Numerical simulation of the solar chimney power plant systems coupled with turbine

Numerical simulations have been carried out on the solar chimney power plant systems coupled with turbine. The whole system has been divided into three regions: the collector, the chimney and the turbine, and the mathematical models of heat transfer and flow have been set up for these regions. Using the Spanish prototype as a practical example, numerical simulation results for the prototype with a 3-blade turbine show that the maximum power output of the system is a little higher than 50 kW. Furthermore, the effect of the turbine rotational speed on the chimney outlet parameters has been analyzed which shows the validity of the numerical method advanced by the author. Thereafter, design and simulation of a MW-graded solar chimney power plant system with a 5-blade turbine have been presented, and the numerical simulation results show that the power output and turbine efficiency are 10 MW and 50%, respectively, which presents a reference to the design of large-scale solar chimney power plant systems.     

Chimney shape numerical study for solar chimney power generating systems

A large number of researchers have paid great attention to solar chimney (SC) power generating technology, but only a few have studied the chimney configuration. Taking a 10 MW SC system as an example, the physical and mathematical models illustrating the fluid flow, heat transfer and output power features of the system are established. Based on constraints such as equal chimney bottom section area or equal chimney surface area, the impact of several sizes of three different chimney configurations upon the chimney outlet air temperature and velocity, system output power and efficiency is analyzed and the influence of the height‐to‐diameter ratio (H/D) of the cylindrical chimney on system performance is studied as well. After a comprehensive analysis of system output power and efficiency, it is proved by the numerical simulation that the cylindrical chimney would be the best choice among the three basic configurations, whose optimum H/D value ranges from 6 to 8. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of operational control strategies applicable to solar chimney power plants

Numerical simulations are carried out to study the performance of two schemes of power output control applicable to solar chimney power plants. Either the volume flow or the turbine pressure drop is used as independent control variable. Values found in the literature for the optimum ratio of turbine pressure drop to pressure potential vary between 2/3 and 0.97. It is shown that the optimum ratio is not constant during the whole day and it is dependent of the heat transfer coefficients applied to the collector. This study is a contribution towards understanding solar chimney power plant performance and control and may be useful in the design of solar chimney turbines.     

太阳能烟囱发电装置的CFD模拟

用Fluent软件对太阳能烟囱发电装置内的气流进行了数值模拟，获得了太阳能烟囱发电装置内气流流速、温度等分布，并将温度场模拟计算值和试验检测值进行了比较。结果表明：气流在集热棚中从四周向中部汇流是一个加速的过程；从地面到烟囱，随着高度的增加温度呈递减分布。温度分布模拟与试验检测结果的规律基本相似。但由于进行了稳态假设，也存在一定差别。数值模拟结果以集热棚中心呈对称分布。然而，由于集热棚南部接收的太阳辐射大于北部，在试验检测中南边的温度明显高于北边的温度，温度的峰值向南边偏移，呈不对称分布。     

Modeling and numerical simulation of solar chimney power plants

The solar chimney power plant is a simple solar thermal power plant that is capable of converting solar energy into thermal energy in the solar collector. In the second stage, the generated thermal energy is converted into kinetic energy in the chimney and ultimately into electric energy using a combination of a wind turbine and a generator. The purpose of this study is to conduct a more detailed numerical analysis of a solar chimney power plant. A mathematical model based on the Navier-Stokes, continuity and energy equations was developed to describe the solar chimney power plant mechanism in detail. Two different numerical simulations were performed for the geometry of the prototype in Manzanares, Spain. First, the governing equations were solved numerically using an iterative technique. Then, the numerical simulation was performed using the CFD software FLUENT that can simulate a two-dimensional axisymmetric model of a solar chimney power plant with the standard k-epsilon turbulence model. Both the predictions were compared with the available experimental data to assess the validity of the model. The temperature, velocity and pressure distributions in the solar collector are illustrated for three different solar radiations. Reasonably good quantitative agreement was obtained between the experimental data of the Manzanares prototype and both the numerical results.     

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.     

Performance evaluation of solar chimney power plants in Iran

The solar chimney power plant is a simple solar thermal power plant that is capable of converting solar energy into thermal energy in the solar collector. In the second stage, the generated thermal energy is converted into kinetic energy in the chimney and ultimately into electric energy using a combination of a wind turbine and a generator. The purpose of this study is to evaluate the performance of solar chimney power plants in some parts of Iran theoretically and to estimate the quantity of the produced electric energy. A mathematical model based on the energy balance was developed to estimate the power output of solar chimneys as well as to examine the effect of various ambient conditions and structural dimensions on the power generation. The solar chimney power plant with 350 m chimney height and 1000 m collector diameter is capable of producing monthly average 1-2 MW electric power over a year.     

