一种简捷的定日镜跟踪角度计算方法

针对目前各种定日镜跟踪角度计算方法非常复杂的问题,提出一种基于镜场分布坐标的简捷定日镜跟踪角度的计算方法。采用该方法可方便地确定定日镜场中,任意定日镜随太阳运动时,定日镜镜面法线的高度角和方位角。     

智能算法在聚光镜场调度中的应用研究

以系统获得最佳效率为目的,结合定日镜的反射率、余弦效率和大气透射率等因素,建立聚光镜场调度的数学模型,并将该调度模型转换为0-1背包问题进行描述。针对该问题,采用贪婪算法并将此算法与微粒群算法及遗传算法相结合进行求解,分别得到各时刻系统最佳时,需投入运行的定日镜数量和分布。圆形聚光镜场的算例表明了上述算法的有效性与混合遗传算法的优越性。进一步提出分时段优化的调度策略,可降低聚光镜场的运行成本、提高调度策略的可行性。     

塔式太阳能吸热器表面热流密度预测及优化

以塔式太阳能聚光集热系统为研究对象,耦合蒙特卡洛光线追踪法和卷积法,通过综合考虑定日镜阴影和遮挡因子以及反射光束对热流密度的影响,建立一种精度高、计算量小的吸热器表面热流密度分布预测数学模型,获得考虑光线遮挡、余弦损失、溢出损失及大气衰减等因素时单定日镜及全镜场下的光迹追踪路线及热流密度分布规律。并根据镜场光学效率与镜面所处的位置关系提出一种镜场布局优化方式。优化后12:00时镜场的光学效率从43.5%提高到45.6%,日平均光学效率提高约2%,太阳热流密度分布更加均匀。     

塔式太阳能热发电镜场中余弦效率仿真研究

参考eSolar塔式发电站中的矩形定日镜场,通过参数设计得到密集的轴对称交错排列布置方案;建立了余弦效率的数学模型,对一天中不同时刻的太阳入射角变化趋势进行了仿真,得出位于接收塔南北区域余弦效率状况;对矩形定日镜场的余弦效率分布做了进一步研究。仿真结果验证了太阳入射角的变化趋势,并得出塔的高度对余弦效率的影响。     

小尺寸稀疏镜场能流密度分布模拟研究

基于接收面的光斑等效法,通过MATLAB软件模拟,提出了一种优化接收器表面能流密度分布计算时间的方法,分析单台定日镜和定日镜场的光斑能流密度分布规律。通过研究光斑边缘的能流密度与光斑中心能流密度的比值来分析小尺寸定日镜形成光斑的均匀性。结果表明：提出的计算方法不需要直接算出接收面网格点所有能流密度,对比蒙特卡洛法可缩短68.47%的计算时间;上午随着太阳从东升起,光斑能量主要集中在接收面的中偏右区域;下午随着太阳向西落下,光斑能量主要集中在接收面中偏左区域;采用小尺寸定日镜得到比大型定日镜更加均匀的光斑,在夏至日正午12点时,能流密度均匀性比值可以达到0.238。     

塔式太阳能电站定日镜场优化调度的光功率控制研究

针对定日镜场优化调度的光功率控制问题,鉴于目前调度数学模型不准确、算法运行效率低、速度慢等缺点,改进并优化设计调度模型和调度算法,通过考虑镜场的能耗因素,提高模型的精度和准确性;设计一种混合式遗传算法,采用惩罚项建立适应度函数,引入自适应搜索空间提高算法效率和运行速度。仿真结果验证了该调度模型和算法的准确性和快速性。     

塔式电站定日镜场布置范围的理论分析

采用MALAB编程,计算了余弦效率、大气透过效率以及吸热器开口平面上的截断效率,并将这三项效率的乘积定义为地面利用效率用于限制定日镜场的布置范围,进而分析了一些参数对定日镜场布置范围的影响。分析结果表明,地面利用效率可有效限定定日镜场的布置范围。与接收塔光学高度和吸热器开口的倾斜角度相比,吸热器的开口尺寸和定日镜的整体误差大小在很大程度上限定了定日镜场的布置范围。要增大电站容量,必须增大吸热器开口尺寸。而提高定日镜的整体性能不但可提高定日镜场的光学效率,也可有效扩大定日镜场的布置范围,增大电站容量。     

