Detailed exergetic analysis of a packed bed thermal energy storage unit in combination with an Organic Rankine Cycle

Thermal energy storage systems (TESS) can reduce or overcome the issues that appear when an Organic Rankine Cycle (ORC) is adopted to a fluctuating heat source. However, detailed exergetic studies about the optimization potential and the influence of the TESS on the overall system are still missing for this application and TESS in systems in general. Therefore, in this work a detailed exergetic evaluation considering the influence of physical aspects on the exergetic efficiencies of components and the overall system is numerically performed for a packed bed TESS in combination with an ORC. For the chosen boundary conditions, the overall pressure drop and the heat resistance from the heat transfer fluid (HTF) to the particle have the highest influence on the overall exergetic efficiency. By optimizing the parameters of the storage unit by means of a downhill-simplex method, the overall exergetic efficiency can be increased from 36% to 43% and the influence of the physical aspects is much lower and more balanced.