Analysis of chimney height for solar chimney power plant

Current in solar chimney power plant that drives turbine generators to generate electricity is driven by buoyancy resulting from higher temperature than the surroundings at different heights. In this paper, the maximum chimney height for convection avoiding negative buoyancy at the latter chimney and the optimal chimney height for maximum power output are presented and analyzed using a theoretical model validated with the measurements of the only one prototype in Manzanares. The results based on the Manzanares prototype show that as standard lapse rate of atmospheric temperature is used, the maximum power output of 102.2 kW is obtained for the optimal chimney height of 615 m, which is lower than the maximum chimney height with a power output of 92.3 kW. Sensitivity analyses are also performed to examine the influence of various lapse rates of atmospheric temperatures and collector radii on maximum height of chimney. The results show that maximum height gradually increases with the lapse rate increasing and go to infinity at a value of around 0.0098 K m^?1, and that the maximum height for convection and optimal height for maximum power output increase with larger collector radius.     

关于太阳能建筑气流电站的设想

一前言 最早的"烟囱"形太阳能气流电站是由上百吨钢板建造的,其缺陷是大烟囱耗费材料多,在室外日晒雨淋薄钢板容易生锈,使用寿命短.为解决大烟囱经久耐用的问题,则需要投入更多的材料和人力,耗费巨大,成为气流电站推广使用的拦路虎.     

Numerical simulations of solar chimney power plant with radiation model

A three-dimensional numerical approach incorporating the radiation, solar load, and turbine models proposed in this paper was first verified by the experimental data of the Spanish prototype. It then was used to investigate the effects of solar radiation, turbine pressure drop, and ambient temperature on system performance in detail. Simulation results reveal that the radiation model is essential in preventing the overestimation of energy absorbed by the solar chimney power plant (SCPP). The predictions of the maximum turbine pressure drop with the radiation model are more consistent with the experimental data than those neglecting the radiation heat transfer inside the collector. In addition, the variation of ambient temperature has little impact on air temperature rise despite its evident effect on air velocity. The power output of the SCPP within the common diurnal temperature range was also found to be insensitive to ambient temperature.     

Thermodynamic study of a simplified model of the solar chimney power plant

A simplified model of solar chimney power plant (SCPP) consists of a heating air collector, turbine and chimney. Thermodynamic interpretation of processes occurring in these SCPP components is based on the derived energy and exergy balances. The examples of the energy and exergy flow diagrams show how the SCPP input of 36.81 MW energy of solar radiation, corresponding to 32.41 MW input of radiation exergy, is distributed between the SCPP components. Responsive trends to the varying input parameters are studied. Additionally, the concept of mechanical exergy (ezergy) of air is applied and it allowed for quantitative determination of the effect attributed to the terrestrial gravity field on the component processes of the SCPP.     

荒漠中的发电站——太阳能烟囱发电站

一前言 太阳能烟囱发电技术是通过集热棚吸取太阳热能使棚内空气温度升高,根据烟囱的原理,在烟囱内将形成强大的气流,利用这股气流形成的风力驱动风机,带动发电机发电。太阳能烟囱发电系统主要由透光的采光大棚、烟囱及风力涡轮机构成,如图1所示。     

太阳能热气流发电系统的性能分析

基于太阳能热气流发电系统的原理,分析了系统的发电功率和能量转换效率.数学模型的建立考虑了太阳辐射和系统尺寸参数对系统最大输出功率和最大能量转换效率的影响.以西班牙试验电站系统为例进行了数值模拟,数值计算结果与理论分析具有良好的一致性.系统最大输出功率不仅是烟囱高度的函数,同时也与系统其他尺寸和环境参数有关;在太阳辐射强度为1000W/m2条件下,当烟囱高度为300m时,系统的最大能量转换效率达到1%,当烟囱高度为1000m时,系统的最大能量转换效率可超过3%.     

