Assessing the Impacts of Depot Charging for Medium- and Heavy-Duty Electrified Fleets on the Distribution Grid

This study introduces a comprehensive framework for investigating the impacts of depot charging on distribution grids. The framework is applied to a synthetic electric bus fleet modeled after real-world transit routes in San Antonio, Texas. Two charging strategies—unmanaged and managed—are proposed, incorporating varying initial state-of-charge conditions, fleet operational constraints, and depot power capacity limitations. The managed strategy optimizes charging schedules by leveraging electricity rates to shift demand to off-peak periods with lower costs. The resulting depot load profiles are analyzed to determine their effects on a synthetic distribution feeder. The findings reveal that the existing grid infrastructure can accommodate small to medium-scale electrification without voltage violations. However, full-scale electrification, involving more than 700 transit vehicles, leads to significant voltage drops that exceed operational limits, even under managed charging. These results underscore the necessity of advanced, grid-aware charging management strategies to mitigate voltage violations and support the sustainable integration of large electrified fleets.