Advances in thermal energy storage materials and their applications towards zero energy buildings: A critical review

Buildings are responsible for one-third of the world's energy consumption, of which 60% is due to heating and cooling. To accomplish the low-carbon energy goal in the building sector, thermal energy storage offers a number of benefits by reducing energy consumption and promoting the use of renewable energy sources. This manuscript reviews recent advances in the development of thermal energy storage materials for building applications oriented towards zero energy buildings. Volumetric heat capacity of sensible, latent and thermochemical energy storage materials developed for low-to-moderate temperature applications are reviewed and assessed with a special focus on their technical characteristics and development stage. This encompasses most recent publications, international programmes and projects, and commercially available solutions. Physical, thermodynamic, kinetic and chemical properties are addressed, as well as costs. Advantages, drawbacks and challenges of the diverse alternatives are discussed. The analysis shows that solutions with the highest potential for competitive energy efficiency measures are based on latent and sensible energy storage systems, which present a volumetric thermal energy storage density up to 430 and 250 MJ/m3 respectively. Their applications in free-cooling ventilation systems, solar energy storage solutions for short and long-term storage periods, and demand-side management strategies towards the road to zero energy buildings are highlighted as promising, leading to a reduction of energy consumption of more than 30%. On the other hand, thermochemical energy storage does not yet show clear advantages for building applications, despite the potentially high energy density (up to 1510 MJ/m3) and heat availability for long-term storage periods. Currently, there is no available material for thermochemical energy storage that satisfies all the requirements for building operations. Besides, thermochemical solutions require different tanks and heat exchangers that should be carefully addressed for small-scale applications. Additional research efforts are needed to optimise operation conditions, efficiency, costs and system designs.