A hybrid system formed by a photovoltaic module and a thermoelectric module has a great potential to enhance the solar-to-electricity efficiency. A mathematical model based on the first law of thermodynamics and the heat transfer analyses of the hybrid system is built, where the overall efficiency of the system is enhanced by optimizing the system as a whole. The model is used to study hybrid systems formed by commercially available photovoltaic modules and thermoelectric modules. It is found that, due to a limited incoming heat flux for the thermoelectric module, the overall performance of the hybrid system depends not only on the intrinsic properties of the materials forming such a hybrid system, but also on their working conditions, such as incoming solar radiation, geometry of each module, and interfacial properties. The results indicate that only photovoltaic modules with low temperature coefficient and low efficiency can truly benefit from forming such hybrid system, and the optimization of a hybrid system must be done as a whole.