Theoretical And Experimental Research Of Focal Spot Flux Density Distribution Of Solar Energy Concentrators

The theory and measuring technique of flux density distribution on the focal planes of solar energy concentrators play a key-role in optimizing the system efficiency. In order to redistribute solar flux density on receiving plane, the theory model must be studied on the basis of considering many factors. In addition, the measurement of flux density distribution based on theoretical analysis has important meaning in practical application.This paper is to calculate the flux density distribution of parabolic concentrator, and the influences of many factors are taken into account at the same time. Furthermore, on the basis of absorbing advanced experience of foreign countries and considering the requirement of solar energy technique research in our country, a flux density distribution measurement system of parabolic concentrator is developed and studied by experiments. All in all, the following research works have been done in this paper:1. Monte Carlo estimation of flux density distribution of focus spot of parabolic concentrator. The optical paths of concentrator system are analyzed. The flux density distributions on receiving planes are calculated. The main factors influencing flux density distribution are taken into account more fully, so the calculation model is more closed to the practical situation and the effects of these factors on flux density distribution are also analyzed. The optimizing design method of rotation parabolic concentrator is put forward based on Monte Carlo method. Considering loss of the gap area between two adjacent small mirrors, the optimal number of mirrors in radial and circumferential direction is obtained. Consequently, the optimizing design method provides theoretical base for fabrication of rotational parabolic concentrator.2. Finite element analysis of flux density distribution of focus spot of parabolic concentrator. Considering optical properties of concentrators, the finite element method is used to calculate the flux density distribution on the focal plane of parabolic concentrator and parabolic cylindrical concentrator. The method is certified by comparing the calculation results of Monte Carlo method with those of finite element method. In order to prove versatility of the method, hemispherical and cylindrical receivers are calculated respectively. For other shapes of concentrators or receivers, the flux density distribution of focus spot can also be calculated as long as the lattice subdivision method is changed. Consequently, the finite element method not only overcomes the shortcoming of short versatility of existing algorithms, but also provides a new approach for calculating flux density distribution.3. Developing of the flux density distribution measuring system of parabolic concentrator. By using an indirect method based on CCD camera and Lambert target, a flux density distribution measurement system of point focusing concentrating equipment is developed. The whole measurement system is designed and the calibration methods of the flux density and the coordinates of measuring point on receiving plane are investigated. Then nonlinearity and the heterogeneity of CCD camera are corrected.4. Experimental investigations on the flux density distribution of focus spot of parabolic concentrator. The flux density distributions on focus plane and many defocusing planes are measured by the measurement equipment and focusing characteristics of the spots on each plane are also analyzed. The measurement result of flux density distributions on focal plane is compared with that by Monte Carlo method. In addition, some parameters evaluating concentrating performance of concentrator are calculated, which conclude optical efficiency, geometric concentrating ratio, energy concentrating ratio and the relative percent of greatest disagreement of the flux density. At last, the uncertainty of the measurement system is analyzed.