In this paper, different types of Thermal Energy Storage (TES) systems are reviewed and discussed, including sensible heat storage, latent heat storage and aquifer thermal storage. Design criteria, materials selection and numerical models employed have been analysed. The TES systems taken into account are: two types of concentric-tube latent heat systems with Phase Change Material (PCM), a latent heat system employing PCM and metal foam, a packed-bed molten salt thermocline system and an aquifer.