Researchers from Hunan University of Technology in China have found that adjusting the rate at which air is injected into underground compressed air energy storage (CAES) caverns can improve storage efficiency.
The study compared four different air injection methods while keeping the total amount of stored air the same. Researchers found that gradually increasing the airflow rate from 10 kg/s to 150 kg/s raised the energy storage rate to 87.5% compared with 85.5% under a constant injection rate.
The increasing flow method also raised the average cavern temperature by about 1 kelvin and pressure by 0.13 MPa. The work done on the compressed air increased by around 12.7%, while heat loss to the surrounding rock rose by approximately 11%.
The researchers also examined the impact of wellbore size and the thermal properties of surrounding rocks. Increasing the wellbore diameter from 0.5 metres to 2 metres significantly reduced heat loss during air transport.
The findings could help improve the design and operation of large underground CAES facilities, which store energy by compressing air and releasing it later to generate electricity. The study was published in Case Studies in Thermal Engineering.