It was a football game on TV that sparked Nancy Skinner’s interest in bidirectional charging, an emerging technology that allows an EV’s battery to not just soak up energy but to discharge it, too — to a home, to other cars or even back to the utility grid.

“There was a commercial for the Ford F-150 truck,” recalls Skinner, a California state senator who represents San Francisco’s East Bay. “This guy is driving up to the mountains and plugs his truck into a cabin. Not to charge the truck, but to power the cabin.”

With its 98-kWh battery, an F-150 Lightning can keep the power on for up to three days. That could be extremely useful in California, which has seen nearly 100 substantial outages in the last five years, more than any other state except Texas. In September 2022, a 10-day heat wave saw California’s power grid reach an all-time high of more than 52,000 megawatts, nearly knocking the electric grid offline.

In January, Skinner introduced Senate Bill 233, which would require all electric cars, light-duty trucks and school buses sold in California to support bidirectional charging by model year 2030 — five years before the state is set to ban the sale of new gas-powered cars. A mandate for bidirectional charging would ensure that carmakers “can’t just put a premium price on a feature,” said Skinner.

“Everyone has to have it,” she added. “If they choose to utilize it to help offset high electricity prices, or to power their home during a blackout, they’ll have that option.”

SB-233 cleared the state Senate in May by a 29-9 vote. Not long after, several automakers, including GM and Tesla, announced that they’d be making bidirectional charging standard in upcoming EV models. Currently, the F-150 and the Nissan Leaf are the only EVs available in North America with bidirectional charging enabled beyond the most rudimentary capability.

But progress doesn’t always move in a straight line: In September, SB-233 died in committee in the California Assembly. Skinner says she’s looking for “a new path” to ensure that all Californians benefit from bidirectional charging. 

As natural disasters, severe weather and other effects of climate change become more evident, Americans are increasingly turning to renewable energy options like electric vehicles and solar power. Falling prices on EVs and new tax credits and incentives are helping to speed that transition.

Now the prospect of bidirectional charging offers yet another reason for considering EVs: the potential to use your car as a backup power source that could save you in a blackout or earn money when you’re not using it.

To be sure, there are some road bumps ahead. Manufacturers and municipalities are just beginning to examine the infrastructure changes they’ll need to scale up to make this feature useful. Necessary accessories are unavailable or expensive. And there’s a lot of educating to be done for consumers, too.

What’s clear, though, is that this technology has the potential to dramatically change the way we power our lives.

What is bidirectional charging?

With most EVs, electricity goes one way — from the charger, wall outlet or other power source into the battery. There’s an obvious cost to the user for the electricity and, with more than half of all car sales expected to be EVs by the end of the decade, an increasing burden on already overtaxed utility grids.

Bidirectional charging lets you move energy the other way, from the battery to something other than the car’s drivetrain. During an outage, a properly linked EV can send electricity back to a house or business and keep the power on for several days, a process known as vehicle-to-home (V2H) or vehicle-to-building (V2B). 

More ambitiously, your EV could also provide power to the network when demand is high — say, during a heat wave when everyone is running their air conditioners — and avoid instability or blackouts. That’s known as vehicle-to-grid (V2G).

Considering that most cars sit parked 95% of the time, it’s a tempting strategy.

But having a car with bidirectional capability is only part of the equation. You also need a special charger that allows energy to flow both ways. We could see that as early as next year: In June, Montreal-based dcbel announced that its r16 Home Energy Station had become the first bidirectional EV charger certified for residential use in the US. 

Another bidirectional charger, the Quasar 2 from Wallbox, will be available for the Kia EV9 in the first half of 2024.

Aside from the hardware, you’ll also need an interconnection agreement from your electric company, ensuring that sending power upstream won’t overwhelm the grid.

And if you want to recoup some of your investment with V2G, you’ll need software that directs the system to maintain a level of charge you’re comfortable with while getting you the best price for the energy you sell back. The big player in that area is Fermata Energy, a Charlottesville, Virginia-based company founded in 2010.

“Customers subscribe to our platform and we do all that grid stuff,” says founder David Slutzky. “They don’t have to think about it.” 

Fermata has partnered on numerous V2G and V2H pilots across the US. At the Alliance Center, a sustainability-minded coworking space in Denver, a Nissan Leaf is plugged into a Fermata bidirectional charger when it’s not being driven around. The center says Fermata’s demand-peak predictive software is able to save it $300 a month on its electric bill with what’s known as behind-the-meter demand charge management.

In Burrillville, Rhode Island, a Leaf parked at a wastewater treatment plant earned almost $9,000 over two summers, according to Fermata, by discharging electricity back to the grid during peak events.

Right now most V2G setups are small-scale commercial trials. But Slutzky says residential service will soon be ubiquitous.

