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; Al-2(SO4)(3)center dot 18H(2)O and MgSO4 center dot 7H(2)O, CaCl2 center dot 6H(2)O, MgCl2 center dot 6H(2)O, and SrCl2 center dot 6H(2)O 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 center dot 6H(2)O has the highest energy density and lowest dehydration temperature so that >80% of its energy density can be stored at <90 degrees C. Thermal cycling the composite materials revealed that up to 29 kWh/m(3) and 7.3 kWh/m(3) 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. (C) 2018 Elsevier Ltd. All rights reserved.