IEEE websites place cookies on your device to give you the best user experience. By using our websites, you agree to the placement of these cookies. To learn more, read our Privacy Policy.

But is vehicle-to-home (V2H) technology ready for the bright lights?

The 2022 Ford F-150 Lightning Pro, pictured here, which the American automaker says will be available later this year.

Starting this year, thousands of battery-powered electric-drive Volkswagen vehicles capable of both loading and off-loading current—bidirectional charging, as the industry calls it—have been rolling off production lines in eastern Germany.

And in the last two weeks, one of the largest utility companies in the United States, Pacific Gas & Electric Company, announced plans to work with General Motors in experiments with their bidirectional-charging technologies. Ford, another auto-industry titan, has also made bidirectional charging a selling point of its F-150 Lightning electric truck, reportedly slated to roll off the lines this year.

The general principle for bidirectional charging is that EVs can either feed power from a charged vehicle back into the house (vehicle-to-home or V2H) or interact with the electric grid itself (vehicle-to-grid or V2G). These V2H/V2G-enabled vehicles offer some three to 10 days powering the fridge and lights in case the power goes down. A side benefit could be plugging in appliances to the car while camping rough.

After years (and depending on how you count it, decades) of work, momentum may be close to pushing bidirectional-charging technologies into the mainstream. It’s not quite ready for the mainstream yet, though. The ratio of marketing and expectations to the intake of real-world information is still steep. And plenty of technology remains left to be worked out, including the complex supporting infrastructure, business models, and various forms of electric plugs and chargers, alongside their sometimes confounding range of pin configurations.

Ford’s brawny new entrant into the mix is its new F-150 Lightning, out this year with an estimated 482 kilometers (300 miles) of range on a full charge with a 454-kilogram (1,000-pound) payload. The pickup boasts 563 horsepower, does 0 to 60 in 4 seconds, and wields 1,050 newton meters (775 pound-feet) of torque.

According to Ford, a driver can roll this beast into a garage mounted with the $1,310 80-amp Ford Charge Station Pro, where its AC pins can deliver a full overnight charge at a 19-kilowatt output to the truck’s 98-kilowatt-hour (131 kWh if you have the extended extra-big-range) lithium-ion battery. In case of power outage at home, the DC pins in the charger can send juice back into the house, keeping the lights on. According to Ford, that translates to three days for an average 30 kilowatt-per-hour-per-day house with the extended-range Lightning battery, or as long as 10 days when used with a home solar-power system that is equipped with a transfer switch that disconnects the house from the grid.

America’s largest panel producer, Sunrun, of California, has teamed up with Ford to offer solar roof panels integrated into the transfer switch setup in sync with Ford’s Intelligent Backup Power installation. Tesla, right now the world’s best-selling manufacturer of electric vehicles, is already marketing an integrated setup involving solar panels and a large wall-mounted battery as a kind of nascent virtual utility in Germany and in the United Kingdom.

For its part, General Motors—the power behind Chevrolet and GMC—is now set to work with San Francisco–based Pacific Gas & Electric to test forthcoming GM electric vehicles as on-demand power sources for homes. No word yet on which EVs will take part. (GM produces the Chevy Volt and GMC Hummer EV and is preparing its 2023 launch of the Silverado EV.) The GM tests reportedly start in a few months at PG&E’s applied technology services lab in San Ramon, Calif., with the aim to try out GM EVs first in pilots and then in larger customer-home trials by the end of 2022, utility spokesman Ari Vanrenen says. PG&E’s testing with Ford starts with five customer homes receiving their vehicles this April—for test purposes ideally in high-fire-threat districts that could be affected by an event causing public-safety-related power shutoff.

One of the first uses of bidirectional charging followed the Great East Japan Tōhoku earthquake, tsunami, and nuclear power plant accident at Fukushima. Battery-electric Nissan Leafs in the region were able to deliver spot backup power between the rolling blackouts in those days. But while bidirectional backup from EVs promises lights on when the power’s out, the utility testing will be done to ensure safe interconnection. The electric truck and battery is considered a generation of technology similar to rooftop solar and home energy-battery storage, and in PG&E’s service area (which is northern California) Lightning owners with bidirectional charging to the home will need to apply for approval to connect the charger to the grid.

