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-{{For|other uses|Energy efficiency (disambiguation)}}
-[[Image:Compact-Fluorescent-Bulb.jpg|thumb|upright|A spiral-type integrated [[compact fluorescent lamp]], which has been popular among North American consumers since its introduction in the mid-1990s.<ref>{{cite web|title=Philips Tornado Asian Compact Fluorescent | publisher=Philips | accessdate=2007-12-24 | url=http://www.lamptech.co.uk/Spec%20Sheets/Philips%20CFL%20Tornado.htm}}</ref>]]
-{{Sustainable energy}}
-'''Efficient energy use''', sometimes simply called '''energy efficiency''', is the goal to reduce the amount of energy required to provide products and services. For example, [[building insulation|insulating a home]] allows a building to use less heating and cooling energy to achieve and maintain a comfortable temperature. Installing [[fluorescent lights]] or natural [[Skylight (window)|skylights]] reduces the amount of energy required to attain the same level of illumination compared with using traditional [[incandescent light bulbs]]. [[Compact fluorescent lights]] use one-third the energy of incandescent lights and may last 6 to 10 times longer.  Improvements in energy efficiency are most often achieved by adopting a more efficient technology or production process.<ref>[[Mark Diesendorf|Diesendorf, Mark]] (2007). ''[[Greenhouse Solutions with Sustainable Energy]]'', UNSW Press, p. 86.</ref>
-There are many motivations to improve energy efficiency.  Reducing energy use reduces energy costs and may result in a financial cost saving to consumers if the energy savings offset any additional costs of implementing an energy efficient technology.  Reducing energy use is also seen as a solution to the problem of reducing carbon dioxide emissions.  According to the [[International Energy Agency]], improved energy efficiency in [[Energy efficient buildings|buildings]], industrial processes and [[Sustainable transportation|transportation]] could reduce the world's energy needs in 2050 by one third, and help control global emissions of greenhouse gases.<ref>{{cite web|author=Sophie Hebden |url=http://www.scidev.net/News/index.cfm?fuseaction=readNews&itemid=2929&language=1 |title=Invest in clean technology says IEA report |publisher=Scidev.net |date=2006-06-22 |accessdate=2010-07-16}}</ref>
-Energy efficiency and [[renewable energy]] are said to be the ''twin pillars'' of [[sustainable energy]] policy<ref>{{cite web|url=http://aceee.org/store/proddetail.cfm?CFID=2957330&CFTOKEN=50269931&ItemID=432&CategoryID=7 |title=The Twin Pillars of Sustainable Energy: Synergies between Energy Efficiency and Renewable Energy Technology and Policy |publisher=Aceee.org |date= |accessdate=2010-07-16 |archiveurl = http://web.archive.org/web/20080505041521/http://aceee.org/store/proddetail.cfm?CFID=2957330&CFTOKEN=50269931&ItemID=432&CategoryID=7 |archivedate = 2008-05-05}}{{dead link|date=August 2013}}</ref> and are high priorities in the sustainable [[energy hierarchy]]. In many countries energy efficiency is also seen to have a national security benefit because it can be used to reduce the level of energy imports from foreign countries and may slow down the rate at which domestic energy resources are depleted.
