Uniform concentrating design and mold machining of Fresnel lens for photovoltaic systems

Fresnel lens arrays are widely applied as the core optical component in concentrated photovoltaic (CPV) systems for concentrating light on a solar cell. To improve the photoelectric conversion efficiency of CPV systems, a Fresnel lens design is proposed, in which both uniform concentration and machining feasibility are pursued by means of simpler structure. In this design, the concentrating facets of the Fresnel lens are conical ones with different inclined angles, and the light passing through these conical facets can be superposed on the same position. The optical performance of the lens is analyzed to optimize its geometrical parameters. Towards this uniform concentrating design with a simple structure, an ultra-precision diamond cutting process based on B axis rotation is also developed to machine the Fresnel lens mold. In this process, the V-shaped diamond tool is rotated from right to left to machine the micro grooves of the lens mold with a maximum cutting depth of the groove height, so that the grooves can be prevented from being cut by the tool tip with low strength. Cutting tests of the factors influencing the machining accuracy and surface quality are carried out to optimize the cutting trajectory planning and machining parameters. The Fresnel lens molds with no sharp corner defects and no surface scratches are machined, and dimensional accuracy of 1.0 μm and surface roughness of better than 13 nm are achieved. Then, a silicone rubber lens is cast based on this mold. Concentrating uniformity test of the lens is conducted, and a concentrating uniformity of better than 75% is achieved. The results show the effectiveness of the uniform concentrating design and the feasibility of the B axis rotating machining process.