This paper presents the performance evaluation of an integrated photovoltaic thermal (PVT) collector-phased change material (PCM) thermal energy storage (TES) system. The PVT collectors can generate both electricity and low-grade thermal energy during the daytime, and the thermal energy generated can be temporarily stored in the PCM TES unit and used for space heating during the night-time. Taguchi method and analysis of variance are used for the simulation design and data analysis, respectively. The thermal performance of the proposed system was evaluated in terms of the useful energy stored in the TES system. The results showed that the outlet air temperature of the TES unit remained at least 2°C higher than the inlet air temperature during the discharging process in the selected test day. The PCM type and the PCM charging air flow rate were the most important factors influencing the useful energy stored in the TES system.