The role of cushion gas in hydrogen storage

The global commitment to mitigate climate change necessitates a transition of energy systems from fossil fuels to renewable sources. However, renewable energy technologies—such as wind and solar—provide intermittent supplies of clean energy. To manage this variability and minimize curtailment, storing excess energy as hydrogen presents a promising solution. A significant portion of the capital expenditure in subsurface hydrogen storage is attributed to the need for both working gas and cushion gas. Cushion gas refers to the volume of gas that remains permanently in the reservoir to maintain the pressure required for effective withdrawal of the working gas during injection–withdrawal cycles. Similar to CO₂ storage projects—where high upfront costs have been identified as a key barrier to implementation—hydrogen storage in porous media faces substantial capital costs. In fact, cushion gas can account for over 80% of total CAPEX in these systems (1), highlighting the critical need to reduce this cost. In this presentation, I will introduce three strategies to reduce the cost of cushion gas in hydrogen storage. Firstly, I will propose rethinking cushion gas not as a sunk operational cost, but as a recoverable and strategic national energy reserve—transforming it into an investment in energy security. Secondly, I will explore the use of alternative cushion gases, such as CO₂, to reduce overall storage costs. This will include a novel strategy using a case study from the Southern North Sea basin. Finally, and drawing on insights from the EMStor project (2), I will present a phased, cost-efficient development model. This approach begins with a moderately sized storage project, pre-designed for future expansion, thereby encouraging long-term investment.

1. https://doi.org/10.1016/j.ijhydene.2022.11.292
2. The UK's largest inland hydrogen cluster | East Midlands Hydrogen