基于自适应引力搜索算法的定日镜场优化布置

针对塔式太阳能热发电电站中定日镜场优化布置问题,提出一种基于自适应引力搜索算法的定日镜场优化布置方法。以Campo布置规则为基础建立比目标定日镜场大1.5倍的密集型初始镜场,将定日镜所在环的半径作为输入变量并将年均效率作为镜场优化布置的评价标准。通过在引力搜索算法中引入动态调整因子α,可提高算法在高维搜索问题方面的求解能力。最后以塞维利亚Gemasolar电站的定日镜场为例进行优化布置,证明使用自适应引力搜索算法优化后的定日镜场具有更高的年均效率。     

塔式太阳能热发电镜场定日镜清洗装置设计

设计了一种应用于塔式太阳能热发电镜场的定日镜清洗装置。该定日镜清洗装置具备自动循迹、根据镜面自动调整清洗面角度、自动进行清洗水流控制的功能,并采用无线通信技术实现清洗装置与镜场控制系统间的信息交互,保证清洗完毕的定日镜立即恢复为正常运营状态,尽量减少镜场能量损失。通过实际测试,该清洗系统能够有效地实现预定的控制功能和清洗功能,其清洗装置通过一次清洗可将镜面清洁度从0.85提高到0.95。     

浅析一种用于塔式太阳能热发电站的定日镜全自动清洗车

在塔式太阳能热发电站中,定日镜的表面清洁度与其聚光集热效率直接相关,合理的清洗策略和高效的清洗设备有助于提升定日镜镜场的平均清洁度,提高其聚光集热效率,进而提升整个太阳能热发电站的发电效率。介绍了一种定日镜全自动清洗车,其基于导航系统和镜场整体控制来完成定日镜镜场的自动清洗工作。     

A new method for the design of the heliostat field layout for solar tower power plant

A new method for the design of the heliostat field layout for solar tower power plant is proposed. In the new method, the heliostat boundary is constrained by the receiver geometrical aperture and the efficiency factor which is the product of the annual cosine efficiency and the annual atmospheric transmission efficiency of heliostat. With the new method, the annual interception efficiency does not need to be calculated when places the heliostats, therefore the total time of design and optimization is saved significantly. Based on the new method, a new code for heliostat field layout design (HFLD) has been developed and a new heliostat field layout for the PS10 plant at the PS10 location has been designed by using the new code. Compared with current PS10 layout, the new designed heliostats have the same optical efficiency but with a faster response speed. In addition, to evaluate the feasibility of crops growth on the field land under heliostats, a new calculation method for the annual sunshine duration on the land surface is proposed as well.     

Site selection for hillside central receiver solar thermal plants

In this article, a new tool is introduced for the purpose of locating sites in hillside terrain for central receiver solar thermal plants. Provided elevation data at a sufficient resolution, the tool is capable of evaluating the efficiency of a heliostat field at any site location. The tool also locates suitable sites based on efficiency and average annual normal insolation. The field efficiency, or ratio of radiation incident to the receiver to direct normal solar radiation, is maximized as a result of factors including projection losses and interference between heliostats, known respectively as cosine efficiency, shading, and blocking. By iteratively defining the receiver location and evaluating the corresponding site efficiency by sampling elevation data points from within the defined heliostat field boundary, efficiency can be mapped as a function of the receiver location. The case studies presented illustrate the use of the tool for two field configurations, both with ground-level receivers and hillside heliostat layouts. While both configurations provide acceptable efficiencies, results from case studies show that optimal sites for ground-level receivers are ones in which the receiver is at a higher elevation than the heliostat field. This result is intuitive from the perspective of minimizing cosine losses but is nevertheless a novel configuration.     

A new code for the design and analysis of the heliostat field layout for power tower system

A new code for the design and analysis of the heliostat field layout for power tower system is developed. In the new code, a new method for the heliostat field layout is proposed based on the edge ray principle of nonimaging optics. The heliostat field boundary is constrained by the tower height, the receiver tilt angle and size and the heliostat efficiency factor which is the product of the annual cosine efficiency and the annual atmospheric transmission efficiency. With the new method, the heliostat can be placed with a higher efficiency and a faster response speed of the design and optimization can be obtained. A new module for the analysis of the aspherical heliostat is created in the new code. A new toroidal heliostat field is designed and analyzed by using the new code. Compared with the spherical heliostat, the solar image radius of the field is reduced by about 30% by using the toroidal heliostat if the mirror shape and the tracking are ideal. In addition, to maximize the utilization of land, suitable crops can be considered to be planted under heliostats. To evaluate the feasibility of the crop growth, a method for calculating the annual distribution of sunshine duration on the land surface is developed as well.     

