A new design of nontracking seasonally adjusted plane mirror linear trough solar concentrator with a flat horizontal absorber

This paper presents an optical design based on a single-reflection criterion, and performance characteristics of an east-west aligned nontracking seasonally adjusted linear trough solar concentrator with a flat horizontal absorber, using plane mirror elements. The design procedure allows the use of any desired number of mirror elements to reflect solar energy onto the base absorber in one reflection. The angle of inclination of each mirror element with respect to the absorber surface, and the width of the mirror element, are determined so that a ray incident on the extreme upper edge of the mirror element at a specified angle to the normal to the concentrator aperture (acceptance half-angle), after reflection, strikes the extreme edge of the absorber on the opposite side of the mirror element. Other rays making angles less than the design acceptance half-angle are also reflected onto the base absorber in one reflection. Concentrator designs resulting from this approach appear to have the important characteristic of relatively smaller heights, and hence appear highly cost-effective in terms of the amount of material required for fabrication. Some numerical calculations have been carried out to illustrate the performance of concentrators for different acceptance half-angles. Results obtained are presented in graphic and tabular forms, and are discussed.     

Some geometrical design aspects of a linear fresnel reflector concentrator

A somewhat new approach to the design of solar concentrators of Fresnel reflector geometry is outlined. the constituent mirror elements of the concentrator surface are characterised by three parameters, shift, tilt and width. the evaluation of these parameters and the concentration characteristics are investigated on the basis of a simple ray optical model.     

Mirror rearrangement optimization for uniform flux distribution on the cavity receiver of solar parabolic dish concentrator system

The nonuniform and high‐gradient solar radiation flux on the absorber surface of solar dish concentrator/cavity receiver (SDCR) system will affect its operational reliability and service lifetime. Therefore, homogenization of the flux distribution is critical and important. In this paper, 2 mirror rearrangement strategies and its optimization method by combining a novel ray tracing method and the genetic algorithm are proposed to optimize the parabolic dish concentrator (PDC) so as to realize the uniform flux distribution on the absorber surface inside the cavity receiver of SDCR system. The mirror rearrangement strategy includes a mirror rotation strategy and mirror translation strategy, which rotate and translate (along the focal axis) each mirror unit of the PDC to achieve multipoint aiming, respectively. Firstly, a correlation model between the focus spot radius and mirror rearrangement parameters is derived as constraint model to optimize the PDC. Secondly, a novel method named motion accumulation ray‐tracing method is proposed to reduce the optical simulation time. The optical model by motion accumulation ray‐tracing method and optimization model of SDCR system are established in detailed, and then, an optimization program by combining a ray‐tracing code and genetic algorithm code in C++ is developed and verified. Finally, 3 typical cavity receivers, namely, cylindrical, conical, and spherical, are taken as examples to fully verify the effectiveness of these proposed methods. The results show that the optimized PDC by mirror rearrangement strategies can not only greatly improve the flux uniformity (ie, reduce the nonuniformity factor) and reduce the peak local concentration ratio of the absorber surface but also obtain excellent optical efficiency and direct useful energy ratio. A better optimization results when the PDC is optimized by mirror rotation strategy at aperture radius of 7.0 m, focal length of 6.00 m, and ring number of 6; the nonuniform factor of the cylindrical, conical, and spherical cavity receivers is greatly reduced from 0.63, 0.67, and 0.45 to 0.18, 0.17, and 0.26, respectively; the peak local concentration ratio is reduced from 1140.00, 1399.00, and 633.30 to 709.10, 794.00, and 505.90, respectively; and the optical efficiency of SDCR system is as high as 92.01%, 92.13%, and 92.71%, respectively. These results also show that the dish concentrator with same focal length can match different cavity receivers by mirror rearrangement and it can obtain excellent flux uniformity.     

Review on Development of Small Point-Focusing Solar Concentrators

The technology of small point-focusing concentrator of solar energy has been developing rapidly in recent years owing to its compact structure and high collecting efficiency. This report presents important developments of small point-focusing concentrator in the past decade. This kind of solar concentrator refers to the parabolic dish concentrator, the point-focusing Fresnel lens, and the Scheffler reflector. Technological advances of these concentrators and the related performances have been presented. There are three main mirror fabrication technologies for dish concentrator, which are high polishing metal, silver-glass mirror and vacuum-membrane. Polymethyl methacrylate is widely used as material in Fresnel lens. Many scholars have proposed new lens shape to improve the uniformity of focusing. The Scheffler reflector has a characteristic of fixed focus, but its design parameters are not perfect so current research focuses on the theoretical calculation of the mirror. In addition, typical applications of the small point-focusing concentrator in photovoltaic system, solar thermal system, solar chemical system, and day-lighting system are summarized. Upon listing the important publications in open literature, a category of main applications of such kind of solar collector is provided based on the working characteristics of the system.     

