New salt hydrate composite for low-grade thermal energy storage

This study aims to develop a new salt-based thermochemical composite for long-term storage of low-grade thermal energy which enables overcoming mismatch between energy demand and supply. The energy density and dehydration behaviour of five different salts; Al2(SO4)3·18H2O and MgSO4·7H2O, CaCl2·6H2O, MgCl2·6H2O, and SrCl2·6H2O are examined. Subsequently, the performance of two low cost host porous structures; expanded clay and pumice, impregnated with the most suitable salt for storing low-grade thermal energy is studied over a few number of cycles using a lab-scale packed bed reactor. The results showed that SrCl2·6H2O has the highest energy density and lowest dehydration temperature so that >80% of its energy density can be stored at <90 °C. Thermal cycling the composite materials revealed that up to 29 kWh/m3 and 7.3 kWh/m3 energy can be stored using expanded clay-SrCl2 (40 wt%) and pumice-SrCl2 (14 wt%), respectively. However, the performance of expanded clay dropped sharply over four cycles while the generated power using pumice composite was sustained almost constant over ten cycles. Although pumice-SrCl2 is a promising composite in terms of cyclability, further research is required to improve its energy storage capacity to make it attractive for large scale applications.