A numerical approach to the flux density integral for reflected sunlight

A computer model of the central receiver system must evaluate the flux density on the receiver due to sunlight reflected by the heliostats in the collector field. Several approaches are available but each has its limitations. The Monte-Carlo approach represents all of the heliostat behavior but is relatively slow in terms of CPU time and is not suitable for optimization purposes. FLASH is an analytically exact approach for flat polygonal heliostats but is slow and not applicable to dished heliostats or aureole effects. Cone optics programs evaluate the flux density by a direct numerical integration of the double integral, but this method is very slow if accuracy is required. HCOEF is a two dimensional Hermite polynomial method which is relatively fast and can be extended to include canting, focusing, solar limb, and guidance error effects. However, the polynomial approximation breaks down for near heliostats, small guidance errors, and aureole effects. The new image generators based on KGEN overcome this limitation, but running times compare to FLASH and are 3 or 4 slower than HCOEF.The new approach proposed in this study assumes isotropic gaussian guidance errors. Hence, the flux density integral reduces to several iterated single integrals which can be precalculated and stored in a table for interpolation as needed. The LBL solar telescope data are fed into a convolution integral which represents the guidance errors. Aureole effects can be switched on or off at this point. A vector of convoluted solar data is input to another integration which gives the table of normalized flux contributions. The tabular values depend on the position of the flux point with respect to an edge of the heliostat as seen in the image plane. The image map of the heliostat is linear unless ripples or irregularities occur; hence, effects due to canting and dishing can be included by a ray trace of the heliostat vertices.The use of tabular interpolation is not as fast as expected because of the time required to calculate the distance between the flux point and the image of the vertices. The accuracy of this method is limited by interpolation errors, and better results can be obtained with the same CPU time if more core is used for a larger table. It is possible to eliminate the table by introducing a Romberg type of integrator which bisects the interval until sufficient accuracy is achieved; however, this approach is inefficient unless the images are relatively small compared to the receiver.The convolution process in KGEN is fast and can be used to calculate moments for HCOEF and coefficients for FLASH which utilize the LBL data.     

Efficiency assessment for a small heliostat solar concentration plant

In this paper, a small non‐imaging focusing heliostat is presented, and an analytical model for assessing its performance is described. The main novelty of the system lies in the tracking mechanism and the mirror mount, which are based on off‐the‐shelf components and allow a good trade‐off between accuracy and costs. The concentrator mirrors are moved by this two‐axis tracking machinery to reflect the sun's rays onto a fixed target, the dimensions of which can be varied to suit the user's needs. A prototype plant to be located in central Italy was designed and simulated with a ray‐tracing algorithm, and it comprises 90 heliostats for a total reflective area of 7.5 m². The reflected solar rays are tracked taking the mechanical positioning errors of the tracking system into account. The total flux of radiation energy hitting the target was determined, and intensity distribution maps were drawn. Simulations showed that the system's optical efficiency can exceed 90% in summer, despite the tracking errors, mainly because of the smaller distance between the heliostats and the receiver. The solar concentration ratio over a receiver of 250 mm in diameter reached 80 suns with a very good uniformity. Over a 400‐mm receiver, the concentrated radiation was less uniform, and the solar concentration ratio reached 50 suns, with a higher optical efficiency and collected solar radiation. The present concentration ratio is still suitable for many applications ranging from the electric power production, industrial process heat, and solar cooling. Copyright © 2014 John Wiley & Sons, Ltd.     