Analysis of output power smoothing method of the solar chimney power generating system

Severe fluctuation of the output power is a common problem in the generating systems of various renewable energies. The concept of output power fluctuation factor of renewable energy power generating systems was put forward in this paper. Aiming to decrease the fluctuation factor of output power in solar chimney power generating systems (SC), a novel hybrid energy storage system made of water, and sandstone was employed to replace the traditional sandstone energy storage system. The mathematical models of fluid flow, heat transfer and power generating features of SC were established and the influences of material, depth, areas and location of the energy storage layer upon output power were analyzed. The simulation results indicated that adopting the hybrid energy storage of water and sandstone can effectively decrease the fluctuation factor of SC output power and hence smooth the SC output power. In addition, according to the largest daily power generating capability or the smallest peak fluctuation factor, the corresponding optimum depth of the water energy storage layer would be 5 cm or 20 cm, respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

烟囱阴影对风力增压太阳能烟囱电站性能的影响:基于西班牙原型电站规模的数值案例研究

为研究烟囱阴影效应,本文采用太阳射线追踪算法对基于西班牙原型电站规模的太阳能烟囱电站(SCPP)和风力增压型太阳能烟囱电站(WSSCPP)进行了三维数值模拟.烟囱阴影区面积随着太阳光线入射角的增加而增加,本文研究了入射角从0°变化到30°下系统的温度和速度分布;还研究了在几个SCPP综合系统中的烟囱阴影效应.结果表明:...     

Modeling of the optimum tilt of a solar chimney for maximum air flow

The aim of this work is to develop a mathematical model to determine the tilt that maximizes natural air flow inside a solar chimney using daily solar irradiance data on a horizontal plane at a site. The model starts by calculating the hourly solar irradiation components (direct, diffuse, ground-reflected) absorbed by the solar chimney of varying tilt and height for a given time (day of the year, hour) and place (latitude). In doing so it computes the transmittance and absorbance of the glazing for the various solar irradiation components and for various tilts. The model predicts the temperature and velocity of the air inside the chimney as well as the temperatures of the glazing and the black painted absorber. Comparisons of the model predictions with CFD calculations delineate the usefulness of the model. In addition, there is a good agreement between theoretical predictions and experiments performed with a 1 m long solar chimney at different tilt positions.     

Experimental investigation of solar tower with chimney effect installed in CRTEn,Tunisia

This paper studies the performance of a solar tower power plant (STPP) with chimney effect based on renewable energy proposed for electricity production. That's way, a solar tower prototype was constructed and tested in the Research and Technology Centre of Energy (CRTEn), Borj Cédria, northern Tunisia.The design involves heating air using solar energy and the chimney effect to raise the hot air up the chimney stack. The hot air velocity increases by the use of a convergent nozzle to reach a suitable velocity which can run the wind turbine. The kinetic energy of the hot air is then converted to electricity by the wind turbine.During this study, the influence of the climatic conditions of Borj Cédria site (insulation, ambient temperature) as well as the chimney height and the collector diameter on the amount of electricity production were investigated.The distribution and the evolution of the temperature at different positions of the prototype as well as the electrical energy produced were determined.The results reveal that when the temperatures reach 45 °C, the electric power reaches an average value of about 0.3 W/m² for a solar tower prototype with 8 m of diameter and 2 m of height chimney.     

Numerical analysis on an industrial-scaled solar updraft power plant system with ambient crosswind

Existing research indicated that the ambient crosswind (ACW) has very complex influences on the SUPPS both through the chimney outlet and collector inlet as demonstrated by numerical analysis from the Spanish prototype. But what influence exert ACW through chimney outlet and collector inlet independently on the overall performance of SUPPS is still unclear. In this research, two geometrical models are constructed for numerical simulation on industrial-scale SUPPS in the vicinity of 10 MW. In model 1, ACW acts on both chimney outlet and collector inlet; in model 2, ACW acts only on the chimney outlet. Fluid flow, heat transfer and power output performances of SUPPS are investigated and discussed. It is found that, the negative effect of ACW only occurs at the collector inlet, with cold ambient air into the collector resulting in changing of fluid distribution and deterioration of buoyant driving force, whereas the positive effect occurs at the chimney outlet, with strong ACW passing by the chimney outlet causing entrainment of buoyant airflow within the chimney outlet. To avoid deterioration and to improve the overall performance of SUPPS, effective measures can be taken to prevent ACW from entering the collector inlet and also to induce beneficial effects of high altitude strong ACW blowing across the chimney outlet.     

