Based on known theories of twinning in semiconductor crystal growth, a new model is proposed to study the occurrence of twins during the solidification of photovoltaic multicrystalline silicon ingots. It is expected that twins will appear on facets existing at the grain boundary solid liquid triple line. Necessary conditions for the existence of facets are derived and it is shown that twinning remains a function of the probability of nucleation of twinned nuclei. It is demonstrated that this probability is in qualitative agreement with the experimental observation for cases where the grain orientation is such that an angle of 132 degrees occurs between a facet and a grain boundary. However, full validation of the model requires accurate values of interfacial energies at the melting point, which are currently lacking.