Critical evaluation of solar chimney power plant performance

This paper evaluates the influence of a recently developed convective heat transfer equation, more accurate turbine inlet loss coefficient, quality collector roof glass and various types of soil on the performance of a large scale solar chimney power plant. Results indicate that the new heat transfer equation reduces plant power output considerably. The effect of a more accurate turbine inlet loss coefficient is insignificant, while utilizing better quality glass enhances plant power production. Models employing Limestone and Sandstone soil produce virtually similar results to a Granite-based model. The plant collector height is found to differ from previously obtained optimal values.     

太阳能热气流发电流道优化分析

以西班牙太阳能热气流电站为原型进行数值模拟,得出了太阳能烟囱内的速度场、压力场和温度场分布;研究了集热棚坡度、分流板高度和弧度等因素对系统发电性能及涡轮机位置的影响。研究结果表明:集热棚坡度增加时,烟囱的抽吸作用增强,空气流速增加,有利于提高太阳能热气流发电的输出功率;当集热棚坡度约为0.5°时,其作用最为明显,对于提高系统发电性能最为有利;增加分流板有利于气流发电站的优化,当分流板高度略微高于集热棚高度时,优化效果较好;分流板弧度越小,越有利于系统的优化;集热棚坡度对涡轮机位置有影响,改变分流板的几何因素对涡轮机位置没有影响。     

Analysis of a solar chimney power plant in the Arabian Gulf region

A simplified thermodynamics analytical model for steady airflow inside a solar chimney is performed. A simplified Bernoulli equation combined with fluid statics and ideal gas equation was implemented and solved using EES solver to predict the performance of the solar chimney power plant. The analytical model matched the experimental data and numerical study available in the literature. The developed analytical model was used to evaluate the effect of geometric parameters on the solar plant power generation. The analysis showed that chimney height and turbine pressure head are the most important physical variables for the solar chimney design. The study showed that second-law efficiency has non-monotonic relation with turbine pressure head. The model shows that second-law efficiency and power harvested increase with the increase of chimney height and/or diameter. The developed model is used to analyze the feasibility of solar chimney power plants for the UAE climate which possesses typical characteristics of the Gulf climate. The solar characteristics of the UAE are shown along with characteristic meteorological data. A solar chimney power plant with a chimney height of 500 m and a collector roof diameter of 1000 m would produce at least 8 MW of power. The amount of power produced during the summer would be higher where the demand in the Gulf area is the highest.     

Performance of solar chimney power plant in Qinghai-Tibet Plateau

A solar chimney power plant (SCPP) is proposed to be built in Qinghai-Tibet Plateau where there is abundant solar radiation, high direct solar radiation low atmospheric temperature, large diurnal temperature range, and lots of salt lakes working as heat storage system, which can help to improve the power output of SCPP. The plant is expected to power local railway traffic lines and act as a solar power base to supply power for national development. The performance of the SCPP that will be built in Qinghai-Tibet Plateau is analyzed and power potential estimated by developing a simple mathematical model. It is found that SCPP if built in the plateau can produce twice more power than an SCPP built on the same latitude of other regions. The yearly power potential for SCPP in Qinghai-Tibet Plateau is estimated to be 86.8 million TJ. When 10–20% of the plateau land is used for the SCPP, the yearly power output may reach 8.7 million TJ to 17.4 million TJ, accounting for 10.7–21.3% of China's energy consumption in 2008 which stood at 81.6 million TJ. It is found that the SCPP in the plateau can support local and national development together with other renewable energy resources such as hydroelectric power and wind power.     

