EVs are one step closer to becoming roaming grid batteries

University of Delaware professor Willett Kempton is a pioneer of vehicle-to-grid (V2G) technology. In fact, he and his team of EV researchers at the university have been turning electric vehicles into grid batteries since 2007, when they kicked off a first-of-a-kind experiment that’s since been replicated in V2G projects around the world.

But Kempton is well aware of the technology and policy gaps that are holding V2G back from mainstream adoption. That’s why he’s spent years working with colleagues and students on updates to a technology standard that he hopes will make mass-market V2G a realistic option for automakers, utilities and drivers alike.

The standard is called SAE J3068, and last month, automotive standards organization SAE International formally adopted key new V2G capabilities for it. Kempton calls them a ​“practical, low-cost and implementable” way to turn every EV into a roaming grid battery.

Now he’s hoping that automakers will quickly build these new capabilities into their EVs and that utilities will invest in the communications and control systems they’ll need to work with them. If the technology takes off, it could help millions of EV owners use their spare battery power to earn extra money — and provide what experts say would be a significant boost to an increasingly stressed power grid.

As a first step, his team at the University of Delaware’s Science, Technology and Advanced Research Campus plans to start a pilot project next month with Delaware-based utility Delmarva Power, one of six regulated utilities owned by Chicago-based Exelon. That pilot will test the newly standardized capabilities on a handful of utility-owned vehicles.

The big challenge, Kempton said, is providing utilities with all of the data points they need in order to feel comfortable receiving power from EVs. ​“When something’s pushing power onto the grid, they want to know what that is,” Kempton said. ​“They don’t want to be like, ​‘We’re 95 percent sure which car it is.’”

What’s so complicated about V2G? 

To understand why V2G hasn’t taken off yet, it’s important to consider all the things that utilities need to know will happen for an EV battery to safely and seamlessly send power back to the grid. At present, the charging technologies in use in EVs and charging stations just aren’t set up to provide and manage that information, Kempton said.

V2G is particularly complicated when it’s the EV itself, rather than the charging station it’s plugged into, that needs to communicate with the utility. And that’s likely to be the most common arrangement. That’s because Level 1 and Level 2 chargers — the kinds of chargers that people use at home, at workplaces or in longer ​“dwell-time” locations like shopping mall parking garages — are the lowest-cost and most abundant chargers, but their alternating-current (AC) charging systems are not equipped to send utilities the data they need for V2G.

In contrast, direct-current fast-charging systems — the kind meant to top off EV batteries as fast as possible — contain inverters, devices that convert AC grid power to direct current. These inverters manage the interplay of the grid with the charger and vehicle. But with Level 1 and Level 2 charging, ​“the inverter is in your car,” Kempton said.

In essence, that makes every V2G-capable EV ​“a roaming inverter” — and it’s more complicated for utilities to certify an inverter to push power onto their grids when it moves from place to place, compared to one that’s permanently connected to the same point of the grid.

At present, the SAE technology standard used for Level 1 and Level 2 charging, J1772, is simply not capable of telling utilities everything they need to know, he said. The current standard ​“can say three or four things,” including whether it’s ​“connected to a charging station” and whether it’s ​“ready to charge.” It can also limit how much power an EV draws from the charging station.

“That’s the whole repertoire of signals,” he said. ​“That’s great if you want to plug in and charge — but not for much else.”

By contrast, EVs that comply with the newly adopted standard would be equipped with ​“about 200 signals,” he said. What’s more, instead of using the simple analog communications system used in the previous iteration, the new standard adopts technology that uses digital communications that can be carried via an existing wire in the power charging cord itself or via wireless signals.

That makes the new standard far more useful for communicating all kinds of things that most of today’s chargers can’t, he said. For example, EVs using the old standard can’t send the various diagnostic codes and error signals that charging stations rely on to troubleshoot charging glitches that can cause charging errors — a gap that’s partly responsible for the problematic performance of many public EV chargers today.

Last year, SAE adopted another update to the standard, J3068/1, that includes the diagnostic and identifying capabilities that EV drivers, automakers and charging station operators are eager to tap into to better troubleshoot charging problems. It can also identify the car or account to the charging station, enabling payment without always swiping a credit card.

J3068/2, the V2G-capable version of the standard approved last month, allows all of these features to be put to use for managing bidirectional power flows between cars and the grid, Kempton explained. That includes using EV batteries to back up homes and buildings during power outages or helping them to provide power in ways that don’t feed electricity back to the grid — known as vehicle-to-home and vehicle-to-building capabilities — which don’t require the same kind of utility integration as V2G operations.

Enabling EVs to move from serving as a backup battery to being a grid-connected resource is more complicated, however. Kempton highlighted key features of the J3068/2 standard that can make that task easier. One is its ability to provide ​“electrical certification” of individual vehicles, he said — in essence, recognizing each EV via a unique digital identifier that utilities can reference to check whether they’re authorized to supply power to the grid.

The same certification system can enable the utility to communicate ​“grid codes” with EVs to stop discharging power if local grid circuits are overloaded, for example, or to request that it supply power to mitigate grid disruptions, he said. And importantly, it can allow utilities to pay EV owners for volunteering their battery capacity.

