Storage of heat is seen as a major issue for the development of solar energy for house heating and cooling under all climates. Most of the storage systems available oil the market use water as the storage medium. The idea studied here was to add a phase change material (PCM) module at the top of a hot-water storage tank with stratification. An experimental solar pilot plant was constructed to test the PCM behaviour in real conditions. The PCM module geometry adopted was to use several cylinders. A granular PCM-graphite Compound was chosen Lis the PCM for the experiments presented here. (c) 2005 Elsevier B.V. All rights reserved.