Calculation of the monthly-average transmittance-absorptance product

A method is presented for estimating the ratio of the monthly average transmittance-absorptance product for a solar collector surface to the value of this product for normal incidence. Theoretical and experimental determinations of the (direct) beam component contribution to the transmittance-absorptance product are discussed. A calculation of the monthly average daily solar radiation per unit area absorbed on a collector plate is given for the Madison, Wisconsin climate. (SPH)