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1、精选优质文档-倾情为你奉上英文资料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 t
2、o 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
3、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 c
4、onverted 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,
5、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
6、 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
7、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 m
8、aterials 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 negat
9、ive 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
10、 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
11、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.
12、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 conv
13、erting 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 sa
14、tellites. 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 provi
15、de 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 r
16、equired 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 p
17、hotovoltaic 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. How
18、ever, 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
19、 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). W
20、here 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 an
21、d 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 tim
22、es 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 interc
23、epts 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 sys
24、tems 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 he
25、ating 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
26、 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 t
27、hermal 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
28、 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 ax
29、is 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 operat
30、ing 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
31、) 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 flu
32、id 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 capabilit
33、y 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
34、 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 r
35、emote 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 compress
36、ed 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 focusin
37、g 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
38、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 t
39、owers 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: Jul
40、y 2008Sources: Energy Information Administration, Electric Power Annual, Form EIA-860, Annual Electric Generator Report database.来自太阳的能源太阳产生能量已有数十亿年，太阳能是太阳辐射到地球的能量。太阳能可以直接或间接地转换为其他形式的能源，如热能和电能。 主要缺点(问题，或者问题有待克服)太阳能是： ( 1 )间歇方式到达地球表面， ( 2 )大面积收集在一个大容器中。 太阳能被用于加热家庭用水，供暖建筑物，干燥农产品， 发电和电力能源。 在1830年代， 英国天
