Preliminary design of surrounding heliostat fields

Recently, the author has shown elsewhere a simplified model that allows quick evaluations of the annual overall energy collected by a surrounding heliostat field. This model is the combination of an analytical flux density function produced by a heliostat, developed by the own author, and an optimized mirror density distribution developed by University of Houston for the Solar One Project. As main conclusion of this previous work, it was recognized that such pseudo-continuous simplified model should not substitute much more accurate discrete evaluations, which manage thousands of individual heliostat coordinates. Here in this work, the difficulty of generating a preliminary discrete layout of a large number of heliostats is addressed. The main novelty is the direct definition of thousands of heliostat coordinates through basically two parameters i.e. a simplified blocking factor and an additional security distance. Such procedure, which was formerly theoretically suggested by the author, is put into practice here, showing examples and commenting their problems and advantages. Getting a previous set of thousands of heliostat coordinates would be a major first step in the complex process of designing solar power tower (SPT).     

One-point fitting of the flux density produced by a heliostat

Accurate and simple models for the flux density reflected by an isolated heliostat should be one of the basic tools for the design and optimization of solar power tower systems. In this work, the ability and the accuracy of the Universidad de Zaragoza (UNIZAR) and the DLR (HFCAL) flux density models to fit actual energetic spots are checked against heliostat energetic images measured at Plataforma Solar de Almería (PSA). Both the fully analytic models are able to acceptably fit the spot with only one-point fitting, i.e., the measured maximum flux. As a practical validation of this one-point fitting, the intercept percentage of the measured images, i.e., the percentage of the energetic spot sent by the heliostat that gets the receiver surface, is compared with the intercept calculated through the UNIZAR and HFCAL models. As main conclusions, the UNIZAR and the HFCAL models could be quite appropriate tools for the design and optimization, provided the energetic images from the heliostats to be used in the collector field were previously analyzed. Also note that the HFCAL model is much simpler and slightly more accurate than the UNIZAR model.     

《塔式太阳能光热发电站设计标准》结构设计内容解析

  目的  《塔式太阳能光热发电站设计标准》GB 51307是塔式光热电站的综合性标准,标准对相关特种结构设计给出了原则性的规定。为使大家在应用《塔式太阳能光热发电站设计标准》进行相关结构设计时能够正确理解条文和条文说明,本文对该标准结构设计部分的相关规定进行了详细的解释和解析。  方法  结合标准规定从一般规定、抗震设计、地基与基础、吸热塔结构和熔盐泵支架等几个方面阐述了标准制定背景,介绍了国内外常见的吸热塔结构型式、熔盐泵基础型式、定日镜基础型式等,对结构控制指标、吸热塔阻尼比等特殊问题进行了分析和讨论。  结果  通过标准制定背景和特种结构型式的介绍,以及特殊问题的分析和讨论,对塔式太阳能电站中特种结构的设计、原则性规定有了更进一步的认识。  结论  为《塔式太阳能光热发电站设计标准》的工程应用奠定了基础,并给出了进一步研究的建议。     

An approximate model for sizing and costing a solar thermal collector-central receiver system

An approximate generalized theoretical model is presented for the geometry and energy transfer of a solar thermal collector-central receiver system. Equations permit sizing the receiver, tower, and heliostat field. Cost functions correlate data from Department of Energy studies. Based on a set of assumed conditions, simplified, optimized sizing equations yield the minimum capital cost. The costs of the tower and central receiver will change with plant and equipment cost indices, while heliostat costs are expected to diminish as annual production increases. The heliostat cost is the major cost component even at lowest projected unit cost; therefore optimization tends toward minimum heliostat area. The model permits order-of-magnitude cost estimates to be made very quickly, compared to detailed simulation.     

