Groundwater flow impacts on very high temperature borehole thermal energy storage performance

• Very High Temperature BTES systems offer nearly cost-free and emission-free heating. • Groundwater flow reduces SCOP and Return of Investment (RoI) period of VHT-BTES. • Below a critical groundwater flow rate, SCOP and RoI are practically not affected. • Re-optimization of boreholes reduces the negative impact of higher flow rates. • Different re-optimization approaches are applied and their impacts are compared. Ground source heat pumps (GSHP) are known for their high heating and cooling efficiency. Specifically, in regions with predominantly longer heating seasons, such as Nordic countries, a Very High-Temperature Borehole Thermal Energy Storage (VHT-BTES) system, charged by concentrated solar collectors, offers a transformative and game-changing solution. This system can achieve remarkable heating efficiency, leading to practically cost-free and emission-free operation. Effective VHT-BTES design is based on minimizing energy losses and maximizing thermal energy utilization. A critical consideration, however, is the potential impact of groundwater flow on system performance. This study investigates the effects of groundwater flow on the Seasonal Coefficient of Performance (SCOP) and Return of Investment (RoI) of a model VHT-BTES system under Uppsala’s climatic conditions, benchmarked against a design for no-flow condition. Furthermore, it explores various borehole configurations and design adaptations to mitigate the adverse effects of groundwater flow. Our findings demonstrate that Darcy velocities below 0.3m/month have negligible practical impact on SCOP and RoI. For higher velocities, while negative effects emerge, they can be significantly eliminated through re-optimization of borehole configurations or the addition of extra boreholes. The simulation results encourage investors, showcasing the viability and high performance of VHT-BTES systems for achieving zero-emission targets, even in the presence of groundwater flow.