storage by latent heat systems becomes the appropriate solution in several solar heat applications. In this context, we lead the proposed study concerning the thermal storage by latent heat in a solar domestic water heater. A quantitative comparison has been developed to sort out the performances of a given unit of latent heat storage (LHS) under the effect of some physical parameters. The inlet velocity and inlet temperature of the heat transfer fluid (HTF) and geometrical parameters like the radius of the storage pipe are considered as the influent parameters in this issue. The obtained results show that the increase of the inlet velocity and temperature allows the increase of rate fusion of the PCM and reduces the fusion time. However, the increase of the radius of the pipe makes the time of fusion relatively long