There’s a technology sitting idle in garages and driveways across America that provides a solution to its own potential problem. As more and more electric vehicles tap the grid, their giant batteries add to the system’s load. Timing is also a challenge: When people get home from work and plug their cars in, so too is everyone elsewhere switching on their own appliances, like washing machines and ovens and such.

But instead of being burdens to the electrical system, a clever trick is putting EVs on a trajectory to help save it. More models feature the ability to send their energy back to the grid in times of high demand — a trick known as vehicle-to-grid, or V2G — forming a vast network of backup power across a city. As demand wanes through the night, they charge up, ensuring an EV owner has enough juice to get to work in the morning.

However, a new study warns that for V2G to fully compensate for all those batteries plugging in, the technology needs an assist, in the form of infrastructural improvements like new transformers and transmission lines. That will create a more resilient system and encourage the growth of renewables. “You have to upgrade your power system as soon as possible,” said Ziyou Song, an energy systems engineer at the University of Michigan and co-author of a new paper describing the findings. “V2G is really helpful, for sure — 100 percent. But just to some extent, V2G itself cannot resolve the charging demand of so many electric vehicles in the future.”

For this study, the researchers modeled scenarios for the San Francisco Bay Area, projecting how quickly EVs and solar power will be adopted — that is, how much demand will be put on the grid as renewable energy increases. Drilling deeper, they also projected where and when EVs might charge. (As with any modeling, there are some uncertainties here: EV adoption might happen slower or faster than expected, for example. The loss of federal tax credits for buying the vehicles might be reducing demand, but on the other hand, the gasoline price shock from the Iran war might drive more folks to go electric.) They also considered what it would cost to upgrade the grid over the same period.

All told, the modeling found that the cheapest option is to proactively upgrade the grid in anticipation of these changes, instead of doing so in phases over time in reaction to them. Then, as more EVs plug in, the vehicles will be able to draw enough power without the system straining. And with V2G, they’ll form a fleet of batteries that grid operators can tap to meet demand. In other words: EVs can help stabilize the grid, so long as they’re equipped with the technology to provide power in addition to taking it. “V2G plus the proactive power system upgrade will address the entire issue,” Song said.

This, in turn, can help smooth the “intermittency” challenge of renewables. Any grid must constantly balance the amount of electricity it’s generating with what its customers need at any given moment. With fossil fuels, utilities can just burn more gas or coal as demand rises. But renewable energy works differently, because the sun isn’t always shining and the wind isn’t always blowing. That’s why utilities are investing in batteries that store that power for later use: At one point late last month, they met 43 percent of demand in California, or six times the output of Hoover Dam.

The promise of V2G isn’t that it will replace battery farms, but instead essentially break them up into smaller ones spread across town. If the sun goes down at 5 p.m. when everyone is getting home and demand is rising, a utility can call on its battery facilities, but also on EVs, to send electricity into the system. (Anyone participating in the program would be paid for that juice.) Alternatively, those vehicles can electrify individual homes, divorcing those abodes from the grid, further reducing overall demand. All of this is good for EV owners, too, as they’re not drawing electricity when it’s most expensive. It wouldn’t just be passenger vehicles, either: Pilot projects are turning electric school buses — and their jumbo batteries — into reliable assets for the grid.

In these early days of V2G, utilities are still working out how to incentivize EV owners to participate, and how much to compensate them for sending power to the grid. The idea is to reach a sort of critical mass, where there’s enough people involved that it won’t matter if some folks choose to opt out. “When you’re operating 3,000, 30,000, 300,000, then any individual customers having different behavior won’t matter,” said Chris Rauscher, vice president and head of grid services at the battery storage and solar company Sunrun, which has been running V2G pilot projects.

The idea is to turn a vehicle from a depreciating asset into a source of income for the owner. One wrinkle, though, is that V2G could reduce the lifetime of a battery, due to the extra cycles of charging and discharging. Still, utilities are already repurposing old EV batteries — which need to be replaced when they drop to 70 to 80 percent of their original capacity — as stationary assets on the grid. “That’s a good way to keep getting value out of them,” said Patricia Hidalgo-Gonzalez, director of the Renewable Energy and Advanced Mathematics Laboratory at the University of California San Diego, who studies the grid but wasn’t involved in the new paper. “The program could even swap the battery for the EV owner. So, say, if you sign up for this pilot where you provide V2G services, after three years, we replace your battery with a new one.”

This tech can be paired with another powerful technique for supporting the grid, known as active managed charging. This opt-in program uses algorithms to stagger when EVs charge at night, instead of them all drawing power at 5 pm. When participants get home, they plug in, but the electrons might not flow until midnight, when most folks are asleep and not using much energy. The system also recognizes when an EV owner leaves for work in the morning, and how much battery they need, so charging switches on with enough time to spare.

Still, even combined, active managed charging and V2G alone can’t fix the grid of tomorrow. “We have to upgrade our power system as soon as possible,” Song said, “because V2G is not a silver bullet.”