Thermochemical energy storage with zeolite 13X: results from a full-scale solar heat application

Thermo-chemical thermal storage offers high energy density and appropriate temperature levels for solar heat applications. The water–zeolite working pair is promising for both residential and industrial use. This study investigates a full-scale zeolite–water thermal storage system comprising two adsorbent beds, each filled with 756 kg of dry zeolite 13X in an 8 m3 vacuum steam reactor. Hot water circulates through a multi-U-tube heat exchanger embedded in the zeolite bed, while steam condensation occurs an external heat exchanger connected to a phase-change reactor. Three complete charge–discharge cycles were performed under varying pressure and temperature conditions. The system showed consistent performance, with thermal storage efficiencies ranging from 35.6 % to 54.6 %. Volumetric energy storage densities varied between 19.7 and 50.1 kWh/m3, and gravimetric densities between 31.7 and 80.8 Wh/kg. The temperature–pressure trajectories followed the ideal cycle closely, confirming effective system design and control. These results confirm the feasibility of commercial-scale thermo-chemical storage using zeolite–water pairs. Key findings highlight a strong dependence of storage efficiency on regeneration pressure and temperature, and a repeatable performance across cycles, suggesting stable adsorption–desorption behavior over time.