The present paper numerically investigates the performance of latent heat storage systems during solidification, which involves phase change material (PCM) capsules. Paraffin wax is considered as the PCM and water plays the role of heat transfer fluid (HTF). The simulation is conducted for two inlet temperatures, 30 degrees C and 40 degrees C, while the capsules' diameter varies in the range of 10 mm-60 mm. Among various existing models, the effective packed bed model which is not only able to provide temperature gradient data but also is capable of reporting entropy generation details. Results indicated that both reduction in capsules' diameter and the HTF inlet temperature unfavorably increase the amount of the system's irreversibility. However, it is demonstrated that the increase in the irreversibility does not essentially result in a reduction in performance of the latent heat storage system. In other words, the efficiency of the storage system is not a pure function of entropy generation number. In fact, the reduction in the diameter results in an improve in the second low efficiency while the inlet temperature reduction diminishes the efficiency. Results also implies that decisive parameters vary significantly only when the diameter reduces to 20 mm and further reduction doesn't affect the system performance noticeably. (C) 2017 Elsevier Ltd. All rights reserved.