Solar energy collection using vee-grooved surfaces

Abstract

The thesis presented is a study of the absorption characteristics of diffusely and specularly reflecting V-grooved surfaces. Concepts are developed for the so-called "apparent" absorptance of a V-groove cavity, as well as for the "effective" absorptance of a V-grooved surface. These concepts are formulated in closed form mathematical equations, which facilitate both the optimization of V-grooved surfaces and their engineering design. In order to verify the theoretical analysis, experiments are carried out on 34 V-grooved brass specimens. In addition, the experiments are meant to provide information about the behaviour of such surfaces used for solar energy collection. For that purpose, the specimens are exposed to simulated sunlight, and their effective absorptances, as well as their absorption efficiencies, are determined by a calorimetric method. The highlights among the results are: 1. V-grooves - carefully optimized and applied to a solar energy absorbing surface - can raise its absorptance almost to unity and improve its absorption efficiency. 2. Best performances at elevated temperatures can be expected from using metal surfaces which are provided with specular V-grooves having a small groove angle (< 30⁰). 3. The optimal groove angle is dependent on (1) the reflection properties of the surface, (2) the absorptance of the surface material, and (3) the ratio of groove depth to width of land which occurs between grooves.