Abstract In this paper, the charging/melting of phase change materials (PCM) in thermal energy storage is discussed. An oil-driven system is considered in which oil acts as a heat-transfer fluid while solar salt (KNO3 – NaNO3) is used as a PCM. The aim of this study is to analyze the influence of increasing the number of heat transfer fluid HTF tubes during the charge cycle as a geometrical factor. The effect of changing inlet temperature is also examined. Four cases of geometric configurations are analyzed in this research in order to understand the effect of increasing the number of HTF tubes on the total melting time of PCM. Moreover, three inlet temperature conditions are considered to study their influences on melting time. Results indicate that by increasing the number of HTF tubes, total melting time of PCM decreases as it liquefies in four tube cases in almost 165 min, as compared with a single tube which took 234 min to completely melt. Furthermore, inlet temperature plays an essential role in reduction of total melting time.