Getting V2G from pilot projects to a mass-market grid tool

The lack of a common standard for accomplishing all these communications between EVs and utilities isn’t the only barrier to V2G becoming a widespread commercial reality. Automakers have long worried that allowing utilities to tap their EVs could subject their expensive batteries to the risk of premature degradation or run the risk of leaving EV owners stranded without adequate power after a mismanaged V2G session.

But that’s starting to change. Nissan’s Leaf EVs have been capable of bidirectional charging for years, and automakers including Ford, GM, BMW, Volkswagen and Hyundai are marketing the ability of their EVs to power homes.

Meanwhile, utilities and regulators have been working for years to set rules for how EVs can safely and reliably send power to the grid without causing unexpected problems. Those can range from accidentally electrocuting utility workers repairing downed power lines they didn’t expect to be energized to overloading local grid circuits and transformers if lots of EVs start discharging their stored power at the same time.

Because of these potential complications, V2G applications have so far been limited mostly to direct-current (DC) fast chargers, which can serve as a control point for utilities and operators to manage the interplay of power between grids and vehicles.

“In the case of DC [chargers], your inverter is bolted to the ground,” said Hamza Lemsaddek, vice president of technology at Nuvve, a V2G company that was spun out of Kempton’s work at the University of Delaware. Nuvve is coordinating moneymaking V2G projects in several European countries and in Japan, as well as in Delaware and California, all of which use charging stations as the control center rather than EVs themselves.

“When you move to AC V2G, you have a roaming inverter, and you have to ensure that wherever it connects, it has the proper settings as required by the local utility to inject power,” he said.

DC fast chargers use a standard called ISO 15118-20 to manage vehicle-to-grid communications and operations. That standard is ​“great for DC V2G, but it is missing some key signals and functionalities for AC V2G,” he said. U.S. utility pilots have concentrated on vehicle-to-home applications, which avoid the complications of feeding power stored in EVs back to the grid, or they have relied on less well-suited standards and one-off technology workarounds to test true V2G.

Some types of EVs that use DC fast-charging stations, such as electric school buses, are good candidates for V2G since they run on regular schedules and are charging for long periods of time. In fact, almost all of Nuvve’s V2G projects in California are with electric school buses.

But most EV drivers will use DC fast chargers to quickly charge up and go, not linger — making it unlikely that most passenger cars at fast chargers will be available for V2G charging. AC charging, which takes place at home, at work, at shopping centers and other places where people leave their cars plugged in for hours, is a much more suitable setting for V2G for the mass market.

Managed charging or ​“smart charging” is already a standard feature of most utility charging plans, which use alerts, time-varying prices or other methods to encourage customers to shift when they charge EVs to avoid adding stress to the grid. But cars spend most of their time parked, and EVs usually require only a fraction of that parked time to charge up their batteries. Allowing utilities to tap their fully charged batteries the rest of the time could significantly expand their grid value, compared to simply shifting when they charge.

A 2021 study by University of California, Irvine professor Brian Tarroja and Rochester Institute of Technology professor Eric Hittinger found that V2G could make a big difference for California’s grid. They calculated that the combined value of the energy-storage capacity of V2G-enabled EVs in California is ​“approximately an order of magnitude larger than that for smart charging.”

Putting the J3068/2 standard to use in real-world utility operations will be important to enable V2G for EVs that are starting to include on-board bidirectional capabilities at scale, Lemsaddek said. Nuvve is participating in the University of Delaware’s upcoming utility pilot project to test J3068/2 for V2G, he said.

One tricky issue with J3068/2 is that it may require EV owners to install a less expensive, but different, communications chip than those used for Combined Charging System (CCS) EV charging connectors, he noted. Besides Tesla and some EVs made by Asian automakers, almost every EV available in the U.S. to date is designed to work with CCS connectors. CCS has also been the primary charging connector technology used by chargers in North America.

But Tesla’s North American Charging System (NACS) standard was also certified by SAE for use by other charging manufacturers last month, Lemsaddek noted. That certification got more media attention than J3068/2, given the high-profile decisions by automakers Ford and GM to shift future EV models to using the NACS charging protocol rather than CCS.

But that new NACS standard, dubbed J3400, also has relevance for V2G, he pointed out. That’s because NACS supports a different communications technology that’s simpler and cheaper to implement than CCS’ technology, he said — one that can also be easily adapted to work with J3068/2. That ​“opens the door for massive adoption of that technology standard.”

EV charger manufacturers are also gearing up to enable AC V2G capabilities in their chargers, said Eduard Castañeda, chief innovation officer at Spanish-based charger manufacturer Wallbox. ​“We anticipate this standard will accelerate AC bidirectional charging in the U.S. and likely enable it ahead of even Europe,” which is generally more advanced than the U.S. on EV charging.

Kempton emphasized the importance of getting utilities and automakers on the same page on V2G. ​“There are some significant [automakers] planning to put in J3068 technology and sensing” into upcoming EV models, he said. ​“That’s an implementation decision that requires forward-looking engineering” but adds very little cost in exchange for much greater AC charging functionality and reliability.

Utilities also need to establish the interconnection processes for V2G-capable EVs and payment programs that make it worthwhile for EV owners to sign up, Kempton said. At that point, the path for his two decades of V2G work to come to fruition is relatively clear, he added — ​“you just need to have enough EVs” to make it happen.