-==Overview==
-{{Further|Domestic energy consumption}}
-Energy efficiency has proved to be a cost-effective strategy for building economies without necessarily increasing [[energy consumption]]. 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.<ref>{{cite book|last=Zehner|first=Ozzie|title=Green Illusions|year=2012|publisher=UNP|location=London|pages=180–181|url=http://greenillusions.org}}</ref>  As part of its strategy, California implemented a "loading order" for new energy resources that puts energy efficiency first, renewable electricity supplies second, and new fossil-fired power plants last.<ref>{{cite web|url=http://www.energy.ca.gov/2005publications/CEC-400-2005-043/CEC-400-2005-043.PDF |title=Loading Order White Paper |format=PDF |date= |accessdate=2010-07-16}}</ref>
-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."{{Citation needed|date=December 2012}} 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. The same holds true for home-owners, leaky ducts have remained an invisible energy culprit for years. In fact, researchers at the US Department of Energy and their consortium, Residential Energy Efficient Distribution Systems (REEDS) have found that duct efficiency may be as low as 50-70%. The US Department of Energy has stated that there is potential for energy saving in the magnitude of 90 Billion kWh by increasing home energy efficiency.<ref>{{cite web|url=http://www.greencollaroperations.com/weatherization-austin-tx.html |title=Weatherization in Austin, Texas |publisher=Green Collar Operations |date= |accessdate=2010-07-16}}</ref>
-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.<ref name= NYT292006>{{cite news|title= Energy Use Can Be Cut by Efficiency, Survey Says
-|url= http://www.nytimes.com/2006/11/29/business/29energy.html |accessdate= November 29, 2006|newspaper=the newyork times |date= November 29, 2006|author= STEVE LOHR}}</ref> 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</ref>
-==Appliances==
-{{See also|green computing|solar lamp|energy saving lamp|power usage effectiveness}}
-[[Image:EU energy label.png|thumb|Example [[European Union energy label|EU energy label]] for [[washing machine]].]]
-Modern appliances, such as [[refrigerators]], [[freezers]], [[oven]]s, [[stoves]], [[dishwashers]], and clothes washers and dryers, use significantly less energy than older appliances.  Installing a clothesline will significantly reduce your energy consumption as your dryer will be used less. Current energy efficient refrigerators, for example, use 40 percent less energy than conventional models did in 2001. Following this, if all households in Europe changed their more than ten-year-old appliances into new ones, 20 billion kWh of electricity would be saved annually, hence reducing CO<sub>2</sub> emissions by almost 18 billion kg.<ref>{{cite web|url=http://ecosavings.electrolux.com/#int_en |title=Ecosavings |publisher=Electrolux.com |date= |accessdate=2010-07-16}}</ref> In the US, the corresponding figures would be 17 billion kWh of electricity and {{convert|27000000000|lb|kg|abbr=on}} CO<sub>2</sub>.<ref>{{cite web|url=http://www.electrolux.com/ecosavings_us |title=Ecosavings (Tm) Calculator |publisher=Electrolux.com |date= |accessdate=2010-07-16}}</ref> According to a 2009 study from McKinsey & Company the replacement of old appliances is one of the most efficient global measures to reduce emissions of greenhouse gases.<ref>McKinsey & Company (2009). ''Pathway to a Low-Carbon Economy : Version 3 of the Global Greenhouse Gas Abatement Cost Curve'', p. 7.</ref> Modern power management systems also reduce energy usage by idle appliances by turning them off or putting them into a low-energy mode after a certain time. Many countries identify energy-efficient appliances using [[energy input labeling]].<ref name=app>{{cite web|author=Environmental and Energy Study Institute |url=http://www.eesi.org/buildings_efficiency_0506 |title=Energy-Efficient Buildings: Using whole building design to reduce energy consumption in homes and offices |publisher=Eesi.org |date= |accessdate=2010-07-16}}</ref>
-The impact of energy efficiency on peak demand depends on when the appliance is used.<ref>{{cite web|url=http://www.energydsm.org/energy-efficiency |title=The impact of energy efficiency on peak demand |publisher=Energydsm.com |date= |accessdate=2010-07-16}}</ref>  For example, an air conditioner uses more energy during the afternoon when it is hot.  Therefore, an energy efficient air conditioner will have a larger impact on peak demand than off-peak demand.  An energy efficient dishwasher, on the other hand, uses more energy during the late evening when people do their dishes.  This appliance may have little to no impact on peak demand.
