Energy Storage and Applications

Pure calcium hydroxide, Ca(OH)₂, and magnesium hydroxide, Mg(OH)₂, are limited in their applicability for the storage of medium-temperature heat due to their high dehydration temperatures. Modification of the hydroxides by doping with appropriate materials is a viable method for solving this problem. In this work, samples of Ca(OH)₂ and Mg(OH)₂ have been doped with various proportions of boron nitride (BN) and potassium nitrate (KNO₃) to reduce their dehydration temperatures. The results showed that the doping processes were successfully achieved as desired, but there was a reduction in their surface areas and porosity, which could impact their thermodynamic behavior. However, the thermal analysis on the samples revealed that the KNO₃ had a more positive effect on the Mg(OH)₂ material than Ca(OH)₂. For instance, a reduction of 23 °C in the dehydration temperature and an increase of 6% in heat storage capacity were achieved with 5 wt% KNO₃-doped Mg(OH)₂, thus making it applicable for heat storage in the temperature range of 293–400 °C. Thermodynamic and kinetic studies on this composite material are therefore encouraged to establish its full potential.

Hydrogen storage is vital to the development of renewables, especially in low-infrastructure countries. Metal hydrides offer a small but safe solid-state candidate for hydrogen storage at medium pressures and near-ambient temperature, yet large-scale applications face heat-management challenges. In this article, we numerically analyze examples of two large-scale lanthanum pentanickel (LaNi₅)-based metal hydride reactor configurations with shell-and-tube heat exchangers. This research studies two large-scale shell-and-tube metal hydride reactor configurations: a tube-side cooling reactor with hydride powder packed in the shell and coolant flowing through internal tubes, and a shell-side cooling reactor using annular hydride pellets with coolant circulating through the shell. The thermal and kinetic performance of these large-scale reactors was simulated using COMSOL Multiphysics (version 6.1) and analyzed under different geometries and operating conditions typical of industrial scales. The tube-side solution provided 90% hydrogen absorption in 1500–2000 s at 30 bar, while the shell-side solution reached the same level of absorption in 430 s at 10 bar. Results show that tube-side cooling has higher storage, while shell-side cooling improves heat removal and kinetics. For energy and maritime transport applications, these findings reveal optimization insights for large-scale, efficient hydrogen storage systems.

The waste heat generated by high-performance computing (HPC) represents an opportunity for advancing the decarbonization of energy systems. Seasonal storage is necessary to regulate the balance between waste heat production and demand. High-temperature aquifer thermal energy storage (HT-ATES) is a particularly well-suited technology for this purpose due to its large storage capacity. However, integrating HT-ATES into energy systems for district heating is complex, affecting existing components. Therefore, this study applies a bi-objective mixed-integer quadratically constrained programming (MIQCP) approach to optimize the energy system at Forschungszentrum Jülich (FZJ) regarding total annualized costs (TAC) and global warming impact (GWI). The exascale computer Jupiter, which is hosted at FZJ, generates a substantial amount of renewable waste heat that is suitable for integration into district heating networks and seasonal storage. Case studies show that HT-ATES integration into the investigated system can reduce GWI by 20% and increase TAC by 1% compared to the reference case. Despite increased TAC from investments and heat pump (HP) operation, summer charging of the HT-ATES remains flexible and cost-effective. An idealized future scenario indicates that HT-ATES with a storage capacity of 16,990 MWh and HPs could cover most of the heating demand, reducing GWI by up to 91% while TAC increases by 6% relative to the reference system.