Second stage concentration with tapers for fluorescent solar collectors

Abstract

Light concentration of fluorescent sheet collectors can be enhanced by providing the output edges with a taper of a higher refractive index with reflecting surfaces. Concentration ratios achievable by this means are computed for two shapes of tapers, one with a plane boundary towards the collector and one with an additional cylindric lens. The general limitation of concentration ratio is given by Liouville's theorem or Abbe's sine condition. Computed second stage concentration ratios are: 1) For plane boundary taper andn ₁=1.5,n ₂=2 and three reflections in the taper:C=1.49, and 2) for the lens-taper combination under the same conditions:C=1.76, nearly reaching the Liouville limit, 1.79.