Planar micro-optic solar concentration using multiple imaging lenses into a common slab waveguide

Abstract

Conventional CPV systems focus sunlight directly onto a PV cell, usually through a non-imaging optic to avoid hot spots. In practice, many systems use a shared tracking platform to mount multiple smaller aperture lenses, each concentrating light into an associated PV cell. Scaling this approach to the limit would result in a thin sheet-like geometry. This would be ideal in terms of minimizing the tracking system payload, especially since such thin sheets can be arranged into louvered strips to minimize wind-force loading. However, simply miniaturizing results in a large number of individual PV cells, each needed to be packaged, aligned, and electrically connected. Here we describe for the first time a different optical system approach to solar concentrators, where a thin lens array is combined with a shared multimode waveguide. The benefits of a thin optical design can therefore be achieved with an optimum spacing of the PV cells. The guiding structure is geometrically similar to luminescent solar concentrators, however, in micro-optic waveguide concentrators sunlight is coupled directly into the waveguide without absorption or wavelength conversion. This opens a new design space for high-efficiency CPV systems with the potential for cost reduction in both optics and tracking mechanics. In this paper, we provide optical design and preliminary experimental results of one implementation specifically intended to be compatible with large-scale roll processing. Here the waveguide is a uniform glass sheet, held between the lens array and a corresponding array of micro-mirrors self-aligned to each lens focus during fabrication.