The energy production provided by a heat excess or a discontinuous source (solar radiation, waste heat, etc.) involves the utilization of a thermal storage systems. In this work, an experimental study of a storage system using paraffin as phase change material (PCM) has been done. This system takes the form of two rectangular cavities incorporating behind the absorber of a flat plat solar collector. Measurements were performed during different weather conditions and illustrate that the PCM contributes to increase the performance of the solar collector at night. An analysis of the temperature stratification inside the PCM-filled cavities was also carried out. Theoretical solid-liquid of phase change material model is used to evaluate the PCM melted volume fraction, liquid-solid interfaces, PCM temperature and melting/solidification flow in the PCM-filled cavity used in the present experimental study. (C) 2013 Elsevier Ltd. All rights reserved.