In Oakland, California, 74 electric school buses returned 1,7 GWh of electricity to the grid over two years. This is not just eco-friendly transport: the fleet works as a distributed battery that relieves the power system precisely when electricity is needed most. The technology is called vehicle-to-grid (V2G), that is, "from vehicle to grid."
The daily cycle looks like this. At night the buses charge when the tariff is low. During the day on their routes they use 20–40 % of their charge, and after lessons end they connect to Tellus Power bidirectional charging stations. The total battery capacity of the fleet is 11,5 MWh, and simultaneous output reaches about 2 MW. With average evening household consumption of about 2 kW, this is enough for roughly a thousand households. The peak coincides with the moment when people return home and turn on air conditioners, lighting and household appliances.
It is important to understand one detail: V2G does not produce anything. The buses merely shift energy in time — they buy it when it is cheap and give it back when the price is high. That is why the economics rest on the difference in tariffs. According to estimates by publications that covered the project, through such arbitrage the fleet earned hundreds of thousands of dollars, though the exact sum has not been disclosed in open sources.
Reliability matters too. According to Electrek, over two years of operation the system's availability exceeded 99,5 %. Tellus Power, a charging equipment manufacturer from Irvine, has been producing chargers with a capacity of up to 480 kW since 2010. According to the company, a V2G depot can be deployed in months, whereas building and connecting a conventional power plant takes years. The chargers do not need large on-site transformers, which speeds up and reduces the cost of installation.
The roles in the project are distributed as follows. Zum, a school transport operator, purchased the buses and bidirectional chargers with funds from the federal Clean School Bus program and the California Air Resources Board (CARB), operates the fleet and manages it through an AI platform. Pacific Gas & Electric is responsible for the depot's power supply and its grid connection, which must work in both directions.
California is moving in the same direction, although the rules are structured differently from what is often written. The state does not require all new school buses to be equipped with V2G, but it does require bidirectional capability for vehicles purchased with state grants: since 1 January 2024 this condition has applied in the HVIP program. In addition, Governor Gavin Newsom signed a law under which all newly purchased school buses must be zero-emission starting in 2035. The Emergency Load Reduction Program is also in operation: during heat waves, school buses with bidirectional charging have already helped reduce peak load on the grid.
Similar projects are underway elsewhere as well. In San Francisco, Tellus Power is working on a project for 104 school buses, which is planned to be expanded to 238 vehicles. In Fremont, PG&E, together with The Mobility House, launched a V2G project with 14 electric buses of the Fremont Unified school district. According to WAMC, about 6700 electric school buses are already in operation in the United States, so the potential for scaling is very large.
Why school buses specifically? They have large batteries, they sit idle for most of the day and they travel on predictable routes. The operator knows in advance when a vehicle will be at the depot and how much energy will remain in it. That is why the buses are easily combined into a virtual power plant that reduces load on the grid and brings revenue to school districts.
The Oakland case shows that transport can not only carry children but also support the power system of entire districts. If such fleets grow, school and municipal buses are capable of noticeably smoothing peak loads and making energy supply more resilient in regions where demand for electricity is growing rapidly.
