Energy storage systems have been recognized as one of the most important technologies for conservation and utilization of renewable energy sources. In this study, core-shell phase change material (PCM) nanofibers were fabricated by using coaxial electrospinning of polyethylene glycol (PEG1000) as the core material (i.e., PCM) and polyamide 6 (PA6) as the shell (supporting) material. The effects of inner core solution flow rate and PEG content on the morphology, structure, and phase change behavior of the produced composite fibers were studied thoroughly by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The experimental results indicated that by increasing the flow rate of the core solution, slightly thicker fibers can be produced, and the onset temperature of melting is reduced. Also, as the PEG concentration rises, the peak temperature increases and higher amounts of latent heat enthalpy are achieved. The results indicate that the fabricated core-shell structure has almost resolved the leakage instability normally associated with other types of PCM fibers and hence, has the potential to improve thermal storage capacity. (C) 2017 Elsevier Ltd. All rights reserved.