-==Building design==
-{{See also|Building performance|Energy-efficient landscaping|Window insulation film|Phase-out of incandescent light bulbs}}
-[[File:Empire State Building from the Top of the Rock.jpg|thumb|Receiving a Gold rating for energy and environmental design in September 2011, the [[Empire State Building]] is the tallest and largest LEED certified building in the United States and Western Hemisphere.<ref name="inhabitat1">{{cite web|url=http://inhabitat.com/nyc/empire-state-building-achieves-leed-gold-certification/ |title=Empire State Building Achieves LEED Gold Certification &#124; Inhabitat New York City|publisher=Inhabitat.com |accessdate=October 12, 2011}}</ref>]]
-A building’s location and surroundings play a key role in regulating its temperature and illumination. For example, trees, landscaping, and hills can provide shade and block wind. In cooler climates, designing northern hemisphere buildings with south facing windows and southern hemisphere buildings with north facing windows increases the amount of sun (ultimately heat energy) entering the building, minimizing energy use, by maximizing [[passive solar heating]]. Tight building design, including energy-efficient windows, well-sealed doors, and additional thermal insulation of walls, basement slabs, and foundations can reduce heat loss by 25 to 50 percent.<ref name=app/>
-Dark roofs may become up to 39 C° (70 F°) hotter than the most reflective white surfaces, and they transmit some of this additional heat inside the building. US Studies have shown that lightly colored roofs use 40 percent less energy for cooling than buildings with darker roofs. White roof systems save more energy in sunnier climates. Advanced electronic heating and cooling systems can moderate energy consumption and improve the comfort of people in the building.<ref name=app/>
-Proper placement of windows and skylights as well as the use of architectural features that reflect light into a building can reduce the need for artificial lighting. Increased use of natural and task lighting has been shown by one study to increase productivity in schools and offices.<ref name=app/> [[Compact fluorescent lights]] use two-thirds less energy and may last 6 to 10 times longer than [[incandescent light bulbs]]. Newer fluorescent lights produce a natural light, and in most applications they are cost effective, despite their higher initial cost, with payback periods as low as a few months.<ref name=cflsavings>{{cite web|url=http://www.green-energy-efficient-homes.com/cfl-savings-calculator.html |title=CFL savings calculator |publisher=Green-energy-efficient-homes.com |date=2013-08-06 |accessdate=2013-08-21}}</ref>
-Effective energy-efficient building design can include the use of low cost Passive Infra Reds (PIRs) to switch-off lighting when areas are unnoccupied such as toilets, corridors or even office areas out-of-hours. In addition, lux levels can be monitored using daylight sensors linked to the building's lighting scheme to switch on/off or dim the lighting to pre-defined levels to take into account the natural light and thus reduce consumption. Building Management Systems (BMS) link all of this together in one centralised computer to control the whole building's lighting and power requirements.<ref>Creating Energy Efficient Offices - Electrical Contractor Fit-out Article</ref>
-The choice of which space heating or cooling technology to use in buildings can have a significant impact on energy use and efficiency. For example, replacing an older 50% efficient [[Furnace#Household furnaces|natural gas furnace]] with a new 95% efficient one will dramatically reduce energy use, carbon emissions, and winter natural gas bills. [[Ground source heat pump]]s can be even more energy efficient and cost effective. These systems use pumps and compressors to move refrigerant fluid around a thermodynamic cycle in order to "pump" heat against its natural flow from hot to cold, for the purpose of transferring heat into a building from the large thermal reservoir contained within the nearby ground. The end result is that heat pumps typically use four times less electrical energy to deliver an equivalent amount of heat than a direct electrical heater does. Another advantage of a ground source heat pump is that it can be reversed in summertime and operate to cool the air by transferring heat from the building to the ground. The disadvantage of ground source heat pumps is their high initial capital cost, but this is typically recouped within five to ten years as a result of lower energy use.
