Determining the optical quality of focusing collectors without laser ray tracing

Abstract

This paper describes a .novel alternative to the lase~ ray trace technique for evaluating the optical quality of focusing solar collectors. The new method does not require any-equipment beyond that which is used for measuring collector efficiency; it could therefore become part of routine collector testing. The total optical errors resulting from imperfect specularity and from inaccuracies in reflector position or slope are characterized by an angular standard deviation O'opticalt the r~ deviation of the reflected rays from the design direction. The method is• based on the fact that the off-axis performance of a concentrator depends on a optical• An angular scan is performed; i.e., the collector output is measured as a function of misalignment angle over the entire range of angles for which there is measurable output (typically a few degrees). This test should be carried out on a very clear day, with the receiver close to ambient temperature (if the ' latter condition cannot be satisfied, appropriate corrections are nec_essary). The parameter a optical is then determined by a leastsquares fit • between the measured and the calculated angular scan. We tested the method on a parabolic trough collector manufactured by Hexcel, but it is suitable for parabolic dishes as well.

Indoor characterization of reflective concentrator optics

“…The mean slope error may be measured by various techniques, see e.g. [3], [5]. With our setup we measure the concentration distribution in the solar cell plane.…”

Determining The Optical Quality of Focusing Collectors without Laser Ray Tracing

“…The brightness distribution of the sun has been measured by the Lawrence Berkeley Laboratory circumsolar telescope as brightness Bsun, radial (6) in W/m2 steradians at an ~ngle a from the center of the solar disk. To yield the dimensionless intercept factor, Bsun must be normalized by the beam irradiance:…”

“…The variation of the brightness distribution between clear days (ratio of circumsolar over beam irradiance less than one percent) is sufficiently small that the analysis of the misalignment data can be based on thP standard scan in Table 4-1 uf Ref. [6] i t a circumsolar telescope is not available.…”