Optical simulation model for flat mirror concentrators

Different simulation models for solar concentrators were developed to obtain the irradiance distribution on the absorber. Usually these optical simulations were valid only for a particular concentrator. Other simulations adequate for different concentrator shapes are based on ray tracing algorithms requiring high computing resources. An optimized reverse ray tracing model for flat mirror concentrators that allows to reduce the noise and the computing time necessary for such simulations is described.     

二次反射多碟太阳能聚光器设计与性能分析

设计一种小规模的光线向下式焦点固定的多碟聚光集热系统,其特点是焦点固定,光线向下汇聚,吸热器开口向上,并提出该系统的追踪方式。通过对一次镜场和二次反射镜的分析和优化设计,使设计工况下吸热器入口的平均能流密度达到420 kW/m²,光学效率为87.4%,可为实现光线向下式焦点固定聚光系统的发展和优化提供技术方案。     

Impact of heliostat curvature on optical performance of Linear Fresnel solar concentrators

The present paper gives a numerical investigation of the effect of mirror curvature on optical performance of a Linear Fresnel Reflector solar field installed recently in Morocco. The objective is to highlight and discuss the effect of mirror curvature on the flux density distribution over the receiver and the system optical efficiency. For this purpose, a Monte Carlo-ray tracing simulation tool is developed and used to optimize the optical design taking into account the curvature degree of the heliostat field. In order to assess the accuracy of the numerical code developed and the validity of simulation results, a set of verification tests were developed and detailed within this article. Then, the optical performance of the system is evaluated as a function of mirror curvature and receiver height. The major challenge of this study is to find a trade-off between heliostat curvature and receiver height since lower and smaller receivers may reduce the system cost. It has been found that the flux distribution over the receiver and the optical efficiency of the system are relatively sensitive to the mirror curvature. We have demonstrated quantitatively how the use of curved mirrors can enhance the optical performance and reduce the required receiver size.     

太阳能会聚器的优化设计

讨论了用光学设计软件CODE V对太阳能会聚器进行优化设计的问题。在描述了太阳能会聚器的主要设计参数后，我们分析了抛物型会聚器的特性。利用光学设计软件，设计出一类新的高次非球面会聚器。实验结果表明，此类会聚器可实行间断跟踪太阳，且接收面光能量分布均匀，提高了系统转换效率，还具有节约能量、降低成本等优点。     

Optimal geometries of a seasonally adjusted discrete-mirror solar concentrator employing a tubular absorber

The geometrical profile of a seasonally adjusted solar concentrator composed of plane mirror elements and employing a tubular absorber has been optimized. The procedure maximizes concentration for any specified number of mirror elements, and for acceptance angle, with the height of the concentrator or the reflector area as a constraint. The geometrical characteristics of the optimal concentrators have been analysed in detail. The results for a tubular absorber are compared with those for a flat horizontal absorber. Detailed results for a wide range of number of mirror elements, reflector heights, and reflector areas are provided as a design aid. Designs using a glazed tubular absorber are also considered.     

A new trough solar concentrator and its performance analysis

The operation principle and design method of a new trough solar concentrator is presented in this paper. Some important design parameters about the concentrator are analyzed and optimized. Their magnitude ranges are given. Some characteristic parameters about the concentrator are compared with that of the conventional parabolic trough solar concentrator. The factors having influence on the performance of the unit are discussed. It is indicated through the analysis that the new trough solar concentrator can actualize reflection focusing for the sun light using multiple curved surface compound method. It also has the advantages of improving the work performance and environment of high-temperature solar absorber and enhancing the configuration intensity of the reflection surface.     

