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.     

The thermal efficiency improvement of a steam Rankine cycle by innovative design of a hybrid cooling tower and a solar chimney concept

In the present work, a dry cooling tower and a solar chimney design are recombined in order to increase the thermal efficiency of a steam Rankine cycle. The rejected heat from the condenser into the dry cooling tower supplemented by the solar radiation gained through its transparent cover are the sources of wind energy generation that is captured by a wind turbine which is located at the beginning of the chimney. In this research a case study for a 250 MW steam power plant of Shahid Rajaee in Iran has been performed. A CFD finite volume code is developed to find the generated wind velocity at the turbine entrance for a 250 m dry cooling tower base diameter and a chimney height of 200 m. Calculations have been iterated for different ambient temperatures and solar irradiances, representing temperature gradient within day length. A range of 360 kW to 3 MW power is obtained for the change in the chimney diameter from 10 to 50 m. The results show a maximum of 0.37 percent increase in the thermal efficiency of a 250 MW fossil fuel power plant unit; which proves this design to be a significant improvement in efficiency of thermal power plants, by capturing the heat that is dissipated from dry cooling towers.     

太阳能烟囱与垂直轴风机耦合发电可行性分析

通过分析太阳能烟囱热气流发电和垂直轴风力机发电的技术及特点,提出了太阳能热气流烟囱与垂直轴风力机耦合发电的方法。对风力机—太阳能热气流烟囱互补发电系统的可行性进行了分析。互补发电的功率输出持续、稳定,具有大规模并网的良好条件,是实现太阳能与风能综合利用的有效途径。     

A complete design data and performance parameter evaluation of a pilot scale solar updraft tower

Abstract

Renewable energy sources are the best alternative for giving solution to the energy shortage and CO₂ emission problems. Solar updraft tower is a relative novel technology for electricity production from solar energy. It consists of three main components; a solar air collector with absorber plate, central chimney, and a turbine. The objective of this work is to present complete design parameters of individual components of a small and less expensive prototype solar updraft tower. The main contents of this study are; solar radiation calculations, chimney design, solar wind turbine design calculations, heat loss and pressure loss estimations for collector. The pilot solar chimney power plant considered in this work consists of an air collector diameter of 3.5-m, the chimney diameter and height are 0.6 and 6?m, respectively. Theoretically the maximum velocity of air is achieved at chimney base is 1.9?m/s. The overall efficiency of the plant is estimated as 0.0019%.     

Numerical simulation of cooling performance of wind tower (Baud-Geer) in hot and arid region

In the present study, an attempt is made to study the cooling performance of a wind tower in a hot and dry region, Yazd, in Iran. For the relevant experiments and numerical studies, at first, the temperature and wind velocity inside and outside of the wind tower measured. Based on four-day measurements during last summer, a computer program was designed with language C⁺⁺ to solve the equations. Also in the study the effects of parameters including wind tower height, variety of the materials used in the wind tower walls, the amount of vaporized water, the temperature of input and output air, the wind velocity and the relative humidity were investigated.Furthermore, to develop, a natural flow of air, for days without blowing a wind the role of solar chimney was considered.Finally, to evaluate the method of integral view and take information about streamlines of airflow in wind tower (Baud-Geer), velocity, pressure, humidity, temperature and density profile of fluid, Fluent software is applied to analyze the air flow in the wind tower in differential view for three-dimensional and steady state conditions with water spraying at the top of wind tower.The results indicate that the evaporative cooling is very effective in a hot and dry region. The temperature decreases considerably, if the wind towers are equipped with the water vaporization system. This causes the air becomes heavier and a natural motion of air through downside of wind tower to be produced.     

LiDAR measurements for an onshore wind farm: Wake variability for different incoming wind speeds and atmospheric stability regimes

Wind measurements were performed with the UTD mobile LiDAR station for an onshore wind farm located in Texas with the aim of characterizing evolution of wind‐turbine wakes for different hub‐height wind speeds and regimes of the static atmospheric stability. The wind velocity field was measured by means of a scanning Doppler wind LiDAR, while atmospheric boundary layer and turbine parameters were monitored through a met‐tower and SCADA, respectively. The wake measurements are clustered and their ensemble statistics retrieved as functions of the hub‐height wind speed and the atmospheric stability regime, which is characterized either with the Bulk Richardson number or wind turbulence intensity at hub height. The cluster analysis of the LiDAR measurements has singled out that the turbine thrust coefficient is the main parameter driving the variability of the velocity deficit in the near wake. In contrast, atmospheric stability has negligible influence on the near‐wake velocity field, while it affects noticeably the far‐wake evolution and recovery. A secondary effect on wake‐recovery rate is observed as a function of the rotor thrust coefficient. For higher thrust coefficients, the enhanced wake‐generated turbulence fosters wake recovery. A semi‐empirical model is formulated to predict the maximum wake velocity deficit as a function of the downstream distance using the rotor thrust coefficient and the incoming turbulence intensity at hub height as input. The cluster analysis of the LiDAR measurements and the ensemble statistics calculated through the Barnes scheme have enabled to generate a valuable dataset for development and assessment of wind farm models.     

