© 2021 Elsevier LtdIn this paper, thermal charging and discharging processes of a phase change material (PCM) dispersed with graphene nanoplatelets (GN) are investigated in a horizontal cylinder for thermal energy storage. The heat transfer and phase change processes are modeled using the enthalpy-porosity method. The momentum and energy equations are solved using a commercial code. The numerical simulations are validated by comparison with experimental and numerical data of the literature. The results showed that GN concentrations (i.e. ϕ = 0, 0.5 and 1 wt% GN) expedite the charging time while a slight reduction in melting time is obtained for ϕ = 3 wt%. The solidification time reduced by up to 50% whereas the thermal storage capacity declined by up to 14%. These results can help designing efficient thermal energy storage systems.