Economic analysis of power generation from floating solar chimney power plant

Solar chimney thermal power technology that has a long life span is a promising large-scale solar power generating technology. This paper performs economic analysis of power generation from floating solar chimney power plant (FSCPP) by analyzing cash flows during the whole service period of a 100 MW plant. Cash flows are influenced by many factors including investment, operation and maintenance cost, life span, payback period, inflation rate, minimum attractive rate of return, non-returnable subsidy rate, interest rate of loans, sale price of electricity, income tax rate and whether additional revenue generated by carbon credits is included or not. Financial incentives and additional revenue generated by carbon credits can accelerate the development of the FSCPP. Sensitivity analysis to examine the effects of the factors on cash flows of a 100 MW FSCPP is performed in detail. The results show that the minimum price for obtaining minimum attractive rate of return (MARR) of 8% reaches 0.83 yuan (kWh)^?1 under financial incentives including loans at a low interest rate of 2% and free income tax. Comparisons of economics of the FSCPP and reinforced concrete solar chimney power plant or solar photovoltaic plant are also performed by analyzing their cash flows. It is concluded that FSCPP is in reality more economical than reinforced concrete solar chimney power plant (RCSCPP) or solar photovoltaic plant (SPVP) with the same power capacity.     

Partial geometric similarity for solar chimney power plant modeling

A solar chimney power plant derives its mechanical power from the kinetic power of the hot air which rises through a tall chimney, the air being heated by solar energy through a transparent roof surrounding the chimney. In our previous studies, the achievement of complete dynamic similarity between a prototype and its models imposed the use of different solar heat fluxes between them. It is difficult to conduct an experiment by using dissimilar heat fluxes with different physical models. Therefore, this study aimed to maintain dynamic similarity for a prototype and its models while using the same solar heat flux. The study showed that, to achieve the same-heat-flux condition, the roof radius between the prototype and its scaled models must be dissimilar, while all other remaining dimensions of the models are still similar to those of the prototype. In other words, the models are ‘partially’ geometrically similar to the prototype. The functional relationship that provides the condition for this partial similarity is proposed and its validity is proved by scaling the primitive numerical solutions of the flow. Engineering interpretations of the similarity variables are also presented.     

Feasibility study of a solar chimney power plant in Jordan

A solar chimney power plant system is theoretically designed for future erection in Jordan. Analytical analysis of the system is simulated by mathematical software. The actual values of solar irradiation in Jordan are used in the simulation to predict the power output of the solar chimney power plant. The output results of the maximum (inlet) values of velocity, pressure, and mass flow rate of air versus the chimney height variation are obtained. Furthermore, the electrical power output and the efficiency of chimney versus chimney height variation were determined. For a solar collector diameter of 40 m and a chimney diameter of 3.5 m, the maximum power output (85 kW) was obtained for a chimney height of 210 m.     

A single dimensionless variable for solar chimney power plant modeling

The solar chimney power plant is a relatively new technology for generating electricity from solar energy. In this paper dimensional analysis is used together with engineering intuition to combine eight primitive variables into only one dimensionless variable that establishes a dynamic similarity between a prototype and its scaled models. Three physical configurations of the plant were numerically tested for similarity: fully geometrically similar, partially geometrically similar, and dissimilar types. The values of the proposed dimensionless variable for all these cases were found to be nominally equal to unity. The value for the physical plant actually built and tested previously was also evaluated and found to be about the same as that of the numerical simulations, suggesting the validity of the proposition. The physical meaning of this dimensionless (similarity) variable is also interpreted; and the connection between the Richardson number and this new variable was found. It was found also that, for a fixed solar heat flux, different-sized models that are fully or partially geometrically similar share an equal excess temperature across the roof outlet.     

