【正文】 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 unlight energy and stored it in the plex organic molecules that made up their bodies, which were then pressed and concentrated. With the development of society, alarge 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 fossi 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 bee 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 mercial 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 2 supply only temporarily. Peak world petroleum resources production will be reached within a few years. Since the first energy crisis of 19731974, some concrete actions have even taken place. However, the severalfold increase in crude oil prices since 1973 has extacted a toll. In the . and other industrialized nations, the economy has been plagued by inflation, recession, unemployment, and obsolescence of industrial equipment. The economies of some petroleumdeficient developing countries have been devastated by energy prices. Energy crisis was acpanied 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 copperproducing nations to acpuire foreign currency by copper export. As known to all,the availability and cost of energy has bee 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 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 costeffective 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 earth39。 in the morning and the evening. At such an angle, the light gathering ability of the cell is essentially zero, resulting in no output. As the day progresses to midday, the angle of incidence approaches 0 176。 as possible. By tilting the solar panel to continuously face the sun, this can be achieved. This process of sensing and following the position of the sun is known as Solar Tracking. It was resolved that realtime tracking would be necessary to follow the sun effectively, so that no external data would be required in operation. II. THE SENSING ELEMENT AND S IGNAL PROCESSING Many different methods have been proposed and used to track the position of the sun. The simplest of all uses an LDR – a Light Dependent Resistor to detect light intensity changes on the surface of the resistor. Other methods, s