Simultaneous multiple surface concentrators for large acceptance angles and gap losses control

Abstract

Gap losses in solar concentrators have always been a difficult issue to resolve, especially for wide acceptance angle optics. Flow-line optics (such as the CPC) may be designed for wide acceptance angles but need the mirrors to touch the receiver. Any gap created between the mirrors of the concentrator and its receiver can lead to rays being lost and maximum concentration not being reached. The gap is imposed by the need to eliminate the contact between mirrors and receiver, which creates a thermal short-circuit which would reduce thermal efficiency. SMS optics may be designed to avoid contact between the optical surfaces and receiver, but mostly have only found application in small acceptance angle configurations. Here we propose a double SMS, double reflective configuration that can control the gap losses and be designed for large acceptance-angles (low concentration factors). By using only mirrors, this optic may be made in a large size and used in large solar concentrators. Its wide acceptance angle makes it suitable to be used also as a second stage element in a primary-secondary optic configuration. A raytracing technique to calculate the performance is used and the results show that these optics virtually achieve maximum concentration.