Performance investigation of high-temperature sensible heat thermal energy storage system during charging and discharging cycles

This paper presents the thermal modelling and performance predictions of high-temperature sensible heat storage (SHS) models of 50 MJ capacity designed for solar thermal power plant applications in the temperature range of 523-648 K. The SHS unit is a regenerator-type heat exchanger which stores/releases the heat on passing hot/cold heat transfer fluid (HTF) through the tubes embedded into it. A mathematical model of cylindrical configuration with embedded multi-tube is developed employing concrete and cast steel as the storage media. The number of embedded charging/discharging tubes in the storage model is optimized based on the charging time using the finite element method-based simulation tool, COMSOL Multiphysics. Numerically predicted results match well with the data reported in the literature. Thermal performance parameters of SHS bed such as charging/discharging time, energy stored/recovered, charging/discharging energy efficiency and overall efficiency have been evaluated. Axial variations of HTF temperature during charging/discharging cycle are analysed, and the parametric studies are carried out by varying the flow rate of HTF. For cast steel bed, the increase in HTF velocity resulted in the proportional reduction in charging/discharging time, while these effects in concrete were less because of its low thermal conductivity.