In Winter, side A (Fig. 2) always remains unshaded, therefore the beam irradiance PbA on this side is given by eq. (38) or eq. (39). Side B may be partially shaded and the beam irradiance PshbB is given by eqs. (45), (46) or (47) where the collector azimuth is 180°, therefore, ys is replaced by (ys-180°). The total beam irradiance on the catenary tent collector in winter is: In summer, early in the morning and late in the afternoon, side A is partially shaded, therefore, the beam irradiance P^g is given by eq. (38) with the azimuth s-180°, i.e., thus the beam irradiance on both sides of the tent collector for early morning and late afternoon hours is: Diffuse Irradiance The irradiance on a concave collector is equivalent to the irradiance on a flat plate collector of the same aperture. This applies to direct as well as to indirect irradiances. Therefore, the difference irradiance Pd on the catenary is given by
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