Cowa is developing compact thermal energy storages to boost renewables in buidlings and in thermal energy systems. The technology is based on capsules filled with a high energy density material. The capusles are stacked into water tanks increasing their capacity by up to factor four. The targeted application is photovoltaic driven heat pump systems, which will become much more self-sufficient. The materials used are cost-effective, fully recycable salt water mixtures based on food additives.