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Energy Source
Energy means the power which does work and drives machines.
All living things (including humans) rely on the sun as a source of energy. Coal, petroleum, and natural gas are energy sources available today because organisms in the past captured sunlight energy and stored it in the complex organic molecules that made up their bodies, which were then compressed and concentrated.
With the development of society, a large of energy sources have been used,such as coal, petroleum, natural gas, geothermal energy, nuclear fission power, nuclear fusion power, solar energy, and Hydrogen gas. however, under the circumstances, the quantity of energy source is limited. unlimited usage of energy source results in energy crisis.
At present, most of the energy consumed by humans is produced from fossil fuels. The greatest recoverable fossil is in the form of coal and lignite. Although world coal resources are enomous and potentially can fill energy needs for a century or two, their utilization is limited by environmental disruption from mining and emissions of carbon dioxide and sulfur dioxide. These would become intolerable long before coal resources were exhausted.
Only a small percentage of coal and lignite has been utilized to date, whereas much of the recoverable petroleum and natural gas has already been consumed. Petroleum has several characteristics that make it superior to coal as a source of energy. Its extraction causes less environmental damage than does coal mining. It is a more concentrated source of energy than coal, and it burns with less pollution, and it can be moved easily through pipes. These characteristics make it an ideal fuel for automobiles.
Since first commercial oil well in 1859, somewhat more than 100 million barrels of oil have been produced in the United States, most of it in recent years. In 1990 world petroleum consumption was at a rate of about 65 million barrels per day. Projected use of petroleum and natural gas indicates rapid depletion. Alaskan oil can help the petroleum supply only temporarily. Peak world petroleum resources production will be reached within a few years.
Since the first "energy crisis" of 1973-1974, some concrete actions have even taken place. However, the several-fold increase in crude oil prices since 1973 has extacted a toll. In the U.S. and other industrialized nations, the economy has been plagued by inflation, recession, unemployment, and obsolescence of industrial equipment. The economies of some petroleum-deficient developing countries have been devastated by energy prices.
Energy crisis was accompanied by worldwide shortages of some foods and minerals, followed in some cases by surpluses, such as the surplus wheat resulting from increased planting and a copper surplus resulting from the efforts of copper-producing nations to acpuire foreign currency by copper export.

As known to all,the availability and cost of energy has become dominant factors in society today. Obviously, solving the "energy crisis" makes good sense. Many schemes has been proposed for conserving present energy resources and for developing new ones. It is always possible to use less energy in any process. Therefore, energy engineer is created and developed. The first goal of energy engineer is to determine the methods by which energy utilization is reduced but the output remains the same, or even increases.The second goal is to determine which methods of using less energy are cost effective.
Conventional engineering techniques are used to evaluated the mechanisms of energy use. Economic considerations are of equal importance and life cycle cost and saving techniques are used to determine cost-effective measures. The evaluation focuses on those uses which are significant in the overall picture and attempts to determine those technical measures that can reduce usage and save money.
Meanwhile, looking for ideal energy sources is also very important to solve energy crisis. The recipe for an ideal energy source calls for one that is unlimited in supply, widely available, and inexpensive; it should not add to the earth's total heat burden or produce chemical air and water pollutants. Solar energy fulfills all of these criteria. Solar energy does not add excess heat to that which must be radiated from the earth. On a global basis, utilization of only a small fraction of solar energy reaching the earth could provide for all energy needs.
Solar energy is unlimited in supply, but its exploitation and utilization are limited owing to the limitation of technology and conditions.
Solar energy
utilization needs an enormous amount of land, and there are economic and environmental problems related to the use of even a fraction of this amount of land for solar energy collection. Certainly, many residents of Arizona would not be pleased at having so much of the state devoted to solar collectors, and some environmental groups would protest the resultant shading of rattlesnake habitat.
Solar power cells for the direct conversion of sunlight to electricity have been developed and are widely used for energy in space vehicles. With present technology, however, they remain too expensive for large-scale generation of electricity. Therefore, most schemes for the utilization of solar power depend upon the collection of thermal energy, followed by conversion to electrical energy. The simplest such approach involves focusing sunlight on a steam-generating bioler. Parabolic refkectors can be used to focus sunlight on pipes containing heat-transporting fluids. Selective coatings on these pipes can be used so that only a small percentage of incident energy is reradiated from the pipes.
With the installation of more heating devices and the probable development of some cheap, direct solar electrical generating capacity, it is likely that during the coming centry solar energy will be providing an appreciable percentage of energy needs in areas receiving abundants.