Injection strategy analysis of high-temperature aquifer thermal energy storage system, an insight from the study case in Burgwedel, Germany

High-temperature aquifer thermal energy storage (HT-ATES) systems have significant potential to balance the seasonal mismatch between the energy supply and demand. Due to the monthly global temperature variation, the energy supply and requirement may vary during summer and winter. However, the current investigation rarely discusses the fluctuation of the ATES flow rate (injection and production rates). In this study, a thermal-hydraulic model is employed to investigate the performance of HT-ATES systems under variable operational flow conditions. Specifically, the injection and production rates are assumed to follow a normal distribution, or alternatively, water is injected or produced only during a defined portion of the injection period. Results show that the injection strategy significantly impacts the HT-ATES performances when the ambient groundwater flow velocity is considerable. The energy recovery rate is proportional to the timely water injection ratio, defined as the volume of water injected during the second half of the injection period over the total injected volume. The maximum discrepancy in energy recovery rate reaches nearly 5 % between different injection strategies when the groundwater flow is 0.2 m/d. The production strategy presents an opposite influence on the injection strategies. Furthermore, the HT-ATES demonstrate the capability to deliver higher peak power output in winter while maintaining the energy recovery rate.