Optical modeling for a two-stage parabolic trough concentrating photovoltaic/thermal system using spectral beam splitting technology

A two-stage parabolic trough concentrating photovoltaic/thermal (PV/T) system is described, which contains a concentrator, a spectral beam splitting filter, an evacuated collector tube and the solar cell components. The nondimensional optical model with the focal length of the concentrator as the characteristic length has been developed to analyze the properties of the concentrating system using the beam splitting filter. The geometry concentration ratio and the size of solar image at different structure parameters have been obtained. Based on the ray tracing algorithms, a detailed three-dimensional model is set up to evaluate the local radiation flux density distribution on the elements’ surfaces. And the effects of the solar brightness distribution and optical errors (e.g., alignment error and tracking error) are also involved. Furthermore, the spectral distribution of the solar radiation is illustrated with the beam splitting filter, which has been specially designed using the needle optimization method. It is shown that using the filter the heat load of the cell can be reduced by 20.7%, up to 10.5% of the total incident solar energy can be recovery by the receiver, and the overall optical efficiency in theory is about 0.764.