“This isn’t in the future,” he says. “It’s already happening, really. It’s just that it’s about to scale.”  

The origins of bidirectionality

The buzz on bidirectional charging has actually been in the air for more than a century. In the 1910s, as electrification was still rolling out across the US, utility companies were generating more electricity than there was demand for. But if they let the amount of power dip too low, it could unbalance their networks.

“So the utilities had these fleets of electric trucks that they used, not so much for delivery, but to store electricity,” says historian and energy policy analyst Matthew Eisler.

It was still the early years of the automobile, and battery-powered vehicles were not uncommon.

After World War I, though, electrical grids were quickly built out nationwide, and energy could soon be pushed across time zones and even international borders. The need for mass storage evaporated

“Now with all the capacity available from renewables and the increased demand from EVs themselves, we’re back facing the storage problem again,” says Eisler, author of Age of Auto Electric: Environment, Energy, and the Quest for the Sustainable Car.

The idea of using EVs to stabilize the grid reemerged at the turn of the 21st century, by which point many states had deregulated electricity. That change, according to many analysts, led to serious infrastructure deterioration and disincentivized the building of new power plants.

In 1996, California became the first state to deregulate. By 2000, it was suffering a crippling electricity crisis marked by soaring prices and rolling blackouts.

At about the same time, engineers at AC Propulsion, a pioneering EV company in San Dimas, California, were running experiments proving the feasibility of bidirectional charging. They weren’t thinking about balancing the grid, though: With battery capacity and range much more limited at the time, they were trying to figure out how one EV might share a charge with another — essentially providing a jump start for a vehicle that had run out of power.

In 2007, AC Propulsion unveiled the world’s first V2G-capable automobile, the eBox, made from a converted Scion xB hatchback.

By then, though, interest in EVs was fizzling: In 2002, GM discontinued the EV1, the first mass-produced electric car from a major automaker. Tesla introduced the Roadster in 2008, and Chevy rolled out the Volt in 2010, but neither generated much interest outside the enthusiast crowd.

Then, in March 2011, a magnitude 9.1 earthquake struck off the northeast coast of Japan, followed by a tsunami with 130-foot waves. Amid the devastation, two nuclear power plants in Fukushima suffered major damage and partial meltdowns, leaving nearly 5 million households without power.

Oil refineries were shut down and roadways were too clogged for gasoline deliveries. The Nissan Leaf, introduced in Japan just months earlier, came to the rescue. Unlike European and American EV charging systems, the Japanese standard, Chademo, automatically enables bidirectional charging.

Nissan dispatched a fleet of 66 Leafs to affected areas and, in addition to transporting first responders and critical supplies, the vehicles were used to provide heat, charge cellphones and power medical equipment until generators could be set up.

“Even during the darkest days of rolling blackouts, the Leafs kept rolling,” Nissan said in a 2015 release recounting the disaster. The blackouts would typically happen during the day, when the cars were in operation. At night, when the power returned, the Leafs could charge up for another day’s work.

Nissan quickly ratcheted up bidirectional technology: Today, a fully charged 62-kWh battery in a Nissan Leaf E+ can power a typical Japanese home for up to four days. 

The company continues to send EVs to help after natural disasters. When Typhoon Faxai knocked out power for nearly a million people around Tokyo in September 2019, Nissan Leafs powered fans, air conditioners and refrigerators to combat high temperatures and humidity.

Bidirectional charging: vehicle to home

The simplest form of bidirectional power is known as vehicle to load, or V2L. With it, you can charge camping equipment, power tools or another electric vehicle (known as V2V). There are more dramatic case uses: Last year, Texas urologist Christopher Yang announced he had completed a vasectomy during an outage by powering his tools with the battery in his Rivian R1T pickup. 

You might also hear the term V2X, or vehicle to everything. It’s a bit of a confusing catchall that can be an umbrella term for V2H or V2G or even just managed charging, known as V1G. But others in the auto industry use the abbreviation, in a different context, to mean any kind of communication between the vehicle and another entity, including  pedestrians, streetlights or traffic data centers.

Of the various iterations of bidirectional charging, V2H has the broadest support, as human-caused climate change and poorly maintained electrical grids have made outages much more common. There were more than 180 widespread sustained disruptions across the US in 2020, according to a Wall Street Journal review of federal data, up from fewer than two dozen in 2000.

EV battery storage has several benefits over diesel or propane generators, including that, after a disaster, electricity is usually restored faster than other fuel supplies. And traditional generators are loud and cumbersome and spew noxious fumes.  

Aside from providing emergency power, V2H can potentially save you money: If you use stored energy to power your home when electricity rates are higher, you can lower your energy bills. And you don’t need an interconnection agreement because you’re not pushing electricity back to the grid.

But using V2H in a blackout only makes sense to a point, says energy analyst Eisler.

