In Eq. (1), all of the terms are known, except for the intercept factor of the STSC, which is necessary to consider the geometric model of the STSC. Eq. (2) corresponds to the estimation of the intercept factor, and the total energy incident on the reflector (denominator) is easily established by substituting the value of the direct radiation and the aperture opening area. However, to determine the amount of energy intercepted (numerator), it is necessary to develop the terms of the numerator, which involve the geometric and optical models of the STSC.