外文翻譯--來自太陽的能源-精品.doc

英文資料ENERGY FROM THE SUNThe sun has produced energy for billions of years. Solar energy is the solar radiation that reaches the earth. Solar energy can be converted directly or indirectly into other forms of energy, such as heat and electricity. The major drawbacks (problems, or issues to overcome) of solar energy are: (1) the intermittent and variable manner in which it arrives at the earths surface and, (2) the large area required to collect it at a useful rate. Solar energy is used for heating water for domestic use, space heating of buildings, drying agricultural products, and generating electrical energy. In the 1830s, the British astronomer John Herschel used a solar collector box to cook food during an expedition to Africa. Now, people are trying to use the suns energy for lots of things. Electric utilities are trying photovoltaics, a process by which solar energy is converted directly to electricity. Electricity can be produced directly from solar energy using photovoltaic devices or indirectly from steam generators using solar thermal collectors to heat a working fluid. Out of the 14 known solar electric generating units operating in the US at the end of 2004, 10 of these are in California, and 4 in Arizona. No statistics are being collected on solar plants that produce less than 1 megawatt of electricity, so there may be smaller solar plants in a number of other states. PHOTOVOLTAIC ENERGYPhotovoltaic energy is the conversion of sunlight into electricity through a photovoltaic (PVs) cell, commonly called a solar cell. A photovoltaic cell is a nonmechanical device usually made from silicon alloys. Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. When photons strike a photovoltaic cell, they may be reflected, pass right through, or be absorbed. Only the absorbed photons provide energy to generate electricity. When enough sunlight (energy) is absorbed by the material (a semiconductor), electrons are dislodged from the materials atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface.When the electrons leave their position, holes are formed. When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cells front and back surfaces creates a voltage potential like the negative and positive terminals of a battery. When the two surfaces are connected through an external load, electricity flows. The photovoltaic cell is the basic building block of a PV system. Individual cells can vary in size from about 1 cm (1/2 inch) to about 10 cm (4 inches) across. However, one cell only produces 1 or 2 watts, which isnt enough power for most applications. To increase power output, cells are electrically connected into a packaged weather-tight module. Modules can be further connected to form an array. The term array refers to the entire generating plant, whether it is made up of one or several thousand modules. As many modules as needed can be connected to form the array size (power output) needed. The performance of a photovoltaic array is dependent upon sunlight. Climate conditions (e.g., clouds, fog) have a significant effect on the amount of solar energy received by a PV array and, in turn, its performance. Most current technology photovoltaic modules are about 10 percent efficient in converting sunlight with further research being conducted to raise this efficiency to 20 percent. The pv cell was discovered in 1954 by Bell Telephone researchers examining the sensitivity of a properly prepared silicon wafer to sunlight. Beginning in the late 1950s, pvs were used to power U.S. space satellites. The success of PVs in space generated commercial applications for pv technology. The simplest photovoltaic systems power many of the small calculators and wrist watches used everyday. More complicated systems provide electricity to pump water, power communications equipment, and even provide electricity to our homes. Photovoltaic conversion is useful for several reasons. Conversion from sunlight to electricity is direct, so that bulky mechanical generator systems are unnecessary. The modular characteristic of photovoltaic energy allows arrays to be installed quickly and in any size required or allowed. Also, the environmental impact of a photovoltaic system is minimal, requiring no water for system cooling and generating no by-products. Photovoltaic cells, like batteries, generate direct current (DC) which is generally used for small loads (electronic equipment). When DC from photovoltaic cells is used for commercial applications or sold to electric utilities using the electric grid, it