One of the most successful applications in renewable energy is the utilisation of solar energy for domestic water heating systems. Depending on the location, about 70% of consumed energy in the residential sector is for space heating/cooling, hot water usage and appliances in cold climates. However, the full deployment of solar energy in domestic water heating is only possible when a good performance energy storage system at an acceptable price is available. Within the past decade, various types of systems deploying phase change materials as an energy storage unit or part of it were introduced. Some of these designs offer several advantages including high storage capacity, low storage volume, and isothermal operation during the charging and discharging phases. In this paper, the technical specifications and economic viability of some of the introduced designs are compared to each other under specific circumstances. This study is important and indicative to facilitate and pave the way for future research and developments of these products.