太阳能路灯控制系统外文资料.doc

.吉林工程技术师范学院信 息 工 程 学 院学 士 学 位 论 文中英文资料学生姓名： 张建木专 业： 电子信息工程班 级： D0745学 号： 11号论文起止日期：2011年4月至6月英文原文：PHOTOVOLTAIC POWER GENERATIONABSTRACTThis report is an overview of photovoltaic power generation. The purpose of the report is to provide the reader with a general understanding of photovoltaic power generation and how PV technology can be practically applied.There is a brief discussion of early research and a description of how photovoltaic cells convert sunlight to electricity. The report covers concentrating collectors, flat-plate collectors, thin-film technology, and building-integrated systems. The discussion of photovoltaic cell types includes single-crystal, poly-crystalline, and thin-film materials. The report covers progress in improving cell efficiencies, reducing manufacturing cost, and finding economic applications of photovoltaic technology. Lists of major manufacturers and organizations are included, along with a discussion of market trends and projections.The conclusion is that photovoltaic power generation is still more costly than conventional systems in general. However, large variations in cost of conventional electrical power, and other factors, such as cost of distribution, create situations in which the use of PV power is economically sound. PV power is used in remote applications such as communications, homes and villages in developing countries, water pumping, camping, and boating. Grid-connected applications such as electric utility generating facilities and residential rooftop installations make up a smaller but more rapidly expanding segment of PV use. Furthermore, as technological advances narrow the cost gap, more applications are becoming economically feasible at an accelerating rate.INTRODUCTIONThis report is the result of Gale Greenleafs October 19, 1998 request for proposal. Bill Louk and Tom Penick responded to her request with a proposal, dated October 30, 1998, to continue earlier research on photovoltaic power generation. The proposal was approved and resulted in continued research followed by a presentation on November 30, 1998 and this final report on photovoltaic power generation.PHOTOVOLTAIC TECHNOLOGYScientists have known of the photovoltaic effect for more than 150 years. Photovoltaic power generation was not considered practical until the arrival of the space program. Early satellites needed a source of electrical power and any solution was expensive. The development of solar cells for this purpose led to their eventual use in other applications.DISCOVERY AND DEVELOPMENT OF PHOTOVOLTAIC POWERThe photovoltaic effect has been known since 1839, but cell efficiencies remained around 1% until the 1950s when U. S. researchers were essentially given a blank check to develop a means of generating electricity onboard space vehicles. Bell Laboratories quickly achieved 11% efficiency, and in 1958, the Vanguard satellite employed the first practical photovoltaic generator producing a modest one watt. In the 1960s, the space program continued to demand improved photovoltaic power generation technology. Scientists needed to get as much electrical power as possible from photovoltaic collectors, and cost was of secondary importance . Without this tremendous development effort, photovoltaic power would be of little use today.POWER OUTPUT AND EFFICIENCY RATINGSThe figures given for power output and efficiency of photovoltaic cells, modules, and systems can be misleading. It is important to understand what these figures mean and how they relate to the power available from installed photovoltaic generating systems.Power RatingsPhotovoltaic power generation systems are rated in peak kilowatts (kWp). This is the amount of electrical power that a new, clean system is expected to deliver when the sun is directly overhead on a clear day. We can safely assume that the actual output will never quite reach this value. System output will be compromised by the angle of the sun, atmospheric conditions, dust on the collectors, and deterioration of the components. When comparing photovoltaic systems to conventional power generation