Hybrid Nanofluid-based Thermal Energy Storage for Next-generation Concentrated Solar Power System

This study presents an experimental analysis of thermal energy storage (TES) system at high temperatures combined with a parabolic trough solar collector. The system utilizes solar salt (NaNO₃–KNO₃ eutectic) for thermal storage and a graphene–TiO₂/ethylene glycol hybrid nanofluid as the heat transfer medium. The main aim is to assess the impact of the hybrid nanofluid on the charging and discharging performance in outdoor solar operating conditions. A 100-L TES tank with 360 sealed solar saltmodules was charged with an average thermal input of 2.3 kW provided by the solar collector. The temperature changes along the axis during charging and discharging were tracked with several thermocouples. The findings demonstrate enhanced heat transfer during charging, decreased thermal layering close to the melting point of solar salt, and prolonged heat-release time during discharging with the application of the hybrid nanofluid. The system's charging efficiency, discharging efficiency, and round-trip efficiency were 48.6%, 81.6%, and 39.6%, respectively. The results indicate the capability of hybrid nanofluid-assisted heat transfer to improve the thermal performance of molten-salt-based TES systems used in concentrated solar powerapplications.