Exploring the prospects and challenges of underground hydrogen storage for a sustainable energy future

Compared to fossil fuel-based energy sources, renewable energy sources are gaining momentum worldwide due to climate control agreements. The Hydrogen Energy Roadmap proposes to generate hydrogen using renewable energy sources such as hydro, biomass, and solar. However, renewable energy source like hydrogen often has an unstable flow of energy supply, which can lead to temporary underproduction of the required supply. Underground storage options like depleted gas or oil reservoirs, aquifers, and salt caverns are used to address this issue. These underground gas storage alternatives have been used for various applications, including hydrogen storage. Underground hydrogen storage is possible in two geological sites: porous media and cave storage. Salt caverns are suitable for seasonal hydrogen storage at high pressures, while aquifers have the potential for hydrogen storage due to their widespread distribution. However, it is crucial to note that adequate reservoir properties and an impermeable layer are necessary for hydrogen storage in underground structures to prevent gas migration. Microbial and geochemical activities, often overlooked but crucial in hydrogen storage, can pose challenges due to their existence.