This story was originally published by Wired and appears here as part of the Climate Desk collaboration.

At first glance, electric vehicles seem like rolling disasters for the power grid. Surely the ancient, creaky network in the United States can’t handle the demand for charging those massive batteries. But a new analysis suggests that just a fraction of EV owners could make the grid more flexible and reliable by plugging into a system called vehicle-to-grid charging (V2G), or bidirectional charging.

V2G means that when demand spikes, utilities can pay EV owners to tap into their idle car batteries — a distributed network of ready-to-go backup power. That’ll be critical as we transition to renewables: Wind and solar power won’t always be available, so we need to bank energy when supplies are low. “We can use some energy that’s already stored in our EVs to give back to the grid,” says Chengjian Xu, an industrial ecologist at Leiden University in the Netherlands and lead author of the paper, which was recently published in Nature Communications. Last year, the Natural Resources Defense Council estimated that if California exploited all of the 14 million EVs it’ll have by 2035, it could power every home in the state for three days.

Xu’s modelling finds that by the year 2030, only 30 per cent of the world’s EV owners would need to opt in to V2G programs to meet energy storage demand. That’s a global average; each country differs in how quickly it’s adopting EVs, how much energy it uses, and the pace at which it’s switching to renewables, among other variables. Depending on the country, the modelling found that participation rates of between 12 and 43 per cent of EVs would suffice.

Better yet, the paper suggests that over time, the system won’t even need to rely on parked cars — their old batteries could be semi-retired and repurposed into large stationary power storage arrays. EV batteries usually need replacing once they get to 70 or 80 per cent capacity and a vehicle’s range begins to suffer. Depending on how much you drive and the climate where you live, a battery might last 10 to 20 years — which means that batteries in early models of popular EVs, like Teslas and the Nissan Leaf, are now reaching retirement.

The team’s modelling finds that if we did that for half of used batteries, we’d need less than 10 per cent of EV owners to participate. “Thankfully, battery degradation doesn’t seem to be limiting the total available energy that could be used for V2G,” says Paul Gasper, a staff scientist at the National Renewable Energy Lab who studies battery degradation and co-authored the paper.

Using parked cars as battery banks is a powerful way to shift energy demand. If drivers charge their cars during the day at offices or as they run errands (when the sun is shining and there’s lots of solar power being fed to the grid), they can drive home and provide extra power to their community in the early evening, right as demand soars because people are returning home and switching on appliances. EV owners would also agree that their power company could tap into their battery during extreme heat events when lots of people are running air conditioners.

The key is to stagger supply and demand between when people need the power to drive and when they need it to run their homes. “Yes, if everyone plugged in at the same time and charged a car at full power, that would not work on this antiquated model of charging,” says Jan Kleissl, director of the Center for Energy Research at the University of California, San Diego, who wasn’t involved in the new modelling. “But if we are able to vary demand, then we can certainly make it work because no vehicle needs to charge 24 hours a day.”

Commercial and government vehicles, like public transit or school buses, can also hook into V2G. A company called Nuvve, which develops V2G technology, has been working with school districts in Southern California to turn their buses — with their prodigious batteries — into V2G assets. School buses run on a reliable schedule, so their batteries can feed power to the grid after the kids are dropped off, then recharge in time to pick them up the next day. On weekends and holidays, a bus battery would be available at all times.

Hey, EV owners: It’d take a fraction of you to prop up the grid. #ElectricVehicles #EVs #PowerGrid #V2G #Energy #Nuvve

One of the perks of V2G is that it can subsidize the cost of owning an EV: The more it sits in your garage, the more money you make. “If you’re the type of person who can work from home and doesn’t have to drive your electric vehicle very often, then participating in V2G could likely make some revenue,” says Gasper. “So you’re providing more utility for the vehicle to help divert the cost of owning the vehicle, which is huge.”

You might think extra use would rapidly degrade the battery, but that’s not always true. “If you own an EV and don’t drive it very often, V2G could actually extend the lifetime of your vehicle battery,” says Gasper. Discharging it from time to time is essentially exercising it to keep it healthy. “There are two ways to kill a battery, and one is to have it sit fully charged all the time — why laptop batteries die very quickly. And the other one is to use it constantly.”