-[[Smart meter]]s are slowly being adopted by the commercial sector to highlight to staff and for internal monitoring purposes the building's energy usage in a dynamic presentable format. The use of Power Quality Analysers can be introduced into an existing building to assess usage, harmonic distortion, peaks, swells and interruptions amongst others to ultimately make the building more energy-efficient. Often such meters communicate by using [[wireless sensor networks]].<ref>{{cite web|url=http://www.ecowizard.net/ |title=Wireless smart meter by ecowizard |publisher=Ecowizard.net |date= |accessdate=2010-07-16}}</ref>
-[[Green Building XML]] (gbXML) is an emerging schema, a subset of the [[Building Information Modeling]] efforts, focused on green building design and operation. gbXML is used as input in several energy simulation engines. But with the development of modern computer technology, a large number of building energy simulation tools are available on the market. When choosing which simulation tool to use in a project, the user must consider the tool's accuracy and reliability, considering the building information they have at hand, which will serve as input for the tool. Yezioro, Dong and Leite<ref>{{cite journal |doi=10.1016/j.enbuild.2007.04.014 |title=An applied artificial intelligence approach towards assessing building performance simulation tools |year=2008 |last1=Yezioro |first1=A |last2=Dong |first2=B |last3=Leite |first3=F |journal=Energy and Buildings |volume=40 |issue=4 |page=612}}</ref> developed an artificial intelligence approach towards assessing building performance simulation results and found that more detailed simulation tools have the best simulation performance in terms of heating and cooling electricity consumption within 3% of mean absolute error.
-A [[deep energy retrofit]] is a whole-building analysis and construction process that uses to achieve much larger energy savings than conventional [[green retrofit|energy retrofits]]. Deep energy retrofits can be applied to both residential and non-residential (“commercial”) buildings. A deep energy retrofit typically results in energy savings of 30 percent or more, perhaps spread over several years, and may significantly improve the building value.<ref>http://jeancarassus.zumablog.com/images/2128_uploads/Fuerst_New_paper.pdf</ref> The [[Empire State Building]] has undergone a deep energy retrofit process that was completeted in 2013. The project team, consisting of representatives from [[Johnson Controls]], [[Rocky Mountain Institute]], [[Clinton Climate Initiative]], and [[Jones Lang LaSalle]] will have achieved an annual energy use reduction of 38% and $4.4 million.<ref name=ESB>{{cite web|url=http://esbnyc.com/sustainability_energy_efficiency.asp |title=Visit > Sustainability & Energy Efficiency &#124; Empire State Building |publisher=Esbnyc.com |date=2011-06-16 |accessdate=2013-08-21}}</ref> For example, the 6,500 windows were remanufactured onsite into [[superwindows]] which block heat but pass light. [[Air conditioning]] operating costs on hot days were reduced and this saved $17 million of the project's capital cost immediately, partly funding other retrofitting.<ref>{{cite web |url=http://www.foreignaffairs.com/articles/137246/amory-b-lovins/a-farewell-to-fossil-fuels |title=A Farewell to Fossil Fuels |author=Amory Lovins |date=March/April 2012 |work=Foreign Affairs }}</ref> Receiving a gold [[Leadership in Energy and Environmental Design|Leadership in Energy and Environmental Design (LEED)]] rating in September 2011, the Empire State Building is the tallest LEED certified building in the United States.<ref name="inhabitat1" />
-The [[Indianapolis City-County Building]] recently underwent a deep energy retrofit process, which has achieved an annual energy reduction of 46% and $750,000 annual energy savings.
-==Industry==
-Industry uses a large amount of energy to power a diverse range of manufacturing and resource extraction processes.  Many industrial processes require large amounts of heat and mechanical power, most of which is delivered as [[natural gas]], [[Petroleum|petroleum fuels]] and as [[electricity]].  In addition some industries generate fuel from waste products that can be used to provide additional energy.
-Because industrial processes are so diverse it is impossible to describe the multitude of possible opportunities for energy efficiency in industry.  Many depend on the specific technologies and processes in use at each industrial facility. There are, however, a number of processes and energy services that are widely used in many industries.
