Holographic solar concentrators

Abstract

The approach selected is the fabrication of holographic optical elements which will focus to either a line or a point. A concentrating mirror is replicated in the hologram, which consists of dichromate gelatin exposed to a laser beam. The dichromate gelatin can be processed to produce a non-uniform microstructure, which gives the hologram a significant waveband width. Even so, it becomes necessary to stack at least three holograms, with each reflecting a different region of the solar spectrum, if we are to reflect most of the solar energy. To achieve high efficiency, it is necessary to obtain adjacent quasi-square waves for the efficiency—wavelength profile of each of the holograms in the stack. Profile information was obtained by the use of a monochromator coupled to a computer. An optical efficiency in excess of 50% was measured for a three-hologram stack. This represents approximately 70% of the efficiency achievable within the limited measuring range of the monochromator. A line-focus holographic concentrator model has been built for demonstration purposes. A cost analysis for mass producing holographic concentrators indicates that holographic concentrators become cost effective in relation to mass-produced conventional concentrators when the holographic optical efficiency exceeds 70%. To surpass this number, it becomes necessary to produce a five-hologram stack and to broaden the monochromator optical sensitivity range.