Energy efficiency encyclopedia topics

Energy efficiency and 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"

Energy efficiency and 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.

Energy efficiency in power supplies

Computer power supplies are generally about 70–75% efficient; 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.

References

External links

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Wikipedia

Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat. Energy conversion efficiency is not defined uniquely, but instead depends on the usefulness of the output. All or part of the heat produced from burning a fuel may become rejected waste heat if, for example, work is the desired output from a thermodynamic cycle.

eta = frac{P_mathrm{out}}{P_mathrm{in}}

Even though the definition includes the notion of usefulness, efficiency is considered a technical or physical term. Goal or mission oriented terms include effectiveness and efficacy.

Generally, energy conversion efficiency is a dimensionless number between 0 and 1.0, or 0 to 100%. Efficiencies may not exceed 100%, e.g., for a perpetual motion machine. However, other effectiveness measures that can exceed 1.0 are used for heat pumps and other devices that move heat rather than convert it.

Related, more specific terms include

Electrical efficiency, useful power output per electrical power consumed;
Mechanical efficiency, where one form of mechanical energy (e.g. potential energy of water) is converted to mechanical energy (work);
Thermal efficiency or Fuel efficiency, useful heat and/or work output per input energy such as the fuel consumed;
'Total efficiency', e.g., for cogeneration, useful electric power and heat output per fuel energy consumed. Same as the thermal efficiency.

Fuel heating values and efficiency

In Europe the usable energy content of fuel is typically calculated using the lower heating value (LHV) of that fuel, i.e. the heat obtained by fuel combustion (oxidation), measured so that the water vapor produced remains gaseous, and is not condensed to liquid water. Using the LHV, a condensing boiler can achieve a "heating efficiency" in excess of 100% which violates the first law of thermodynamics. This is because the apparatus recovers part of the heat of vaporization, which is not included in the definition of the lower heating value of fuel. In the U.S. and elsewhere, the higher heating value (HHV) is used, which includes the latent heat for condensing the water vapor, and thus the thermodynamic maximum of 100% efficiency cannot be exceeded with HHV's use.

Efficiency in society

The energy efficiency of a consumer item is generally defined as the relative amount of power used (usually in the form of electricity) by an item in satisfying its purpose. For example, a washing machine is designed to wash clothes. The more energy efficient the washing machine, the less electricity that is consumed in performing this task.

To fully evaluate the energy efficiency of a consumer item however, running costs and expected life must be included in the calculation. Energy consumption can be measured per kilogram, for example, when comparing the efficiency of a full washing machine load to a smaller one. Energy Star and the European Union energy label are energy labels system that allow buyers to easily make comparisons between the power consumption statistics of similar electrical appliances.

Energy intensity is the macroeconomic measure of energy consumption. Energy demand management aims to reduce energy consumption on the demand side during specific times, while energy conservation is the broader practice of taking actions to increase energy efficiency.