Numerical investigation of a novel approach to coupling compressed air energy storage in aquifers with geothermal energy

Compressed air energy storage in aquifers is considered a potential large-scale energy storage technology that can balance electricity supply and demand. Inspired by geothermal energy acting as a thermal energy exporter, research on the coupled system is promising. To resolve the conflict of obtaining geothermal energy in an appropriate cyclic pressure, a novel coupled system adopting U-shaped wellbore is proposed. Focusing only on the underground process, the basic model for the coupled system is developed based on the Huntorf plant and numerical simulation is used to analyze its availability. The results show that not only is the cyclic pressure variation similar to that in the original system, but also a percentage of geothermal energy can be obtained in the coupled system. It results in higher air production temperature and more energy produced (even larger than the injection energy) than those in the original system. In addition, the impacts of air injection temperature and geothermal temperature distribution on the energy performance are investigated. It is found that relatively low air temperature is beneficial for obtaining geothermal energy, but the sustainability of the system can be influenced. The higher initial geothermal temperature distribution can help enhance energy production, because the path length and duration of heat transfer from geothermal reservoir become longer and the rate of supplementary geothermal energy flux becomes larger. The research on the proposed coupled system will help the development of efficient, economical and environmentally friendly large-scale energy storage system.