基于Cassegrain 线聚光和三维CPC的高聚光光伏系统的优化设计和性能研究

With the rapid development of multi-junction (MJ) solar cells based on III-V semiconductors, the cost and technical advantages of high concentrating photovoltaic (HCPV) over plat-plate PV have been emerging, and this make it possible that the cost of electricity from HCPV is close to the cost of conventional electricity generation in the near future. However, the cost of concentrators is usually much higher than that of MJ in HCPV systems, thus, the development of cheap, high efficiency, reliable and practical concentrators with a high concentration is one of effective way to reduce the cost from HCPV. In this proposal, a HCPV based on a linear Cassegrain concentrator tracking the sun with a horizontal single-axis and three-dimensional CPCs is proposed where the Cassegrain concentrator consists of a primary parabolic reflector (PPC) and a secondary mirror and the total internal reflection based 3D-CPC is shaped by a symmetric CPC oriented in direction of the sun-tracking axis crossing an asymmetric CPC oriented in the direction perpendicular to the sun-tracking axis (TIR-CACPC). The proposal system shares advantages of beam-downwards focusing in Cassegrain optical systems, simple structure in horizontal single-axis sun-tracking and high concentration in the TIR-CACPC. The program will focus on theoretical and experimental investigations on issues related to the design optimization of the system, characteristics of energy transfer and photovoltaic conversion as well as thermal environment in MJ.

随着基于III-V族多节高效聚光太阳电池(MJ)的快速发展，高聚光光伏（HCPV）的技术和经济优势逐渐凸显出来，使其发电成本有望接近常规发电成本。但在HCPV系统中，聚光系统的成本远高于MJ的成本，因此，开发价廉、高效、可靠、实用的高聚光系统是降级HCPV发电成本的有效途径之一。本课题提出了基于水平单轴跟踪Cassegrain线聚光器和三维CPC的高聚光光伏系统，Cassegrain线聚光器由初级抛物聚光器（PPC）和二次反射镜面（SM）组成，三维CPC为基于全内反射的轴向对称复合抛物聚光器（CPC）和横向非对称CPC交叉所形成的几何结构（TIR-CACPC）,系统吸取了Cassegrain光学系统向下聚光、水平轴跟踪结构简单和TIR-CACPC高聚光的优点。课题将围绕系统的优化设计、光能传输、光电转换和MJ热环境相关的科学问题开展理论和实验研究。

随着基于III-V族多节高效聚光太阳电池(MJ)的快速发展，高聚光光伏（HCPV）的技术和经济优势逐渐凸显出来，使其发电成本有望接近常规发电成本。但在HCPV系统中，聚光系统的成本远高于MJ的成本。本课题提出了基于水平单轴跟踪Cassegrain线聚光器和三维内反射交叉非对称三维CPC的高聚光光伏系统，旨在开发一种高效、简单、实用、可靠、聚光比达200以上的高聚光光伏系统。课题围绕光能在系统内的传输和转换过程的机理、影响因素开展理论和实验研究。研究结果显示，对于反射式线聚光器，轴线投影入射角不等于投影反射角，而对于电介质线聚光器横向投影入射角与折射角不满足Snell关系，因此太阳辐射在系统内的传输必须采用三维辐射传输模型；与反射式二维CPC，基于电介质的CPC的几何聚光增加取决于其安装取向、倾角调整模式和每天有效运行时间，但大于折射指数(n); 设计合理的二维和三维交叉CPC的光学损失主要源自电介质的吸收，而因不能发生全内反射漏光所引起的光学损失极少；以双曲面作为二次反射面所构成的线性Cassegrain聚光器的几何聚光比最大、其焦面位于抛物槽的底部附近、为最佳结构； 基于双曲面水平轴跟踪Cassegrai线聚光器和交叉非对称CPC所构成的高聚光系统的最大几何聚光比与地理纬度、抛物槽的焦数、跟踪精度及安装取向有关，抛物槽的最佳焦数为0.6，南北向安装最佳，纬度越低，其最大几何聚光比越大；在昆明地理纬度下，当选用n=1.52的电介质作为三维CPC的制作材料，其最大几何聚光器为310，太阳电池上的光照强度为185个太阳，满足MJ所要求的100个太阳的要求。项目的研究，加深了对太阳辐射在聚光光伏系统传输和转换过程的机理的认识，为系统的实际应用提供了理论和技术支持。