ON THE FACTORIZATION OF INCIDENCE ANGLE MODIFIERS FOR CPC COLLECTORS

It has been suggested earlier that the incidence angle modifier K-tau alpha for low concentrating collectors with tubular absorbers could be factorised according to K-tau alpha(theta(t), theta(l)) proportional to K-tau alpha(theta(t), 0)K-tau alpha(0, theta(l)), where theta(t) an d theta(l) are the projected incidence angles in the transversal and l ongitudinal projection planes, respectively. Ray-tracing calculations on low-concentrating CPC collectors with flat absorbers parallel to th e cover show that a K-tau alpha factorisation overestimates the annual delivered energy from the collector by about 4-5%, when compared to c alculations using the full incidence angle modifier. Data from outdoor testing has been used for characterization of incidence angle behavio ur for a truncated CPC with a concentration of C=1.56. Multiple linear regression analysis was used. This analysis technique makes feasible the determination of angular dependent incident angle modifiers and is an efficient tool to use for all collectors which cannot be character ised by standard equations of the incidence angle dependence. (C) 1997 Elsevier Science Ltd.