Adapting Smart Materials for Efficient Thermal Energy Storage Systems

Thermal energy storage (TES) systems are fundamental to achieving net-zero greenhouse gas emissions by 2050, the main objective of the European Green Deal. The increasing penetration of renewable energy sources (RES) and the need for improved energy efficiency require flexible energy systems capable of managing the intermittent nature of renewables. TES supports this transition through electricity load shifting, reducing peak demand and enhancing sector coupling and demandside flexibility. Conventional sensible heat storage systems are widely spread but are limited by low energy density and consequent space requirements, motivating the development of innovative storage materials. Thermochemical materials (TCMs) offer the highest values of energy storage density through reversible chemical reactions, enabling long-term storage with minimal losses. Phase change materials (PCMs) provide high volumetric energy density by storing latent heat during phase transitions at constant temperature. A wide variety of PCMs with different thermophysical properties and phase change temperatures are available, making them suitable for different applications. The combination of TCMs and PCMs in hybrid systems creates a beneficial synergy: TCMs enable longduration energy storage while PCMs can provide thermal buffering and temperature control. The development of a system of this kind is the objective of the ECHO project, in which the employment of a closed-loop TCM reactor allows to build a compact, modular system for residential applications. In the system, PCMs are used for three purposes: as enhancer for thermal insulation, integrated in a buffer storage, and in a cooling unit to be used in warmer climates. The charging of the system is possible through a heat pump, taking advantage of electricity overproduction, or directly connecting the system to on-site RES. The project demonstrates the potential of integrating TCMs and PCMs to improve the efficiency and flexibility of TES systems.