新型多平面太阳能聚光器性能分析

提出一种新型多平面太阳能聚光器,该型聚光器由若干矩形小平面镜和抛物型结构的框架组合而成,适用于太阳能在中温领域的应用。利用几何学原理和Monte Carlo方法研究新型多平面太阳能聚光器的几何光学特征及焦平面能流密度分布,分析不同综合误差对几何聚光比及能流密度分布的影响。研究结果表明:相比传统碟式聚光器,新型多平面聚光器在焦平面的光斑面积增大且能流密度分布均匀;该型聚光器的几何聚光比随着镜面排数M的增加而增加,在镜面排数M分别为7、9、11时,相应几何聚光比可达69、125、210,满足中温领域的使用要求;在相同的外部条件下,其运行性能受综合误差的影响较传统碟式聚光器小。     

均匀能流密度槽式聚光器设计及光学特性北大核心CSCD

太阳能聚光系统中接收器表面能流密度分布不均匀,会对其光电转换效率以及自身结构的稳定性造成一系列不良影响。为提高接收器能流密度均匀性,文章将微元法与几何构造法相结合,提出Ⅰ型和Ⅱ型两种聚光器模型,利用Trace Pro软件对这两种聚光器的光学特性进行模拟分析,确定出最优模型,进而分析几何聚光比、跟踪误差、安装误差对该模型能流密度分布的影响。结果表明:Ⅱ型聚光器光学特性最优,当几何聚光比为20时,分别以平行光及太阳光入射,接收器上能流密度均匀分布的区域分别占接收器区域的80.18%和75.17%,其光学效率达到99%和95%。此外,随着跟踪误差和安装误差的增大,接收器能流密度均匀分布的区域都减小。本研究对聚光器的优化设计和提高聚光型太阳能系统能源利用效率具有参考意义。     

采用真空柱状接收器的碟式集热器光热特性研究

提出利用柱状真空管作为碟式太阳能聚光系统的接收器,强化碟式抛物面太阳能聚光器的接收效率、降低系统对跟踪精度的要求,进而降低整个系统的工程造价,实现系统低成本运行。对系统结构进行光学和传热性能分析,给出几何聚光比随接收器几何参数的变化规律。结果表明,接收器在跟踪误差为0.5°时,几何聚光比仍可达到理想情况时的80%。结合传热学计算和Tracepro光学仿真,得到接收器热损失系数随接收表面温度,以及局部能量聚光随跟踪误差的变化规律,为此类碟式太阳能聚光集热器的优化设计提供依据。     

可实现均匀能流分布的太阳能碟式/三角形腔体接收系统的光学特性研究

提出一种三角形腔体接收器应用到抛物碟式聚光系统,实现腔体接收器底部吸热器表面的能流均匀化。基于OptisWorks光学软件研究三角形腔体接收器的截面尺寸、腔体高度、腔体侧壁面的反射特征(镜面反射或漫反射)和反射率等对其光学性能的影响。光学性能指标包括腔体接收器的光学效率、吸热器表面的能流非均匀因子及其接收的总太阳辐射能。分析聚光器的扇形缺角、正方形聚光器和跟踪误差,以及三角形截面和腔体底部的裁剪对接收器光学性能的影响。结果表明,腔体接收器的壁面反射特征和反射率对其光学性能影响显著,提高腔体侧壁面的反射率和选择镜面反射材料能使吸热器获得更多的太阳辐射能。在腔体截面尺寸和壁面反射特征一定时,总存在一个较佳的腔体高度使吸热器表面的能流非均匀因子减小到0.1以下。此外,将三角形腔体裁剪成六边形或正六边形截面时也能获得均匀的能流分布。该文研究为吸热器表面能流均匀化提供了一种新的解决方案,可应用于碟式聚光集热和碟式聚光光伏领域。     

空间薄膜抛物面聚光系统辐射能流密度的研究

结合薄膜聚光器的光学特性,同时考虑空间太阳形状模型、薄膜表面反射误差的概率模型,采用蒙特卡罗光线追迹法计算空间薄膜抛物面聚光系统接收面上辐射能流密度,分析薄膜聚光器的表面反射误差、焦径比、接收器的遮挡作用和接收器的位置对系统接收面上辐射能流密度分布的影响,为空间薄膜聚光系统的参数设计和性能分析提供参考。     

槽式均匀聚光系统设计及分析

为提高槽式聚光系统的聚光均匀性,提出一种槽式均匀聚光系统,建立了该系统反射聚光器模型,并对其聚光效果进行了分析.对系统的几何参数分析表明,随着反射镜面数量的增加其宽度在逐渐减小而其倾角却在逐渐增加,系统最大几何聚光比随系统的几何高宽比δ增大而增加.利用蒙特卡罗光线追迹方法对该聚光器的聚光效果进行模拟,结果表明该系统的聚光均匀性明显优于传统的槽式聚光器聚光效果,能够满足设计需求.     

