Thermal energy storage is very important to eradicate the discrepancy between energy supply and energy demand and to improve the energy efficiency of solar-energy systems. The latent heat thermal energy storage (LHTES) systems have gained greater attention recently due to their reliability and high storage density at nearly constant thermal energy. The present work explores numerically the solidification process of a phase change material (PCM) in a triplex tube heat exchanger (TTHX) equipped with internal and external fins to enhance the heat transfer during the charging and discharging of the PCM. A two-dimension (2D) numerical model is developed using the Fluent 6.3.26 software program; the pure conduction and natural convection are considered for the simulation. Experimental and numerical data were adopted to validate the model from the literature; a good agreement has been found. Predicted results indicated that the solidification rate time of the TTHX with internal and external fins was about 50% of the solidification time of the TTHX without fins.