不同海况及伺服系统作用下10 MW单桩式风力机地震易损性研究

为探究不同海况及伺服系统下单桩式近海风力机的地震易损性,以DTU 10 MW风力机为研究对象,建立风浪相关的地震-湍流风-波浪多物理场模型,研究其在变速变桨伺服系统下的动力特性,基于增量动力分析方法评估其地震易损性。结果表明：变速变桨伺服系统可有效缓解风力机高风速下无地震作用时的塔顶振动;当风轮在大推力下,较小的波浪载荷一定程度上可降低风力机塔顶振动及塔底弯矩;随地震动强度增加,风力机各临界损伤状态失效概率逐渐增加;风力机地震易损性主要由地震动强度决定,波浪载荷与湍流风载荷对风力机地震易损性影响较小。     

Simulation studies of the position of the auxiliary heater in thermosyphon solar water heating systems

This paper investigates the effect of the physical location of the auxiliary source of energy in thermosyphon solar water heaters and shows that the performance of the system can be optimised with respect to the geometry of the system components. The investigation has been based on a domestic thermosyphon solar water heating system, which was simulated using the TRNSYS programme. The annual solar fraction of the system, at the weather and socioeconomic conditions of Cyprus, is, at best, approximately 77% with an in-tank auxiliary heater configuration and 86% with an external auxiliary heater. It is demonstrated that the arrangement with the external auxiliary unit has a higher collector efficiency and results in a higher annual solar fraction. In the case of in-tank auxiliary, the system performance increases with the height of the auxiliary position from the bottom of the storage tank; with the auxiliary at the bottom of the storage tank the annual solar fraction is approximately 59%, compared to 77% when the auxiliary is located at the top of the tank. The system performance also depends on the height of the collector return from the bottom of the tank.     

水平轴风力机塔架的频率和振型特性实验研究

为了研究风力机塔架的振动特性,文章利用动态信号采集分析系统,对水平轴风力机塔架进行了实验模态分析和运行模态分析测试,得到了塔架静止与振动两种工况下的固有频率与模态振型,分析了塔架的振动特性。通过对风力机振动信号的频谱分析发现,风速小于10 m/s时,只能激励起塔架挥舞方向与摆振方向的二阶模态;通过对风力机塔架的模态分析发现,风力机发生振动,塔架固有频率与模态振型发生小幅度改变;随着风速和振动烈度的增大,塔架模态参数的变化幅度随之增大。该研究可以为风力机塔架优化设计提供借鉴。     

Simulation of a novel hybrid solar photovoltaic/wind system to maintain the cell surface temperature and to generate electricity

A hybrid solar photovoltaic/wind system is proposed and investigated theoretically. The hybrid system is based on attaching a converging inclined duct beneath the photovoltaic (PV) panels and directed upward after the end of the panels. A wind turbine is attached at the exit of the converging duct. The converging duct will capture wind currents that at its inlet and enhances these current by buoyancy effect created by the rejected heat from the panels. The mixed convection air flow is used in cooling the PV panels and in generating electricity by driving the wind turbine at the duct exit. A mathematical model is proposed to describe the system hydrodynamic and thermal behavior. In addition to the mixed convection case, the pure free convection case, when there is no wind speed, has been tested. The design of the wind duct capturing system is not included in this study, which should be carefully manufactured to eliminate the reversed flow. The simulation results show that the integration of both systems not only enhances the performance of PV cell due to the effective cooling but also generates more electric power from the inserted turbine. At low wind speeds, it is found that the ducting system helps more in cooling the panels rather than driving the wind turbine. At these low wind speeds, the buoyancy effect may have a significant effect. However, at high wind speeds, the ducting system acts in both cooling the panels and driving the turbine, and at these high speeds, the buoyancy effect is insignificant.     

