Renewable energy is a potential alternative energy provider with fewer CO2 emissions. However, the mismatch between energy supply and demand is the main disadvantage. Therefore, thermal energy storage becomes an essential technology for enhancing renewable energy efficiency and providing energy supply to the end user. In solar thermal energy systems, hot water tanks are widely used as sensible heat storage technology. Moreover, water storage usually requires large volumes and their improvement has been studied in terms of shape and arrangement. Latent heat storage materials are a potential technology for implementation in water storage tanks in order to reduce their volume and to enhance their efficiency. In this paper, the incorporation of shape high density polyethylene spheres with PCM into domestic hot water tanks is studied. Undesired results obtained in the water tank set-up lead the authors to analyse the PCM leakage in the laboratory. Laboratory analysis pointed out that the PCM-spheres must be thermally cycled and cleaned before their implementation in real application of domestic hot water in order to stabilize the PCM content inside the PCM- spheres.