Characterisation of a 300× photovoltaic concentrator system with one-axis tracking

A solar concentrator with one-axis tracking is being developed at our institute. This concentrator system achieves a high geometrical concentration ratio of 300 using a parabolic trough mirror and a three-dimensional second stage consisting of compound parabolic concentrators. The design of the system as well as the characterisation of the second stage is described in this paper.     

Optical design of a flat-facet solar concentrator

We present a procedure to design a facet concentrator for laboratory-scale research on medium-temperature thermal processes. The facet concentrator approximates a parabolic surface with a number of flat square facets supported by a parabolic frame and having two edges perpendicular to the concentrator axis. The optimum size and position of each facet are found by employing Monte Carlo ray tracing analysis to achieve desired flux characteristics in the focal plane. A 164-facet concentrator with realistic specularly-reflecting surface and facet positioning accuracy will deliver up to 8.15 kW of radiative power over a 15 cm radius disk located in the focal plane, with average concentration ratio exceeding 100.     

Optimization of the tubular absorber using a compound parabolic concentrator

The paper deals with the optimization of the tubular absorber of a compound parabolic concentrator (CPC) solar collector. In order to minimize the radiation thermal losses from the absorber, a modified absorber with multi-cavities is proposed. The cavities are introduced at the circumferential area with relatively high solar intensities. These areas were determined by the use of a ray-tracing technique. This has been adopted using the AutoCAD^® package. The analysis was carried out and applied to a CPC with an acceptance angle of 10 and a concentration ratio of × 4.0.     

An optical analysis of a static 3-D solar concentrator

Concentrating technology is long established in the field of solar thermal applications. However, there is still scope for improvement due to innovation in design, materials and manufacturing methods. The optical efficiency of a solar concentrator depends largely on the geometry of the concentrator profile. This paper evaluates the optical performance of a static 3-D Elliptical Hyperboloid Concentrator (EHC) using ray tracing software. Ray tracing has been used extensively to calculate the optical efficiency of the static 3-D EHC. Performance parameters such as effective concentration ratio, optical efficiency and geometric concentration ratio are also evaluated for different aspect ratios of the elliptical profile. Optimization of the concentrator profile and geometry is also carried out to improve the overall performance; this parametric study includes the concentrator height, solar incidence angle and aspect ratio of the ellipse. The overall performance of the concentrator was assessed based on the acceptance angle, effective concentration ratio and optical efficiency. Finally, the flux distribution on the receiver area for different concentrator heights is also presented.     

Experimental and numerical investigation on solar concentrating characteristics of a sixteen-dish concentrator

The concentrated solar flux distributions of a sixteen-dish concentrator (SDC) were measured applying a thermal infrared imager in combination with water-cooled Lambert target, and predicted using a Monte Carlo ray tracing method (MCRT). A slope error of 2.2 mrad is detected by comparing the experimental and numerical results. Then, a two-stage concentrator system, formed by the SDC in tandem with a three-dimensional compound parabolic concentrator (3D CPC–SDC), is constructed based on the geometrical optics approach. The interception performances and the energy concentration ratio images (ECR) are presented for both the SDC and the 3D CPC–SDC. The results show that the ECR profiles of the SDC depend on the receiver sizes, whereas that of the 3D CPC–SDC is rather steady because most sunlight enters the receiver via several reflections with the 3D CPC mirror. The 3D CPC–SDC is capable of increasing the geometric concentration ratio (GCR) at the expense of a little interception efficiency.     

A novel multiple curved surfaces compound concentrator

A novel multiple curved surfaces compound concentrator is developed in this paper. It is composed of a parabolic and a flat contour. This new concentrator has a focus at the backside which is extremely useful and convenient for some applications. The reflected rays here are transmitted forward instead of backward as in the conventional parabolic concentrators. The design method of the concentrator is introduced. Some of important parameters are discussed and the value rang of them is determined. Simple comparisons between proposed concentrators and traditional paraboloid and CPC are made. Light rays tracing are carried out in the concentrator.     

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.     

Analysis of two models of (3D) Fresnel collectors operating in the fixed-aperture mode with a tracking absorber

In this paper, we study the reflection behavior of (3D) Fresnel collectors operating in the fixed-aperture mode with a tracking absorber. The aim of the study is to investigate the possibility of the use of this type of installation for applications in medium temperature processes (200–300°C). Two models of (3D) Fresnel concentrator are developed for this purpose. One is based on the approximation of the optical behavior of a parabolic concentrator, and the other on that of a spherical one. Via a computer simulation which includes ray-tracing, we evaluate the sensitivity of the geometric concentration ratio to concentrator design parameters, and the option of using curved versus flat elementary mirrors. The numerical results show that there is no large difference between the two models of Fresnel concentrator. For the spherical model, which seems to be slightly more suitable for this type of application, we propose a simple solution for the receiver displacement, which consists of a single-sided absorber moving tangentially to a sphere centered in the concentrator’s center.     

Performance improvement of a static concentrator module with an asymmetric v-groove backsheet structure

A light-trapping type concentrator module with a new asymmetric V-groove structure at the rear surface is proposed to improve the performance of static concentrator module. Fundamental optical properties of various asymmetric V-grooves are calculated using a ray-tracing method. Based on these results, yearly integrated irradiance ratios of the concentrator module to a conventional flat-plate module are calculated using meteorological data. By the use of Ag as a reflection material, yearly integrated irradiance ratio of concentrator module with an asymmetric V-groove is 1.34, and the occupation area of Si cells in a module can be reduced to 74% compared with a conventional flat-plate module.     

A fresnel-winston tandem concentrator system

Some geometrical concentration characteristics of a solar concentrator system employing a Fresnel reflector concentrator and a compound parabolic concentrator in tandem are discussed.     