41、文学家约翰赫在一个探险队到非洲在烹调食物时采用太阳能集热箱。 现在，人们正试图用太阳的能量做很多东西。 电力部门正试图利用光伏发电，是太阳能直接转化为电能一个过程。 电流可以直接由太阳能利用光电器件或间接从蒸汽发生器产生，使用太阳能热收藏家热工质收藏。 在美国2004年年底已出现的14个已知太阳能发电营运单位， 其中主要在加州和亚利桑那州。统计数据显示正在收集的太阳能，可以产生小于1兆瓦的电力， 因此， 在其他一些国家可以应用较小的太阳能电厂。光伏发电 光伏发电是把太阳光转换为电能，通过光伏( PV )的电池板，即俗称的太阳能电池。 光伏电池是一个非机械装置，通常制成硅合金。 日光是由光子或粒
42、子组成的太阳能， 这些光子含有不同量的能量相应于不同波长的太阳光谱。 当光子通过光伏电池可以反映出来，穿过的，或者被吸收，利用吸收光子的能量来发电。 当阳光不足(能源)时将所吸收的材料(半导体) ，利用电子赶出了材料的原子。 特殊处理的材料表面在制造使得锋面的细胞更容易接受自由电子， 所以电子自然迁移到地表。当电子离开自己的位置，就形成空穴。 当许多电子，带负电荷的电子运动形成电流， 由此产生的不平衡电荷之间产生电位从而由负极流向正极。 两个电极通过外部负载形成回路而产生电流。光伏电池的基本构造光伏系统。 电池板规模可大可小，可从1厘米( 1 / 2英寸)到10厘米( 4英寸)。 但是，一块小
43、的电池板只产生1或2瓦特，这对于大多数负载来说是远远不够用的。 需要增加输出功率，将许多小的电池板模块连接成一个紧凑模块。 模块可以进一步连接组成一个电池板组。 任期阵列指的是整个发电厂的，不论它是由一个或几个单元组成。正如很多模块需要连接组成一定大小的阵列。光伏阵列受到阳光的影响。气候条件(例如，云 雾)对光伏阵列收到的太阳能有重大影响。目前大多数科技光伏组件约有10%高效日光转换，进一步的研究正在进行中，以把效率为提高为20% 。 在1954年由贝尔电话研究者研究的敏感性，发明光伏电池，利用硅片吸收阳光。 50年代后期，被用于美国在太空的卫星。 由于在太空的成功应用， 光伏技术逐渐应用于商
44、业。许多小型计算器和手表都用最简单的光伏电源系统。更为复杂的系统，提供电力抽水，电力通讯设备，甚至向用户提供电力。 光电转换是有很多优点。 利用阳光直接产生电力，使得笨重机械发电机系统逐渐被取代。 模块化特性光伏发电阵列很快发展成可以满足任何尺寸要求。同时， 光伏发电系统对环境的影响是非常小的，它无需水冷却系统，也不会产生副作用。 光伏电池，产生直流电 ，即一般用于小负载(电子设备) 。 当直流的光伏电池用于商业应用或利用电力网出售给电力企业， 它必须用逆变器转换成交流电，固态装置转换成直流电源空调。 在过去，光伏电池已用于在远程站点提供电力。 然而， 根据市场分布，使开发与分拆输电和配电成本
45、上涨。无数小型发电机，配电馈线能改善经济性和可靠性的分配制度。 热力太阳能目前供暖游泳池，热水供国内使用， 和空间加热建筑物大量应用太阳能热能。 为实现上述目的，一般的做法是使用平板型太阳能储藏提供一个固定的方向(位置) 。 如供暖主要是考虑效率最高，用固定平板式集热器获得，可以放到向南斜坡上的一个角到地平线约15度。太阳能集热器可分为两大类： 非集中和集中。在非集中型中的集热器面积(即该地区拦截太阳辐射)是相同的吸热面积(即该地区吸收的辐射) 。 在集中收藏，该地区拦截太阳辐射较大，比吸热面积有时高几百倍。 在温度低的情况下，如供暖， 平板集热器的类型非集中普遍使用。 有很多平板式集热器的设
46、计，但一般都包括下列内容： ( 1 )平板式减震器， 拦截，又吸收了太阳能， ( 2 )透明覆盖板 ，使太阳能通过，降温的吸收剂， ( 3 )传热流体(空气或水) ，流经管道，以消除热量的吸收， ( 4 )有保温的后盾。 太阳能采暖系统，可以划分为被动或主动。被动式采暖系统， 空气中散发了以往太阳能热表面和通过建设由对流(即较稠密趋于上升，而更密冷空气向下移动)流过未经使用的机械设备。 主动的供暖系统，风机和水泵是用来流通空气或吸收热流体。太阳热能发电厂 太阳能热电厂从传热系统利用太阳光照射的地热流体， 可用于生产蒸汽。 蒸汽，继而 转化为机械能的涡轮机发电，从常规发电机耦合的涡轮机。 太阳能
47、热发电是相同的技术，但在传统技术的能源来源 从能量储存在化学燃料释放的燃烧。 太阳能热利用技术体系选矿厂因高温所需要的工作流体。抛物槽抛物槽，是用最大的太阳能发电设备，在世界上位于莫哈韦沙漠 克雷默路口，加州，本基金运作以来， 1980年到2004年占了大多数太阳能发电产生的电力。抛物槽集热器的线性抛物面形反射器，重点是太阳的辐射呈线性接收机位于 焦点的抛物线。 珍藏轨道太阳沿一条轴线从东到西，白天，以确保太阳 不断集中的接收机。 由于其抛物线形， 槽能集中的太阳30至100倍的正常强度(浓度比) ，在接收管 地处焦线的低谷，实现了操作温度超过400摄氏度。 集热领域包含了大量的外地单轴跟踪抛
48、物面槽式集热器。 太阳能领域的模块化性质，是由许多平行排列整齐的太阳能集热器对准了 南北横轴。 工作(传热)液加热，因为它通过循环接收并返回一系列热 交换机在一个中央地点流体是用来产生高压蒸汽。 蒸汽，然后喂常规汽轮机/发电机产生电力。 工作流体通过换热器，冷却液循环通过太阳能领域。 植物通常是旨在全面运作时，额定功率使用太阳能单，如果有足够的太阳能。 然而， 所有植物杂交太阳/植物化石，有火的能力，可用于补充的太阳输出期间低太阳能等。该电厂是一个天然气混合。太阳能碟太阳能碟式/发动机系统采用集中太阳能集热器跟踪太阳在两条轴线上， 集中精力在联络点，因为它总是指向太阳。 他的太阳菜的浓度比例要
49、高得多，太阳谷底的时候，通常超过2，000元， 同一个工作流体温度超过750。发电设备用太阳能碟可以挂载在联络点的菜， 使之适合于远程操作，或与太阳能海槽 能源，可从收集到的一些设备，并转换为电力的一个中心点。发动机太阳能碟式/发动机系统的热量转化为机械功压缩的工作流体时，它是 冷，暖气压缩的工作流体， 然后扩大流体通过涡轮或与活塞生产工作。 发动机耦合的发电机把机械功率电力。太阳能发电塔一个太阳能塔或中央接收机产生的电力来自阳光的重点集中太阳能塔装热 换热器(接收机) 。 这个系统使用了几百至几千单位太阳跟踪镜反映和集中太阳的能量转嫁 中央接收塔。 能源，可以集中高达1500倍的能量来自太阳。 能量损失，从热能源的交通工具，尽量利用太阳能直接转反思，从单一接收机，而不是穿