In this paper, an analysis of the thermal performance of triple concentric-tube latent heat storage systems filled with a commercial phase change material (PCM: RT50) is presented. The triple concentrictube storage systems incorporating PCM are connected with a flat-plate solar collector. Water acting as heat transfer fluid (HTF) flows in the solar collector and receives solar thermal energy. The latter is then transferred by forced convection to the PCM and stored as latent heat in the storage unit. The finite volume method is used to model and numerically investigate the melting and heat transfer processes. The effect of natural convection on the melting heat transfer is taken into consideration through an effective thermal conductivity of the liquid phase of PCM. The thermal performance of the triple concentric-tube latent heat storage unit is evaluated and compared with the performance of the double concentric-tube storage unit under the meteorological conditions of a typical day of the month of July in Marrakesh city, Morocco. The results reveal that the combined solar collector with triple concentric-tube storage unit owns higher storage and collection efficiencies than that combined with double concentric-tube unit. (C) 2018 Elsevier B.V. All rights reserved.