Charging and discharging analysis of thermal energy using magnesium nickel hydride based thermochemical energy storage system

A concentrated solar power plant integrated with thermal energy storage system helps to operate the plant during non-sunshine hours. This helps to increase the power generation capacity and improve the dispatchability of the power plant. Thermal energy systems are classified into sensible, latent, and thermochemical energy storage systems. Thermochemical energy storage with high energy storage density is one of the potential energy storage techniques available. The metal hydride-based thermal energy storage system has high energy storage density, better chemical reversibility, long cyclic, and high temperature stability. A dual bed metal hydride system uses high and low-temperature metal hydrides. High temperature metal hydride is used as energy storage media, while low-temperature metal hydride is used as hydrogen storage media. In this article, a detailed discussion on the energy sorption (absorption and desorption) analysis of a metal hydride suitable for high temperature in a dual bed metal hydride-based thermal energy storage system is performed. A 3-D model of Magnesium Nickel alloy in cylindrical geometry with radially distributed axial tubes is developed in COMSOL Multiphysics 5.5. The energy absorption and desorption analysis of metal hydride with variation in the number of heat transfer fluid tubes and different aspect ratio geometry are performed in detail. Study on variation of the number of heat transfer fluid tubes includes identifying the requirement of the adequate number of heat transfer fluid tubes to supply/remove heat to/from metal hydride during energy absorption/desorption. Variation of aspect ratios on the heat energy sorption characteristics and heat transfer phenomenon is studied in detail for both energy absorption and desorption cycle. The adequate number of heat transfer fluid tubes for the aspect ratio 0.5, 1, and 2 are found as is 32, 48, and 72, respectively. The stored and released energy for absorption and desorption study for the aspect ratio 0.5, 1, and 2 are 274.83 kJ, 255.44 kJ, and 240.27 kJ and 250.11 kJ, 234.43 kJ, and 224.10 kJ, respectively. The energy storage efficiency of the metal hydride bed for aspect ratios 0.5, 1, and 2 is 91%, 91.77%, and 93.27% respectively, while the overall system efficiency of the metal hydride bed for aspect ratios 0.5, 1, and 2 is 70.46%, 71.23%, and 72.39% respectively. The outcomes of this study helps to design the metal hydride based thermochemical energy storage system for process heating and power generation.