Thermocline thermal storage systems for concentrated solar power plants: One-dimensional numerical model and comparative analysis

• One-dimensional mathematical model for high temperature thermocline thermal storage tank.
• Temperature dependent thermophysical properties of the HTF.
• Heat loss from tank walls considered using overall heat loss coefficient.
• Cyclic behaviour indicates independence from initial conditions.
• Storage temperature difference, cut-off criteria and type of HTF have high impact on cycle durations.

Concentrated solar power plants have attracted increasing interest from researchers and governments all over the world in recent years. An important part of these plants is the storage system which improves dispatchability and makes the plant more reliable. In this paper, a one-dimensional transient mathematical model for a single-tank thermocline thermal energy storage system is presented. The model used temperature dependent correlations to obtain the thermophysical properties for the heat transfer fluid and considered heat loss through the tank wall. The effect of variation in important system parameters like the type of heat transfer fluid, the storage temperature difference and the cycle cut-off criterion on system performance was investigated. The results suggest that two important aspects for assessing the performance of the system are the cyclic behaviour of the system and the time required to attain equilibrium conditions. These aspects directly influence the discharge capacity and discharge power of the storage system, and therefore play an essential role in understanding the start-up characteristics of the system and provide an insight regarding the availability of storage when designing the power cycle for concentrated solar power applications. It was also observed that the cycle durations and the time required to attain cyclic conditions are highly sensitive to not only the storage temperature difference, but also the cut-off temperature difference.