systems, one should bear in mind that the PV systems are only productive during the daytime. Therefore, a 100 kW photovoltaic system can produce only a fraction of the daily output of a conventional 100 kW generator.Efficiency RatingsThe efficiency of a photovoltaic system is the percentage of sunlight energy converted to electrical energy. The efficiency figures most often reported are laboratory results using small cells. A small cell has a lower internal resistance and will yield a higher efficiency than the larger cells used in practical applications. Additionally, photovoltaic modules are made up of numerous cells connected in series to deliver a usable voltage. Due to the internal resistance of each cell, the total resistance increases and the efficiency drops to about 70% of the single-cell value. Efficiency is higher at lower temperatures. Temperatures used in laboratory measurements may be lower than those in a practical installation.CONVERTING SUNLIGHT TO ELECTRICITYA typical photovoltaic cell consists of semiconductor material (usually silicon) having a p-n junction as shown in Figure 1. Sunlight striking the cell raises the energy level of electrons and frees them from their atomic shells. The electric field at the p-n junction drives the electrons into the n region while positive charges are driven to the p region. A metal grid on the surface of the cell collects the electrons while a metal back-plate collects the positive charges.Figure 1.How solar cells workThin Film TechnologyThin-film solar cells are manufactured by applying thin layers of semiconductor materials to a solid backing material. The composition of a typical thin-film cell is shown in Figure 2. Sunlight entering the intrinsic layer generates free electrons. The p-type and n-type layers create an electric field across the intrinsic layer. The electric field drives the free electrons into the n-type layer while positive charges collect in the p-type layer. The total thickness of the p-type, intrinsic, and n-type layers is about one micron. Although less efficient than single- and poly-crystal silicon, thin-film solar cells offer greater promise for large-scale power generation because of ease of mass-production and lower materials cost. Thin-film is also suitable for building-integrated systems because the semiconductor films may be applied to building materials such as glass, roofing, and siding.Figure 2 Typical thin-film amorphous silicon constructionsUsing thin films instead of silicon wafers greatly reduces the amount of semiconductor material required for each cell and therefore lowers the cost of producing photovoltaic cells. Gallium arsenide (GaAs), copper indium diselenide (CuInSe2), cadmium telluride (CdTe) and titanium dioxide (TiO2) are materials that have been used for thin film PV cells. Titanium dioxide thin films have been recently developed and are interesting because the material is transparent and can be used for windows.Tin Oxide Tin oxide is a conductive material that is transparent when in a thin layer. Tin oxide is used in place of a metallic grid for the top layer of thin film photovoltaic sheets.Amorphous Silicon (a-Si) Amorphous (uncrystallized) silicon is the most popular thin-film technology. It is prone to degradation and produces cell efficiencies of 5-7%. Double- and triple-junction designs raise efficiency to 8-10%. The extra layers capture different wavelengths of light. The top cell captures blue light, the middle cell captures green light, and the bottom cell captures red light. Variations include amorphous silicon carbide (a-SiC), amorphous silicon germanium (a-SiGe), microcrystalline silicon (mc-Si), and amorphous silicon-nitride (a-SiN).Cadmium Telluride (CdTe) and Cadmium Sulphide (CdS) Photovoltaic cells using these materials are under development by BP Solar and Solar Cells Inc .Poly-crystalline Silicon Poly-crystalline silicon offers an efficiency improvement over amorphous silicon while still using only a small amount of material.Copper Indium Diselenide and Copper Indium Gallium Diselenide These materials are currently being investigated, and