The integration of thermal energy storage (TES) systems is key for the commercial viability of concentrating solar power (CSP) plants. Furthermore, TES units can be integrated in different power cycles as a source of flexibility and stability for the grid, particularly in locations with high renewable penetration, and can be employed in industrial processes, to reduce the requirement and waste of thermal energy. A packed bed TES consists of storage material elements in various shapes and sizes and the use of an HTF that flows between these elements. The TES unit exploits the heat capacity of the particulate material in order to store energy.