The effect of non-direct insolation on the radiative performance of trapezoidal grooves used as solar energy collectors

Abstract

Some possible applications of solar energy require heat at temperatures above those associated with flat-plate collection but below those usually associated with an economical focusing collector. Collection temperatures in this range may be economically obtained using moderately concentrating, non-focusing, trough-like collectors. In this paper the radiative performance (the effective solar absorptivity and concentration ratio) of moderately concentrating collectors, composed of east-west aligned parallel, trapezoidal grooves, is examined. Both direct and non-direct insolation performance is discussed. Results are presented indicating performance degradation due to non-direct insolation. Finally, nomographs are presented which allow one to determine the radiative performance of the grooved collectors when exposed to various combinations of direct and non-direct insolation.