Thermocline Thermal Storage for Concentrated Solar Power Applications: Characterization of Novel Nitrate Salt Mixtures

Parabolic trough concentrated solar power (CSP) plants are particularly promising renewable sources of energy, whose easy integration with thermal energy storage (TES) systems allows to mitigate the intermittency of electricity generation. Currently, molten nitrates, with two tanks arrangement, are mainly used for sensible heat accumulation. To reduce costs and make the CSP storage systems more manageable, single tank configurations have been proposed, where the cold and hot fluids are stored in the same container and separated because of their density difference. The aim of the present work is to study the storage performances presented by two novel ternary and quaternary mixtures, proposed within the European project IN POWER. An experimental campaign was preliminarily performed to investigate the fluids thermo-physical properties, and the obtained values were utilized as input data to model the discharge phase in a thermocline tank. The simulation results were compared with the ones acquired considering two commercial materials, namely, solar salt and Hitec XL (R). Overall, considering same temperature ranges, higher discharging times are obtained for the quaternary and ternary mixtures, with the ternary presenting a smaller thermocline thickness than the solar salt while this parameter is the same considering the quaternary and Hitec XL (R).

Automated summary

Parabolic trough CSP plants are a promising renewable energy source that can be integrated with TES systems to address electricity generation intermittency. Current storage systems use molten nitrates in two tanks, but single tank configurations have been proposed for cost reduction and manageability improvement. This study investigates the storage performance of ternary and quaternary mixtures proposed in the IN POWER project. Experimental data on the thermo-physical properties of the fluids were used to model the discharge phase in a thermocline tank. The results show that, compared to solar salt and Hitec XL, the ternary and quaternary mixtures have longer discharging times.