title: Wide-angle lenses and image collapsing subreflectors for nontracking solar collectors.
abstract: This paper presents new optical methods for the design of nontracking solar energy concentrators with acceptance angles of 60 degrees in the elevation (altitude) plane and +/-50 degrees in azimuth sectors. We have designed and constructed a two-point corrected cylindrical stepped prism lens (SPL) with 30.48-cm aperture height and F/D congruent with 1, which focuses well over the acceptance interval. Image collapsing subreflector (ICS) surfaces are synthesized that reflect the incident illumination refracted by the lens onto a small fixed absorbing area or shelf ~7.6 cm wide resulting in near maximum theoretical concentration ratios for these broad acceptance angles. Nearly 100% of the incident optical rays intercept the absorber shelf. The wide-angle and image collapsing optical properties were confirmed by laser and solar experiments. Rooftop thermal tests on a 30.5 x 30.5-cm collector section using selectively absorbing tubes with water as circulant were conducted that indicate aperture efficiencies of ~60% could be exected on large area collectors based on this design.
authors.forename: C J
authors.initials: CJ
authors.lastname: Sletten
authors.forename: F S
authors.initials: FS
authors.lastname: Holt
authors.forename: S B
authors.initials: SB
authors.lastname: Herskovitz