In this study, the melting heat transfer in plate heat exchanger LHTES(Latent Heat Thermal Energy Storage) systems was numerically investigated. In the numerical analyses, using the Finite Volume Method (FVM), the phase change process was examined for different heat exchanger geometries (Geometry a, b and c), different heat transfer fluid (HTF) inlet temperatures (52 degrees C, 57 degrees C and 62 degrees C), different steel plate thicknesses (0.4mm, 0.6mm and 0.8mm) and different PCMs(Phase Change Materials) (RT-35 and n-octadecane). The numerical analyses were performed by simplifying the problem down to two dimensions. From the results, time-dependent average PCM temperatures, and liquid fraction contours and graphs were produced. The results showed that for the same PCM, boundary conditions and geometrical characteristics, the complete melting time of the PCM in a plate heat exchanger LHTES system with different geometries could be decreased by 75% in comparison to a cylindrical LHTES system of the same PCM volume. The maximum thermal performance achieved was recorded for the following conditions: Geometry a, a HTF inlet temperature of 62 degrees C, a steel plate thickness of 0.6mm and n-octadecane as the PCM. (C) 2019 Elsevier Ltd. All rights reserved.