非跟踪非对称复合平面型太阳能聚光器设计与光学性能模拟

提出一种新型的非跟踪非对称复合平面型反射聚光器,给出设计方法,利用基于蒙特卡罗光线追迹法的光学仿真软件,分析光学效率及吸收器上的能流分布。结果表明,增大平面镜数量n和设计角θ_0均可增大聚光器的几何聚光比CR。CR相同的聚光器在入射角大于θ0时具有相同的光学效率,聚光均匀性较好,且减小n值有利于获得更均匀的光强分布。     

对太阳能热发电走向成功之路的思考

从理论方面对降低太阳能热发电投资成本的方式进行了分析,认为可通过扩大规模来降低投资成本,依靠扩大发电系统的规模和优化镜场设计来提高太阳能热发电系统的光电转换效率;碟式和点聚焦菲涅耳聚光系统的光热转换效率高,竞争力较强。当采用超大功率蒸汽轮机时,可使发电系统的规模扩大10倍、热电转换效率提高25%;按照光学效率和接收器热效率均达到92%计算,碟式聚光系统的光热转换效率可达到84.64%,而塔式聚光系统的光热转换效率为57.73%,前者比后者提高了46.62%,使碟式太阳能热发电系统的光电转换效率比塔式太阳能热发电系统的提高了83.3%,从而使碟式太阳能热发电系统的总投资成本比塔式太阳能热发电系统的下降了45.4%,共用跟踪系统使其总投资成本又下降了4.8%,再加上碟式太阳能热发电系统的中发电系统规模扩大10倍,最终,碟式太阳能热发电系统的总投资成本可比塔式太阳能热发电系统的降低75.2%。在不考虑材料和制造技术方面进步的情况下,太阳能热发电的上网电价可从目前的1元/kWh降至约0.25元/kWh,使太阳能热发电成为未来有竞争力的主要能源技术。     

旋转曲面式两级反射系统的太阳能聚集与传输特性分析

提出一种改进型卡塞格林反射太阳能聚集系统,将其二次镜面方位进行旋转变换,接收面可据此灵活布置,对聚集系统的结构优化具有重要应用价值。通过建立旋转曲面式两级反射系统的数理模型,根据几何光学原理推导二次镜最大可旋转角度,并用射线踪迹蒙特卡洛法(MCRTM)模拟接收面能流分布特性。结果表明,此系统下聚集光斑遵循高斯分布,虽然聚光比同单级碟式抛物面有所降低,但可在保持较高聚光比的同时灵活改变光路方向。     

考虑太阳张角的聚光器设计北大核心CSCD

通过聚光等形式提高光能密度,减少光伏材料的使用量,有助于保护环境和节约能源。文章提出一种新型聚光器设计方案,其在分析太阳张角对光路影响基础上,对聚光器模型进行改进,并得到接收器上反射光线分布规律。根据节省材料比和聚光硅电池效率选取聚光器参数,建立聚光器三维模型,在TracePro软件中进行仿真,得到接收器表面的辐照度分布和总光通量,与传统光伏聚光器聚光效果对比,验证聚光器模型的有效性,为聚光光伏发电系统的实物设计奠定了理论基础。     

Prediction and optimization of the performance of parabolic solar dish concentrator with sphere receiver using analytical function

Parabolic solar dish concentrator with sphere receiver is less studied. We present an analytic function to calculate the intercept factor of the system with real sun brightness distribution and Gaussian distribution, the results indicate that the intercept factor is related to the rim angle of reflector and the ratio of receiver angle to the optical error when the optical error is larger than or equal to 5 mrad, but is related to the rim angle, receiver angle and optical error in less than 5 mrad optical error. Furthermore we propose a quick process to optimize the system to provide the maximum solar energy to net heat efficiency for different optical error under typical condition. The results indicate that the parabolic solar dish concentrator with sphere receiver has rather high solar energy to net heat efficiency which is 20% more than solar trough and tower system including higher cosine factor and lower heat loss of the receiver.     

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.     

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.     

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.     