换热工质参数对熔盐蒸汽发生系统性能的影响研究

蒸汽发生系统(steam generation system,SGS)是塔式太阳能热发电站的重要组成部分。采用仿真模拟软件Thermoflex对塔式太阳能热发电站的熔盐SGS进行了建模,并基于实际工程数据验证了所搭建模型的准确性。以此为基础,仿真研究了熔盐SGS的换热工质参数(给水温度、主蒸汽温度、主蒸汽压力)对熔盐SGS性能的影响,其中,水侧温度和压力的变化对熔盐侧参数(熔盐流量、熔盐SGS出口的熔盐温度)和换热设备的换热功率均存在较大影响。研究得到的不同换热工质参数对熔盐SGS性能和整个塔式太阳能热发电站的影响规律可为熔盐SGS的设计提供理论依据。     

Design optimization of a solar tower power plant heliostat field by considering different heliostat shapes

The present study focuses on the optimization of solar tower power plant heliostat field by considering different heliostat shapes including rectangular, square, pentagon, hexagon, heptagon, octagon, and circular heliostat shapes. The optimization is carried out using an in-house developed code-based MATLAB program. The developed in-house code is validated first on a well-known PS10 Solar Thermal Power plant having rectangular heliostats shape and the resulting yearly unweighted heliostat field efficiency of about 64.43% could be obtained. The optimized PS10 heliostat field using different heliostat shapes showed that the circular and octagon heliostat shapes provide better efficiency with minimum land area. The yearly efficiency is increased from 69.65% for the rectangular heliostat shape to 70.96% and 71% for the octagon and circular shapes, respectively. In addition, the calculated field area (land area) is reduced for the case of circular and octagon heliostat shapes with a gain of about 11.10% and 10.93% (about 42.0436 × 10³ and 41.4036 × 10³ m²), respectively, in comparison with the PS10 field area.     

塔式太阳能热发电站圆月夜聚光实验研究

在塔式太阳能热发电系统中,吸热器采光面上的聚光能流密度分布的测量对优化整个系统的光热性能有着重要意义。本文提出一种基于月光聚光信息的塔式电站定日镜场聚光能流密度分布的间接测量方法。主要介绍2018年9月24日晚在延庆塔式电站开展的两种对月聚光实验：一种是通过塔上布置的照度计标定电荷耦合元件（Charge-coupled Device, CCD）相机拍摄的光斑图像,得到定日镜场聚光光斑的照度分布;另一种是使聚光光斑扫描过照度计,得到不同时刻的照度计数值,通过高斯拟合得到聚光光斑的照度分布。将聚光光斑的照度分布与月光测光站测得的月光法向直射照度对比,得到塔上聚光光斑的相对能流密度分布。实验结果表明,通过月光聚光实验,可以得到塔式电站的聚光光斑的相对能流密度分布（即聚光比分布）,为后续依据太阳和月亮之间的亮度分布关系,转换为日光聚光能流密度分布提供实验数据支持。     

熔盐塔式光热电站仿真机设计与开发

[目的]为了解决熔盐塔式光热电站建设和运维过程中,控制逻辑难以验证以及运行人员缺乏操作经验的问题.[方法]开发了一套用于塔式熔盐光热电站的仿真机.逻辑组态方面采用了虚拟DPU技术与软件化对象配置技术,采用了与实际电站完全相同的数值模型和设计参数.[结果]仿真试验结果表明该仿真机能够很好的实现电站生产过程中的工况模拟和仿...     

Optimized working temperatures of a solar central receiver

Recent developments in solar tower technology, aimed at the achievement of high temperatures (above 1100 K) for the operation of advanced power conversion units (gas turbine and combined cycle), require careful analysis of their optimal operating parameters. This study presents a method of optimization for design parameters, such as the receiver working temperature and the heliostat field density. This method aims at maximizing the overall efficiency of the three major subsystems that constitute the entire plant, namely, the heliostat field and the tower, the receiver and its accompanying secondary optics, and the power block. The results of this optimization process are shown and analyzed. The principal result demonstrates that the operating temperature has an optimal value and its further increase can lower the overall efficiency of the system.     

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.     

