Jet fighters can’t carry a huge tank of fuel because it would slow them down. Instead they have recourse to air-to-air refueling, using massive tanker planes as their gas stations.
What if electric cars could do the same thing, while zooming down the highway? One car with charge to spare could get in front of another that was short of juice, and the two could extend telescopic charging booms until they linked together magnetically. The charge-rich car would then share some of its largesse. And to complete the aerial refueling analogy, just add a few big “tanker trucks” bearing enormous batteries to beef up the power reserves of an entire flotilla of EVs.
The advantages of the concept are clear: It uses a lot of battery capacity that would otherwise go untapped, and it allows cars to save time in transit by recharging on the go, without taking detours or sitting still while topping off.
Yeah, and the tooth fairy leaves presents under your pillow. We’re too far into the month for this kind of story. Right?
Maybe it’s no April Fool’s joke. Maybe sharing charge is the way forward, not just for electric cars and trucks on the highways but for other mobile vehicles. That’s the brief of professor Swarup Bhunia and his colleagues in the department of electrical and computer engineering at the University of Florida, in Gainesville.
Bhunia is no mere enthusiast: He has written three features so far for IEEE Spectrum (this, this, and this). And he and his coworkers—Prabuddha Chakraborty, Robert Parker, Lili Du and Shuo Wang—have published their new proposal in arXiv, an online forum for preprints that have been vetted, if not yet fully peer reviewed. The researchers call the concept peer-to-peer car charging.
The point is to make a given amount of battery go further and thus solve the two main problems of electric vehicles—high cost and range anxiety. In 2019, batteries made up about a third of the cost of a midsize electric car, down from half just a few years ago but still a huge expense. And though most drivers typically cover only short distances, they usually want to be able to go very far if need be.
Mobile charging works by dividing a car’s battery pack into independent banks of cells. One bank runs the motor, the other one accepts charge. If the power source is a battery-bearing truck, you can move a great deal of power—enough for “an extra 20 miles of range,” Bhunia suggests. True, even a monster truck can charge only one car at a time, but each newly topped-off car will then be in a position to spare a few watt-hours for other cars it meets down the road.
Peer-to-peer car recharging, like aerial refueling, uses steerable booms to fashion a transmission channel.Credit Illustration: Swarup Bhunia
We already have the semblance of such a battery truck. We recently wrote about a concept from Volkswagen to use mobile robots to haul batteries to stranded EVs. And even now you can buy a car-to-car charge-sharing system from the Italian company Andromeda, although so far no one seems to have tried using it while in motion.
If all the cars participated (yes, a big “if”), then you’d get huge gains. In computer modeling, done with the traffic simulator SUMO, the researchers found that EVs had to stop to recharge only about a third as often. What’s more, they could manage things with nearly a quarter less battery capacity.
A few disadvantages suggest themselves. First off, how do two EVs dock while barreling down the freeway? Bhunia says it would be no strain at all for a self-driving car, when that much-awaited creature finally comes. Nothing can hold cars in tandem more precisely than a robot. But even a human being, assisted by an automatic system, might be able to pull off the feat, just as pilots do during in-flight refueling.
Then there is the question of reciprocity. How many people are likely to lend their battery to a perfect stranger?
“They wouldn’t donate power,” explains Bhunia. “They’d be getting the credit back when they are in need. If you’re receiving charge within a network”—like ride-sharing drivers for companies like Uber and Lyft—“one central management system can do it. But if you want to share between networks, that transaction can be stored in a bank as a credit and paid back later, in kind or in cash.”
In their proposal, the researchers envisage a central management system that operates in the cloud.
Any mobile device that moves about on its own can benefit from a share-and-share-alike charging scheme. Delivery bots would make a lot more sense if they didn’t have to spend half their time searching for a wall socket. And being able to recharge a UAV from a moving truck would greatly benefit any operator of a fleet of cargo drones, as Amazon appears to want to do.
Sure, road-safety regulators would pop their corks at the very mention of high-speed energy swapping. And, yes, one big advance in battery technology would send the idea out the window, as it were. Still, if aviators could share fuel as early as 1923, drivers might well try their hand at it a century later.