Operational grid and environmental impacts for a V2G-enabled electric school bus fleet using DC fast chargers

Abstract

As states replace diesel school buses with electric ones, utilities will want to control charging schedules to capture potential benefits on the grid and avoid all buses charging at the same time, adding a large electric load. Vehicle-to-grid (V2G) services can provide more grid stability and reduced carbon dioxide emissions than simple controlled charging systems, yet the grid impacts of V2G school buses have not been modeled using realistic school bus schedules. This paper develops a methodology for simulating the effect of managed charging of electric school buses on peak shaving in the state of North Carolina using V2G interactions and DC fast chargers to determine potential emissions reductions by minimizing peak load periods. The V2G-Sim model is used to manage fleet-wide charging, while minimizing peak generation of electricity on the grid and flattening the load curve under different battery capacities, charger power ratings, and fleet sizes. Historic annual peak hours are examined to determine the feasibility of reducing generation capacity, and the daily peak hours are examined to determine the potential peak shaving and subsequent avoided emissions. The results demonstrate that at full electric school bus replacement, 14,000 V2G buses can aggregate and shift 2.6 GWh in North Carolina, avoiding up to 1,130 t of carbon dioxide emissions per day, assuming decreased dependence on natural gas peaker plants. An additional 1,500 t of CO2 can be avoided by replacing diesel-powered buses compared to the 320,000 t total daily CO2 emissions from all activities in North Carolina. Additional emissions are avoided by the replacement of diesel buses with electric buses. The largest greenhouse gas emission benefit is the replacement of diesel with electric school buses, and the ability to shave peak loads is maximized on weekend days in the winter. The model can be used by researchers, the utility, and states as these entities evaluate the environmental and operational grid benefits of a V2G school bus program.