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In Physics and Engineering , including Mechanical and Electrical engineering, energy efficiency is a Dimensionless number, with a value between 0 and 1 or, when multiplied by 100, is given as a percentage. The energy efficiency of a process, denoted by Eta , is defined as : where ''output'' is the amount of Mechanical Work (in Watt s) or energy released 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 See Also: Global warming Making homes, vehicles, and businesses more energy efficient is seen as a largely untapped solution to addressing Global Warming and Energy Security . 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. As a result, the state's energy consumption has remained flat over 30 years 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. A key feature in the Vienna Climate Change Talks 2007 was a United Nations report that showed how energy efficiency could yield significant cuts in emissions at low cost. SEE ALSO
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