Studies on the light permeance characteristic of a Fresnel lens group applied in high concentration solar energy

A key point to limit wide applications of solar energy is the exploitation cost. With the advantages of compact volume, less weight, small focal length and low cost Fresnel lenses are suitable for solar radiation concentration and system modularization. The optical efficiency of transmitted solar radiation is improved compared to thick ordinary lenses and the solar tracking accuracy required by a Fresnel lens group is lower than for other reflection schemes. In this study, a modular device composed of a two-stage Fresnel lens is presented and its performance is investigated. Based on the analysis of rays passing through the wedge structure of the lens, the optical efficiency is obtained under different incidental angles. Facular point image qualities of a Fresnel lens are compared using simulation results. As for the Fresnel lens 100 mm in diameter, 220 mm in focal length, when the incident angle is kept within 1°, the focal point will not move out of the receiver domain with the dimensions of 10 mm × 10 mm and the relationship between incident angle against receiver dimension is obtained. Optical efficiency measurements have been carried out on a practical Fresnel lens group which includes another Fresnel lens 30 mm in diameter with the small-size secondary lenses integrated into an intermediate panel combined with the first Fresnel lens plane to improve the performance of the integral battery system at high concentration ratio. According to experimental studies, the positions of the focal spot varying with the incident angles of solar radiation are recorded continuously. It has been found that 50–60% of the collected solar radiation can pass through the Fresnel lens group under a condition of over 1000 suns, and the deviation range of the focal spot fundamentally agrees with the result of the simulation.