“If you’re looking at a situation where the grid is unreliable and might even crash, you have to ask yourself, how long is that crash going to last,” he says. “Are you going to be able to recharge that EV when you need to?” 

A similar critique came from Tesla — during the very same investors day press conference in March at which it announced it would add bidirectional functionality. At that event, CEO Elon Musk downplayed the feature as “extremely inconvenient.”

“If you unplug your car, your house goes dark,” he remarked. Of course, V2H would be a direct competitor to the Tesla Powerwall, Musk’s proprietary solar battery.

Bidirectional charging: vehicle to grid

Homeowners in many states can already sell the surplus energy they generate with rooftop solar panels back to the grid. What if the more than 1 million EVs expected to be sold in the US this year could do the same?

According to researchers at the University of Rochester, drivers could save between $120 and $150 a year on their energy bill.

V2G is still in its infancy — power companies are still figuring out how to prepare the grid and how to pay customers who sell them kilowatt hours. But pilot programs are launching around the world: California’s Pacific Gas and Electric, the US’ largest utility, has started enrolling customers in an $11.7 million pilot to figure out how it will ultimately integrate bidirectionality.

Under the plan, residential customers will receive up to $2,500 toward the cost of installing a bidirectional charger and will be paid to discharge electricity back to the grid when there’s an anticipated shortage. Depending on the severity of the need and the capacity people are willing to discharge, participants could make between $10 and $50 per event, PG&E spokesperson Paul Doherty told dot.LA in December, 

PG&E has set a goal of supporting 3 million EVs in its service area by 2030, with more than 2 million of them capable of supporting V2G.

V2G in commercial fleets

PG&E has also launched a pilot program for business customers, with incentives of up to $5,000. V2G may actually be ideal for commercial vehicles, which operate on predictable schedules and are overseen by central decision-makers. 

School buses, in particular, are something of a V2G dream, with their large batteries and the daylight hours they spend sitting idle. San Diego Gas & Electric launched the first V2G program in the US in July 2022, using eight electric buses in El Cajon, California, to push electricity back to the grid and power more than 450 homes during a scorching heat wave. 

The buses recharged during off-peak hours, when there was less demand, and the Cajon Valley Union School District received $2 per kilowatt-hour from SDG&E as part of the utility’s Emergency Load Reduction Program.

“If we are able to reduce our energy and vehicle maintenance costs as a result of this project, it frees up more resources for our schools and students,” says Scott Buxbaum, assistant superintendent for the Cajon Valley Union School System.

Similar V2G fleet programs have been launched in Massachusetts, Virginia and other states. The nearly 500,000 buses in this country that sit idly for up to 18 hours a day “represent a vast untapped energy storage resource,” says Miguel Romero, SDG&E’s vice president for energy innovation.

According to the Environmental Protection Agency, if just half of the buses went electric and were V2G-enabled, it could provide power for 15 million laptops for a month, enough for nearly every high school student in the US.

While the upfront costs are substantial — a new electric bus can cost two to three times as much as a traditional diesel-powered one — supplying power back to the grid could subsidize those costs. In addition, electric buses have fewer moving parts, meaning they’re cheaper to maintain, and fuel is significantly cheaper over the life of the bus.

The Utrecht experiment

But buses are only one option. Last year, Dutch car-share operator We Drive Solar drafted 25 Hyundai Ioniq 5 SUVs to double as mobile energy storage systems in Utrecht, the Netherlands’ fourth-largest city.

When users plug the EVs into We Drive Solar’s proprietary bidirectional chargers, they capture power from thousands of rooftop solar panels on the roof of a local insurance company. At night, the batteries send energy back to the building, allowing the power to stay on.

We Drive Solar plans to expand to 500 cars next year and continue scaling quickly after that. By 2028, there should be at least 10,000 EVs using bidirectional charging, according to company founder Robin Berg. That’s less than a tenth of the automobiles in the city today but enough to fully balance its electrical demand with renewables, according to research from the University of Utrecht.

With the Netherlands set to ban new gas-powered automobiles in 2030, Berg says, the time is ripe.

“The grid operators in the Netherlands really see a big value in this technology,” he says. “It will take them 10 to 20 years to build out a new grid to support renewable energy. They need bidirectional charging to cover the period until then, and after that so it can keep available all the energy being generated by wind and solar.”

We Drive Solar will only let its V2G cars go down to 25% or 30% of a full charge. Software connecting the car reservation platform and the chargers lets the company know when a car will be in use. The predictability of the car-sharing makes it easy to forecast usage and to employ the car battery efficiently, Berg says.

He noted that the project has been possible thanks to buy-in from the city, the utility company and carmakers — not to mention the Dutch government, which has eased regulations while We Drive Solar scales its plan.

