Construction method and optical characterization of parabolic solar modules for concentration systems

A process to build modular solar reflectors by using plane mirrors and a sandwich structure has been developed. We applied this process to manufacture parabolic modules that can be assembled in a parabolic dish of 5 m in diameter with the focus at 2.5 m. This paper discusses the evaluation of the light collection performances of a single parabolic module. The reflectance of the mirror material was characterized by means of a UV-Vis spectrophotometer, in the 250-1200 nm wavelength range, and of a pyrheliometer, with respect to a direct solar spectrum. The illumination profile of a module mounted on a sun-tracking system was tested by power density measurements in and out of the focal plane, and spots were compared with a theoretical one. In order to evaluate the high-flux solar energy arriving at the focus of a module, a flat-plate calorimeter was built. The study was carried out by measuring the energy absorbed by the water flow and the external losses due to convection. Based on an energy balance, the intercept factor and the overall optical efficiency of the collector were estimated.