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.     

Ray tracing and simulation for the beam-down solar concentrator

The ray tracing equations for the beam-down solar concentrator have been derived in this paper. Based on the equations, a new module for the simulation of the beam-down solar concentrating system has been developed and incorporated into the code HFLD. To validate the ray tracing equations, a simple beam-down solar concentrating system consisting of 3 heliostats and a hyperboloid reflector is simulated. The concentrated spots at the lower focal point of the hyperboloid reflector for the beam-down system are calculated by the modified code HFLD and then compared with that calculated by the commercial software Zemax. It is found that the calculated results coincide with each other basically. Furthermore, a beam-down solar concentrator consisting of 31 heliostats, a tower reflector and a CPC is designed and simulated by using the modified code HFLD. The concentrated spots of the beam-down solar concentrator are calculated.     

Advanced 3‐D CPC solar collector for thermal electric system

In this paper, the authors propose an innovative non‐tracking three‐dimensional compound parabolic concentrator (3‐D CPC) solar collector, which has excellent thermal efficiency for a high‐temperature range (100–200°C). In the past studies, in order to improve the thermal efficiency of the solar collector in a high‐temperature range, very high concentration ratios and tracking systems have been adopted. However, conventional high concentration solar collectors are not cost‐effective and are inappropriate for small‐rating thermal electric generation systems for residential use. The proposed 3‐D CPC collector has a moderate concentration ratio and does not need tracking. Initially, the tentative 3‐D CPC collector was fabricated and its thermal performance was tested. Next, numerical simulations of the optical characteristics of the 3‐D CPC collector were carried out via the ray‐tracing method. Finally, the specification of the optimal 3‐D CPC collector was clarified. Applications of the thermal electric system will also be mentioned. © 2006 Wiley Periodicals, Inc. Heat Trans Asian Res, 35(5): 323–335, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20121     

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。     

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.     

Comment on: “Experimental and numerical investigation on solar concentrating characteristics of a sixteen dish concentrator”. By Xia et al., International Journal of Hydrogen Energy 2012; 37(24):18694–18703

For the sake of discussion to concentrating characteristics of multi dish concentrator, a simple calculation method of layout is given. By comparative study, the key of designing identical multi dish solar concentrator is confocal is deduced. In confocal and suitable f/D ratio conditions the smaller receiving aperture could be ensured, and the compound paraboloid receiver is not necessary.     

Linear Fresnel lenses, their design and use

A linear Fresnel lens (LFL) designed according to Fermat's principle is slightly modified with respect to used technology for mass production from glass. Manufactured Fresnel lenses are used in a fully tracking concentrating collector with aperture about 36 m² and in a collector with stationary concentrator and movable absorber, which may serve as solar collector with temperature and illumination control. A combination of linear Fresnel lenses with PV cells may reduce cost of autonomous solar installations.     

Two-phase flow modelling of a solar concentrator applied as ammonia vapor generator in an absorption refrigerator

A detailed one-dimensional numerical model describing the heat and fluid-dynamic behavior inside a compound parabolic concentrator (CPC) used as an ammonia vapor generator has been developed. The governing equations (continuity, momentum, and energy) inside the CPC absorber tube, together with the energy equation in the tube wall and the thermal analysis in the solar concentrator were solved.The computational method developed is useful for the solar vapor generator design applied to absorption cooling systems. The effect on the outlet temperature and vapor quality of a range of CPC design parameters was analyzed. These parameters were the acceptance half-angle and CPC length, the diameter and coating of the absorber tube, and the manufacture materials of the cover, the reflector, and the absorber tube. It was found that the most important design parameters in order to obtain a higher ammonia–water vapor production are, in order of priority: the reflector material, the absorber tube diameter, the selective surface, and the acceptance half-angle.The direct ammonia–water vapor generation resulting from a 35 m long CPC was coupled to an absorption refrigeration system model in order to determine the solar fraction, cooling capacity, coefficient of performance, and overall efficiency during a typical day of operation. The results show that approximately 3.8 kW of cooling at −10 °C could be produced with solar and overall efficiencies up to 46.3% and 21.2%, respectively.     

Optical performance analysis of an innovative linear focus secondary trough solar concentrating system

The parabolic trough solar concentrating system has been well developed and widely used in commercial solar thermal power plants. However, the conventional system has its drawbacks when connecting receiver tube parts and enhancing the concentration ratio. To overcome those inherent disadvantages, in this paper, an innovative concept of linear focus secondary trough concentrating system was proposed, which consists of a fixed parabolic trough concentrator, one or more heliostats, and a fixed tube receiver. The proposed system not only avoids the end loss and connection problem on the receiver during the tracking process but also opens up the possibility to increase the concentration ratio by enlarging aperture. The design scheme of the proposed system was elaborated in detail in this paper. Besides, the optical performance of the semi and the whole secondary solar trough concentrator was evaluated by using the ray tracing method. This innovative solar concentrating system shows a high application value as a solar energy experimental device.     