Volkswagen's current ID models with a 77-kWh battery option now come ready for bidirectional charging.Volkswagen

The bidirectional networked future won’t necessarily arrive with an overnight flick of the switch, however. Market watchers and researchers alike are wary of potential compatibility and standards issues, and consumer uptake is unpredictable.

From the owner’s perspective there will be concerns in bidirectional use about battery drain and wear and tear, says Philip Krein, of the Grainger Center for Electric Machinery and Electromechanics at the University of Illinois in Urbana-Champaign. And he’s skeptical about the cost factor in home bidirectional charge points. “Most charging, except for those relatively few long-range trips, can be supported with a conventional 120-volt or 220-volt outlet,” he argues. And that’s much cheaper than a new $1,300 kit.

Peter Andersen, a distributed energy resources researcher in Denmark, also wonders about how charge points will be deployed and used in more crowded urban centers—places where few people have garages and it's harder to get around in a big pickup truck—as well as the way in which network hardware will be developed. “There’s still a lack of interoperability,” he says. “So you essentially need to buy everything from the same provider.” Just as there is an Apple ecosystem, so with home and EV-battery systems you could wind up with a Ford setup, a Tesla setup, or a VW setup. Not so independent.

Even so, world events are putting wind in the sails for backup power. On 16 March there was another earthquake near Fukushima—luckily a much milder one, though still knocking out power to 2 million people. The Ukraine war is playing havoc with energy pricing and market stability. Cleaner power—and energy sourcing—is a more pressing concern. “Maybe it's not out of necessity that you don't have access to the grid,” Andersen says. “Maybe it can also be that you want to pursue some energy autonomy.”

Michael Dumiak is a Berlin-based writer and reporter covering science and culture and a longtime contributor to IEEE Spectrum. For Spectrum, he has covered digital models of ailing hearts in Belgrade, reported on technology from Minsk and shale energy from the Estonian-Russian border, explored cryonics in Saarland, and followed the controversial phaseout of incandescent lightbulbs in Berlin. He is author and editor of Woods and the Sea: Estonian Design and the Virtual Frontier.

A century later, Nikola Tesla’s dream comes true

A power-beaming system developed by PowerLight Technologies conveyed hundreds of watts of power during a 2019 demonstration at the Port of Seattle.

Wires have a lot going for them when it comes to moving electric power around, but they have their drawbacks too. Who, after all, hasn’t tired of having to plug in and unplug their phone and other rechargeable gizmos? It’s a nuisance.

Wires also challenge electric utilities: These companies must take pains to boost the voltage they apply to their transmission cables to very high values to avoid dissipating most of the power along the way. And when it comes to powering public transportation, including electric trains and trams, wires need to be used in tandem with rolling or sliding contacts, which are troublesome to maintain, can spark, and in some settings will generate problematic contaminants.

Many people are hungry for solutions to these issues—witness the widespread adoption over the past decade of wireless charging, mostly for portable consumer electronics but also for vehicles. While a wireless charger saves you from having to connect and disconnect cables repeatedly, the distance over which energy can be delivered this way is quite short. Indeed, it’s hard to recharge or power a device when the air gap is just a few centimeters, much less a few meters. Is there really no practical way to send power over greater distances without wires?

To some, the whole notion of wireless power transmission evokes images of Nikola Tesla with high-voltage coils spewing miniature bolts of lightning. This wouldn’t be such a silly connection to make. Tesla had indeed pursued the idea of somehow using the ground and atmosphere as a conduit for long-distance power transmission, a plan that went nowhere. But his dream of sending electric power over great distances without wires has persisted.

To underscore how safe the system was, the host of the BBC science program “Bang Goes the Theory” stuck his face fully into a power beam.

Guglielmo Marconi, who was Tesla’s contemporary, figured out how to use “Hertzian waves,” or electromagnetic waves, as we call them today, to send signals over long distances. And that advance brought with it the possibility of using the same kind of waves to carry energy from one place to another. This is, after all, how all the energy stored in wood, coal, oil, and natural gas originally got here: It was transmitted 150 million kilometers through space as electromagnetic waves—sunlight—most of it millions of years ago.

Can the same basic physics be harnessed to replace wires today? My colleagues and I at the U.S. Naval Research Laboratory, in Washington, D.C., think so, and here are some of the reasons why.