It might not be so easy to get everyone to play nice in the US. But any country that’s serious about transitioning to renewables, Berg says, “will need to figure out how to make this work.” 

What’s holding back bidirectional charging?

Not everyone is convinced V2X is the future. There are still a lot of unanswered questions about the costs involved, what charging and discharging will do to the battery and whether motorists will even get on board with the whole idea.

Scott Moura is dubious about the hype surrounding bidirectional charging. He teaches engineering at the University of California, Berkeley, and is faculty director for California Partners for Advanced Transportation Technology, a research outfit that develops carbon-neutral transportation systems. 

He acknowledges that using your EV to keep the lights on during a brief outage would have a “negligible” effect on your battery. Even 47 hours of V2H over the course of a year — essentially two days as emergency backup — would add no more than 2% of mileage to the battery, according to Moura.

But the cost of a bidirectional charger is not unsubstantial: The 9.6-kW JuiceBox 40, one of the most popular unidirectional EV chargers, is just just$600. Fermata’s upcoming 20-kW bidirectional charger, the FE-20, retails for $11,500.

“This is not the type of charger you buy off Amazon for your EV,” Moura says. “For that kind of money, you could buy a dedicated Tesla Powerwall that operates even when your vehicle is on the road.” 

And while the cost of adding bidirectionality to an EV is minimal, some experts say it could jack the price by as much as $3,700 to meet warranty requirements and advanced clean cars regulations.

There’s also the question of what all the charging and discharging involved in V2G will do to the battery itself. If an EV owner drives 30 miles a day, they’re discharging 9 kWh and then charging another 9 to replace it, for a total of 18 kWh buffered through the battery for the purposes of transportation.

The typical American household consumes about 30 kWh in a day. If they devote just 10% to V2G, says Moura, the author and energy analyst, that’s 3 kWh going out and in, or 6 kWh total. That’s adding a third more wear and tear on your battery than if you only used it to drive and charge up.

“If all you can earn is $150 a year, then it doesn’t make much economic sense,” Eisler says. “For the technocrats that are excited to try it, by all means. But it’s not a mass-market solution.”

The bottom line, he says, is that the EV battery has been designed for the duty cycle of an automobile, not as a storage device. 

“There are a number of entities doing that research right now,” Eisler says. “But the fleets are so new, it’s still really an unknown.” 

On the other side is Fermata Energy’s Slutzky, who says the idea that bidirectional charging degrades batteries quickly is “utter nonsense.” He cites peer-reviewed journal articles from the University of Warwick that found that, with proper management, V2G can actually extend battery life.

Slutzky also said giving EV owners who participate in V2G enticing tax credits, similar to the ones states like California make available for people with stationary storage devices, could defray any additional costs.

“They’re subsidizing the least cost-effective solution to the problem,” Slutzky says. “If that subsidy became available for V2X, it would take off.”

But will EV owners want to share?

In 2018, Pecan Street, a residential energy research collective, launched a V2G pilot program in Austin, Texas. A Nissan Leaf with a 40kWh battery helped balance the load when the Electric Reliability Council of Texas, which operates most of the state’s electrical grid, expected demand to be at its highest.

Communication between ERCOT and the system’s 10-kW bidirectional charger made sure the battery never dropped below a 20% charge and the Leaf always had at least 40 miles of range available.

According to Pecan Street’s researchers, in the experiment’s first year “no significant battery degradation occurred from the daily charge/discharge events.”  

Even so, Jeremy Michalek, the co-founder of Carnegie Mellon’s Vehicle Electrification Group, said it’s going to be hard to convince EV owners to participate in load sharing.

“Many drivers will prefer to have their vehicles fully charged, just in case they need to take a sudden long trip,” Michalek says. “When my sister went into labor, I dropped everything and drove several states away to be there.”

Even Ty Jagerson, GM’s leader for V2X, sees this mentality as the chief hurdle to the adoption of even just managed charging.

“The biggest problem at this point … is just getting people to understand what the heck you’re doing and … that you’re not somehow hijacking their car or going to leave them with their vehicle drained, sitting as a doorstop in their driveway,” Jagerson told Catalyst podcast host Shayle Kann in August. 

Bidirectional charging in every garage?

Ultimately, says Skinner, the California state senator, bidirectional charging via EVs will be critical to avoid the worst aspects of climate change. 

During the unprecedented stress on California’s electrical grid last summer, she notes, the state was able to avoid blackouts because it deployed utility-grade energy storage. But she warns that projections point to more and more stressful days ahead.

“If we can use those electric vehicles as either a grid resource or to power a home,” she says, “then we’ll lessen the need for diesel generators and for fossil fuel and natural gas power plants. It’s one of the many things that we have to do to address the climate crisis.”

California is already ahead of the curve when it comes to storage, she says, but having a mobile resource in every garage “would be a game-changer.”

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