Optimization of the parabolic mirror position in a solar cooker using the response surface method (RSM)

The main objective of this study is to develop and improve the thermal and radiative performance of solar cookers. A solar cooker has been designed, constructed and experimentally analyzed to achieve this goal. The designed system contains three narrow, adjustable flat mirrors that are mounted on a parabolic curved substrate in order to concentrate the reflected solar beam onto the absorber plate. The efficiency of this system depends on many variables that were kept fixed with the exception of the parabolic mirror position and operation time. The response surface method was used as the basis of the design and analysis of the experiments. The analysis of the results provided the mathematical function of the effective and overall efficiencies based on the experimental variables that can be adopted to optimize the mirror positions at any given time. As a result, a new system was developed with adjustable mirrors that yields 32.07% and 35.5% increase in the effective and overall efficiencies, respectively. The results have been validated by variance analysis and comparing theoretical and experimental efficiency. The experiments were carried out in Mashhad, Iran at latitude 37, longitude 54, and a height of 985 m above sea level.     

Stationary mirror systems for solar collectors

An angle in solar geometry termed the EWV altitude is defined, and its variation with time and season is shown. This variation indicates the necessary acceptance angle of a stationary mirror system for solar collectors. It is shown that a completely stationary mirror cannot give any useful concentration, but that if the tilt is varied with the seasons, an eastwest cylindrical parabolic mirror without diurnal movement can yield a concentration of approximately three. This may be increased to about four with the aid of a small auxiliary (fixed) mirror to provide a second stage of optical concentration.     

Effects of geometrical parameters of a dish concentrator on the optical performance of a cavity receiver in a solar dish‐Stirling system

Dish‐Stirling concentrated solar power (DS‐CSP) system is a complex system for solar energy‐thermal‐electric conversion. The dish concentrator and cavity receiver are optical devices for collecting the solar energy in DS‐CSP system; to determine the geometric parameters of dish concentrator is one of the important steps for design and development of DS‐CSP system, because it directly affects the optical performance of the cavity receiver. In this paper, the effects of the geometric parameters of a dish concentrator including aperture radius, focal length, unfilled radius, and fan‐shaped unfilled angle on optical performance (ie, optical efficiency and flux distribution) of a cavity receiver were studied. Furthermore, the influence of the receiver‐window radius of the cavity receiver and solar direct normal irradiance is also investigated. The cavity receiver is a novel structure that is equipped with a reflecting cone at bottom of the cavity to increases the optical efficiency of the cavity receiver. Moreover, a 2‐dimensional ray‐tracking program is developed to simulate the sunlight transmission path in DS‐CSP system, for helping understanding the effects mechanism of above parameters on optical performance of the cavity receiver. The analysis indicates that the optical efficiency of the cavity receiver with and without the reflecting cone is 89.88% and 85.70%, respectively, and former significantly increased 4.18% for 38 kW XEM‐Dish system. The uniformity factor of the flux distribution on the absorber surface decreases with the decreases of the rim angle of the dish concentrator, but the optical efficiency of the cavity receiver increases with the decreases of the rim angle and the increase amplitude becomes smaller and smaller when the rim angle range from 30° to 75°, So the optical efficiency and uniformity factor are conflicting performance index. Moreover, the unfilled radius has small effect on the optical efficiency, while the fan‐shaped unfilled angle and direct normal irradiance both not affect the optical efficiency. In addition, reducing the receiver‐window radius can improve the optical efficiency, but the effect is limited. This work could provide reference for design and optimization of the dish concentrator and establishing the foundation for further research on optical‐to‐thermal energy conversion.     

Optical and thermal characterization procedure for a variable geometry concentrator: A standard approach

Concentrating solar collectors are mentioned in the International Standards, but the general testing methods for solar collectors mentioned cannot easily be applied to such unusual collector designs. In this study, the best optical and thermal model for a variable geometry solar concentrator has been investigated. In the particular case of a collector with a fixed mirror concentrator, the relative position of the receiver with respect to the reflector is not constant during the day, and this variable geometry is not taken into account in the current testing Standards. An optical characterization of the prototype using a ray-tracing program has been performed, and the results have been used as an initial hypothesis to define two thermal models adapted from the European Standard. Those two different models have been compared. The optical results obtained from experiments have been compared to ray-tracing simulation results, and they have been found to be quite similar, considering the measurement uncertainties. This validation procedure of the optical simulation could be an important point to be taken into account in a future Standard revision for variable geometry collector types for which the normal incidence is not easy to obtain.     

Optimal geometries of plane mirror solar collectors

This paper presents an analytical study of a stationary plane mirror solar concentrator. It is composed of an array of East-West oriented trapezoidal channels with two sided reflecting walls and a tubular absorber as a receiver at the base. We have analysed and identified the most practical design parameters for a trough like concentrator. The one- and two-faceted plane side wall configurations with tubular receiver at the base of the trough have been studied in detail. It has been concluded that large savings in reflecting surfaces are possible while sacrificing some reduction in concentration. A theoretical prediction for the dependance of absorber efficiency on temperature has been obtained.     

