This paper presents the results of a numerical study on the thermal performance of large horizontal thermal energy storage tanks. The numerical model was validated using measurements obtained from Drake Landing Solar Community (DLSC), which is located in Alberta, Canada. A total of seven different baffle configurations were assessed for a range of operating conditions. Characterization of the tank performance was done by monitoring the tank outlet temperature and computing the Huhn efficiency, which is a characterization index based on the second law of thermodynamics. Results show that the current tanks at DLSC experience excessive mixing due to fluid entrainment from the inlet jet. A newly introduced design that confines the inlet jet mixing shows the potential to enhance the level of stratification during charging or discharging at a constant temperature. In addition, most designs tested have a relatively high level of stratification during charging, discharging, and simultaneous charging and discharging, but fail to sustain the level of stratification when a positive buoyant jet is introduced.