Large scale thermal energy storage for solar heating applications can be accomplished in the ground through the installation of an array of vertical heat exchange boreholes or U-tubes. Simulation modeling of the storage subsystem and its integration with the total system is essential for design and performance evaluation. Although U-tube storage design is especially attractive in clay soils and preferable to boreholes in many geological conditions, only a borehole simulation model is currently available, validated, and integrated into a system simulation model. This article presents a comparative analysis of the heat transfer from boreholes and U-tubes using analytical solutions, finite element modeling, and the available simulation model. The analysis is used to support the development of a methodology by which the heat transfer of any U-tube configuration can be modeled by appropriately specifying parameters in the borehole storage simulation model. The borehole model can then be used to model the storage subsystem integrated within a total system simulation model.