点聚焦太阳炉设计方法与研制实践

从聚光原理、光学计算、硬件设计,到安装与调试,详细介绍了点聚焦太阳炉的研制过程。根据当地用户的需求和太阳能资源,通过自行设计的光学软件,计算出典型日一次反光定日镜在二次聚光器截光口平面上的照射情况、二次聚光器的最佳焦距以及焦平面焦点处的峰值热功率。模块化设计的一次反光定日镜,不仅降低了制造成本,提高了生产效率,简化了一次反光定日镜的整体支架,同时给运输和安装带来了方便。单元反光镜反光面采用12点支撑,为定日镜的单元镜面调平创造了条件。同样采用模块化设计的二次聚光器,有利于制造成本的降低,方便运输和现场安装。反光镜单元面型可调,大大增强了点聚焦太阳炉参数的适应性。通过样机研制,验证了设计方法的可行性。     

A 100-sun linear photovoltaic solar concentrator design from inexpensive commercial components

The optical design for a high-efficiency linear photovoltaic solar concentrator assembled from readily-available inexpensive components is presented. Accounting for all geometric and material-related optical losses, we find that it should easily produce flux levels of 50–100 suns with homogeneous irradiance of the absorber. This is well suited to the peak-performance point of concentrator solar cells.     

A solar dish concentrator based on ellipsoidal polyester membrane facets

The design of a solar parabolic dish concentrator is proposed based on an array of polyester mirror membrane facets that are clamped along their edges by elliptical rims and focused by applying a slight vacuum underneath the membranes, creating an ellipsoidal shape. The axes ratio of the elliptical rims varies with the position on the dish to approach the paraboloidal shape. The elastic mirror membrane deformation under uniform pressure load is simulated by finite element structural analysis and the resulting radiative flux distribution at the focal plane of the dish is determined by the Monte Carlo ray-tracing technique. Optimization of the membrane deflection is accomplished for maximum solar flux concentration at the focal plane. Two dish geometries are examined: (i) a 1.5-m radius 3-m focal length small dish, comprising 19 facets of 0.275-m radius with four different curvatures, yielding a peak solar concentration ratio of 5515 suns and a mean solar concentration ratio of 1435 suns with an intercept factor of 90% over a 3-cm radius disk target and (ii) a 10.9-m radius 11-m focal length large dish, comprising 121 facets of 0.9-m radius with 15 different curvatures, yielding a peak solar concentration ratio of 23,546 suns and mean solar concentration ratio of 8199 suns with an intercept factor of 90% over a 10.4-cm radius disk target. The performance of the second geometry is compared to that of the more conventional design of a multi-facet dish concentrator consisting of identical circular facets and shown to reach – on the same target area – a 12% higher mean solar concentration ratio as well as a 6.6% higher intercept factor. The simulated membrane shape is experimentally verified with photogrammetrical measurements carried out on a prototype facet of the small dish.     

Concentration characteristics of a two stage solar concentrator: Effect of primary mirror surface errors

The concentration characteristics of a two-stage linear solar concentrator employing a perfectly tracked parabolic trough as the primary and a seasonally adjusted compound parabolic concentrator as the secondary stage with a flat horizontal absorber are studied. The Monte Carlo ray trace technique is used for this purpose. The effect of randomly distributed primary mirror surface errors on the concentration characteristics of the two stage concentrator is also investigated.     

碟式聚光器的月光聚光比分布计算模型

碟式聚光器和塔式聚光器均是点聚光系统,为了用月光法间接测量塔式聚光系统的聚光比分布,适宜用聚光稳定的碟式聚光器研究不同月相的光源亮度分布对聚光比分布的影响。主要建立月光下碟式聚光器的聚光比分布计算模型,首先依据拍摄的月相灰度图像建立分块均匀的光源亮度分布模型,再基于三维激光扫描点云数据生成准确的反射镜面形;在光线追迹过程中均匀采样镜面上的反射点,且考虑聚光器的跟踪误差;镜面的光学误差与光源的亮度分布合并为等效的光源亮度分布。模拟聚光比分布与实验聚光比分布的余弦相似度α>95%,光学模型准确性高。