-Various industries generate [[steam]] and electricity for subsequent use within their facilities.  When electricity is generated, the heat that is produced as a by-product can be captured and used for process steam, heating or other industrial purposes. Conventional electricity generation is about 30% efficient, whereas combined heat and power (also called [[co-generation]]) converts up to 90 percent of the fuel into usable energy.<ref name=indust>{{cite web|author=Environmental and Energy Study Institute |url=http://archives.eesi.org/publications/Fact%20Sheets/EC_Fact_Sheets/EE_Industry.pdf |title=Industrial Energy Efficiency: Using new technologies to reduce energy use in industry and manufacturing |publisher=Eesi.org |date= |accessdate=2010-07-16}}{{dead link|date=August 2013}}</ref>
-Advanced boilers and furnaces can operate at higher temperatures while burning less fuel. These technologies are more efficient and produce fewer pollutants.<ref name=indust/>
-Over 45 percent of the fuel used by US manufacturers is burnt to make steam.  The typical industrial facility can reduce this energy usage 20 percent (according to the [[US Department of Energy]]) by insulating steam and condensate return lines, stopping steam leakage, and maintaining steam traps.<ref name=indust/>
-[[Electric motors]] usually run at a constant speed, but a [[variable speed drives|variable speed drive]] allows the motor’s energy output to match the required load. This achieves energy savings ranging from 3 to 60 percent, depending on how the motor is used. Motor coils made of [[superconducting]] materials can also reduce energy losses.<ref name=indust/> Motors may also benefit from [[voltage optimisation]].
-Industry uses a large number of [[pumps]] and [[compressors]] of all shapes and sizes and in a wide variety of applications.  The efficiency of pumps and compressors depends on many factors but often improvements can be made by implementing better [[process control]] and better maintenance practices.  Compressors are commonly used to provide [[compressed air]] which is used for sand blasting, painting, and other power tools. According to the US Department of Energy, optimizing compressed air systems by installing variable speed drives, along with preventive maintenance to detect and fix air leaks, can improve energy efficiency 20 to 50 percent.<ref name=indust/>
-==Vehicles==
-{{main|Energy efficiency in transportation}}
-[[Image:NYPD Traffic Enforcement RMP In White.jpeg|thumb|left|[[Toyota Prius]] used by [[NYPD#Traffic Enforcement|NYPD Traffic Enforcement]]]]
-The estimated energy efficiency for an automobile is 280 Passenger-Mile/10<sup>6</sup> Btu.<ref>Richard C. Dorf, ''The Energy Factbook'', McGraw-Hill, 1981</ref>  There are several ways to enhance a vehicle's energy efficiency. Using improved [[aerodynamics]] to minimize drag can increase vehicle fuel efficiency. Reducing vehicle weight can also improve fuel economy, which is why [[composite materials]] are widely used in car bodies.
-More advanced tires, with decreased tire to road friction and rolling resistance, can save gasoline. Fuel economy can be improved by up to 3.3% by keeping tires inflated to the correct pressure.<ref>{{cite web|url=http://www.fueleconomy.gov/feg/maintain.shtml |title=Tips to improve your Gas Mileage |publisher=Fueleconomy.gov |date= |accessdate=2010-07-16}}</ref> Replacing a clogged air filter can improve a cars fuel consumption by as much as 10 percent on older vehicles.<ref name=auto>[http://www.eesi.org/publications/Fact%20Sheets/EC_Fact_Sheets/EE_Autos.pdf Automotive Efficiency: Using technology to reduce energy use in passenger vehicles and light trucks]{{dead link|date=July 2010}}</ref>  On newer vehicles (1980s and up) with fuel-injected, computer-controlled engines, a clogged air filter has no effect on mpg but replacing it may improve acceleration by 6-11 percent.<ref>http://www.fueleconomy.gov/feg/pdfs/Air_Filter_Effects_02_26_2009.pdf</ref>
-[[Image:Piracicaba 10 2008 151 Gast station selling four fuels.jpg|thumb|Typical [[Brazil]]ian filling station with four [[alternative fuel]]s for sale: [[biodiesel]] (B3), [[gasohol]] (E25), neat [[ethanol fuel|ethanol]] ([[Neat alcohol fuel|E100]]), and [[compressed natural gas]] (CNG). [[Piracicaba]], [[Brazil]].]]
