Most people think of electric vehicles as another draw on an already over-burdened electric grid. However, some models offer the ability to send energy back to the grid during periods of high demand. Vehicle-to-Grid, or V2G, enables electric vehicles to feed electricity back to the power grid when demand is high or renewable energy supply is abundant.

But the job requires infrastructural improvements like new transformers and transmission lines, according to a new study published in the journal Joule.

“V2G is really helpful, for sure: 100%,” said Ziyou Song, energy systems engineer at the University of Michigan and co-author of the study. “But … V2G itself cannot resolve the charging demand of so many electric vehicles in the future.” He believes the power system needs to be upgraded as soon as possible in order to create a resilient system and encourage the growth of renewable energy.

Researchers modeled scenarios for the San Francisco Bay Area in the study, projecting how quickly EVs and solar power might be adopted, how much demand could be put on the grid as renewable energy increases, and where and when EVs might charge. They also estimated costs to upgrade the grid.

The results indicated that the most economical option is to proactively upgrade the grid in anticipation of changes rather than phasing in changes over time, which will enable EVs to draw power without straining the system. With V2G, it will create a fleet of batteries across town able to provide power to the grid during times of high demand, thus stabilizing the grid and reducing the “intermittency” challenge of renewables, or to individual homes that would no longer need to draw from the grid, thereby reducing overall demand.

In addition to saving money for homeowners who aren’t drawing electricity from the grid during expensive peak times, the program incentivizes those who provide electricity to the grid. The idea is to turn a vehicle from a depreciating asset into a source of income.

The downside is that V2G could reduce the lifetime of a battery, due to extra charging and discharging cycles. Batteries need to be replaced when they reach 70% to 80% of their original capacity.

One answer to this problem is for utilities to repurpose old EV batteries 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. Similarly, some pilot projects are turning the large batteries in electric school buses into reliable assets for the grid.

Another idea is active managed charging, an opt-in program that uses algorithms to stagger when EVs charge at night. The system recharges EVs when there’s little draw on the grid. Because it recognizes when an EV owner leaves in the morning and how much battery they need, charging switches in time.