Wide-scale V2G faces some major challenges, though. For one thing, not every EV is equipped to do bidirectional charging, though automakers are increasingly adopting those capabilities for vehicles like the new Nissan Leaf and the Ford F-150. It also requires a special charger that reverses the current to pull energy out of the battery. Given those limitations, V2G is still in early development, with around 100 pilot programs running worldwide.

For another, there’s no industry standard for the intersecting components of V2G: Right now, there’s a patchwork of vehicles from different manufacturers plugging into different charging systems that themselves plug into different grids.

And utilities might offer different compensation, whether to individual EV owners or fleet operators. “One of the things we really need to learn is: What are the incentives that we need to offer drivers in both categories to get them to participate?” says Joseph Vellone of, which makes software that regulates EV charging and is working with a consortium of charger manufacturers and automakers to test V2G strategies.

A utility might subsidize or rebate the cost of bidirectional chargers, for example. Or a state might enact a law that says its utilities have to pay a certain rate for a specific amount of battery power, the way homeowners who install solar panels are compensated for sending excess power back to the grid. “We have this asset, and if we have a certain degree of flexibility, we can leverage it when the grid might need it the most,” says Patricia Hidalgo-Gonzalez, who is director of the Renewable Energy and Advanced Mathematics Laboratory at the University of California, San Diego, and wasn’t involved in the new paper. “The question is: How this will get materialized in the different utilities?”

And finally, EVs remain expensive, often out of reach for lower-income drivers. “A lot of the cheaper vehicles that people will be buying will be secondhand EVs, and they won’t have the bidirectional charging in them unless they get retrofitted,” says Paul Behrens, an industrial ecologist at Leiden University and co-author of the new paper. Plus, if you’re not a homeowner, you may not have the luxury of a dedicated garage socket you can plug your car into; apartment buildings with chargers are few and far between.

Yet, while there are still hurdles to overcome, automakers, charger manufacturers, and some utilities are already collaborating to turn EVs into grid assets, not burdens.

“Bidirectional charging is really the key to enabling EVs as being a viable backup power option, and that’s really where the future lies,” says Paul Doherty, a spokesperson for the Pacific Gas and Electric Company, one of California’s utilities.

“It’s just such a huge shift in the way we think about EVs and personal vehicles overall. It’s not just about getting from point A to point B anymore.”

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Good to see discussion getting down to brass tacks.

Now that we're at that point, my brain needs to understand the mechanism that facilitates bidirectional charging.

The analogy I always use to understand the grid is a municipal water supply; their is a source of water that is fed into the pipes at a constantly changing rate (volume per unit of time) but maintaining a fixed pressure (within specified tolerance). As more kitchen taps are opened more water is pushed into the pipes. This analogy only holds, however, for a unidirectional grid.

An even simpler analogy of a battery is to overfill a spare pneumatic tire to, say, 40 PSI and then use that extra pressure to inflate other tires to, oh, 15 PSI. That works until the "battery" tire's pressure drops to 15 PSI at which time it needs recharging.

Q: how is the EV able to push electrons back into the grid at a higher pressure than it nominally holds?

Can anyone provide a link to an explanation? Thanks.

An EV battery provides a DC voltage, much like a regular 12 Volt car battery, but at a much higher voltage. The grid provides an AC voltage - alternates between + 120 volts and -120 volts, 60 times every second. To charge an EV battery, one needs an inverter to change AC to DC, and a controller to make sure the voltage provided to the battery is appropriate and to make sure the battery isn't overcharged. If the EV battery is going to feed back into the grid, it again needs the inverter to change DC to AC, and this time the controller must not only provide the appropriate voltage to the grid, but it must also make sure the AC cycles match (are in phase with) the AC cycles on the grid. It's like your analogy of the water system. If you are going to put water back into the municipal water supply, you need provide a pump to increase the pressure just above the municipal water pressure, but not too high or you will burst the plumbing. It takes energy to run the pump. Similarly it takes some of the energy from the EV battery to run the inverter-controller.