Counter-rotating turbines for solar chimney power plants

An efficiency model at design performance for counter-rotating turbines is developed and validated. Based on the efficiency equations, an off-design performance model for counter-rotating turbines is developed. Combined with a thermodynamic model for a solar chimney system and a solar radiation model, annual energy output of solar chimney systems is determined. Two counter-rotating turbines, one with inlet guide vanes, the other without, are compared to a single-runner system. The design and off-design performances are weighed against in three different solar chimney plant sizes. It is shown that the counter-rotating turbines without guide vanes have lower design efficiency and a higher off-design performance than a single-runner turbine. Based on the output torque versus power for various turbine layouts, advantageous operational conditions of counter-rotating turbines are demonstrated.     

Analysis and feasibility of implementing solar chimney power plants in the Mediterranean region

This paper analyzes the feasibility of solar chimney power plants as an environmentally acceptable energy source for small settlements and islands of countries in the Mediterranean region. For the purpose of these analyses, two characteristic geographic locations (Split and Dubrovnik) in Croatia were chosen and simplified model for calculation of produced electric power output is also developed. These locations possess typical characteristics of the Mediterranean climate. The solar characteristics of the chosen geographic locations are shown along with characteristic meteorological data. A solar chimney (SC) power plant with a chimney height of 550 m and a collector roof diameter of 1250 m would produce 2.8–6.2 MW of power. The average annual electric power production of this SC power plant would range between 4.9 and 8.9 GWh/year, but in reality from 5.0 to 6.0 GWh/year in average. An approximate costs analysis, which included a total investment estimate, was performed. The levelized electricity cost was also calculated. It is found that the price of produced electric energy by solar chimney power plant in Mediterranean region is considerably higher compared to the other power sources.     

A simplified analytical approach for evaluation of the optimal ratio of pressure drop across the turbine in solar chimney power plants

In this paper, a simplified analytical approach for evaluating the factor of turbine pressure drop in solar chimney power plants is presented. This characteristic factor (or pressure drop ratio in turbines, according to the total pressure drop in the chimney) is important because it is related to the output power. The determined factor (or ratio) values of the turbine pressure drop are found to be within a value range consistent with other studies. It was concluded that for solar chimney power plants, turbine pressure drop factors are in the range of 0.8–0.9. This simplified analytical approach is useful for preliminary analysis and fast evaluation of the potential of solar chimney power plants.     

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.     

Performance of a direct steam generation solar thermal power plant for electricity production as a function of the solar multiple

This paper describes the influence of the solar multiple on the annual performance of parabolic trough solar thermal power plants with direct steam generation (DSG). The reference system selected is a 50 MW_e DSG power plant, with thermal storage and auxiliary natural gas-fired boiler. It is considered that both systems are necessary for an optimum coupling to the electricity grid. Although thermal storage is an opening issue for DSG technology, it gives an additional degree of freedom for plant performance optimization. Fossil hybridization is also a key element if a reliable electricity production must be guaranteed for a defined time span. Once the yearly parameters of the solar power plant are calculated, the economic analysis is performed, assessing the effect of the solar multiple in the levelized cost of electricity, as well as in the annual natural gas consumption.     

Parametric study of a thermal trap solar energy collector

A parametric study of a thermal trap solar energy collector with the help of a modified Hottel-Whillier-Bliss equation, is presented. The developed analysis is used to optimize the typical parameters, namely the trap's thickness and the number of flowing channels. The variation of the rating parameters of a collector with typical quantities, such as the fin distance, mass flow rate and thickness of the absorber plate, is discussed in detail.     

Cost analysis of solar chimney power plants

Several cost models for large-scale solar chimney power plants are available in the literature. However, the results presented vary significantly, even in cases where the input parameters and the used models are supposedly very similar. The main objective of this paper is to clarify this matter by comparing previous cost models to a newly developed alternative model. Further, the impact of carbon credits on the levelised electricity cost is also investigated.A reference plant is introduced, with dimensions and financial parameters chosen specifically for the purpose of making the results of this analysis comparable to those of previous publications. Cost models are presented for the main components of a solar chimney power plant, i.e. the collector, the chimney and the power conversion unit. Results show that previous models may have underestimated the initial cost and levelised electricity cost of a large-scale solar chimney power plant. It is also shown that carbon credits significantly reduce the levelised electricity cost for such a plant.     

Optimum power from a solar thermal power plant using solar concentrators

In this paper, the optimum temperature of operation of a solar concentrator and thus the maximum power obtained from a solar thermal power plant has been calculated. Results are plotted graphically and discussed.