There have been sporadic efforts over the past century to use electromagnetic waves as a means of wireless power transmission, but these attempts produced mixed results. Perhaps the golden year for research on wireless power transmission was 1975, when William Brown, who worked for Raytheon, and Richard Dickinson of NASA’s Jet Propulsion Laboratory (now retired) used microwaves to beam power across a lab with greater than 50 percent end-to-end efficiency. In a separate demonstration, they were able to deliver more than 30 kilowatts over a distance of about a mile (1.6 kilometers).

These demonstrations were part of a larger NASA and U.S. Department of Energy campaign to explore the feasibility of solar-power satellites, which, it was proposed, would one day harvest sunlight in space and beam the energy down to Earth as microwaves. But because this line of research was motivated in large part by the energy crisis of the 1970s, interest in solar-power satellites waned in the following decades, at least in the United States.

Although researchers revisit the idea of solar-power satellites with some regularity, those performing actual demonstrations of power beaming have struggled to surpass the high-water mark for efficiency, distance, and power level reached in 1975. But that situation is starting to change, thanks to various recent advances in transmission and reception technologies.

During a 2019 demonstration at the Naval Surface Warfare Center in Bethesda, Md., this laser beam safely conveyed 400 watts over a distance of 325 meters.U.S. Naval Research Laboratory

Most early efforts to beam power were confined to microwave frequencies, the same part of the electromagnetic spectrum that today teems with Wi-Fi, Bluetooth, and various other wireless signals. That choice was, in part, driven by the simple fact that efficient microwave transmitting and receiving equipment was readily available.

But there have been improvements in efficiency and increased availability of devices that operate at much higher frequencies. Because of limitations imposed by the atmosphere on the effective transmission of energy within certain sections of the electromagnetic spectrum, researchers have focused on microwave, millimeter-wave, and optical frequencies. While microwave frequencies have a slight edge when it comes to efficiency, they require larger antennas. So, for many applications, millimeter-wave or optical links work better.

For systems that use microwaves and millimeter waves, the transmitters typically employ solid-state electronic amplifiers and phased-array, parabolic, or metamaterial antennas. The receiver for microwaves or millimeter waves uses an array of elements called rectennas. This word, a portmanteau of rectifier and antenna, reflects how each element converts the electromagnetic waves into direct-current electricity.

Any system designed for optical power transmission would likely use a laser—one with a tightly confined beam, such as a fiber laser. The receivers for optical power transmission are specialized photovoltaic cells designed to convert a single wavelength of light into electric power with very high efficiency. Indeed, efficiencies can exceed 70 percent, more than double that of a typical solar cell.

At the U.S. Naval Research Laboratory, we have spent the better part of the past 15 years looking into different options for power beaming and investigating potential applications. These include extending the flight times and payload capacities of drones, powering satellites in orbit when they are in darkness, powering rovers operating in permanently shadowed regions of the moon, sending energy to Earth’s surface from space, and distributing energy to troops on the battlefield.

You might think that a device for sending large amounts of energy through the air in a narrow beam sounds like a death ray. This gets to the heart of a critical consideration: power density. Different power densities are technically possible, ranging from too low to be useful to high enough to be dangerous. But it’s also possible to find a happy medium between these two extremes. And there are also clever ways to permit beams with high power densities to be used safely. That’s exactly what a team I was part of did in 2019, and we’ve successfully extended this work since then.

One of our industry partners, PowerLight Technologies, formerly known as LaserMotive, has been developing laser-based power-beaming systems for more than a decade. Renowned for winning the NASA Power Beaming Challenge in 2009, this company has not only achieved success in powering robotic tether climbers, quadcopters, and fixed-wing drones, but it has also delved deeply into the challenges of safely beaming power with lasers. That’s key, because many research groups have demonstrated laser power beaming over the years—including teams at the Naval Research Laboratory, Kindai University, the Beijing Institute of Technology, the University of Colorado Boulder, JAXA, Airbus, and others—but only a few have accomplished it in a fashion that is truly safe under every plausible circumstance.

There have been many demonstrations of power beaming over the years, using either microwaves [blue] or lasers [red], with the peak-power record having been set in 1975 [top]. In 2021, the author and his colleagues took second and third place for the peak-power level achieved in such experiments, having beamed more than a kilowatt over distances that exceeded a kilometer, using much smaller antennas.David Schneider

Perhaps the most dramatic demonstration of safe laser power beaming prior to our team’s effort was by the company Lighthouse Dev in 2012. To underscore how safe the system was, the host of the BBC science program “Bang Goes the Theory” stuck his face fully into a power beam sent between buildings at the University of Maryland. This particular demonstration took advantage of the fact that some infrared wavelengths are an order of magnitude safer for your eyes than other parts of the infrared spectrum.