-Energy-efficient vehicles may reach twice the fuel efficiency of the average automobile. Cutting-edge designs, such as the diesel [[Mercedes-Benz Bionic]] concept vehicle have achieved a fuel efficiency as high as {{convert|84|mpgus }}, four times the current conventional automotive average.<ref name=auto/>
-The mainstream trend in automotive efficiency is the rise of [[electric vehicle]]s (all@electric or hybrid electric).  Hybrids, like the [[Toyota Prius]], use [[regenerative braking]] to recapture energy that would dissipate in normal cars; the effect is especially pronounced in city driving.<ref>{{cite web|author=Nom * |url=https://www.lenergieenquestions.fr/prius-toyota-modele-reference-voitures-hybrides/ |title=La Prius de Toyota, une référence des voitures hybrides &#124; L'énergie en questions |publisher=Lenergieenquestions.fr |date=2013-06-28 |accessdate=2013-08-21}}</ref>  [[Plug-in hybrid]]s also have increased battery capacity, which makes it possible to drive for limited distances without burning any gasoline; in this case, energy efficiency is dictated by whatever process (such as coal-burning, hydroelectric, or renewable source) created the power.  Plug-ins can typically drive for around {{convert|40|mi}} purely on electricity without recharging; if the battery runs low, a gas engine kicks in allowing for extended range.  Finally, all-electric cars are also growing in popularity; the [[Tesla Roadster]] sports car is the only high-performance all-electric car currently on the market, and others are in preproduction.<ref name="Car and Driver">{{cite web|url=http://www.caranddriver.com/reviews/hot_lists/car_shopping/green_machines/2008_tesla_roadster_car_news |title=2008 Tesla Roadster - Car News |publisher=Car and Driver |date= |accessdate=2010-07-16}}</ref>
-==Alternative fuels==
-{{Main|Alternative fuels}}
-Alternative fuels, known as non-conventional or advanced [[fuel]]s, are any [[material]]s or [[Chemical substance|substance]]s that can be used as [[fuel]]s, other than conventional fuels. Some well known alternative [[fuel]]s include [[biodiesel]], [[bioalcohol]] ([[methanol]],  [[ethanol]], [[n-Butanol|butanol]]), chemically stored [[electricity]] (batteries and [[fuel cell]]s), [[hydrogen]], non-fossil [[methane]], non-fossil [[natural gas]], [[Vegetable oil used as fuel|vegetable oil]], and other [[biomass]] sources.
