Thermal Energy Storage (TES) is a method that can be used to overcome the shortcomings of Solar Water Heater (SWH). TES requires an energy storage medium called the Phase Change Material (PCM). One type of PCM material is paraffin wax because it has a high energy density (200 kj / kg) but the thermal conductivity is low (0.2 W / m.OC), so it is necessary to add other materials that have high thermal conductivity. In this study the PCM mixture used was a mixture of paraffin wax with 10% mass fraction copper powder. The difficulty in experimental research is that when the melting and solidification of the PCM can not be predicted, therefore it need a Computational Fluid Dynamics (CFD) simulation study. One of the objectives of this research is to determine the time of the melting and solidification of the paraffin wax mixture with 10% copper fraction mass powder. The geometry configuration consists of a tank as a Heat Transfer Fluid (HTF) and 32 copper pipes containing a PCM mixture. This simulation using ANSYS Fluent 18.0 which consists of continuous charging and discharging processes. The charging process has a water discharges of 0.6 LPM and 0.9 LPM with a 1200 Watt heat flux heater. While the discharging of 1.5 LPM and 2.5 LPM water discharges. Simulation objects include temperature evolution and melting time and solidification of the PCM mixture. The simulation results show that the greater the flow rate, the faster the melting and solidification time. This is evidenced by the perfect melting time in the charging process variation of 0.6 LPM, which is 3.43 hours and 0.9 LPM which is 2.96 hours. While the time to achieve perfect solidification in the process of continuous discharging at a variation of 1.5 LPM is 0.46 hours and 2.5 LPM is 0.39 hours. The highest value of heat absorption rate occurred at a variation of 0.9 LPM : 638.74 J/s in water, 73.61 J/s in sensible PCM, and 216.43 J/s in latent PCM. At a variation of 0.6 LPM : 557.04 J/s in water, 55.95 J/s in sensible PCM and 228.71 J/s in latent PCM. The highest value of heat release occurred at a variation 2.5 LPM : 810.75 J/s in water, 36.95 J/s in sensible PCM and 7085.00 J/s in latent PCM. Whereas the value of heat release in the variation of 1.5 LPM was: 526.47 J/s in water, 28.55 J/s in sensible PCM and 3298 J/s in latent PCM. The highest value of temperature rise occurred at a variation of 0.9 LPM : 12.76 OC/hour in water and 12.50 OC/hour in PCM. While the increase in temperature at a variation of 0.6 LPM of : 11.12 OC/hour in water and 10.88 OC/hour in PCM. The highest value of temperature reduction occurred at a variation of 2.5 LPM of : 16.19 OC/hour in water and 15.592 OC/hour in PCM. At a variation of 1.5 LPM of : 10.51 OC/hour in water and 10.28 OC/hour in PCM. The deviation value of the 0.6 LPM variation charging test is 32.09 % and the 0.9 LPM variation is 17.80 %. While testing the continuous discharging variation of 1.5 LPM is 61.35 % and at 2.5 LPM variation is 48.79 %.