That strategy works for relatively low-power systems. But as you push the level higher, you soon get to power densities that raise safety concerns regardless of the wavelength used. What then? Here’s where the system we’ve demonstrated sets itself apart. While sending more than 400 watts over a distance that exceeded 300 meters, the beam was contained within a virtual enclosure, one that could sense an object impinging on it and trigger the equipment to cut power to the main beam before any damage was done. Other testing has shown how transmission distances can exceed a kilometer.

Careful testing (for which no BBC science-program hosts were used) verified to our satisfaction the functionality of this feature, which also passed muster with the Navy’s Laser Safety Review Board. During the course of our demonstration, the system further proved itself when, on several occasions, birds flew toward the beam, shutting it off—but only momentarily. You see, the system monitors the volume the beam occupies, along with its immediate surroundings, allowing the power link to automatically reestablish itself when the path is once again clear. Think of it as a more sophisticated version of a garage-door safety sensor, where the interruption of a guard beam triggers the motor driving the door to shut off.

The 400 watts we were able to transmit was, admittedly, not a huge amount, but it was sufficient to brew us some coffee.

For our demonstrations, observers in attendance were able to walk around between the transmitter and receiver without needing to wear laser-safety eyewear or take any other precautions. That’s because, in addition to designing the system so that it can shut itself down automatically, we took care to consider the possible effects of reflections from the receiver or the scattering of light from particles suspended in the air along the path of the beam.

Last year, the author and his colleagues carried out a demonstration at the U.S. Army’s Blossom Point test facility south of Washington, D.C. They used 9.7-gigahertz microwaves to send 1,649 watts (peak power) from a transmitter outfitted with a 5.4-meter diameter parabolic dish [top] over a distance of 1,046 meters to a 2-by-2-meter “rectenna” [middle] mounted on a tower [bottom], which transformed the beam into usable electric power.U.S. Naval Research Laboratory

The 400 watts we were able to transmit was, admittedly, not a huge amount, but it was sufficient to brew us some coffee, continuing what’s become de rigueur in this line of experimentation: making a hot beverage. (The Japanese researchers who started this tradition in 2015 prepared themselves some tea.)

Our next goal is to apply power beaming, with fully integrated safety measures, to mobile platforms. For that, we expect to increase the distance covered and the amount of power delivered.

But we’re not alone: Other governments, established companies, and startups around the world are working to develop their own power-beaming systems. Japan has long been a leader in microwave and laser power beaming, and China has closed the gap if not pulled ahead, as has South Korea.

At the consumer-electronics level, there are many players: Powercast, Ossia, Energous, GuRu, and Wi-Charge among them. And the multinational technology giant Huawei expects power beaming for smartphone charging within “two or three [phone] generations.”

For industrial applications, companies like Reach Labs, TransferFi, MH GoPower, and MetaPower are making headway in employing power beaming to solve the thorny problem of keeping batteries for robots and sensors, in warehouses and elsewhere, topped off and ready to go. At the grid level, Emrod and others are attempting to scale power beaming to new heights.

On the R&D front, our team demonstrated within the past year safe microwave wireless power transmission of 1.6 kilowatts over a distance of a kilometer. Companies like II-VI Aerospace & Defense, Peraton Labs, Lighthouse Dev, and others have also recently made impressive strides. Today, ambitious startups like Solar Space Technologies, Solaren, Virtus Solis, and others operating in stealth mode are working hard to be the first to achieve practical power beaming from space to Earth.

As such companies establish proven track records for safety and make compelling arguments for the utility of their systems, we are likely to see whole new architectures emerge for sending power from place to place. Imagine drones that can fly for indefinite periods and electrical devices that never need to be plugged in—ever—and being able to provide people anywhere in the world with energy when hurricanes or other natural disasters ravage the local power grid. Reducing the need to transport fuel, batteries, or other forms of stored energy will have far-reaching consequences. It’s not the only option when you can’t string wires, but my colleagues and I expect, within the set of possible technologies for providing electricity to far-flung spots, that power beaming will, quite literally, shine.

This article appears in the June 2022 print issue as “Spooky Power at a Distance.”