Commission]].
*[[National Energy Action]] (WWE) (in the UK).
*[[National Electrical Manufacturers Association]] (UFC).
*[[Sensitivity (electronics)]].
*[[Thermal efficiency]].
== References ==
{{reflist}}
==External links==
*[http://www.eeglobalforum.com/ Energy Efficiency Global Forum and Exposition].
*[http://www.sengpielaudio.com/calculator-efficiency.htm Conversion of sensitivity in dB per Watt and meter to energy efficiency in percent for passive loudspeakers]
*[http://www.energysavingtrust.org.uk/what_can_i_do_today/how_efficient_is_your_home Find out how energy efficient your home is]
* [http://www.aceee.org/Motors/epactpdf.pdf Energy Efficiency Program for Certain Commercial and Industrial Equipment: Test Procedures, Labeling, and Certification Requirements for Electric Motors; Final Rule] ([[Office of Energy Efficiency and Renewable Energy]]).
*[http://www.reegle.info Reegle: Information Gateway For Renewable Energy And Energy Efficiency]
*[http://www.cet.or.at: Center for Energy and innovative Technologies]
*[http://www.aceee.org American Council for an Energy-Efficient Economy]
*[http://www.ase.org Alliance to Save Energy]
*[http://www.SmartEnergyLiving.org Smart Energy Living Alliance]
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[[Category:Energy conservation]]
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