Solar gas turbine systems: Design, cost and perspectives

The combination of high solar shares with high conversion efficiencies is one of the major advantages of solar gas turbine systems compared to other solar-fossil hybrid power plants. Pressurized air receivers are used in solar tower plants to heat the compressed air in the gas turbine to temperatures up to 1000 °C. Therefore solar shares in the design case of 40% up to 90% can be realized and annual solar shares up to 30% can be achieved in base load. Using modern gas turbine systems in recuperation or combined cycle mode leads to conversion efficiencies of the solar heat from around 40% up to more than 50%. This is an important step towards cost reduction of solar thermal power. Together with the advantages of hybrid power plants—variable solar share, fully dispatchable power, 24 h operation without storage—solar gas turbine systems are expected to have a high potential for market introduction in the mid term view.In this paper the design and performance assessment of several prototype plants in the power levels of 1 MW, 5 MW and 15 MW are presented. Advanced software tools are used for design optimization and performance prediction of the solar tower gas turbine power plants. Detailed cost assumptions for the solarized gas turbine, the solar tower plant and further equipment as well as for operation and maintenance are presented. Intensive performance and economic analysis of the prototype plants for different locations and capacity factors are shown. The cost reduction potential through automation and remote operation is revealed.     

不同海况下近海超大型风力机动力学响应及结构损伤分析

以超大型DTU 10 MW单桩式近海风力机为研究对象,通过p-y曲线和非线性弹簧建立桩-土耦合模型,选取Kaimal风谱模型建立湍流风场,基于P-M谱定义不同频率波浪分布,并利用辐射/绕射理论计算波浪载荷,采用有限元方法对不同海况下单桩式风力机进行动力学响应、疲劳及屈曲分析。结果表明：不同海况波浪载荷作用下塔顶位移响应及等效应力峰值远小于风及风浪联合作用,其中风浪联合作用下风力机塔顶位移响应及等效应力略小于风载荷;波浪载荷对风载荷引起的单桩式风力机动力学响应具有一定抑制作用,此外相较于波浪载荷,风载荷为控制载荷;风载荷与风浪联合作用下风力机等效应力峰值位于塔顶与机舱连接处,波浪载荷风力机等效应力峰值位于支撑结构与桩基连接处;仅以风载荷预估风力机塔架疲劳寿命将导致预估不足;随着波浪载荷的增大,风力机失稳风险加大,波浪载荷不可忽略;不同海况下,风浪联合作用局部屈曲区域位于塔架中下端,在风力机抗风浪设计时,应重点关注此处;变桨效应可大幅降低风力机动力学响应、疲劳损伤及发生屈曲的风险。     

Simulation model of wind turbine 3p torque oscillations due to wind shear and tower shadow

To determine the control structures and possible power quality issues, the dynamic torque generated by the blades of a wind turbine must be represented. This paper presents an analytical formulation of the generated aerodynamic torque of a three-bladed wind turbine including the effects of wind shear and tower shadow. The comprehensive model includes turbine-specific parameters such as radius, height, and tower dimensions, as well as the site-specific parameter, the wind shear exponent. The model proves the existence of a 3p pulsation due to wind shear and explains why it cannot be easily identified in field measurements. The proportionality constant between the torque and the wind speed is determined allowing direct aerodynamic torque calculation from an equivalent wind speed. It is shown that the tower shadow effect is more dominant than the wind shear effect in determining the dynamic torque, although there is a small dc reduction in the torque oscillation due to wind shear. The model is suitable for real-time wind turbine simulation or other time domain simulation of wind turbines in power systems.     

An application of a combined wind and solar energy system in Izmir

In this work, a combined system which is produced electrical energy from both solar radiation via solar cells and wind energy by using wind turbine was studied. For wind energy, measurements of wind velocities at 12 m height were taken. Then, these values were calculated for 42 m by using Hellmann equation. After that, wind energy converted to the electrical energy. However, value of solar radiation from solar cells was taken at the optimum slope angle of collector which provided higher energy production for each 1 h during this application. Thus, obtained data from each system were used together for finding total energy. For this study, measurements, which would be used in calculation of wind energy and solar energy were taken for four years between 1995 and 1998 in Izmir. As a result, energy of the combined system could support each other when one of them produces energy insufficiently.     

A hybrid TEG/wind system using concentrated solar energy and chimney effect

This paper investigates a novel hybrid system combining thermal electrical generators (TEGs) and a wind turbine. The mathematical model of the system is derived and solved to investigate the performance of the proposed system. In the proposed system, solar energy is converted to heat by an absorber plate. Some portion of this heat is converted to electricity using TEG, while another portion of the heat is used to heat up air flowing in an inclined duct placed underneath the absorber plate. Heating the air inside the system enhances the current speed because of the effect of buoyancy. A wind turbine is placed inside the duct parallel to air flow before it exits to the atmosphere. The wind current is accelerated before passing through the turbine by using venture effect. The TEGs are exposed to the concentrated solar radiation. This can be obtained using a compound parabolic concentrator. The proposed configuration has multiadvantages: (1) the wind is used to drive a wind turbine; (2) air cools the rear surfaces of TEGs to increase the temperature difference between the opposite surfaces, thus generates more electrical power; and (3) it uses buoyancy effect to increase the wind stream speed, thus enhancing the power generated from turbine. It is found that the solar concentration ratio is the most important factor contributing to enhancing the TEG efficiency. The buoyancy effect leads to turbine power boost at high wind speeds more than at low wind speeds.     