must be converted to alternating current (AC) using inverters, solid state devices that convert DC power to AC. Historically, pvs have been used at remote sites to provide electricity. However, a market for distributed generation from PVs may be developing with the unbundling of transmission and distribution costs due to electric deregulation. The siting of numerous small-scale generators in electric distribution feeders could improve the economics and reliability of the distribution system.SOLAR THERMAL HEATThe major applications of solar thermal energy at present are heating swimming pools, heating water for domestic use, and space heating of buildings. For these purposes, the general practice is to use flat-plate solar-energy collectors with a fixed orientation (position). Where space heating is the main consideration, the highest efficiency with a fixed flat-plate collector is obtained if it faces approximately south and slopes at an angle to the horizon equal to the latitude plus about 15 degrees. Solar collectors fall into two general categories: nonconcentrating and concentrating.In the nonconcentrating type, the collector area (i.e. the area that intercepts the solar radiation) is the same as the absorber area (i.e., the area absorbing the radiation). In concentrating collectors, the area intercepting the solar radiation is greater, sometimes hundreds of times greater, than the absorber area. Where temperatures below about 200o F are sufficient, such as for space heating, flat-plate collectors of the nonconcentrating type are generally used. There are many flat-plate collector designs but generally all consist of (1) a flat-plate absorber, which intercepts and absorbs the solar energy, (2) a transparent cover(s) that allows solar energy to pass through but reduces heat loss from the absorber, (3) a heat-transport fluid (air or water) flowing through tubes to remove heat from the absorber, and (4) a heat insulating backing. Solar space heating systems can be classified as passive or active. In passive heating systems, the air is circulated past a solar heat surface(s) and through the building by convection (i.e. less dense warm air tends to rise while more dense cooler air moves downward) without the use of mechanical equipment. In active heating systems, fans and pumps are used to circulate the air or the heat absorbing fluid. SOLAR THERMAL POWER PLANTSSolar thermal power plants use the suns rays to heat a fluid, from which heat transfer systems may be used to produce steam. The steam, in turn, is converted into mechanical energy in a turbine and into electricity from a conventional generator coupled to the turbine. Solar thermal power generation is essentially the same as conventional technologies except that in conventional technologies the energy source is from the stored energy in fossil fuels released by combustion. Solar thermal technologies use concentrator systems due to the high temperatures needed for the working fluid. PARABOLIC TROUGHThe parabolic trough is used in the largest solar power facility in the world located in the Mojave Desert at Kramer Junction, California. This facility has operated since the 1980 and accounted for the majority of solar electricity produced by the electric power sector in 2004.A parabolic trough collector has a linear parabolic-shaped reflector that focuses the suns radiation on a linear receiver located at the focus of the parabola. The collector tracks the sun along one axis from east to west during the day to ensure that the sun is continuously focused on the receiver. Because of its parabolic shape, a trough can focus the sun at 30 to 100 times its normal intensity (concentration ratio) on a receiver pipe located along the focal line of the trough, achieving operating temperatures over 400 degrees Celcius.A collector field consists of a large field of single-axis tracking parabolic trough collectors. The solar field is modular in nature and is composed of many parallel rows of solar collectors aligned on a north-south horizontal axis. A working (heat transfer) fluid is heated as it circulates through the receivers and returns to a series of heat exchangers at a central location where the fluid is used to generate high-pressure superheated steam. The steam is then fed to a conventional steam turbine/generator to produce electricity. After the working fluid passes through the heat exchangers, the cooled fluid is recirculated through the solar field. The plant is usually designed to operate at full rated power using solar energy alone, given