A method of optical design and construction for low-cost Cassegranian type solar concentrators

This paper describes a design method for a two mirror solar concentrator and a fabrication method suitable for applications where light weight, cost and portability are important factors. The geometry of this Cassegranian type mirror system is defined by splitting a fixed radius of primary and secondary reflector into an equal number of complementary contour segments angled to collimate a radiant planar light source located between the two reflectors. The resulting optical design is validated using a ray trace program that simulates the specular reflections occurring within the system. The performance of a sample surface is analysed on the criteria of concentration and tracking error rejection. Construction of reflective surfaces is achieved using aluminised polyester film, supported by precision machined aluminium ribs. The performance of the constructed optical system is estimated using a relative reflectance measurement of the aluminised mirror film.