Blueprint for Medium- and Heavy-Duty Zero-Emission Vehicle Infrastructure: Lowest Cost to Charge for Stockton Unified School District
March 29, 2023
Transportation Energy (600)
Clean Transportation Program
Erik Bigelow, Leslie Eudy, Grace Leslie
This blueprint project used Stockton Unified School District’s bus fleet operation as a case study to analyze the lowest possible cost for charging electric school buses. The Center for Transportation and the Environment partnered with The Mobility House and Sage Energy Consulting (Sage) to complete the analyses.These analyses included costs of alternating current and direct current charging with and without charge energy management, investigating potential value of photovoltaic (PV) energy with and without battery energy storage, optimizing for self-consumption of PV, and value of vehicle-to-grid technology.
The results showed that alternating current is sufficient for the district’s charging needs.There is a marginal difference in the value of the energy compared to direct current charging, which has increased costs associated with infrastructure upgrades and hardware. The project team found that use of a charge management system providedsignificant savings by limiting charging spikes and avoiding high demand charges. Furthermore, photovoltaic and battery energy storage systems under net energy metering3.0 may be difficult to justify if there is a time-of-use rate, sufficient capacity to use the off-peak charging time, and a charge management system in place. Lastly, vehicle-to-grid charging can produce revenue, but it is unclear if it is enough to justify the additional costs.
The project team recommends school districts install alternating current unless there is a need for direct current charging and advise against photovoltaic and battery storage systems under the new net-energy-metering rules and utility rates. Also, the additional costs associated with vehicle-to-grid technology diminish returns and make it hard to justify the potential cost benefits. Vehicle-to-grid use should continue to be researched as policies and technology can change to make bidirectional charging more favorable. These results and recommendations will be valuable to other school districts when planning electric school busfleet transitions.