Blueprint for Medium- and Heavy-Duty Zero-emission Vehicle Infrastructure: Lowest Cost to Charge for Stockton Unified School District

Published: April 2023.
Prepared for: California Energy Commission
Prepared by: The Center for Transportation and the Environment

Overview

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 (ESB). The Center for Transportation and the Environment partnered with The Mobility House (TMH) and Sage Energy Consulting (Sage), a NV5 company, to complete the analyses which 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, as 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 use of a charge management system was found to provide significant savings by limiting charging spikes and avoiding high demand charges. Additionally, photovoltaic and battery energy storage systems under NEM3.0 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 at this time 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 bi-directional charging more favorable. These results and recommendations will be valuable to other school districts when planning electric school bus fleet transitions.

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