Managing High Groundwater Velocities in Aquifer Thermal Energy Storage Systems: A Three-Well Conceptual Model

Aquifer Thermal Energy Storage (ATES) is a promising technology for the seasonal storage of heat, thereby bridging the temporal gap between summer surpluses and peak winter demand. However, the efficiency of conventional ATES systems is severely compromised in aquifers with high groundwater flow velocities, as advective heat transport leads to significant storage losses. This study explores a novel three-well concept that implements an active hydraulic barrier, created by an additional extraction well upstream of the ATES doublet. This well effectively disrupts the regional groundwater flow, thereby creating a localized zone of stagnant or significantly reduced flow velocity, to protect the stored heat. A comprehensive parametric study was conducted using numerical simulations in FEFLOW. The experiment systematically varied three key parameters: groundwater flow velocity, the distance of the third well and its pumping rate. The performance of the system was evaluated based on its thermal recovery efficiency and a techno-economic analysis. The findings indicate that the hydraulic barrier effectively enhances heat recovery, surpassing twice the efficiency observed in a conventional two-well configuration (100 m/a). The analysis reveals a critical trade-off between hydraulic containment and thermal interference through hydraulic short-circuiting. The techno-economic assessment indicates that the three-well concept has the potential to generate significant cost and CO2e savings. These savings greatly exceed the additional capital and operational costs in comparison to a traditional doublet system in the same conditions. In conclusion, the three-well ATES system can be considered a robust technical and economic solution for expanding HT-ATES to sites with high groundwater velocities; however, its success depends on careful, model-based design to optimize these competing effects.