One Dimensional Mathematical Model for a Thermocline Energy Storage Device

Abstract: The rapid rise of highly fluctuating renewables leads to challenges for power plants and power grids. Thermal energy storage is envisaged for e.g. enhancing the low load capabilities and plant dynamics of thermal power plants. As state of the art heat storage media like molten salts are rather expensive and furthermore limited due to their temperature range. In contrast a thermocline energy storage (TES) device is a cost efficient method to store thermal energy. Therefore a great interest is given on this technology. For time dependent studies of the integration of such a storage unit in complex energy systems a mathematical model is necessary. The model should be simple as possible to reduce the computation time for solving the algebraic equations of the model. The objective of the paper is to present experimental data as well as a one-dimensional model for a thermocline energy storage unit. The measurements are done for a charging and discharging process. During the experiments the temperature and the mass flow of the heat transfer fluid (HTF) and also the temperature distribution within the storage device was measured. For the time dependent TES model the energy balance for the storage mass and also for the heat transfer fluid (HTF) are discretised based on the finite volume approach. The measured HTF mass flow and entrance temperature into the TES are used as boundary condition for the simulation. The simulation results for the charging and discharging process of the TES test rig show a good agreement with the measured data.