Electric vehicles are essentially batteries on wheels. Figuring out not only how to charge them for mobility but also use them to put power back on the grid will be one of the challenges of the next decade.
But doing so, much less scaling it for the masses, is more complicated than it seems. The technology — known as bidirectional charging — will depend on policymakers and utilities coordinating, as well as the help of automakers. If they can get their collective act together, bidirectional charging could entice would-be EV customers, who stand to benefit in terms of both finances and peace of mind.
What is bidirectional charging?
To charge an EV, the charger or the car must have a converter that takes alternating current (AC) power from the grid and flips it to direct current (DC) power that the car’s battery can store. Bidirectional charging technology — again, located either in the car itself or in an external charger — can convert that DC power to AC power to feed it back to the grid.
Despite the apparent ease, the technology is still very much in the pilot phase, in part because making use of the power stored in an EV’s battery involves getting utilities on board to feed power back onto the grid. California utility PG&E launched several projects last summer to explore the use of bidirectional charging in different contexts to gauge how cost-effective the technology is.
Why would we want to use EVs to power homes or the grid? Is that even a good idea?
There are a slew of reasons for using bidirectional charging, but they largely fall into two buckets: keeping the lights on and making money. Both are pretty good ideas!
Vehicle-to-home charging gives homeowners more control over their energy use, allowing them to do things such as power their home during a storm-induced blackout or draw on their EV battery for power when electricity prices — which fluctuate throughout the day — are at their highest. There’s a wide range to how much power a single EV battery holds, but a sedan like the Nissan Leaf has a capacity of 40 to 62 kilowatt-hours while a typical U.S. home uses roughly 30 kWh daily. That means keeping a house powered during a daylong outage is well within the realm of possibility.
Vehicle-to-grid charging involves more coordination with utilities. Storage will be increasingly important for ironing out the peaks and valleys of energy supply associated with renewables, and a parked EV represents a potentially valuable storage resource for power companies. Tapping that resource will require connecting each individual EV to the grid and then using software that can assess demand and communicate with utilities.
EV drivers who connect their vehicles to the grid could be in for a payday that could help offset the cost of the car itself. A 2021 National Grid pilot project saw a Nissan Leaf owner earn $4,200 over the course of a single summer by putting power back on the grid when demand shot up. Serving up power to the grid in times of need could be especially lucrative for fleet owners.
How far off is widespread bidirectional charging?
According to Katherine Stainken, vice president of policy at the Electrification Coalition, the biggest barrier to widespread adoption is the fact that utilities and the state-level commissions that regulate them are slow-moving and cautious about change. Even states like California that started looking into vehicle-to-grid charging several years ago are only now figuring out how to structure incentives for EV owners and what meter technology will be required. Stainken expects that in the next three to five years, these programs will be far more widespread.
Vehicle-to-home charging is closer to being ready for prime time, though the technology to integrate bidirectional charging into a home’s energy system is still not widely available. There are a handful of companies — including Emporia and Wallbox — coming out with the tech that could make it a more widespread reality within the next year.
There’s one caveat, though: using an EV to power either a home or the grid depends on getting the local utility’s say-so. An EV owner can’t sell power back to the grid if the utility doesn’t have a program in place to receive it, and supplying power to one’s own home is contingent on having a system in place that tells the utility to stem the flow of power from the grid.
It is possible utilities may actively stand in the way of vehicle-to-grid charging; they may not want to pay customers for the power they provide. Florida Power & Light has resisted allowing rooftop solar owners to sell their excess power back to the grid, which would entail a similar demand-response program.
Are there policies that could foster the technology’s use?
The current bidirectional charging policy landscape is fragmented, though state and federal lawmakers are beginning to push utility commissions to create plans for vehicle-to-grid charging. For instance, the California Public Utilities Commission laid out a vehicle-grid integration framework in 2020 after lawmakers required the agency to do so.
There is no federal law or regulation on the books governing bidirectional charging, though the bipartisan infrastructure law required states to consider how to electrify transportation and amend utility rates to “promote affordable and equitable EV charging.” Stainken said this could provide an opening for states to create more robust vehicle-to-grid policies, though the law does not come with a penalty for states that skip out on this process.
In collaboration with the energy security nonprofit SAFE, the Electrification Coalition recommended that federal lawmakers expand the charging infrastructure tax credit to cover vehicle-to-grid development and encourage the creation of national technical standards. The latter would require coordination with standard-setting bodies like UL or SAE to provide automakers with a road map for ensuring vehicles can handle bidirectional charging.
The Department of Energy, for its part, began to explore best practices for accelerating the use of these technologies earlier this year .
