Thermoelectric generators using the Seebeck effect to generate electricity are increasingly used in various areas of human activity, especially in cases where a cheap high-temperature heat source is available. Despite many advantages, TEG generators have one major disadvantage: very low efficiency of heat conversion into electrical power which strongly depends on the applied load resistance. There is a maximum of generated power between the short and the open circuit in which it is zero. That is why optimization of TEG modules is particularly important. In this paper a method of maximization of generated power in a single TEG module is presented for two cases. The first case concerns a problem with fixed heat flux flow into the hot side of the module whereas the second one concerns a problem with fixed heat transfer parameters in hot heat exchanger i.e. supply gas temperature and heat transfer coefficient. A number of optimization results performed for various values of these parameters are presented and discussed.