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Thermocline storage systems for concentrated solar power plants: One-dimensional mathematical model and numerical analysis
Modi, Anish
Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics; Pérez Segarra, Carlos David
well as governments all over the world in recent years. An important part of these plants, albeit a relatively lesser developed at the same time, is the storage system. The storage system helps in resolving two important operational issues: 1) intermittent nature of the energy source; and 2) reliability of plant operation. A good storage system is capable of improving the plant performance, and thus the economics of operation, by a significant margin. The current study aims to analyse one type of storage structure that is gaining popularity due to the promise of cost benefits involved: the single-tank thermocline storage system. The system is assumed to be a combination of porous filler bed and a fluid moving through the bed during charge and discharge cycles. A one-dimensional transient mathematical model is presented along with analysis of some important system parameters like the type of heat transfer fluid, the operating temperature difference, energy loss from the tank wall, bed porosity and tank diameter. During the analysis, it was observed that two important aspects for assessing the system performance are the cyclic behaviour of the system and the time required to attain this behaviour. This is directly influenced by the discharge capacity and discharge power, and therefore plays an essential role during system sizing. The temperature profiles and cycle cut-off criteria are other relevant parameters in assessing the system behaviour for different cases. It was also observed that Solar Salt performs the best among compared alternatives for heat transfer fluids with the mentioned assumptions; and that the system performance, with respect to storage capacity and discharge efficiency, depends highly on the combination of fluid and filler bed and their respective thermophysical properties. With appropriate system design, taking into consideration the abovementioned aspects, substantial performance improvements and economic benefits can be achieved through minimization of the losses that occur due to internal mixing and the losses to surroundings. The presented model can be further developed by including an analysis of idle state of the tank and more accurate data for mass flow rate, cut-off criteria and ambient conditions.
Universitat Politècnica de Catalunya

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