In this paper, an experimental study of an innovative latent heat storage unit integrated with the condenser of the heat pump system is presented. Novelty: a heat exchanger has been developed and designed to store the heat released from the condenser of the heat pump using a phase change material. For a sustainable and efficient heating system, it is aimed to use the phase change material in the heat pump system. Latent heat storage unit designed for this purpose has been tested in both air source heat pump and solar assisted heat pump systems. In addition, a new double-pass solar collector has been developed for the solar-assisted heat pump. The average coefficient of performance values varied between 2.19 and 2.34 for air source heat pump system and 2.32 & ndash;2.77 for solar-assisted heat pump system. With the use of solar energy, the increase of performance of the heat pump was achieved by 15.67%. It was observed that the instantaneous thermal efficiency of double-pass solar collector could reach up to 79.16%. Phase change material in the latent heat storage unit melted and solidified in 180 and 348 min for air source heat pump system, and 150 and 307 min for solar-assisted heat pump system. This result shows that the melting process accelerates under high solar irradiation, and the total melting time decreases.