An analytic function for the flux density due to sunlight reflected from a heliostat

This paper presents an analytical model for the flux density due to a focused heliostat over the receiver plane of a tower solar plant. The main assumptions are: spherical and continuous surface of the mirror, linear conformal transformation in the complex plane equivalent to the reflection mapping between an on-axis aligned heliostat and the objective located on the receiver at the slant range necessary to produce the minimum circle of confusion, circular Gaussian distribution of the effective sunshape and the concentration function constant on the receiver or the image plane. Under the hypotheses presented earlier an exact convolution is obtained. The result, an analytic flux density function, relatively simple and very flexible, is confronted with experimental measurements taken from four heliostat prototypes of second-generation placed at the Central Receiver Test Facility (CRTF), Albuquerque, New Mexico, and compared indirectly with the predictions of the Helios model for the same heliostats. The model is an essential tool in the problem of the determination of collector field parameters by optimization methods.     

Modelling of the receiver transient flux distribution due to cloud passages on a solar tower thermal power plant

As more and more solar tower thermal power plants are being operated, built or planned, effort is put both on the development and research to bring costs down and increase the plant efficiency. In those plants, the central receiver is one of the key components, accounting for a large investment share. Receivers have to sustain strong thermal stresses caused by irradiation transients, mainly due to cloud passages. To avoid premature failures, increase the receiver cyclic life, and allow longer daily operation periods, an anticipation of the most likely or the worst situations is required. First the calculation of the receiver incident flux distribution is performed, second the cloud and cloud passage characteristics are identified for a given location, third the most likely case is simulated by covering and uncovering the heliostat field, then a worst case configuration is presented, and finally a strategy for the start-up/shut-down of the heliostats is proposed. The value of terms such as the heat flux peak, the maximal flux gradient, the fastest flux transient and total power transients are needed to choose the control strategies regarding heliostat orientation and the receiver operation, as well as the elimination of some bad plant layouts during the design phase.     

Multi-tower solar array

The multi-tower solar array (MTSA) is a new concept of a point focussing two-axis tracking concentrating solar power plant. The MTSA consists of several tower-mounted receivers which stand so close to each other that the heliostat fields of the towers partly overlap. Therefore, in some sectors of the heliostat field neighbouring heliostats are alternately directed to the receivers on different towers. This allows the MTSA to use radiation which would usually remain unused by a conventional solar tower system due to mutual blocking of the heliostats and permits an MTSA to obtain a high annual ground area efficiency (efficiency of usage of ground area). In the sectors close to the towers, where the shading effect predominates, all heliostats are directed to the nearest tower. In sectors further away from the towers, the heliostats are alternately directed to the receivers on two, three, or four different towers. To reduce dilution of the radiation from the field, the number of towers the heliostats in a specific region can be directed to may be limited to two, which causes almost no losses in the annual ground area efficiency.     

Design and evaluation of esolar’s heliostat fields

Central receiver concentrating solar power plants offer significant performance advantages over line-focus systems. However, the high cost of the heliostat field remains a barrier to the widespread adoption of such plants. eSolar has approached the problem of heliostat field cost by emphasizing small size, low cost, easy installation, and high-volume manufacturing of heliostat field components.During 2008 and 2009, eSolar designed, constructed, and began operation of its demonstration facility, which comprises two towers each with heliostat subfields to the north and the south. These heliostat fields are composed of large numbers of small heliostats, creating an arrangement unlike other central receiver plants. This paper describes the design, construction, startup, and testing of these heliostat fields, showing that they perform well and represent a viable alternative to more traditional fields of large heliostats.     

An artificial vision-based control system for automatic heliostat positioning offset correction in a central receiver solar power plant

This paper presents the development of a simplified and automatic heliostat positioning offset correction control system using artificial vision techniques and common CCD devices. The heliostats of a solar power plant reflect solar radiation onto a receiver (in this case, a volumetric receiver) placed at the top of a tower in order to provide a desired energy flux distribution correlated with the coolant flow (in this case air mass flow) through the receiver, usually in an open loop control configuration. There exist error sources that increase the complexity of the control system, some of which are systematic ones, mainly due to tolerances, wrong mirror facets alignment (optical errors), errors due to the approximations made when calculating the solar position, etc., that produce errors (offsets) in the heliostat orientation (aiming point). The approximation adopted in this paper is based on the use of a B/W CCD camera to correct these deviations in an automatic way imitating the same procedure followed by the operators. The obtained images are used to estimate the distance between the sunbeam centroid projected by the heliostats and a target placed on the tower, this distance thus is used for low accuracy offset correction purposes. Basic threshold-based image processing techniques are used for automatic correction.