This paper presents an experimental investigation of the performance of an encapsulated phase change energy storage during the charging and the discharging processes. The spherical capsules, containing water with a nucleation agent as a phase change material (PCM), fill the thermal storage tank. The heat transfer fluid which circulates through the tank and around the capsules is an aqueous solution of monoethylene glycol. A series of experiments were carried out to investigate the effects of various parameters including the inlet heat transfer fluid temperature and flow rate, kinetics of cooling and heating, on the charging and discharging processes. The main results are: - There is a significant influence of the supercooling phenomenon during the charging process. - The lower the inlet coolant temperature and the larger the coolant flow rate are, the faster the storage is. The choice of the couples (flow rate, inlet temperature) must permit to store the total energy in a given time. - When a charge mode follows an incomplete discharge mode, the charge mode is the result of the crystallization of some capsules which present supercooling and of others which do not. The consequence is that the charge mode is made at a higher temperature with a relatively shorter duration. (C) 2009 Elsevier Ltd. All rights reserved.