The present study aims to investigate the solidification characteristics of water based NFPCM (nanofluid phase change material). The NFPCM was prepared by dispersing copper oxide nanoparticles and a nucleating agent in the base PCM (phase change material). The experiments were conducted at various bath temperatures and the NFPCM exhibited a significant reduction in solidification time of about 35% due to enhanced heat transport properties. Further, 50% of total mass solidified during 25% of total solidification time in both PCM and NFPCM. The presence of nucleating agent eliminated the ramifying problem of subcooling in the PCM and this will allow the evaporator to operate at a higher temperature in a chiller. The enhanced heat transfer rate of the NFPCM without subcooling is advantageous for many CFES (cool thermal energy storage) applications. It is construed from the experimental results that considerable energy saving potential is possible in the CTES system by operating the evaporator at a higher temperature. (C) 2014 Elsevier Ltd. All rights reserved.