Design and Development of a Lens-walled Compound Parabolic Concentrator-A Review

Compound parabolic concentrator(CPC) is a representative among solar concentrators, one of whose disadvantage is that the concentration ratio limits the half acceptance angle. Based on this, researchers put forward a novel structure, named the lens-walled CPC. This paper reviews the design and development of lens-walled CPC. The structure of the symmetric and asymmetric lens-walled CPC and the improved ones are presented, and their indoor and outdoor performances are also illustrated. The lens-walled CPC has a larger half acceptance angle and a more uniform flux distribution that is suitable for PV application. Furthermore, the life-cycle assessment for building integrated with PV is performed and it shows that the energy payback time of such integrated system has a significant advantage. In addition, future research areas are also indicated that may provide more functions and more stable performance. The design methods and developmental directions given in this study would provide many references in solar optical research and solar concentrator optimization.     

A compound parabolic concentrator

A compound parabolic concentrator (CPC) for solar energy applications is presented in this work. A prototype was built and its thermal performance was determined. Operating temperatures of the order of 150 °C with a reasonable efficiency can be attained by means of a fixed CPC.     

Quantum dot solar concentrators: Electrical conversion efficiencies and comparative concentrating factors of fabricated devices

A novel, non-tracking concentrator is described, which uses nano-scale quantum dot technology to render the concept of a fluorescent dye solar concentrator (FSC) a practical proposition. The quantum dot solar concentrator (QDSC) comprises quantum dots (QDs) seeded in materials such as plastics and glasses that are suitable for incorporation into building façades. Photovoltaic (PV) cells attached to the edges convert direct and diffuse solar energy collected into electricity for use in the building. Small scale QDSC devices were fabricated. Devices have been characterised to determine current, voltage and power readings. Electrical conversion efficiencies, fill factors and comparative concentrating factors are reported.     

A comparison of compound parabolic and simple parabolic concentrating solar collectors

The compound parabolic and simple parabolic solar collectors are analyzed and compared for their ability to accept non-direct radiation and for their respective reflector arc-lengths. The simple parabolic concentrator (SPC) can make use of some non-direct solar radiation if the absorber tube is intentionally enlarged so as to intercept defocussed radiation. A principal advantage of collecting non-direct radiation with a SPC rather than with a compound parabolic concentrator (CPC) is the reduced materials use in the construction of the reflector, but a principal disadvantage is the reduction of acceptance angle to about that of the CPC. However, a SPC with concentration ratio less than 10 can still collect most of the circumsolar non-direct radiation.     

用于太阳能光电水泵的菲涅耳透镜聚光收集器

报道了具有第二级Ｖ形槽聚光器的玻璃直纹菲涅尔透镜与ＬＧＢＧ高效太阳电池组成的低倍聚光收集器的试验结果。宽度为３０ｍｍ、长度为１．５８ｍ的太阳电池组件，经聚光后峰值功率从７Ｗ增大到４４Ｗ，比常规太阳电池费用减少６０％，系统总费用降低４０％。     

太阳光不平行度对太阳能聚集性能影响的数值研究

对大型对日定向的碟式太阳能反射聚集器,通过数值模拟研究了太阳光不平行度与定向跟踪精度对聚光性能的影响。通过建立锥形光束的概率模型,采用蒙特卡洛法直接模拟了太阳光经碟式反射聚集器后在焦平面上产生的能流分布。比较了不同定向跟踪精度下,不同口径比的反射聚集器对太阳光与平行光的聚集性能差别。     

Reduction of the level of the radiation effect on space SA photoconverters with the use of solar radiation concentrators

The capabilities of the solar radiation concentrators as means of space solar array (SA) photoconverter protection from radiation are considered. The concentrator screening effect with respect to protons and electrons is qualitatively evaluated. It is shown that this effect for SAs with linear lens concentrators is several times larger than that in the case of trough-type mirror concentrating systems.     

Heat retaining integrated collector/storage solar water heaters

An integrated collector/storage solar water heater (ICSSWH) that can significantly reduce heat loss to ambient during non-collection periods has been developed. Two thirds of the ICS vessel is mounted within a concentrating cusp, McIntire ‘W’ modified concentrator and incorporates an inner heat retaining vessel. The remaining upper 1/3 of the vessel is situated outside the reflector cavity and is heavily insulated. Over 60% of the thermal energy stored within the total vessel, and up to 67% of that in the upper immediate draw-off region can be retained over a 16-h non-collection period. Results of an experimental analysis of this design and a comparison with a standard ICS design are presented.     

具有二次聚光器的新型大开口槽式太阳集热器设计与光学性能分析

针对大开口和更高运行温度的槽式太阳能热发电系统,提出一种可实现高聚光比、低辐射热损及能流密度均匀的新型槽式太阳集热器,即在集热管内放置外壁具有太阳选择吸收膜层和内壁具有反射膜层二次聚光器的大开口槽式太阳集热器。建立圆弧为微元段的自适应设计新方法,提出3种典型的二次聚光器面型,利用蒙特卡洛光线追迹方法仿真新型集热器的能流密度分布特性,验证该光学仿真方法,分析影响集热器光学性能的各种因素。结果表明,该集热器可显著提升集热效率。     

聚光型太阳能灯的设计

文章根据上海当地的气候情况,利用非对称CPC聚光器设计了一种聚光型太阳能灯。降低了太阳能路灯系统成本,提高了系统的可靠性。     

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.