Stanford Geothermal WorkshopFebruary 9-11, 2026

Borehole Thermal Energy Storage (BTES) systems provide a sustainable solution for balancing seasonal energy demand, yet their performance is strongly influenced by the heterogeneity of subsurface thermal properties. This study investigates the effects of heterogeneity on the performance of BTES system, and also optimizing BTES operational parameters—specifically, the charging and discharging flow rates of individual boreholes—under both homogeneous and heterogeneous soil conditions. Three-year transient simulations were conducted in FEFLOW using realistic six-month charging and discharging cycles. A Genetic Algorithm (GA) was employed to independently optimize borehole flow rates, with the objective of maximizing overall thermal recovery efficiency. To represent heterogeneity, soil thermal conductivity fields were generated through geostatistical simulations. For the homogeneous case, a constant thermal conductivity equal to the geometric mean of the heterogeneous distribution was applied. Results show that even in homogeneous conditions, optimal flow rates varied among boreholes due to thermal interactions, and this variability became more pronounced in heterogeneous settings. Comparative analysis highlights that increasing subsurface heterogeneity reduces thermal recovery, driven by preferential heat flow pathways that lower overall efficiency. These findings provide valuable guidance for site-specific BTES design and operation, emphasizing the critical role of accounting for thermal conductivity variability in achieving efficient system performance.

Topic: Direct Use