-==Energy conservation==
-{{Main|Energy conservation}}
-[[Image:Illust passive solar d1.gif|thumb|250px|right|Elements of [[Passive solar building design|passive solar energy design]], shown in a direct gain application]]
-[[Energy conservation]] is broader than energy efficiency in including active efforts to decrease energy consumption, for example through behavioural change, in addition to using energy more efficiently.  Examples of conservation without efficiency improvements are heating a room less in winter, using the car less, air-drying your clothes instead of using the dryer, or enabling energy saving modes on a computer.  As with other definitions, the boundary between efficient energy use and energy conservation can be fuzzy, but both are important in environmental and economic terms.<ref>Dietz, T. et al. (2009).[http://www.pnas.org/content/106/44/18452.full Household actions can provide a behavioral wedge to rapidly reduce U.S. carbon emissions]. PNAS. 106(44).</ref>  This is especially the case when actions are directed at the saving of [[fossil fuels]].<ref>Diesendorf, Mark (2007). ''Greenhouse Solutions with Sustainable Energy'', UNSW Press, p. 87.</ref> Energy conservation is a challenge requiring policy programmes, technological development and behavioral change to go hand in hand. Many energy [[intermediary]] organisations, for example governmental or non-governmental organisations on local, regional, or national level, are working on often publicly funded programmes or projects to meet this challenge.<ref>Breukers, Heiskanen, et al. (2009). Interaction schemes for successful demand-side management. Deliverable 5 of the [http://www.energychange.info/index.php CHANGING BEHAVIOUR] project. Funded by the EC (#213217).</ref>
-The National Renewable Energy Laboratory maintains a comprehensive list of apps useful for energy efficiency.<ref>{{cite web|url=http://en.openei.org/apps/ |title=National Renewable Energy Laboratory. (2012) |publisher=En.openei.org |date= |accessdate=2013-08-21}}</ref>
-==Sustainable energy==
-{{Main|Sustainable energy}}
-Energy efficiency and [[renewable energy]] are said to be the “twin pillars” of a sustainable [[energy policy]]. Both strategies must be developed concurrently in order to stabilize and reduce [[carbon dioxide emissions]]. Efficient energy use is essential to slowing the energy demand growth so that rising [[clean energy]] supplies can make deep cuts in fossil fuel use. If energy use grows too rapidly, renewable energy development will chase a receding target. Likewise, unless clean energy supplies come online rapidly, slowing demand growth will only begin to reduce total carbon emissions; a reduction in the carbon content of energy sources is also needed. A sustainable energy economy thus requires major commitments to both efficiency and renewables.<ref>[http://aceee.org/store/proddetail.cfm?CFID=2957330&CFTOKEN=50269931&ItemID=432&CategoryID=7 The Twin Pillars of Sustainable Energy: Synergies between Energy Efficiency and Renewable Energy Technology and Policy]{{dead link|date=August 2013}} ([[American Council for an Energy-Efficient Economy]])</ref>
-==Rebound effect==
-{{Further|Rebound effect (conservation)|Jevons' paradox}}
-If the demand for energy services remains constant, improving energy efficiency will reduce energy consumption and carbon emissions. However, many efficiency improvements do not reduce energy consumption by the amount predicted by simple engineering models. This is because they make energy services cheaper, and so consumption of those services increases. For example, since fuel efficient vehicles make travel cheaper, consumers may choose to drive farther, thereby offsetting some of the potential energy savings. Similarly, an extensive historical analysis of technological efficiency improvements has conclusively shown that energy efficiency improvements were almost always outpaced by economic growth, resulting in a net increase in resource use and associated pollution.<ref>Huesemann, M.H., and J.A. Huesemann (2011). ''Techno-Fix: Why Technology Won't Save Us or the Environment'', Chapter 5, "In Search of Solutions II: Efficiency Improvements", New Society Publishers, Gabriola Island, Canada.</ref> These are examples of the direct [[Rebound effect (conservation)|rebound effect]].<ref name=direct>[http://www.ukerc.ac.uk/Downloads/PDF/07/0710ReboundEffect/0710ReboundEffectReport.pdf The Rebound Effect: an assessment of the evidence for economy-wide energy savings from improved energy efficiency] pp. v-vi.</ref>
-Estimates of the size of the rebound effect range from roughly 5% to 40%.<ref name=Greening>{{Cite journal | doi=10.1016/S0301-4215(00)00021-5 | first=Lorna A. | last=Greening| title=Energy efficiency and consumption—the rebound effect—a survey | coauthors = David L. Greene, Carmen Difiglio| journal=Energy Policy |volume=28 | year=2000 | pages=389–401 | issue=6–7 }}</ref><ref>{{cite web|url = http://repositories.cdlib.org/ucei/policy/EPE-014 | title = The Effect of Improved Fuel Economy on Vehicle Miles Traveled: Estimating the Rebound Effect Using U.S. State Data, 1966-2001 | author = Kenneth A. Small and Kurt Van Dender | date = September 21, 2005 | publisher= University of California Energy Institute: Policy & Economics | accessdate=2007-11-23}}</ref><ref>{{cite web |url=http://www.policyarchive.org/handle/10207/bitstreams/3492.pdf | title = Energy Efficiency and the Rebound Effect: Does Increasing Efficiency Decrease Demand? | accessdate=2011-10-01}}</ref> The rebound effect is likely to be less than 30% at the household level and may be closer to 10% for transport.<ref name=direct/> A rebound effect of 30% implies that improvements in energy efficiency should achieve 70% of the reduction in energy consumption projected using engineering models.
