A recent pilot project demonstrated how school buses can be deployed as backup power generators by selling excess battery power back into the grid.

Advocates tout the nascent vehicle-to-grid, or V2G, technology as a solution to the "duck curve" — the mismatch between times of peak energy demand and renewable energy supply. School buses could export battery power during daytime price surges, when they are not in use.

"It's really about trying to tame that down, and V2G is one way we can do that; we can absorb the renewables on the grid, and then sell them back overnight basically," said Brian Alexander, public relations director at electric bus manufacturer The Lion Electric Co. a collaborator in the school bus study led by Consolidated Edison Co. of New York Inc.

In April, the U.S. Department of Energy entered into a nonbinding agreement with Lion Electric and about a dozen other public- and private-sector stakeholders, including Ford Motor Co., General Motors LLC and Pacific Gas and Electric Co., to explore the feasibility of V2G rollout within the nation's energy infrastructure. Stated aims include establishing test locations, brainstorming use cases, and identifying hurdles.

The announcement came about a week after Con Edison shared its findings from the three-year school bus study. The project tested five "e-school buses" in White Plains, N.Y., that had been retrofitted for bidirectional charging. In an interview, Alexander said the pilot used school buses — as opposed to municipal buses or trucks — because their deployment is well-timed to take advantage of fluctuating energy costs.

Alexander said the average bus route "is less than 40 miles, they stop and go a lot, and they're parked overnight for 12-plus hours as well as part of the middle of the day." That pattern means they can be recharged using AC power instead of direct-current charging, which is faster but requires special infrastructure. School districts or school bus contractors could charge their vehicles overnight when electricity is cheaper, Alexander said, then sell excess electricity at peak hours and "basically make the delta in those energy prices."

Where the most need for development lies, Alexander said, is not in the vehicle technology but "the utility side of it." Recent academic reports have sought to optimize V2G for environmental and economic efficiency — a juggling act of electric load, renewable energy supply, generation costs, and the impact of bidirectional charging on battery lifespan. A report published April 25 in the International Journal of Electrical Power & Energy Systems proposed a model that, when scheduled optimally, could both reduce generation cost and level the load profile.

But another academic review, published online three days later in the journal Energies, called for further research taking battery degradation and charging location — i.e., residential or nonresidential — into account. According to the Con Edison news release on its study, "research showed that using the batteries for both transportation and grid support causes the batteries to degrade just like driving would," raising the possibility of the need for more frequent battery replacements.

But according to Con Edison, the project's findings "support the company's belief that electric school buses could be a resource in helping to keep its service reliable."

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