Faceted concentrators optimized for homogeneous radiation.

For technical reasons, large three-dimensional compound parabolic concentrators (CPC's) are often built from facets with either no or only one-dimensional curvature. We analyze CPC approximations made with various numbers of axial and circumferential subdivisions. Incident radiation within half-angles of 10 degrees and 30 degrees is considered. The reflectivity of the mirrors is assumed to be 90% or 95%. The performance of faceted concentrators can be significantly improved by optimization as compared with heuristic CPC approaches. The highest increase in transmission that we observed was 19% greater as compared with that of a heuristic CPC approximation. The shapes of the optimized concentrators differ from that of a classic CPC, and most of the optimized concentrators are longer than a classic CPC. For practical concentrators with a small number of facets, the optimized geometry provides better performance than a heuristic approximation of the CPC shape.