Development, challenges and potentials of underground energy storage systems

The rapid development of intermittent renewable energy (such as wind and solar power) results in a high demand for large-scale energy storage. Underground energy storage (UES) presents a Gigawatt-scale opportunity to address the growing needs for efficient, reliable, and sustainable energy systems. Although the previous study has analysed or reviewed technical characteristics of UES systems, most was focused on one specific type of technology, while a systematic and quantitative comparison among different categories of UES systems is still limited. This paper comprehensively reviews the existing and emerging UES technologies, providing a science introduction of concepts, principles and technical developments of different UES categories to the community. A systematic comparison of system and engineering parameters among different UES systems is conducted based on the massive data collected from established and proposed projects, which can provide a guidance and reference for designers and engineers to make informed decisions with regards to the optimal UES scheme. To help with the UES site selection and design optimisation, geological and structural properties are further summarised and discussed, which are key components during the play fairway analysis. Besides, new engineering challenges are proposed regarding the deterioration of structural and rock materials in UES multiphysical environments, which will not only affect the accuracy of numerical and theoretical assessment and prediction, but also threaten the serviceability and durability of UES infrastructures. Finally, a global potential map for UES is established to help policy-makers formulate region-specific UES policies and foster international collaboration, further accelerating the deployment of UES infrastructures.