Domestic hot water (DHW) has a significant share in buildings energy consumption. In order to reduce this consumption, various solutions have been proposed such as controlling the system in an efficient way, using renewable sources and using phase change materials (PCM) in the system to increase heat capacity. However, this study is not only offering heat capacity improvement of the DHW storage unit but also proposing that energy efficiency can be improved by controlling the heat releasing time of the PCM. In this study, supercooled PCM tubes are placed in a water tank and charged with a solar assisted heat pump unit, these supercooled PCM tubes can then be discharged anytime when the hot water is required. In this paper, a transient thermodynamic model is built for the whole system including solar collector, heat pump, water tank with PCM and DHW demand profile. System components are modelled and a 24 h of demand profile is used in simulation for a UK home for summer and spring weather conditions. The results show that the PCM tubes effectively compensate the morning peak hot water demand and reduce daily energy consumption around 12.1% and 13.5% by shifting heating provision from immersion heater to solar heat pump. (C) 2020 Elsevier Ltd. All rights reserved.