A novel mechanical energy storage solution using underground CO2 hydrate capsules

Mechanical energy storage can cope with the intermittent power supply of renewable energy sources (e.g. solar and wind). Concurrently, the green transition requires carbon capture and utilization technologies. This paper presents a novel concept of underground impermeable capsules formed by CO2 hydrates, which can be used to pressurize gas and/or fluids (water, air, and/or carbon dioxide) for energy storage. Such capsules can be used for Pumped-Hydro Compressed Carbon Dioxide Energy Storage; in which water is compressed against pressurized gas in the capsule. This “green” use of gas hydrates can deliver both energy storage and carbon utilization objectives, in onshore and offshore applications. The paper first presents the construction phases and working principles of this underground mechanical energy storage. Next, temperature-pressure requirements for CO2 gas hydrate stability are outlined, identifying a depth range of 30 m – 200 m as
ideal for hydrate capsule creation. Finally, a simplified mechanical model based on elasticity is developed to quantify energy storage as a function of capsule geometry and material behavior.