have not been used commercially for photovoltaics.Concentrating CollectorsBy using a lens or mirror to concentrate the suns rays on a small area, it is possible to reduce the amount of photovoltaic material required. A second advantage is that greater cell efficiency can be achieved at higher light concentrations. To accommodate the higher currents in the photocells, a larger metallic grid is used. For example, in a system with a 22X concentration ratio, the grid covers about 20% of the surface of the solar cell. To prevent this from blocking 20% of the sunlight, a prism is used to redirect sunlight onto the photovoltaic material, as shown in Figure 3. A second problem is the higher temperatures of a concentrating system. The cells may be cooled with a heat sink or the heat can be used to heat water.Figure 3.Prism cover for high-current solar cell Only direct sunlight, not scattered by clouds or haze, can be concentrated. Therefore, the concentrating collectors are less effective in locations that are frequently cloudy or hazy, such as coastal areas.CONCLUSIONPhotovoltaic efficiency and manufacturing costs have not reached the point that photovoltaic power generation can replace conventional coal-, gas-, and nuclear-powered generating facilities. For peak load use (no battery storage), the cost of photovoltaic power is around two to four times as much as conventional power. (Cost comparisons between photovoltaic power and conventionally generated power are difficult due to wide variations in utility power cost, sunlight availability, and numerous other variables.)REFERENCES1 “The History of PV,” /pvhistory.html, November 15, 1998.2 Mark Hammonds, “Getting Power from the Sun, Solar Power,” Chemistry and Industry, no. 6, p. 219, March 16, 1998.3 Energy Conversion: Development of solar cells Britannica Online.:180/cgi-bin/g?DocF=macro/5002/13/245.html, October 21, 1998.4 Kenneth Zweibel and Paul Hersch, Basic Photovoltaic Principles and Methods, New York: Van Nosstrand Reinhold Company, Inc., 1984.5 “Volume 3: The World PV Market to 2010,” Photovoltaics in 2010, Luxembourge: Office for Official Publications of the European Communities, 1996.6 “Taking Off of New Photovoltaic Energy Revolution,” Japan 21st, May 1996.中文译文：太阳能光伏发电摘要这份报告是对光伏发电技术的概述。该报告的目的是为读者提供对光伏发电和光伏发电技术如何在实际中应用的一般性理解。有一个简短的早期研究和讨论关于光伏电池如何将太阳光转换为电能的描述。该报告涵盖了集电环，平板集热器，薄膜技术，建筑一体化系统。对光伏电池类型的讨论包括单晶，多晶和薄膜材料。该报告涵盖在提高电池效率的进步，降低制造成本，并寻找光伏技术的经济应用方法。随着市场趋势和预测的讨论，包括了各大厂商和组织。结论是，光伏发电仍然比一般传统系统成本高昂。然而，在常规电力成本中的大变化，还有其他因素，如分销成本，使用光伏发电在经济领域的创建情况。光伏发电是用于远程应用，例如通信，家庭和发展中国家的村庄，抽水，露营，划船等。如电力公司发电设施和住宅屋顶安装的电网连接的应用程序构成了光伏使用较小但更迅速扩大的部分。此外，由于技术进步和成本差距缩小，更多的应用以更快的速度正在变得经济可行。引 言这份报告是盖勒格林利夫在1998年10月19号请求建议的结果。比尔卢克和汤姆佩尼克于1998年10月30日年回应她的建议，继续早前光伏发电研究的要求。该建议获得通过，并于一九九八年十一月三十介绍，这是对光伏发电的最终报告之后继续进行研究的结果。光伏发电技术科学家们已知的光伏效应超过150年。光伏发电并没有考虑到的现实，直到太空计划的到来。早期卫星所需要的电力来源，任何解决方案都是昂贵的。为了这一目标，太阳能电池的发展导致其在其他应用方面的最终使用。光伏发电的发现与开发光伏效应自1939年已经被了解，但直到20世纪50年代，美国研究人员在开发航天器产生的电力的途径上，电池的效率保持在约1，基本上获得了一张空白支票。贝尔实验室很快达到11的效率，并在1958年，先锋卫星采用的第一个实用的太阳能光伏发电产生了适度的1瓦特。在20世纪60年代，空间计划继续要求改善光伏发电技术。科学家需要得到来自太阳能集热器尽可能多的电力，而成本是次要的。如果没有这种巨大的发展努力，光伏发电在今天将没有多大用处。输出功率和额定效率对功率输出和光伏电池，组件效率给出的数字，系统可能会产生误导。重要的是要理解这些数字意味着什么，以及它们如何涉及到权力来自安装光伏发电系统提供。额定功率光伏发电系统的电压被定为峰值千瓦(kWp)。这是一个新的，干净的系统，预计在一个晴朗的日子阳光直射传送的电力量。我们可以安全地假设，实际产量将从未完全达到此值。系统输出将受到损害的太阳，大气条件，在收藏家的尘土，组件的恶化角度。在比较传统的光伏系统，发电系统，每个人都应该牢记，光伏系统只在白天工作效率。因此，一个100千瓦的太阳能光伏系统只能产生常规的100千瓦发电机日产量的一小部分。额定效率一个光伏系统的效率是太阳光转换为电能的能量百分比。最常见的效率数据，是利用小细胞化验结果。小细胞具有较低的内阻和会比在实际应用中使用的大型电池更高的效率。此外，光伏组件是由串联连接到一个可用的电压提供大量的细胞。由于每个细胞内部的阻力，总电阻增大，效率下降约70单细胞值。在较低温度下效率是较高的。在实验室用于测量温度可能比实际安装在一个低。转换阳光为电力一个典型的太阳能电池由半导体材料（通常是硅）有一个PN结，如图1所示。阳光打在细胞提高了电子的能量水平，并释放他们从他们的原子炮弹。在PN结电场驱动到N区，而正电荷的电子被驱赶到P区域。一对细胞表面的金属网格，而收集的电子金属背板收集正电。图1 太阳能电池如何工作薄膜技术薄膜太阳能电池的制造采用的半导体材料薄层以坚实的支撑材料。一个典型的薄膜电池组成如图2所示。阳光进入本质层产生自由电子。 P型和N型层创建一个跨层内电场。电场驱动到n型层的正电荷，而在P型层收集自由电子。该P型，内在的，和N型层，总厚度约一微米。虽然效率不高于单，多晶硅，薄膜太阳能电池为大规模生产发电提供更大允诺，因为容易大批量生产而且材料成本较低。薄膜也是建筑一体化系统的需求，因为半导体薄膜可应用于如玻璃，屋顶和墙板等建筑材料。图2 典型的薄膜非晶硅结构使用薄膜代替硅晶片，大大降低了为每个电池需要的半导体材料的数量，因此降低了生产光伏电池的成本。砷化镓（GaAs），铜铟硒(CuInSe2)，碲化镉（CdTe）和二氧化钛（TiO2）是已为薄膜太阳能电池使用的材料。二氧化钛薄膜最近已开发并有趣，因为材料是透明的，可用于窗户使用。锡氧化物锡氧化物是一种透明导电材料，当薄薄的一层。锡氧化物是用在地方的金属网格，薄膜光伏板顶层。非晶硅（a-