Abstract In this work, we have investigated the detailed melting process of a nano-PCM inside a concentric cylindrical thermal energy storage (C-TES) system. The C-TES system is made of two concentric cylinders where inner cylinder acts as a thermal source having a constant surface temperature. The space between two cylinders is filled with a bio-based nano-PCM. Copper oxide (CuO) nanoparticles are dispersed in coconut oil bio-based PCM to form the nano-PCM in this research. Initially, a mathematical model is developed for the proposed C-TES system in the form of non-linear differential equations. The modelled differential equations are solved numerically to visualize the melting process, track the interface between the solid and liquid phase of nano-PCM, calculate the transient heat transfer rate, and determine the melt fraction. The effect of nanoparticles volume fraction and size of the cylinders on the melting and heat transfer performance are investigated extensively. A comprehensive experimental setup is developed to execute the visualization experiment and compare the melting process of PCM and nano-PCM. Both numerical and experimental results exhibit that the melting rate is faster in nano-CPM when compared to the base-PCM.