These electric buses are more than a green alternative to traditional diesel models. They are equipped with cutting-edge vehicle-to-grid (V2G) technology, allowing them to charge and return power to the electrical grid. This dual capability positions these buses as vital components in the broader push toward renewable energy.
Managing energy storage becomes a critical challenge as the global energy grid transitions from fossil fuels to renewable sources. Renewable sources like solar power are abundant during the day but taper off in the evening when electricity demand peaks. Traditionally, this demand was met by gas-fired power plants, but a renewable-based grid requires innovative solutions for energy storage. One approach is centralized battery banks, which already contribute significantly; for example, on April 30, California sourced over a 5th of its evening electricity from batteries.
EVs with V2G capability can discharge power back to the grid, helping to balance supply and demand. According to the International Energy Agency (IEA), there are different scenarios for energy storage capacity by 2030. In the Stated Policies Scenario (STEPS), the installed capacity is estimated to be around 411 gigawatts (GW). In the Net Zero Emissions by 2050 Scenario (NZE), the capacity could be even higher. Other storage technologies, such as compressed air energy storage, flywheels, and thermal storage, are also considered in these estimates.
Additionally, research company BloombergNEF (BNEF) predicts that energy storage installations worldwide will reach a cumulative 411 GW (equivalent to 1,194 gigawatt-hours) by the end of 2030. This remarkable growth is approximately 15x the storage capacity that was online at the end of 2021. These projections highlight the critical role energy storage will play in meeting global energy needs and supporting the transition to cleaner energy sources. As EV owners participate in V2G programs, they contribute to this expanding energy storage landscape.
School buses are particularly well-suited for V2G. “There’s no uncertainty in terms of the use of the bus,” notes Patricia Hidalgo-Gonzalez, director of the Renewable Energy and Advanced Mathematics Lab at UC San Diego. “Having that clarity on what the transportation needs are makes it much easier for the grid to know when they can use that asset.”
Zum’s electric buses follow a predictable schedule, operating from early morning to mid-morning and again in the afternoon. During school hours, these buses can charge using abundant solar power. In the late afternoon and evening, when grid demand peaks, they can discharge surplus power into the system. "They have large batteries, typically four to six times a Tesla battery, and they drive very few miles," explains Vivek Garg, cofounder and COO of Zum. "So there’s a lot of battery left by end of the day."
The economic feasibility of this transition is bolstered by programs like the EPA’s Clean School Bus Program, which allocates $5 billion from 2022 to 2026 to replace diesel buses with zero-emission and low-emission models. Despite the higher upfront costs of electric buses, their V2G capability offers a financial offset by enabling them to sell excess energy back to the grid. "We have used the V2G revenue to bring this transportation cost at par with the diesel buses," says Garg.
Zum's collaboration with Pacific Gas and Electric (PG&E) is a critical aspect of this initiative. PG&E is piloting a dynamic rate system where V2G participants are compensated for the energy they provide based on real-time supply and demand. "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.
The potential of V2G extends beyond school buses. Passenger cars, delivery vehicles, and other fleet vehicles can also participate, offering diverse sources of energy storage and discharge at different times. This widespread adoption could significantly stabilize the grid, particularly as battery technology continues to improve and costs decline.
However, the increased charging and discharging cycles necessitated by V2G could shorten battery life. "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. Even as EV batteries age and lose capacity, they can still be repurposed for stationary grid storage, further extending their utility.
To realize the full potential of V2G, substantial participation from EV owners and fleet operators is crucial. Proper incentives and supportive regulations will be essential to encourage this transition. "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," Halbright emphasizes. "You don’t need that many, percentage-wise, participating at any one time to make a big impact."
The integration of V2G technology in school buses like those in Oakland not only provides a cleaner, quieter ride for students but also plays a pivotal role in the future of energy management, illustrating how innovative solutions can address multiple challenges simultaneously.
