Phase change materials (PCMs) for thermal energy storage (TES) have become an important subject of research in recent years. Using PCMs for thermal energy storage provides a solution to increase the efficiency of the storage and use of energy in many domestic and industrial sectors. Phase change TES systems offer a number of advantages over other systems (e.g. chemical storage systems): particularly small temperature distance between the storage and retrieval cycles, small unit sizes and low weight per unit of storage capacity. The most important application fields of PCM are energy conversion in buildings. Furthermore they can be used in other various applications like solar energy systems, thermal insulation, green houses and textiles [1,2].