The use of renewable energy sources represents a problem in its time unsteadiness where mismatch between demand and supply take place. To effectively utilize the renewable energy sources in building sector, the energy storage systems can help even out such mismatch. One of the ways to effectively utilize solar energy is to store it in a form of heat or cold. The use of phase change materials (PCMs) as thermal storage provides with higher energy density at smaller temperature difference than the sensible one. This is due to its high latent heat of fusion which is accumulated or released during the phase change process. Higher energy density of thermal storage is especially needed in retrofits of residential buildings where the space problem occurs. The latter occurs due to large volume of water thermal storage tank needed in such system. Therefore in the present research, energy density of existing water thermal storage system with three 100 l tanks connected in series is enhanced. The enhancement is performed with inclusion of PCM capsules inside the water storage tanks. The results from experiment shows that inclusion of PCM capsules led to higher heat storage for 68 % in comparison to water storage tank system. Therefore latent thermal storage with encapsulated PCM can be used for low temperature applications with smaller temperature difference in water heating and cooling systems.

This work was supported by the Slovenian Research Agency through the research program P2-0223 and by the EU Research and Innovation programme Horizon 2020 under grant agreement No. 768921. The authors would like to thank the European Commission and Slovenian Research Agency for enabling the funding.