A fast analytical method for calculating the radiation pattern of solar antennas (SOLANTs) consisting of metasurface-based solar cells is proposed. The proposed method is able to analyse both uniform and non-uniform metasurfaces. In the developed method, the reciprocity theorem along with the transmission line model is used to model the layered structure used in the design of SOLANTs. To model the printed antenna, the cavity model is modified to include the loading effect of solar cells on the antenna. The proposed method is used to analyse three different SOLANTs operating at different frequency regimes, and the results are verified through comparison with full wave numerical results. The proposed model can be used for optimization purposes with the goal of achieving the best possible configurations for SOLANT structures.