Low-priced stable SrCl2@SG composite sorbents for low-grade solar heat storage application in open sorption systems

The combination of thermal energy storage (TES) unit and solar air heater is one of the most efficient methods for long-term utilization of solar energy. In this study, a series of stable SrCl 2 @SG composite sorbents were prepared based on silica gel (SG) pellets and strontium chloride hexahydrate (SrCl 2 ·6H 2 O) to store low-grade solar thermal energy for space heating application. Composite characteristics, kinetic hydration/dehydration performance of SG and SrCl 2 @SG sorbents were thoroughly studied. Results demonstrated that the SrCl 2 @SG_10 sorbent has the largest sorption capacity of 0.34 g/g at the temperature of 25 °C and relative humidity (RH) of 90% without any liquid leakage . Additionally, kinetic hydration experiments showed that RH has a great impact on the water sorption performance of the TES materials , while the temperature effect is relatively insignificant. The TES performance of sorbents was further investigated in a laboratory prototype reactor with a multilayer structure, which was designed following an open sorption system concept. 800 g of sorbent pellets were evenly distributed on each layer of the sieve. Maximum instant output power and energy storage density of the SrCl 2 @SG_10 sorbent at 70% RH are 19.7 W and 100 kWh/m 3 respectively. Furthermore, the open TES system still maintains a comparatively high TES performance after fifteen charging/discharging cycles.