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Due to the depletion of natural energy resources, worldwide, solar energy is accepted as an emerging energy source because it is free, endless and can be convertible to other forms, but it is intermittent. Therefore, in the present study, different energy storage techniques, that is, sensible heat, latent heat and thermochemical heat storage techniques, suitable to store solar thermal energy are discussed and compared. Based on the energy storage density, reaction kinetics, operating temperature range and volume of storage material, the metal hydridebased thermal energy storage (MH-TES) system is observed to be the most promising for thermochemical energy storage applications. In continuation, the current work enlightens on the screening of MHs best-suited to the MH-TES, which results in the alloy pairs of MmNi 4.15 Fe 0.85 -TiCrMn and LaNi 4.85 Al 0.15 -MmNi 4.6 Fe 0.4 , working on high-pressure and low-pressure sides, respectively. The thermodynamic performances are observed to be 140.25 and 188.16 kJ of heat generation with a coefficient of performance of 0.47 and 0.50 for MmNi 4.15 Fe 0.85 -TiCrMn and LaNi 4.85 Al 0.15 -MmNi 4.6Fe 0.4 pairs, respectively, working at a temperature range of 403 (storage), 298 (ambient), 373 (regeneration) and 423 K (heat output). The study is extended to investigate the influence of operating temperatures on system performance and observed that the heat generation may be reduced by~5% by increasing heat output temperature by 20 K due to reduction in mass transfer.

Energy is one of the major inputs for the economic development of any country. However, for developing countries energy is essential for economic growth, which calls for the development of clean and sustainable energy source/carrier. Among all the possible options, hydrogen has been considered as a promising clean energy carrier, which is associated with major challenges of its storage and application. Hydrogen can be stored safely in the form of metal hydrides whose formation and decomposition involve high heat interaction, which can be used for the development of thermodynamic systems like sorption heat pumps, which can transform waste heat to useful high‐grade heat. In the present work, the performance of metal hydride based heat transformer (MHHT) is investigated in terms of variation in MH bed temperature and hydrogen interaction between coupled reactors during hydrogen transfer processes, in addition to thermodynamic performance (ie, Coefficient of Performance (COP), heating capacity, and so on) for the operating temperature of TL = 303 K, TM = 383 K, and TH = 423 K. A pair of La0.9Ce0.1Ni5 and LaNi4.6Al0.4 is chosen for present study based on author's previous work. In the present study, user‐defined functions are employed in ANSYS Fluent, which consist of pressure, mass, and energy variation equations. The results are derived in the form of contours and graphical representations of variations in bed temperature and hydrogen concentration. It is observed that the system produces 40 kJ of upgraded heat with heating capacity of 0.1 kW and COP of 0.46 at 880 seconds of hydrogen transfer time for 250 g of each alloys.

In the present work, thermodynamic simulation and numerical modelling (through a finite volume approach) are carried out to investigate the performance of hydrogen-based thermochemical energy storage (H-TCES) system with the application of LaNi 4.6 Al 0.4 -La 0.9 Ce 0.1 Ni 5 metal hydride (MH) pair. Thermodynamic equations are used to evaluate the H-TCES performance whereas the continuity, energy and pressure equations are solved with the help of the computational fluid dynamics (CFD) approach to predict the heat and mass transfer behaviour of MH beds. The numerical code is validated by comparing the predicted pressure concentration isotherms (PCIs) with the experimentally measured PCIs, which are observed to be in good agreement. The experimental PCI data are used for the performance prediction of H-TCES system operating at 25 C, 100 C, 130 C and 150 C as ambient-, regeneration-, storage-and output temperature respectively. It is found that the energy storage density of the H-TCES system is 243.67 kJ with a COP of 0.48. The overall cycle time is predicted as 2200 seconds, which includes heat storage, heat output, sensible heating and sensible cooling processes. The generated temperature contours illustrate the effect of an increase and decrease in bed temperature during absorption and desorption processes.

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