Analysis of metal hydride storage on the basis of thermophysical properties and its application in microgrid

Abstract

Present study focuses on the analysis of metal hydride hydrogen storage in renewable power generators-based microgrid (µG) system. The design of metal hydride storage unit requires parametric analysis on the basis of its thermophysical properties such as activation/deactivation energy, enthalpy of formation, equilibrium pressure, reaction kinetics and external thermal management system. This parametric analysis helps to assess suitability of the hydride storage with hydrogen generation (electrolyzer) and utilization (fuel cell) units in µG. Application of metal hydride in the µG creates a sophisticated system which requires careful analysis and operating strategy for achieving manifold benefits such as higher efficiency, durability of the components and self-sufficiency. In the present study, different hydrides are selected namely, LaNi5, TiCr1.6Mn0.2, hydroalloy C5 graphite and MgH2 for performance analysis on the basis of their thermophysical properties. The performance is evaluated in different operating modes aiming for higher efficiency, components durability and system self-sufficiency (minimum grid-dependency). A detailed mathematical modelling is performed in the MATLAB simulation tool for performance evaluation of overall µG system, which consists of 5 kW photovoltaic (PV), 1 kW fuel cell (FC), 5 L hydride storage and 0.6 kW electrolyzer. It was observed that the hydrogen charging and discharging processes in the hydride storage unit strongly depend on its thermophysical properties and hence require certain specific operating conditions for efficient working. Considering suitable discharging characteristics at low temperature and pressure, LaNi5 and C5 hydroalloy can be suitable for transient operation with proton exchange membrane fuel cell application. Overall energy efficiency of up to ≈ 95.49% is achieved in such type of storage-based µG. Grid-dependency ratio (load demand met by grid power/total load demand) was found between 0.26 and 5.83% in different operating modes.