COMPARATIVE PERFORMANCES OF ‘TOWER-TOP'' AND ‘TOWER-REFLECTOR'' CENTRAL SOLAR RECEIVERS

The optics of various types of solar tower configurations and receivers are analyzed. The power values that are finally available for the process, for a given field and different optical arrangements at specified operating temperatures (above 1100 K), are compared. At these temperatures the use of secondary concentrators placed in front of the receivers is peremptorily justified from optical and energetical points of view. A model for calculating the efficiencies of central solar receivers with secondary concentrators is presented. This model permits the optimization of these secondary concentrators taking into account the different losses of real devices. The effect of heliostat field density and the performance of ‘tower-top' and ‘tower-reflector' solar plants are discussed and compared.     

基于复合控制的塔式太阳能跟踪控制装置设计

针对塔式太阳能热发电站中定日镜跟踪装置的跟踪精度不高、构建成本较大等问题,提出采用将遗传算法的选择机制与吸热塔能量变化的反馈机制相结合的方式对光热电站的太阳能跟踪控制系统进行改进.在光热电站的少数几台定日镜上配备光电检测元件,并以其控制角度为基准控制其他定日镜的角度调整.采用DSP(digital signal processing)为控制核心,完成了跟踪控制器的通讯框架及控制系统的硬件电路设计.实验表明,该方案在保证光热电站整体控制精度的基础上,减少了光电检测元件安装数量和电站构建成本,并保证了视日轨迹跟踪控制时的自动调整能力.     

Tracking and ray tracing equations for the target-aligned heliostat for solar tower power plants

The tracking and ray tracing equations for the target-aligned heliostat for solar tower power plants have been derived in this paper. Based on the equations, a new module for analysis of the target-aligned heliostat with an asymmetric surface has been developed and incorporated in the code HFLD. To validate the tracking and ray tracing equations, a target-aligned heliostat with a toroidal surface is designed and modeled. The image of the target-aligned heliostat is calculated by the modified code HFLD and compared with that calculated by the commercial software Zemax. It is shown that the calculated results coincide with each other very well. Therefore, the correctness of the tracking and ray tracing equations for the target-aligned heliostat is proved.     

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.     

考虑接收塔阴影的定日镜有效利用率计算

经几何光学分析,导出了考虑接收塔阴影影响的太阳能塔式热发电站的定日镜有效利用率计算公式,并通过算例比较了考虑与不考虑接收塔阴影影响的定日镜有效利用率计算结果,验证了这些计算公式的正确性和考虑接收塔阴影影响的合理性。     

An optimization tool to design the field of a solar power tower plant allowing heliostats of different sizes

The design of a solar power tower plant involves the optimization of the heliostat field layout. Fields are usually designed to have all heliostats of identical size. Although the use of a single heliostat size has been questioned in the literature, there are no tools to design fields with heliostats of several sizes at the same time. In this paper, the problem of optimizing the heliostat field layout of a system with heliostats of different sizes is addressed. We present an optimization tool to design solar plants allowing two heliostat sizes. The methodology is illustrated with a particular example considering different heliostat costs. Copyright © 2017 John Wiley & Sons, Ltd.     

塔式太阳能热发电系统镜场调度方法的研究

提出一种塔式太阳能热发电系统中定日镜调度的方法。根据太阳、定日镜和接收面的光学成像关系,考虑太阳位置、镜面反射率和能见度等因素给出了镜场光能转换效率的计算方法,同时结合定日镜场状态及热力系统所需光功率建立了镜场调度模型。该文将定日镜的调度转化为一个0-1背包问题,设计了一种混合遗传算法来对其求解。采用该调度方法可得到各时刻转换效率最高时所需调用的定日镜数量及其分布,并可调整定日镜瞄准接收靶上分布的目标点,使吸热器上能流分布均匀,降低峰值能流密度,避免过热故障。仿真算例结果表明了该方法的有效性。     

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.     

A concise overview of heliostat fields‐solar thermal collectors: Current state of art and future perspective

Heliostat field or solar tower collector is one of the most promising concentrated solar power technologies available in the market. Due to its high operating temperature, heliostat field collector can be implemented in a wide range of applications from solar power generation to industrial commodity production. There are several currently operating, under construction, and planned heliostat fields around the world. In this paper, a brief overview of the current state of the art, applications, assessment methods, future perspective, and methods of improvement are discussed.