-==Organisations and programs==
-'''International'''
-*[[80 Plus]]
-*[[2000-watt society]]
-*[[IEA Solar Heating & Cooling Implementing Agreement Task 13]]
-*[[International Institute for Energy Conservation]]
-*[[International Energy Agency]] (e.g. [[One Watt initiative]])
-*[[International Electrotechnical Commission]]
-*[[International Partnership for Energy Efficiency Cooperation]]
-*[[World Sustainable Energy Days]]
-'''Australia'''
-* [[Department of Climate Change and Energy Efficiency]]
-* [[Department of the Environment, Water, Heritage and the Arts]]
-*[[Sustainable House Day]]
-'''European Union'''
-*[[Building energy rating]]
-*[[Eco-Design of Energy-Using Products Directive]]
-*[[Energy efficiency in Europe]]
-*[[Orgalime]], the European engineering industries association
-'''Iceland'''
-*[[Marorka]]
-*[[Africa]]
-'''India'''
-*[[88888 Lights Out]]
-*[[Bureau of Energy Efficiency]]
-*[[Energy Efficiency Services Limited]]
-'''Japan'''
-*[[Cool Biz campaign]]
-'''Lebanon'''
-*[[The Lebanese Center for Energy Conservation]]
-'''United Kingdom'''
-*[[The Carbon Trust]]
-*[[Energy Saving Trust]]
-*[[National Energy Action]]
-*[[National Energy Foundation]]
-*[[Creative Energy Homes]]
-'''United States'''
-*[[Alliance to Save Energy]]
-*[[American Council for an Energy-Efficient Economy|American Council for an Energy-Efficient Economy (ACEEE)]]
-*[[Building Codes Assistance Project]]
-*[[Building Energy Codes Program]]
-*[[Consortium for Energy Efficiency]]
-*[[Energy Star]], from [[United States Environmental Protection Agency]]
-*[[Enervee]]
-*[[Industrial Assessment Center]]
-*[[National Electrical Manufacturers Association]]
-*[[Rocky Mountain Institute]]
-*[[Indian energy strategies]]
-==See also==
-{{portal|Renewable energy|Energy|Sustainable development|Ecology}}
-{{div col|colwidth=30em}}
-*[[Cogeneration]]
-*[[Data center infrastructure efficiency]]
-*[[Electrical energy efficiency on United States farms]]
-*[[Electric vehicle#Efficiency]]
-*[[Energy audit]]
-*[[Energy Efficiency Implementation]]
-*[[Energy recovery]]
-*[[Energy resilience]]
-*[[Performance per watt]]
-*[[List of energy storage projects]]
-*[[Negawatt power]]
-*[[Passenger miles per gallon]]
-*[[Renewable heat]]
-*[[Standby power]]
-*U.S. Department of Energy [[Solar Decathlon]]
-*[[The Green Deal]]
-*[[World Energy Engineering Congress]]
-{{div col end}}
-==References==
-{{Reflist|30em}}
-{{DEFAULTSORT:Efficient Energy Use}}
-[[Category:Energy conservation| ]]
-[[Category:Energy policy]]
-[[Category:Industrial ecology]]
-[[Category:Sustainable energy| ]]
-[[es:Mitigación del cambio climático#Eficiencia energética y conservación]]