© 2020 University of Split, FESB.Cooling of photovoltaic panels (PV) by using phase-change materials (PCM) becomes a popular research technique due to the high latent energy storage capacity of PCMs. Therefore, the acceleration of phase-change process and reducing the required time for energy charging and discharging turns out to be a crucial point in these applications. Utilization of fins is an effective way for phase-change acceleration as it promotes heat diffusion into the material and shortens the phase-change time. Besides, the branching fins are also introduced by researchers in order to further accelerate the charging/discharging process by providing larger surface area for the same volume compared to rectangular fins. However, once the melting process is completed, the natural convective heat transfer may be promoted or degraded by the fins, which is worth to be investigated. For this reason, the natural convection heat transfer in a rectangular enclosure that represents a PCM container in a PV/PCM system is numerically investigated in this study by considering three aspect ratios (AR=1, 2 and 4), three Rayleigh numbers (Ra=104, 105 and 106) and two types of fins as rectangular and tree-like branching fin. The rates of increment and decrement in the heat transfer rate are presented taking the finless enclosure as the reference case. The Prandtl number of the molten phase-change material is calculated as 41.22 and kept constant during the simulations. The outcomes of the simulations are presented in terms of streamline and isotherm contours, and mean Nusselt numbers. The computed results revealed that the natural convection can be promoted up to 13% or degraded by 4.5%, depending on Ra and AR by the inclusion of fins. Besides, it is also noticed in this study that utilizing a tree-like branching fin is not as effective as a rectangular fin with the same mass.