The overall objective of this work is to evaluate the potential of compressed expanded natural graphite (CENG) and phase change material (PCM) composites to improve the performance of solar domestic hot water (SDHW) systems. To achieve this target, an original approach has been chosen. Comparatively to other studies, in which the storage material is usually placed on top of the water tank, the proposed approach was to place the composite directly inside a flat plate solar collector in substitution to the traditional copper-based solar absorber. In a previous paper (Haillot et al., 2011), elaboration and characterization of various composites led to the selection of three relevant composites suitable to their integration into a solar thermal collector. The present paper is devoted to the analysis of such a system to evaluate its actual performance. To reach this objective, a numerical model is proposed and its reliability validated by mean of corresponding experimental data. Despite the fact that under summer meteorological conditions the performed simulation highlights an increase of the system efficiency by adding a composite to the solar collector, the cumulative annual performance of such a system is penalized by low efficiency during winter time. However, the obtained simulated results allow us to offer a perspective of work that would maximize the benefits of adding storage composite to a SDHW system. (C) 2011 Elsevier Ltd. All rights reserved.