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The big yellow school bus is a US icon, but perhaps not one that future Americans will remember fondly. Chugging through neighborhoods, idling in front of kids’ houses, the vehicles spew both noise and fossil-fuel pollution all across town. In a city like Oakland, California, that significantly worsens air quality, especially in underserved neighborhoods already struggling with pollution.
This August, though, 1,300 special-needs students in the Oakland Unified School District will start riding into the future aboard 74 fully electric buses, operated by a startup called Zum. “Most special-ed students, they have health issues—asthma and stuff like that. They go to school on this noisy, smelly, rough ride, just to get their access to education,” says Kim Raney, executive director of transportation at the Oakland Unified School District. “So this is really going to be a game-changer.”
But the students won’t just be enjoying a quiet, clean journey to school—they’ll also be helping revolutionize the way we all get electricity. The newfangled buses are no ordinary EVs: They’re equipped with vehicle-to-grid technology, or V2G, which allows them to both charge and give power back to the grid.
The global challenge is that as grids shift from fossil-fuel power to renewables, they’ll need to store a whole lot of energy. Demand on the grid spikes when people get home from work and switch on appliances—washing machines, air conditioners or heat pumps, electric stoves. That demand is easy enough to meet with a gas-fired power plant, since it just burns more gas. But for the renewable grid of tomorrow, that peak is unfortunately timed, because the sun is also setting, so there’s less and less solar power available. Part of the solution is banks of giant batteries, charging and discharging in a dedicated facility. The capacity of these is already sizable: On April 30 between 7 pm and 10 pm, California got more than a fifth of its electricity from batteries.
V2G is a more distributed option for backup battery power. EVs need special hardware to discharge to the grid, but more of them with the feature have been trickling out, like Ford’s F-150 Lightning. (V2G requires a special charger, too.) The idea is for Zum’s buses to eventually join millions of other EVs—fleets of city vehicles, cars sitting in suburban garages—as an array of surplus energy. Last year, researchers calculated that we’d need less than a third of the world’s EV owners to opt into V2G programs to meet the demand for energy storage by the year 2030.
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The school bus is in many ways ideal for V2G. “There’s no uncertainty in terms of the use of the bus,” says Patricia Hidalgo-Gonzalez, director of the Renewable Energy and Advanced Mathematics Lab at UC San Diego, who studies the grid but wasn’t involved in the project. “Having that clarity on what the transportation needs are—that makes it much easier for the grid to know when they can make use of that asset.”
Zum’s buses start operating at 6 or 6:30 am, drive kids to school, and finish up by 9 or 9:30 am. While the kids are in class—when there’s the most solar energy flowing into the grid—Zum’s buses plug into fast-chargers. The buses then unplug and drive the kids home in the afternoon. “They have large batteries, typically four to six times a Tesla battery, and they drive very few miles,” says Vivek Garg, cofounder and COO of Zum. “So there’s a lot of battery left by end of the day.”
After the kids are dropped off, the buses plug in again, just as demand is spiking on the grid. But instead of further increasing that demand by charging, the buses send their surplus power back to the grid. Once demand has waned, around 10 pm, the buses start charging, topping themselves up with electricity from nonsolar sources, so they’re ready to pick up kids in the morning. Zum’s system decides when to charge or discharge depending on the time of day, so the driver just has to plug in their bus and walk away.
On weekends, holidays, or over the summer, the buses will spend even more time sitting unused—a whole fleet of batteries that might otherwise be idle. Given the resources needed to make batteries and the need for more grid storage, it makes sense to use what batteries are available as much as possible. “It’s not like you’re placing a battery somewhere and then you’re only using them for energy,” says Garg. “You’re using that battery for transportation, and in the evening you’re using the same battery during the peak hour for stabilizing the grid.”
Get ready to see more of these electric buses—if your kid isn’t already riding in one. Between 2022 and 2026, the EPA’s Clean School Bus Program is providing $5 billion to swap out gas-powered school buses for zero-emission and low-emission ones. States like California are providing additional funding to make the switch.
One hurdle is the significant upfront cost for a school district, as an electric bus costs several times more than an old-school gas-guzzler. But if the bus can do V2G, the excess battery power at the end of the day can be traded as energy back to the grid during peak hours to offset the cost difference. “We have used the V2G revenue to bring this transportation cost at par with the diesel buses,” says Garg.
For the Oakland schools project, Zum has been working with the local utility, Pacific Gas and Electric, to pilot how this works in practice. PG&E is testing out an adaptable system: Depending on the time of day and the supply and demand on the grid, a V2G participant pays a dynamic rate for energy use and gets paid based on the same dynamic rate for the energy they send back to the 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’s going to scale and make an impact,” says Rudi Halbright, product manager of vehicle-grid-integration pilots and analysis at PG&E.
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Think of the diversity of vehicles on the road. Passenger cars have smaller batteries, sure enough, but many people might not actually need the 300 miles of range they paid for. Getting paid for V2G can offset the cost of the vehicle. (An EV can also act as a backup home battery during a power outage, providing additional value.) If people can fully charge their EVs at work, they might have a good amount of power left when they park in their garage at the end of the day, making their battery available to the grid as demand spikes. Then there are delivery vehicles, which have bigger batteries to tap into, and are also useful because they operate on a more fixed schedule. And there are legions of other fleets—run by city governments, universities, and businesses—that can also plug into V2G, providing battery power at different times of day, depending on their own operating schedules.
Let’s consider, though, that the extra charging and discharging can shorten the life of a battery. “We need to be mindful of that, to make sure that we’re being paid enough for the degradation that we have in our battery,” says Hidalgo-Gonzalez. While an EV battery needs to be replaced when its capacity drops below 70 or 80 percent, it can still support the grid outside of the vehicle: You can bundle a bunch of them together to provide storage at dedicated facilities. And the price of batteries continues to decline, so it’s getting cheaper and cheaper to replace them in EVs.
As V2G matures, different regions might land on different rates for buying back electricity; it’ll depend on the local utility and what state-level regulations are eventually put in place. But to reach its full potential, V2G will have to properly incentivize people to opt in. The more participants, the less the demand on any one battery. Many wheels make light work. “That’s one of the nice things of having 74 buses: You take a little from each,” says Halbright. “Our goal is to have 2 million vehicles by 2030 on the road that we have some control over when they’re charging, or in some cases, discharging. You don’t need that many, percentage-wise, participating at any one time to make a big impact.”
