A closed-analytical expression for the solar heat gain coefficient (SHGC) of a glass-glass photovoltaic module for building-integration is constructed ab initio, from the thermal study of the general case of any number of planar parallel layers with homogeneous absorption of solar radiation. By introducing the optical model of Baenas and Machado, the expressions for the SHGC of the opaque and transparent parts of the module will be provided. The scope of the calculation and the assumed working hypothesis are in line with those of international standards for multiple glazing systems and building-integrated photovoltaic modules. The proposed model has been applied to a real case of study, showing an excellent agreement with the numerical and experimental related data. (C) 2017 The Authors. Published by Elsevier B.V.