A laboratory equipped with the thermal energy storage unit utilizing the solar heat sources was designed and constructed. The spherical capsules which were filled with the phase change material (PCM) were installed inside the unit. The temperatures at inlet and outlet of the thermal energy storage (TES) unit and at the first through seventh layers of heat transfer fluid (HTF) were measured. Many groups of experimental schemes were designed to evaluate the storage unit’s performance. The effects of inlet fluid temperature and flow rate of HTF on the performance of the storage unit were analyzed. The experimental results showed that, with the inlet temperature and flow rate of HTF increasing, the time required to complete the charge process reduced constantly; the efficiency of thermal energy storage is consequently improved. The results provide the basis for designing, optimizing, and applying the TES unit.