Energy efficiency

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This article is about energy efficiency as a ratio. For the term as used in energy economics, see Efficient energy use.

See also: Energy conversion efficiency

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

$\mathrm{efficiency} \ \eta = \mathrm{{output} \over \mathrm{input}}$

where output is the amount of mechanical work (in watts) or energy released by the process (in joules), 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%.

1 Energy efficiency and global warming
2 Energy efficiency and peak oil
3 Energy efficiency in power supplies
4 See also
5 References
6 External links

[edit] Energy efficiency and global warming

Main article: Global warming

Making homes, vehicles, and businesses more energy efficient is seen as a largely untapped solution to addressing global warming, energy security, and 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" ^[1]

[edit] Energy efficiency and peak oil

Peak oil depletion scenarios graph which depicts cumulative published depletion studies by 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 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 petrochemicals), 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 strategies, which will necessarily involve reducing the demand for petroleum through increasing the efficiency of use, as well as expanding the supply of alternatives.

[edit] Energy efficiency in power supplies

Main article: Computer power supply

Computer power supplies are generally about 70–75% efficient;^[2] 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% efficient; higher energy efficiency uses less power directly, and requires less power to cool as well.