74 electric school buses have spent two years feeding power to the grid, enough to supply about 1,000 California homes at once

Seventy-four electric school buses in Oakland, California, have spent about two years sending stored battery power back to the grid, and Electrek reported on Oct. 20 that the fleet can supply about 1,000 homes at once. The buses are run by the student transportation company Zum and fitted with bidirectional chargers from Tellus Power. Between them they hold 11.5 megawatt-hours of storage, can discharge roughly 2 megawatts together, and have returned 1.7 gigawatt-hours of electricity to the grid.

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The arithmetic behind 1,000 homes

The 1,000-home figure comes from Electrek writer Jameson Dow, who took the fleet’s simultaneous discharge of about 2 megawatts and divided it by an assumed average evening draw of roughly 2 kilowatts per home. It describes capacity during the after-school peak rather than a metered count of households served, and the report puts fleet uptime above 99.5 percent. Electrek also notes that the buses spend only a few hours a day on routes, which leaves long stretches for charging and discharging.

The daily rhythm explains why school buses suit the work. According to Electrek’s Oct. 20 report, the buses fill up overnight, use about 20 to 40 percent of their charge on school runs, and then discharge after the afternoon route, when household demand climbs. On holidays and through the summer they can serve the grid all day. Electrek put the value of the electricity delivered at hundreds of thousands of dollars over the past couple of years without giving an exact figure, and described the income as energy arbitrage: buying power when it is cheap and selling it when it is expensive.

The fleet’s design was laid out when the program launched. Canary Media reported on Sept. 3, 2024 that Zum operates the 74 buses, built by BYD, from a former industrial site in East Oakland, serving Oakland Unified School District. Each bus can discharge up to 50 kilowatt-hours on a working day and up to 111 kilowatt-hours, or 80 percent of its battery, on a nonworking day. Zum’s software tracks every route, and Kimberly Raney, the district’s executive director of transportation business operations, said skipping stops where no students are waiting frees battery capacity to return to the grid.

Zum, PG&E and the Oakland launch

Zum announced the project on May 15, 2024, as the nation’s first fully electrified, bidirectional school bus fleet, with Pacific Gas and Electric supplying 2.7 megawatts of load to the company’s EV-ready facility in Oakland. The release described the fleet as a virtual power plant designed to return an estimated 2.1 gigawatt-hours a year and credited funding from the EPA Clean School Bus program, the California Air Resources Board, HVIP vouchers and the Bay Area Air Quality Management District. Electrek’s August 2024 report said the buses debuted as that school year began.

Renewable Energy World quoted Mike Delaney, PG&E’s vice president of utility partnerships and innovation, saying the utility was proud to work with Zum and Oakland Unified on what he called the largest electric school bus fleet in the country.

The launch projection and the new numbers are not directly comparable. The 2.1 gigawatt-hours was an annual estimate published for a brand-new fleet, while the 1.7 gigawatt-hours is Electrek’s cumulative total over roughly two years. Ritu Narayan, Zum’s chief executive, said at launch that the industry should move beyond pilots and deploy sustainability solutions at scale, and the Oakland buses are the fleet Zum pointed to as proof it could be done.

Zum’s ambitions reach well past Oakland. The 2024 release said the company aims to electrify 10,000 bidirectional school buses nationwide, which it estimated could supply about 300 gigawatt-hours to the grid each year, and projected that the Oakland fleet would avoid 25,000 tons of greenhouse gases annually. Electrek’s 2024 coverage added that Zum already operated in 14 states and named San Francisco Unified and Los Angeles Unified as its next targets.

Who pays for the batteries

Canary Media reported that Zum’s five-year, $11.2 million contract with the district is priced at the same cost the district had been paying for a regular bus, according to Vivek Garg, Zum’s chief operating officer. Zum cut the project’s cost by about half by stacking incentives, including grants from California’s Heavy Vehicle Incentive Program and Clean Mobility Options, roughly $100,000 from PG&E’s make-ready program and about $1.2 million in PG&E charger rebates. Predictable grid revenue, the company argued, could also lower the cost of capital from investors and lenders.

The rate structure was still taking shape at launch. Rudi Halbright, a PG&E product manager, described a pilot dynamic rate that would reward charging when prices are low and discharging when they are high, tracking wholesale prices more closely than current EV rates. The state’s Emergency Load Reduction Program pays $2,000 per megawatt-hour but only during occasional grid emergencies, which makes it hard to build a business on.

Electrek’s update lists other Tellus Power vehicle-to-grid projects: four school buses in Burlington, Vermont; two city-bus chargers for Lynch Bus Lines in Burnaby, British Columbia; a pilot at three Illinois school district sites for ComEd; and 104 school buses in San Francisco, scaling to 238. The Oakland figures are estimates and a cumulative total, and no exact earnings number has been published.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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