Approximations to the CPC—a comment on recent papers by Canning and by Shapiro (original) (raw)
Related papers
Performance of compound parabolic concentrators with polygonal apertures
Solar Energy, 2013
The optical performance of CPCs having n-sided polygonal inlet and outlet apertures is investigated by Monte-Carlo ray-tracing. The polygonal CPCs are formed by circumscribing regular polygons about the circular apertures of an underlying revolved CPC. The resulting side walls are extruded 2D CPC profiles with 1-dimensional curvature thus profiting from improved manufacturability compared to the revolved CPC. Furthermore, these designs may be uniformly tiled on flat or curved planes with minimal gap loss for applications requiring multiple absorbers. The principal property of interest is the optical efficiency defined as the fraction of radiant power incident on the inlet aperture which reaches the outlet aperture. The effect of geometry, reflectivity, and surface errors on the optical efficiency is presented. In analyzing these effects, a new approach for calculating the average number of reflections is derived and utilized. Additionally, the flux distributions at the outlet of the concentrators are examined. Especially for large acceptance angles, the performance of polygonal CPCs with reasonable numbers of sides is found to approach that of the revolved CPC, which may be considered a limiting case of the polygonal CPC for n ! 1. It is found that the square CPC (n = 4) has some favorable anomalous behavior, with performance surpassing that of designs with 5 and 6 sides for small acceptance angles. Polygonal CPCs show promise as less expensive alternatives to the revolved CPC for applications including stationary solar concentrators, and secondary concentrators for dish, tower, and trough primaries.
New method of design of nonimaging concentrators
Applied Optics, 1992
A new method of designing nonimaging concentrators is presented and two new types of concentrators are developed. The first is an aspheric lens, and the second is a lens-mirror combination. A ray tracing of three-dimensional concentrators (with rotational symmetry) is also done, showing that the lens-mirror combination has a total transmission as high as that of the full compound parabolic concentrators, while their depth is much smaller than the classical parabolic mirror-nonimaging concentrator combinations. Another important feature of this concentrator is that the optically active surfaces are not in contact with the receiver, as occurs in other nonimaging concentrators in which the rim of the mirror coincides with the rim of the receiver.
Faceted Concentrators Optimized for Homogeneous Radiation
Applied Optics, 2000
For technical reasons, large three-dimensional compound parabolic concentrators ͑CPC's͒ 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°and 30°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.
Second-stage concentrators-a new formalism
Journal of The Optical Society of America, 1983
The concept of second-stage nonimaging concentrators is redefined. A model of an incoherent source of limited emitting angle serves to simulate the input rays to these elements. Hence the second stages may be classified as a subgroup of ideal concentrators that collect all the radiation emitted by such sources and concentrate it up to the maximum achievable limit. As a consequence of this discussion, it becomes obvious that, for any given plane behind a primary, an.ideal second stage can be designed with its entrance aperture located on that plane. Implications for the design of ideal reflectors with shielding windows are discussed.
Compound conical concentrators with elliptical receivers
Solar Energy, 1986
mGeometrical analysis of the compound conical concentrator (CCC) with a receiver of a general shape is given. Special emphasis is given to the concentrator with a receiver of an elliptical shape. Circular and strip receivers emerge as special cases in a generalized treatment. The CCC with a circular receiver has a quasi-parabolic profile, and the CCC with a strip receiver is made up of tangents to a system of confocal parabolas. Various intensity distributions may be obtained with the different receivers. Uniformly distributed concentrated-flux, most suitable for use with photovoltaic systems, can be easily obtained with CCC trough-type reflectors with strip receivers.
Optical analysis of point focus parabolic radiation concentrators
Applied Optics, 1981
A simple formalism is developed for analyzing the optical performance of point focus parabolic radiation concentrators. To account for off-axis aberrations of the parabola, an angular acceptance function is defined as that fraction of a beam of parallel radiation incident on the aperture that would reach the receiver if the optics were perfect. The radiation intercepted by the receiver of a real concentrator is obtained as a convolution of angular acceptance function, of optical error distribution, and of angular brightness distribution of the radiation source. For numerical calculations this method is more accurate and less time-consuming than the ray-tracing method.
Inverse illumination method for characterization of CPC concentrators
Optical Modeling and Measurements for Solar Energy Systems, 2007
The optical characterization of a CPC concentrator is typically performed by using a solar simulator producing a collimated light beam impinging on the input aperture and characterized by a solar divergence (± 0.27°). The optical efficiency is evaluated by measuring the flux collected at the exit aperture of the concentrator, as function of incidence angle of the beam with respect to the optical axis, from which the acceptance angle can be derived.
Flat plate collectors have been widely used for applications that demand temperature below 90ºC and large amount of research efforts are already made. For medium temperature range (90–300ºC) applications, concentrating type collectors are suitable, which are under investigation. Despite such advantages, only limited studies are made. Almost all the 3-D CPC reported are fabricated using vertical segments which have more surface errors. Thus, they need precise techniques for fabrication. The 3-D CP