Design and thermodynamic modeling of a renewable energy based plant for hydrogen production and compression

In the examined paper, a solar and wind energy supported integrated cycle is designed to produce clean power and hydrogen with the basis of a sustainable and environmentally benign. The modeled study mainly comprises of four subsystems; a solar collector cycle which operates with Therminol VP1 working fluid, an organic Rankine cycle which runs with R744 fluid, a wind turbine as well as hydrogen generation and compression unit. The main target of this work is to investigate a thermodynamic evaluation of the integrated system based on the 1st and 2 nd laws of thermodynamics. Energetic and exergetic efficiencies, hydrogen and electricity generation rates, and irreversibility for the planned cycle and subsystems are investigated according to different parameters, for example, solar radiation flux, reference temperature, and wind speed. The obtained results demonstration that the whole energy and exergy performances of the modeled plant are 0.21 and 0.16. Additionally, the hydrogen generation rate is found as 0.001457 kg/s, and the highest irreversibility rate is shown in the heat exchanger subcomponents. Also, the net power production rate found to be 195.9 kW and 326.5 kW, respectively, with organic Rankine cycle and wind turbine. The final consequences obtained from this work show that the examined plant is an environmentally friendly option, which in terms of the system's performance and viable, for electrical power and hydrogen production using renewable energy sources.     

电厂直接空冷系统热风回流的数值模拟

阐述了热风回流的产生机理及热回流率的概念,并对汽轮机空冷系统周围不同环境风场进行了数值模拟.通过对计算结果的分析,找出了空冷系统的不利风向,给出了热回流率随风速的变化规律,并提出了减少热风回流的措施:适当增加空冷平台上部四周风墙高度,或加快空冷平台边缘风机的转速.     

Test and evaluation of a solar powered gas turbine system

This paper describes the test and the results of a first prototype solar powered gas turbine system, installed during 2002 in the CESA-1 tower facility at Plataforma Solar de Almería (PSA) in Spain. The main goals of the project were to develop a solar receiver cluster able to provide pressurized air of 1000 °C and solve the problems arising from the coupling of the receivers with a conventional gas turbine to demonstrate the operability of the system. The test set-up consists of the heliostat field of the CESA-1 facility providing the concentrated solar power, a pressurized solar receiver cluster of three modules of 400 kWth each which convert the solar power into heat, and a modified helicopter engine (OST3) with a generator coupled to the grid. The first test phase at PSA started in December 2002 with the goal to reach a temperature level of 800 °C at the combustor air inlet by the integration of solar energy. This objective was achieved by the end of this test phase in March 2003, and the system could be operated at 230 kWe power to grid without major problems. In the second test phase from June 2003 to August 2003 the temperature level was increased to almost 1000 °C. The paper describes the system configuration, the component efficiencies and the operation experiences of the first 100 h of solar operation of this very successful first test of a solar operated Brayton gas turbine system.     

Wind effect on the performance of a solar organic Rankine cycle

The effects of wind, ambient temperature and solar radiation on the simultaneous productions of mechanical work and heat by a solar Rankine cycle are studied. The on site experimental study uses the pentafluorobutane R365mfc as working fluid in a system consisting of a small-scale single glazed flat plate collector, a micro turbine, a condenser and a pump. The theoretical study focuses on the prediction of the optimum operating temperature of the collector according to the solar radiation, the temperature of air and the wind speed. Then, the total production of mechanical and thermal energy is calculated during a sunny day for which various wind speeds are simulated. The results highlight the effect of wind on the corresponding production and they also establish the value of the recommended evaporating temperature according to weather conditions.     

建筑体对下游垂直轴风力机气动性能影响研究

为有效利用城市风能,提高风力机运行效率,需对建筑体下游风力机位置分布开展研究。采用计算流体力学方法分析不同建筑体结构下游各位置处风速及风力机气动性能。结果表明：建筑体对自由来流的阻塞、加速与偏转作用可有效提高下游部分位置处风速,提升风力机气动性能;圆形建筑体对下游流场影响较小,各位置处平均风速接近自由来流;相比之下,三角形与四边形建筑体下游风速波动较为剧烈,平均风速较高,风力机转矩较圆形建筑体下游风力机的有较大提升;对于相同外廓建筑体,立式矩形较大的受风面积可扩大其背风低压区范围,有效提高下游流场风速,较卧式矩形建筑体具有更好的聚风效果。