Case study (USA): Electric school bus vehicle-to-grid pilot in California
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California regulations require all new school buses to be zero emissions by 2045. The State is piloting use of vehicle-to-grid technology as it converts its fleet of diesel fuel school buses to electric to meet air quality and climate goals.
This case study is supplied by Commissioner Cliff Rechtschaffen at California Public Utilities Commission.
Converting school buses to electric is a top priority for California to meet its air quality and climate goals. Emissions from diesel fuel buses disproportionately affect children, often in communities that suffer significant air pollution.
California has legislated for all new school buses to be zero emissions by 2045, and the State has made $180 million in grants available to school districts to convert to electric buses.
Vehicle-to-Grid (V2G) strategies are key to helping California meet its ambitious transportation electrification goals; keeping costs affordable for consumers while not adversely impacting the grid. Stakeholders have proposed numerous use cases for V2G but few have been tested.
Electric school buses present a unique V2G opportunity as they often finish their routes before peak energy times. In California right now, these fall between 4pm and 9pm. Moreover, school buses don’t typically run during the most stressed summer peak on the grid.
V2G is a subset of vehicle-grid integration (VGI). VGI is an umbrella term for a host of measures and behaviours that better integrate electric vehicle (EV) charging with the electricity grid. This includes smart charging, where vehicles respond to time-varying price signals and V2G where vehicles use their batteries to feed power back to the grid
When electric school buses are plugged in at their depots, they are potentially ready to feed the power they have generated and stored in their batteries back to the grid when California needs it most. They could prevent us from bringing online gas-fired peaking power plants or building new plants to deal with increased electricity load. Because this is such a promising area, several Californian utilities, and others nationwide, are currently running V2G pilots with school bus fleets.
San Diego Gas & Electric (SDG&E), one of California’s private electric utilities, has begun a school bus pilot run by Nuvve, a private V2G company. It is approved by the California Public Utilities Commission (CPUC) and will run for five years, launching in the third quarter of 2021. Data will be collected and reported when the pilot completes its first year.
The project will connect six bi-directional electric school buses to 60kW bi-directional direct current (DC) fast chargers. Each bus will be capable of exporting 60 kW via a DC fast charger. The buses will connect to the grid under a recent addition to California’s CPUC interconnection Rule 21, which allows for more streamlined interconnection for distributed energy projects. The new procedure identifies V2G as energy storage for interconnection purposes.
The participant in this pilot is the Cajon Valley Union School District. They also secured federal funding to buy electric buses that can export power to the grid. Additional State, regional and utility funds are also being used for various aspects of the project. SDG&E is installing all electrical upgrades and charging stations that are needed to enable the bidirectional flow of electricity.
A potential operating schedule for the school buses, below, suggests that they will operate their routes in the morning and charge from about 9am to 2pm. They will then run again to return students to their homes and discharge to the grid between 5pm and 9pm. The fleet can then fully charge overnight.
Illustrative school bus charging and discharging schedule 6am – 9am Take students to school (unplugged) 9am – 2pm Buses absorb renewable energy (charging) 2pm – 5pm Take students home (unplugged) 5pm – 9pm Discharge to grid (discharging) 9pm – 6am Charge buses overnight (charging)
This schedule is only one example, as the project design is focused on market participation in wholesale energy markets. The objective is to examine the wholesale value streams possible with V2G school buses. The bus capacity will bid into California’s day-ahead energy markets run by the California Independent System Operator (CAISO).
Nuvve will make bids via SDG&E, which is a CAISO scheduling coordinator, based on the buses’ ability to contribute energy after meeting its operational needs, while optimising the school district’s electric bill. SDG&E will return bids won and lost for each hour the following day. Nuvve will then provide the requested energy back to the grid at appropriate hours the following day.
Depending on market prices, the buses may discharge at various times during the day although, typically, market prices are highest between 5pm and 9pm.
Through the pilot we are aiming to understand:
- How well the school bus use case is aligned with electric grid needs.
- If a potential future V2G program could improve use of SDG&E’s distribution system.
- How the project will help integrate renewable energy and reduce greenhouse gases.
- The value of V2G as a potential revenue stream for the school districts, which may help us speed up converting our school district fleets to electric.
V2G is a promising area that California and the US federal government are exploring. The Biden Administration’s proposed Infrastructure Framework includes $7.5 billion for electric school and transit buses [see Factsheet: Bipartisan Infrastructure Framework].
A successful pilot will show that electric buses can provide V2G services, helping reduce grid costs and meet peak energy demand. They could also generate revenue for our school districts and transit agencies, accelerating the transition away from diesel buses. The pilot will also help demonstrate the viability and scalability of V2G projects more broadly.
- Emissions from California’s diesel-fuel school buses affect children’s health, often in communities that suffer significant air pollution. Converting our fleets to fully electric could help California meet its air quality and climate goals. Plugged in school buses can potentially feed power back to the grid when California needs it most, preventing the use of gas-fired power plants to manage increased electric load.
- Depending on market prices, the V2G operator will bid into California’s energy markets based on the fleet’s generating capacity. This offers opportunities to both optimise the school district’s utility bill and provide possible ways to generate revenue that could help speed up the switch from diesel to electric as the state moves more and more towards a cleaner, greener transport network.