Development and demonstration of compound parabolic concentrators for solar thermal power generation and heating and cooling applications. Progress report, July--December 1975

Work on the development of Compound Parabolic Concentrators (CPC) is described. A tenfold concentrator with a cavity receiver was constructed and tested. The optical efficiency was very good (65 percent), but the thermal performance was degraded by heat losses of the cavity receiver. A 20 ft/sup 2/ (1.86 m/sup 2/) concentrating collector (5.3x) has been tested for thermal and optical performance, and the optical efficiency was excellent (68 percent). In this collector, aluminum extrusions were used to define the CPC shape and provide the fluid-flow path. A 30 ft (9.14 m) long collector (10x) has been designed and is being built for daily-cycle testing. The expected performance of this collector has been evaluated. The conceptual design of a lightweight collector using evacuated glass tubes around the absorber is presented. Various construction techniques for use with low-cost materials, such as plastics, are being evaluated for this collector. Optical design studies of Compound Parabolic Concentrators for tubular absorbers and for use as secondary concentrators are discussed. Comparison of the CPC with tube and the CPC with one-sided flat absorber shows that the tubular configuration is preferable not only because of lower heat losses but also because of lower collector cost. For tracking concentrators with line focus, the use of second-stage concentrators is found to be cost effective; the CPC is found to be significantly better for this application than a V-trough. A summary of the results of subcontracts described in the previous progress report are presented, and the influence of these results on ANL programs is noted