CHARACTERIZATION OF A SOIL-BOREHOLE THERMAL ENERGY STORAGE SYSTEM

This presentation will focus on the design, construction, and performance evaluation of a soil-borehole thermal energy storage (SBTES) system installed in Golden, Colorado. The system was installed in a colluvial deposit with an annual average water table depth of 7 m. The SBTES system consists of 5 boreholes having a depth of 8 m, connected to each other in parallel. Because of the relatively deep water table, the SBTES system is primarily in the vadose zone. The behavior of the system was simulated using COMSOL, which can consider couple heat and mass transport in unsaturated soils. A relatively close borehole spacing of 1.25 m was selected based on the COMSOL results. The SBTES system was constructed with surficial insulation and hydraulic barrier layers, in order to trap the heat and water vapor in the soil layer during heat injection. The results from a long-term heating test performed with a constant heat source will be presented. The long-term operation of the site started after this characterization test, which involves injection of heat collected from solar thermal panels into the subsurface. The process of up-scaling the results of this relatively small SBTES system to a utility-scale system will also be discussed.