An overview of underground hydrogen storage with prospects and challenges for the Australian context

Moving the energy portfolio from conventional fossil fuel-based to a balanced mix of renewable energies is one of the critical global challenges towards sustainability. Despite having many promising attributes, intermittency and grid instability of renewable energy (i.e., solar and wind) have resulted in growing strains on the electricity grid. Therefore, it is essential to identify cost-effective and efficient solutions for energy storage utilizing sustainable energy carriers. Scientists have hypothesised that hydrogen would play a critical role in the next energy revolution, being recognized as an alternative low or zero-emission energy source/transport medium. Underground Hydrogen Storage (UHS) is the preferred solution for large-scale and long-term energy storage in a hydrogen-based economy, considering economic and safety considerations. Different underground storage options have been identified in depleted hydrocarbon reservoirs, salt caverns, aquifers and underground mine excavations. Despite being a relatively new technology, UHS has many similar attributes to natural gas storage and geological CO2 storage. Nevertheless, the characteristic physicochemical properties of H2, higher penetrability, unusual hydrodynamic behaviour, geo-chemical and biological reactions with the reservoir rock, pore fluids, and residual hydrocarbon create unique scientific challenges. Therefore, the storage options should be carefully evaluated through a detailed geological assessment considering hydrogen storage capacity and containment. In addition, the proximity of hydrogen generation and processing plants, transport infrastructure and the possibility of re-purposing existing infrastructure determines the techno-economic viability. Within this context, this paper provides a concise yet comprehensive overview of UHS technology. It thoroughly explores the geological assessment, technical challenges, recent progress of initiatives, and future opportunities related to UHS technology, thus providing a comprehensive and multi-faceted understanding of UHS. Further, the paper pioneers the exploration of UHS initiatives in Australia, presenting a localised perspective that broadens the applicability of the findings to diverse geographical regions.