Sustainability prediction of a large borehole heat exchanger array considering the impacts of solar radiation and land cover changes

The increasing utilization of shallow geothermal resources has led to the widespread adoption of borehole heat exchangers (BHEs) due to their efficiency and environmental benefits. However, ensuring the long-term sustainability of BHE systems remains a critical challenge, requiring reliable predictions of their thermal behavior and economic viability. This study develops a 3D hydro-thermal modeling approach based on an operational BHE site in Hamburg, Germany, integrating site-specific conditions and complex surface heat transfer processes, including solar radiation, surface cover changes, and topography. The model is calibrated and validated using monitored groundwater temperature and BHE operational data, allowing for a more comprehensive evaluation of subsurface heterogeneity, groundwater flow, and meteorological influences compared to existing modeling approaches. Long-term simulations over the next 25 years confirm the system remains technically and economically sustainable under current thermal energy strategies. Sensitivity analyses show that groundwater flow is the dominant factor affecting SCOP at the Hamburg site, with an average sensitivity indicator of 46 %, followed by solar radiation at 27 % and thermal regeneration at 17 %. These results indicate that the proposed modeling tool can provide reliable predictions of long-term sustainability, while the sensitivity analysis helps to optimize the operation and management of the system.