The need of a more persistent human presence on sea is driving the development of increasingly more efficient Autonomous Underwater Vehicles. A particularly promising solution to power these vehicles is the retrieval of energy from the ocean temperature gradient. This paper investigates the use of thermoelectric generators (TEGs) for that purpose, by presenting a complete model of thermoelectric generators embedded in the hull of an underwater glider. The model includes not only the thermoelectric generators but also the heat transfer process and the behaviour of different heat storage materials. Several simulations are performed, for each storage material, to determine the adequate design parameters leading to sufficient energy generation for a thermal glider. It is shown that the use of Phase Change Materials (PCM) as an energy storage material is highly advantageous over the use of sea water or stainless steel. Furthermore, it is shown that this approach, although leading to a high number of TEGs and mass of PCM, is compatible with current existing glider dimensions.