Although water is a cheap and effective medium for thermal energy storage, other options are currently being studied, to increase the storage density or to reduce the cost of the storage. The authors have been developing a system which combines the advantages of stratified sensible heat storage and latent, phase change heat storage; i.e. a hot water storage tank with stratification where a phase change material (PCM) is included into a spiral tube installed in the top of the tank. The PCM used was a granular PCM-graphite compound of about 90 vol.% of sodium acetate trihydrate and 10 vol.% graphite. This paper presents the results of an experimental investigation of the performance of the new storage concept, and of a conventional hot water storage tank for comparison. The data are further analysed with respect to the energetic and exergetic performance of the two systems. Copyright (C) 2007 John Wiley & Sons, Ltd.