Performance analysis of the power conversion unit of a solar chimney power plant

The power conversion unit (PCU) of a large solar chimney power plant consists of one or several turbogenerators, power electronics, a grid interface and the flow passage from collector exit to chimney inlet. The main goals of this paper are to analyze the performance of the PCU and its interaction with the plant as well as to compare three configurations from an efficiency and energy yield point of view.First, a reference plant is defined and the plant performance data taken from simulations with a model found in the literature are analyzed, and the matching of the turbine(s) to the characteristic of the plant is discussed. It was found that a well designed turbine can be run at high efficiency over the entire operating range, as the plant performance data can be fitted using the ellipse law of Stodola.Loss models for all components of the power conversion unit are then defined, and the impact of the various losses on the overall performance is assessed. Three configurations of the PCU are compared, i.e. the single vertical axis, the multiple vertical axis and the multiple horizontal axis turbine configuration. It is found that the single vertical axis turbine has a slight advantage with regards to efficiency and energy yield because certain loss mechanisms are not present. But its output torque is tremendous, making its feasibility questionable. It is shown that with designing the flow passage in an appropriate manner the aerodynamic losses can be kept low. The assumption made by many other researchers that the total-to-total efficiency of the PCU is 80 % has been confirmed with the present model. Further, it has been shown that the PCU efficiency deteriorates significantly with increasing diffuser area ratio but improves only slightly with reducing the diffuser area ratio below unity.     

Analysis of some available heat transfer coefficients applicable to solar chimney power plant collectors

A solar chimney power plant consists of a translucent collector which heats the air near the ground and guides it into the base of a chimney at its centre. The buoyant air rises in the chimney and electricity is generated through one or more turbines in or near the base of the chimney. Various studies about solar chimney power plant performance have been published. Different calculation approaches with a variety of considerations have been applied to calculate chimney power plant performance. In particular, two comprehensive studies are relevant, namely those of (Bernardes, M.A.d. S., Voß, A., Weinrebe, G., 2003. Thermal and technical analyses of solar chimneys. Solar Energy 75, 511-524; Pretorius, J.P., Kröger, D.G., 2006b. Solar chimney power plant performance. Transactions of the ASME 128, 302-311). The paper compares the methods used to calculate the heat fluxes in the collector, and their effects on solar chimney performance. Reasons for the discrepancies between the predictions of the two models are given. In general the Pretorius model produces higher heat transfer coefficients and higher heat rate fluxes for both the roof and for the ground surfaces. The two approaches lead to very similar air temperature rises in the collector and thus, similar produced power.     

太阳能烟囱发电系统的性能研究

采用通用商业CFD软件ANSYS Fluent 13.0对太阳能烟囱发电系统进行数值模拟,获得太阳能烟囱发电系统的空气流速分布。结果表明:在其他条件不变的情况下,集热棚周边高度对系统的发电功率几乎没有影响;太阳能烟囱发电系统的烟囱直径存在最佳值,使太阳能烟囱发电系统的输出功率最大;集热棚斜度也存在最佳值,使系统输出发电功率最大。     

烟囱性状对太阳能烟囱发电系统效率的影响

采用计算流体动力学（CFD）方法分析了烟囱对太阳能烟囱发电系统效率的影响。通过对烟囱高度、烟囱形状、烟囱内表面粗糙度和温度对系统的影响分析表明：在其它条件不变的情况下,烟囱高度和直径对系统效率影响最为显著,其次是形状,最后是烟囱内表面粗糙度和温度。     

对太阳能气流电站抽气筒的研究

一太阳能气流电站简介最早的太阳能气流电站是由前联邦德国的史兰赫博士于20世纪80年代初期设计建造的。它的主体是电站中央一个高200m、直径10.3m的大"烟囱","烟囱"用波纹薄钢板卷制而成,重约200吨;围绕     

Analytical and numerical investigation of the solar chimney power plant systems

There is a surge in the use of the solar chimney power plant in the recent years which accomplishes the task of converting solar energy into kinetic energy. As the existing models are insufficient to accurately describe the mechanism, a more comprehensive model is advanced in this paper to evaluate the performance of a solar chimney power plant system, in which the effects of various parameters on the relative static pressure, driving force, power output and efficiency have been further investigated. Using the solar chimney prototype in Manzanares, Spain, as a practical example, the numerical studies are performed to explore the geometric modifications on the system performance, which show reasonable agreement with the analytical model. Copyright © 2005 John Wiley & Sons, Ltd.