sufficient solar energy. However, all plants are hybrid solar/fossil plants that have a fossil-fired capability that can be used to supplement the solar output during periods of low solar energy. The Luz plant is a natural gas hybrid. SOLAR DISHA solar dish/engine system utilizes concentrating solar collectors that track the sun on two axes, concentrating the energy at the focal point of the dish because it is always pointed at the sun. The solar dishs concentration ratio is much higher that the solar trough, typically over 2,000, with a working fluid temperature over 750oC. The power-generating equipment used with a solar dish can be mounted at the focal point of the dish, making it well suited for remote operations or, as with the solar trough, the energy may be collected from a number of installations and converted to electricity at a central point. The engine in a solar dish/engine system converts heat to mechanical power by compressing the working fluid when it is cold, heating the compressed working fluid, and then expanding the fluid through a turbine or with a piston to produce work. The engine is coupled to an electric generator to convert the mechanical power to electric power. SOLAR POWER TOWERA solar power tower or central receiver generates electricity from sunlight by focusing concentrated solar energy on a tower-mounted heat exchanger (receiver). This system uses hundreds to thousands of flat sun-tracking mirrors called heliostats to reflect and concentrate the suns energy onto a central receiver tower. The energy can be concentrated as much as 1,500 times that of the energy coming in from the sun. Energy losses from thermal-energy transport are minimized as solar energy is being directly transferred by reflection from the heliostats to a single receiver, rather than being moved through a transfer medium to one central location, as with parabolic troughs. Power towers must be large to be economical. This is a promising technology for large-scale grid-connected power plants. Though power towers are in the early stages of development compared with parabolic trough technology, a number of test facilities have been constructed around the world.Last Revised: July 2008Sources: Energy Information Administration, Electric Power Annual, Form EIA-860, Annual Electric Generator Report database.來自太陽的能源太陽產(chǎn)生能量已有數(shù)十億年，太陽能是太陽輻射到地球的能量。太陽能可以直接或間接地轉(zhuǎn)換為其他形式的能源，如熱能和電能。 主要缺點(diǎn)(問題，或者問題有待克服)太陽能是： ( 1 )間歇方式到達(dá)地球表面， ( 2 )大面積收集在一個(gè)大容器中。 太陽能被用于加熱家庭用水，供暖建筑物，干燥農(nóng)產(chǎn)品， 發(fā)電和電力能源。 在1830年代， 英國天文學(xué)家約翰赫在一個(gè)探險(xiǎn)隊(duì)到非洲在烹調(diào)食物時(shí)采用太陽能集熱箱。 現(xiàn)在，人們正試圖用太陽的能量做很多東西。 電力部門正試圖利用光伏發(fā)電，是太陽能直接轉(zhuǎn)化為電能一個(gè)過程。 電流可以直接由太陽能利用光電器件或間接從蒸汽發(fā)生器產(chǎn)生，使用太陽能熱收藏家熱工質(zhì)收藏。 在美國2004年年底已出現(xiàn)的14個(gè)已知太陽能發(fā)電營運(yùn)單位， 其中主要在加州和亞利桑那州。統(tǒng)計(jì)數(shù)據(jù)顯示正在收集的太陽能，可以產(chǎn)生小于1兆瓦的電力， 因此， 在其他一些國家可以應(yīng)用較小的太陽能電廠。光伏發(fā)電 光伏發(fā)電是把太陽光轉(zhuǎn)換為電能，通過光伏( PV )的電池板，即俗稱的太陽能電池。 光伏電池是一個(gè)非機(jī)械裝置，通常制成硅合金。 日光是由光子或粒子組成的太陽能， 這些光子含有不同量的能量相應(yīng)于不同波長的太陽光譜。 當(dāng)光子通過光伏電池可以反映出來，穿過的，或者被吸收，利用吸收光子的能量來發(fā)電。 當(dāng)陽光不足(能源)時(shí)將所吸收的材料(半導(dǎo)體) ，利用電子趕出了材料的原子。 特殊處理的材料表面在制造使得鋒面的細(xì)胞更容易接受自由電子， 所以電子自然遷移到地表。當(dāng)電子離開自己的位置，就形成空穴。 當(dāng)許多電子，帶負(fù)電荷的電子運(yùn)動(dòng)形成電流， 由此產(chǎn)生的不平衡電荷之間產(chǎn)生電位從而由負(fù)極流向正極。 兩個(gè)電極通過外部負(fù)載形成回路而產(chǎn)生電流。光伏電池的基本構(gòu)造光伏系統(tǒng)。 電池板規(guī)?？纱罂尚。蓮?厘米( 1 / 2英寸)到10厘米( 4英寸)。 但是，一塊小的電池板只產(chǎn)生1或2瓦特，這對于大多數(shù)負(fù)載來說是遠(yuǎn)遠(yuǎn)不夠用的。 需要增加輸出功率，將許多小的電池板模塊連接成一個(gè)緊湊模塊。 模塊可以進(jìn)一步連接組成一個(gè)電池板組。 任期陣列指的是整個(gè)發(fā)電廠的，不論它是由一個(gè)或幾個(gè)單元組成。正如很多模塊需要連接組成一定大小的陣列。光伏陣列受到陽光的影響。氣候條件(例如，云 霧)對光伏陣列收到的太陽能有重大影響。目前大多數(shù)科技光伏組件約有10%高效日光轉(zhuǎn)換，進(jìn)一步的研究正在進(jìn)行中，以把效率為提高為20% 。 在1954年由貝爾電話研究者研究的敏感性，發(fā)明光伏電池，利用硅片吸收陽光。 50年代后期，被用于美國在太空的衛(wèi)星。 由于在太空的成功應(yīng)用， 光伏技術(shù)逐漸應(yīng)用于商業(yè)。許多小型計(jì)算器和手表都用最簡單的光伏電源系統(tǒng)。更為復(fù)雜的系統(tǒng)，提供電力抽水，電力通訊設(shè)備，甚至向用戶提供電力。 光電轉(zhuǎn)換是有很多優(yōu)點(diǎn)。 利用陽光直接產(chǎn)生電力，使得笨重機(jī)械發(fā)電機(jī)系統(tǒng)逐漸被取代。 模塊化特性光伏發(fā)電陣列很快發(fā)展成可以滿足任何尺寸要求。同時(shí)， 光伏發(fā)電系統(tǒng)對環(huán)境的影響是非常小的，它無需水冷卻系統(tǒng)，也不會(huì)產(chǎn)生副作用。 光伏電池，產(chǎn)生直流電 ，即一般用于小負(fù)載(電子設(shè)備) 。 當(dāng)直流的光伏電池用于商業(yè)應(yīng)用或利用電力網(wǎng)出售給電力企業(yè)， 它必須用逆變器轉(zhuǎn)換成交流電，固態(tài)裝置轉(zhuǎn)換成直流電源空調(diào)。 在過去，光伏電池已用于在遠(yuǎn)程站點(diǎn)提供電力。 然而， 根據(jù)市場分布，使開發(fā)與分拆輸電和配電成本上漲。無數(shù)小型發(fā)電機(jī)，配電饋線能改善經(jīng)濟(jì)性和可靠性的分配制度。 熱力太陽能目前供暖游泳池，熱水供國內(nèi)使用， 和空間加熱建筑物大量應(yīng)用太陽能熱能。 為實(shí)現(xiàn)上述目的，一般的做法是使用平板型太陽能儲(chǔ)藏提供一個(gè)固定的方向(位置) 。 如供暖主要是考慮效率最高，用固定平板式集熱器獲得，可以放到向南斜坡上的一個(gè)角到地平線約15度。太陽能集熱器可分為兩大類： 非集中和集中。在非集中型中的集熱器面積(即該地區(qū)攔截太陽輻射)