The school bus is, in many ways, ideal for V2G. “There is no uncertainty in terms of bus use,” says Patricia Hidalgo-González, director of the Renewable Energy and Advanced Mathematics Laboratory at UC San Diego, who studies the network but was not involved in the project. “Having that clarity about what the transportation needs are makes it much easier for the network to know when they can make use of that asset.”
Zum buses start running at 6 or 6:30 am, take the children to school and finish at 9 or 9:30 am. While the kids are in class, when there is more solar energy flowing into the grid, Zum buses connect to fast chargers. The buses then disconnect and take the children home in the afternoon. “They have large batteries, typically four to six times larger than a Tesla battery, and they travel very few kilometers,” says Vivek Garg, co-founder and COO of Zum. “So at the end of the day there’s a lot of battery left.”
After dropping off the kids, the buses connect again, just as demand on the network increases. But instead of increasing that demand further through charging, buses send their excess energy to the grid. Once demand has subsided, around 10 p.m., the buses begin charging, filling themselves with electricity from non-solar sources, so they are ready to pick up the children in the morning. Zum’s system decides when to load or unload depending on the time of day, so the driver just plugs in his bus and goes.
On weekends, holidays or during the summer, buses will spend even more time unused – an entire fleet of batteries that might otherwise sit idle. Given the resources required to manufacture batteries and the need for more storage on the grid, it makes sense to use available batteries as much as possible. “It’s not like you’re putting a battery somewhere and then just using it for power,” Garg says. “You’re using that battery for transportation, and at night you’re using the same battery during rush hour to stabilize the grid.”
Get ready to see more of these electric buses, if your child isn’t already riding one. Between 2022 and 2026, the EPA Clean School Bus Program is providing $5 billion to switch from gasoline-powered school buses to low- and zero-emission ones. States like California are providing additional financing to make the change.
One obstacle is the significant upfront cost for a school district, as an electric bus costs several times more than an old-school gas-guzzling car. But if the bus can run on V2G, excess battery power at the end of the day can be exchanged as power back to the grid during peak hours to make up the cost difference. “We have used V2G revenue to equate this transport cost with that of diesel buses,” says Garg.
For the Oakland schools project, Zum has been working with the local utility, Pacific Gas and Electric, to test how it works in practice. PG&E is testing an adaptive system: Depending on the time of day and supply and demand on the grid, a V2G participant pays a dynamic rate for energy use and receives payment based on the same dynamic rate for energy that sends to the network. system. “Having a fleet of 74 buses, to be followed by other fleets, with more buses with Zum, is perfect for this, because we really want something that will grow and have an impact,” says Rudi Halbright, vehicle product manager. pilots and analysis of network integration at PG&E.