###### Abstract  
Thermal energy storage (TES) systems are essential components of concentrating solar power (CSP) plants that enable uniform generation of green electricity and process heat. The performance of sensible heat TES systems based on granular material and on solid blocks was experimentally analyzed during the discharge process. A granular material TES system was studied in its operation as a regular fluidized bed and as a confined bed that restricted the motion of the granular material via mechanical confinement. The pressure drop required to circulate the heat transfer fluid (HTF) through the TES system made of alumina blocks was measured to be two orders of magnitude lower than that used in the granular material TES system, being uniform and close to 0.2 bar for operation of the fluidized bed and decreasing from 0.65 to 0.3 bar for the confined bed. The evolution of the exergy efficiency of the TES systems along the discharge process was determined by obtaining an inversed exponential reduction for the fluidized bed TES system, a parabolic reduction for the alumina block TES system, and a roughly uniform value for the confined bed TES system. The exergy efficiency of the confined bed TES system, considering the HTF pressure drop as a parasitic consumption of the plant, remained higher than 90% during the complete discharge process. c]Energy Analysis of the Discharge of Sensible Heat Thermal Energy Storage Systems: Granular Material vs. Solid Blocks 2020 aca][PERSON] [1,*]Correspondence: [EMAIL_ADDRESS] [1]Correspondence: asoria@ing.uc3m. sensible heat storage is a less energy-dense alternative and may lead to important heat losses during operation at high temperatures [9], this alternative allows the operation of TES systems at high temperatures and is available at an industrial scale [10]. Sensible heat storage is the most mature option for TES systems coupled to CSP plants [11]. The storage materials used in sensible heat TES systems can be liquids or solids. Among liquids, molten salts operating within a two-tank configuration are generally the preferred option for CSP plants [12]. However, operations with molten salts are restricted to a limited temperature range, with a minimum temperature required to avoid crystallization of the salt and a limited maximum temperature to prevent its decomposition [13]. Generally, the use of solids as storage material allows the operation of TES systems at a higher temperature, promoting the operation of CSP plants with improved power cycles that lead to high efficiency [14]. For solid storage materials, there are two main alternatives: the use of big solid blocks, typically made of concrete or alumina, and the use of granular material or rocks. The high density of alumina and concrete allows them to store significant thermal energy, rendering them effective for sensible heat storage [1]. Moreover, the robust thermal stability and durability of concrete [15] and alumina [16] positions them as reliable long-term storage materials for thermal energy storage. Sensible heat TES systems based on rocks or broad granular materials are typically operated as packed beds, in which thermal segregation is present in the system and a thermocline separating the high- and low-temperature zones of the bed appears [17]. Nonetheless, the thermal gradients present in large solid particles deteriorate the performance of the TES system [18]; so, thermally thin solid particles are preferred for TES systems. Considering the high mass of storage material required for sensible TES systems, the use of sustainable small-particle-size heat-storage materials like silica sand is very relevant [19]. The sustainability and thermal stability of silica sand at high temperature has been demonstrated [20], and its favorable heat-transfer characteristics and proper cyclability have been proven [21; 22]. However, in the presence of an ascending flow of fluid, thin particles are fluidized and the thermal segregation of the system is destroyed [23].