Development of a low-cost dish solar concentrator and its application in zeolite desorption

This paper deals with the development and performance characteristics of a low-cost dish solar concentrator and its application in zeolite desorption. The dish solar concentrator consists of an old damaged satellite dish, purchased from a scrap yard, and a polymer mirror film used as reflecting surface. The proposed concentrator is connected to a sun-tracking system which is based on an electronic circuit that processes the input signals from a set of sensors and drives the dish actuator. The solar thermal energy application to adsorption technology (with the sorption pair water/zeolite) is simulated using the ‘Ice-Quick’ device manufactured by Zeo-Tech GmbH. Samples from two types of zeolites were initially brought to saturation condition and then mounted on the focal point of the dish solar concentrator in order to be regenerated. Experimental results are presented and useful conclusions are drawn.     

Concentration distributions in cylindrical receiver/paraboloidal dish concentrator systems

Concentration distributions on a cylindrical receiver in a paraboloidal dish concentrator are computed for space applications (no atmosphere). A geometric optics method is applied which integrates over the solar disk and the concentrator projected surface, and maps analytically, in implicit closed form, through the concentrator and onto the receiver. Finite sunshape, concentrator surface errors, and pointing system zero-mean and constant offset errors are considered. Results define the section of the receiver surface which receives the majority of the concentrated flux, where the receiver's aperture might be located. Results are given in terms of concentrator geometry, concentrator total system error tolerance, receiver geometry, and pointing offset error. In cases with pointing offset error (nonzero mean pointing error), circumferentially varying concentration distributions are shown.     

Focal region measurements of the 20 m tiled dish at the Australian National University

Focal region characterisation of a 20 m² point focus dish concentrator having approximately 2300 flat, 10 cm square mirror tiles as its reflecting surface has indicated a focal flux distribution having a flat-topped peak with approximately Gaussian limbs. A peak concentration of 970 suns was evident, while a dish optical efficiency of 74% was measured, which is a direct indication of the average dish reflectivity. Total integrated power of 14.8 kW was measured under the focal flux distribution. Predicted fluxes using a ray trace algorithm (COMPREC) developed at the Australian National University (ANU) and utilising 2.0 mrad surface slope error showed a good approximation to the measured distribution. The value of 2.0 mrad also compared well with a photogrammetrically predicted value of 1.8 mrad.     

Evaluation of a large dish‐type concentrator solar lighting system for underground car park

To utilize solar energy more efficiently and reduce lighting power consumption in underground public spaces such as car park, a large dish‐type concentrator solar lighting system is put forward along with its evaluation, which is a unique design to apply a laminated layer of beam split thin‐film coating and thin‐film solar cells onto the dish reflector. The collected sunlight is split into 2 parts, one being reflected into a fiber optical bundle and transmitted for daylighting, while the rest being absorbed by solar cells for electricity generation as the other way to replenish daylighting. A set of 4 solar lighting systems using 3.28‐m diameter dish are designed to meet the lighting requirement in a 1771‐m² underground car park. A mathematical model is adopted to calculate the output power and conversion efficiency of solar cells distributed on the parabolic dish surface. The indoor illuminance distribution is given by lighting simulation. The results indicate that the average daylight illuminance in the car park can vary between 62.7 and 284 lx on February 25, 2016 and between 62.7 and 353 lx on August 17, 2016 for 2 chosen days, respectively. For the presented design, the electricity produced by solar cells is just enough to power light‐emitting diodes for lighting meeting a criterion at night. Considering about 19% conversion efficiency of solar cells and the efficacy of 129.5 lm/W of light‐emitting diodes, the hybrid solar lighting system can have about 40% utilization ratio of solar energy, so it can be concluded that a sufficient lighting provision can be provided by the proposed large dish‐type concentrator solar lighting system for applications in underground car park.     

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。     

Theoretical analysis of error transfer from surface slope to refractive ray and their application to the solar concentrated collector

This paper discusses the error transfer from the slope of optical surface to the focus ray. It presents a general equation to calculate the standard deviation of the refractive ray error from that of slope error of the optical surface through geometric optics analysis, applying the equation to calculate the standard deviation of the focus ray error in 6 kinds of solar concentrator, and providing typical results. The results indicate that the slope errors in two directions are transferred to any one direction of the focus ray when the incidence angle is more than 0; for a point focus Fresnel lens, a point focus parabolic glass mirror, and a line focus parabolic glass mirror, the error transferring coefficient from the optical surface to the focus ray will increase when the rim angle or distance of reflection or refraction point to the axis increases; for a TIR-R concentrator, it will decrease; for a glass heliostat, it relates to the incidence angle and azimuth of the reflecting point. The results show that the slope error of the optical surface may be enlarged more than ten folds to the focus ray to decrease the optical efficiency of the solar concentrator greatly.