Sodium acetate-based hydrated salt for solar thermal storage

Phase-change material (PCM) is a promising thermal storage medium through its state change, which enables the storage of abundant thermal energy and a sustainable supply afterward. Sodium acetate hydrated salt (sodium acetate trihydrate (CH3COONa·3H2O)) is a suitable PCM in the lower-temperature range for solar thermal energy storage. However, its phase separation phenomenon restricts its actual utilization. In this study, disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O) and sodium metasilicate nonahydrate (Na2SiO3·9H2O) were employed as additives for sodium acetate trihydrate hydrated salt to prepare a qualified composite hydrated salt with excellent comprehensive properties. The study indicates that (a) the optimal mass ratio of sodium acetate trihydrate to disodium hydrogen phosphate dodecahydrate is 8.5:1.5, its undercooling degree varying within 2.1°C during 150 heating-cooling cycles, and (b) further addition of 1.5% sodium metasilicate nonahydrate could significantly enhance the stability of the heating-cooling cycle of the optimal composite hydrated salt, the undercooling degree becoming less than 1.3°C, and the heat-release platform is at about 51°C during 200 heating-cooling cycles. © 2021 ICE Publishing: All rights reserved.