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.     

Two-stage concentrator permitting concentration factors up to 300x with one-axis tracking

Economic operation of high-efficiency concentrator solar cells requires solar concentration ratios which up to now can only be achieved with two-axis tracking. In this paper we present a two-stage concentrator approaching concentration ratios up to 300X while being tracked around only one polar axis. Its principle is as follows: a parabolic trough focuses the direct solar radiation onto a line parallel to the polar tracking axis. The half rim angle of this first concentrating stage is chosen to be equal to the sun's maximum declination of 23.5°. The second stage consists of a row of dielectric, nonimaging 3-D-concentrators, which couple the concentrated light directly into square solar cells. In contrast to linear secondaries the 3-D-secondaries make use of the limited divergence of ± 23.5° in the NS-direction to achieve additional concentration. The performance of the system depends sensitively on how well the angular acceptance characteristic of the second stage matches with the square-shaped angular irradiance distribution in the focal line of the parabolic trough. A new concentrator profile has been found that exhibits an almost ideal square acceptance characteristic with a very sharp cut-off. A prototype two-stage concentrator has been constructed with a total geometrical concentration of 214X. In outdoor measurements a total optical efficiency of 77.5% was obtained.     

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.     

Thermal design of parabolic solar concentrator adsorption refrigeration system

This study presents a thermal design of solar-powered adsorption refrigeration with the type of activated carbon-methanol pair. The designed module consists of an evacuated glass tube equipped with a parabolic solar concentrator as generator, sorption bed, evaporator, and condenser units. A thermodynamic design procedure and a mathematical model of a steady state system with activated carbon refrigerator have been developed. The adsorber is heated by solar energy collected by a parabolic solar concentrator. The temperature of the working pair in the adsorber, the amount of methanol leaving and reabsorb bed, and the refrigerated box was estimated. An optimize design of the system to achieve higher cycle COP was presented. Maximum cycle COP = 0.576 and COP_net = 0.375 with T _max reached 157.8°C, T _B = 57.5°C, M _ac = 0.907 kg, and the concentration of methanoldesorped equal to 0.206 kg/kg _ac .     

应用于聚光发电的复合抛物面聚光系统性能仿真研究

构造了一种新型可应用于太阳能聚光发电的复合抛物面聚光器,根据实际尺寸在SolidWorks软件中建模,利用光学分析软件对其进行了光线追迹分析;研究了随入射偏角的变化,太阳电池接受体上接收入射光的变化情况;通过仿真计算模拟,直观地看到了光束在太阳能电池上所形成的焦斑形状、位置和能量分布随入射偏角的变化趋势。模拟计算结果表明,聚光器有效聚光比约为2.61,在测试范围内随着入射偏角增大太阳能电池表面聚焦光斑强度分布渐趋均匀,结论可为槽式太阳能聚光光伏发电的设计和优化提供参考。     

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.     

Study of thermal characteristics of a heating module with parabolic trough concentrator and linear wedge-like photoelectric receiver

New solar modules intended for typical solar collectors containing semiparabolic trough concentrators and receivers that convert solar energy into thermal energy are considered. Mathematical modeling is carried out to develop an algorithm for estimating the structure of a heating module with the assigned energy parameters according to the laws of geometrical optics, as well as heat and mass transfer. When using such modules, which are based on a parabolic concentrator and a receiver with a system of coolant flow, cogeneration plants can be designed to produce electricity and heat. The mockups developed using this procedure are studied on the corresponding facilities and are tested under in-situ conditions. A solar module with an asymmetric parabolic trough concentrator and a linear wedge-like photoelectric receiver of concentrated radiation with a system of coolant flow provides the maximum power of 386 W at a temperature of 40°C and an efficiency of 60%, and 319 W at 60°C and 49%, respectively. Such modules are proposed for use to design solar collectors with the required performance.     

Power losses in an asymmetric compound parabolic photovoltaic concentrator

An asymmetric compound parabolic photovoltaic concentrator (ACPPVC) of geometrical concentration ratio 2 was designed, developed and evaluated for building façade integration. Despite the two times theoretical concentration, the maximum output power achieved was only 1.62 times that of a similar non-concentrating system for a wide range of solar radiation intensities due to a combination of optical and electrical resistance losses. In this paper, the power loss of the ACPPVC system is explained by a comparative power loss analysis of the non-concentrating photovoltaic system for long- and short-tabbed solar cell strings that showed an average of 3.4% electrical power loss due to resistance in the interconnections between each individual solar cell. The optical losses of the ACPPVC were 15% caused by the combined effect of the number of reflections at the reflectors and the misalignment of the imperfection in the reflector geometry solar cells in addition to the power loss due to increased temperature of 0.6%. Good agreement was found between the measured and calculated optical efficiency of the system.     

Design,construction and characterization of a solar concentrator (cooker) using locally available materials

Thermal conversion of solar energy may be used for heating and cooking. Using locally available materials, we have designed, constructed and utilized a conical parabolic solar concentrator. With a concentration ratio of 56, an optimum efficiency of ~4% was recorded on a clear day and of 1% on a cloudy day. Our solar concentrator yields a minimum temperature of ~40 °C and a maximum temperature above 95 °C.     

Cylindrical concentrator with Quasiparabolic directrix

A cylindrical concentrator directrix that provides uniform energy distribution over the back (in the direction of solar ray travel) side of the receiving surface that is normal to the solar radiation has been investigated. The values of the focal parameters of the parabolas forming the directrix are determined. The parametric equations of the curve along which the parabolic foci move are obtained. The configurations of the directrix branches are considered and evaluated.