Optical design of build-up aspherical solar concentrating mirror

In this paper,a build-up aspherical solar concentrating mirror and its design method are presented.It is composed of 38 pieces of revolution surfaces,and each piece of revolution surface is the part of the aspheric surface defined by a set of specific coefficients C,a2,a4,a6,a8,a10. According to the even aspherical equation and the law of reflection in vector form,the relationship between the direction vectors of rays of light reflected from the inner wall of aspheric surface and the coefficients of an aspherical equation,C,a2,a4,a6,a8,a10,has been derived. By appropriately choosing these aspherical coefficients,namely,appropriately adjusting an aspherical surface type,the reflected light beam can have specific direction vectors,which can make the sunbeams incident on an aspherical inner wall focus on a particular area and form a small spot. Each group of specific coefficients is obtained by using particle swarm optimization algorithm. The focusing effect of the solar concentrating mirror with the specific coefficients is demonstrated by using computer simulations and proved experimentally. The theoretical compression ratio for this concentrating mirror is 330∶ 1. The focused spot can be used as a high temperature heat source and the concentrating mirror can be used in a solar heating device.