Do Solar-Powered EVs Make Any Sense? I Drove a Prototype To See How It Could Work
A Dutch startup called Lightyear let us drive a pre-production prototype of its 0 sedan, which is billed as the world’s first “solar electric car.”
When you write about electric cars, sooner or later you get that question: Why can’t we just slap a bunch of solar panels on an EV and enjoy near-unlimited range? Whither the solar cars? The flip answer is, “Because physics.” The real answer is that today’s solar cells simply can’t generate enough energy quickly enough to power a vehicle in the limited space on its surface. (Also, clouds? And dust?)
But it’s reasonable to ask when better photovoltaic technology might deliver solar cells that could partially power a car, or at least add meaningful battery range to an EV that also has a conventional charge port. That moment has now arrived; this summer, I drove a pre-production prototype of the Lightyear 0 sedan, billed as the world’s first “solar electric car” by the Dutch startup responsible for it.
The experience proved you can power a 3,500-pound passenger vehicle solely (and slowly) via sunlight—though there are still a number of kinks to work out, and the tech still has a ways to go before it can be applied to the SUVs and larger trucks that make up an ever-increasing proportion of North American sales.
Skinny Students in Pool Tables on Wheels
Solar panels have appeared on electrified cars for more than a decade, starting with the 2010 Toyota Prius and its “solar moonroof” that powered ventilation fans to pull hot air out of the cabin. But specifically, it’s the World Solar Challenge in Australia that inspired the Dutch auto startup Lightyear. Since 1987, the 15 Challenges held so far required competing teams to build wheeled vehicles to cover 3,000 km (1,864 miles) of sunny Australian outback roads, using only energy they harvest from the abundant sun for propulsion.
Early entrants often had three wheels, with more than a few resembling pool tables covered in solar cells. They were usually piloted by the team’s lightest, skinniest student member hanging underneath. In 2013, the Challenge added a “Cruiser” class to the unlimited single-seater category, with the idea being to work toward a safe, ideally road-legal, solar vehicle with multiple seats. Lightyear was founded in 2016 by five members of a Challenge team from Eindhoven University of Technology, and the four- and five-seat “Stella” cars they’ve built have won that class in all four events held thus far.
That work led directly to the Lightyear 0 I drove, which the company says will start production before the end of this year. (Until it was revealed June 9, the company called its first production car Lightyear 1. Now it’s 0, though the next one is still Lightyear 2 … got that?)
Appearing Solely on Solar Power
My first view of the final design came in the late afternoon, as the two prototype cars proceeded sedately down the long road leading up to the venue in southern Spain. Their speed, perhaps 20 mph, was chosen to keep the power they used roughly equal to the power being generated in real-time by the five square meters (54 square feet) of solar panels on the roof, hood, and liftgate. While no Lightyear can do highway speeds on solar power alone, it’s still an impressive trick to power a 3,500-pound vehicle entirely from the sun at any speed.
We drove a prototype Lightyear 0 through the sunny countryside of Spain’s Navarre region for about 20 minutes, covering 20 kilometers (12 miles). The drive had no highway time and mostly covered two-lane country roads, with a loop through a small village.
Getting into the low, sleek car required careful negotiation for this five-foot 11-inch writer to get his head past the very steeply raked windscreen pillar. Once inside, the seats proved surprisingly comfortable and perfectly bolstered for my shape. I was warned the two pre-production Lightyear 0 prototypes didn’t have final calibrations for their steering or throttle mapping.
The result was a smooth, heavy electric sedan with linear accelerator feel, which underscored its relative slowness. Lightyear execs said the zero-to-62-mph acceleration time was about 10 seconds, but that they expected final motor tuning to deliver about 10 percent more torque with the same efficiency.
More important was the solar aspect. The car’s real-time app showed solar production of 492 and 673 watts from the two cars around noontime. Its maximum solar charging rate is just over one kilowatt, Lightyear said. That can add up to 70 km (43 miles) on the sunniest day of the year, and up to 11,000 km (6,840 miles) over a full year. For a European driver averaging 35 km (22 miles) a day, the sun could extend recharging intervals to as long as two months in a cloudy environment like The Netherlands. In a sunny spot like Portugal (or Arizona, perhaps?), that interval between recharges might go as long as seven months.
From Tesla Roadster to Lightyear 0
You can think of Lightyear’s 0 as an equivalent to the original Tesla Roadster. It’s a proof of concept EV, built in low numbers by a contract manufacturer, to demonstrate that a new technology can actually work. For Tesla, the Roadster showed a high-capacity battery pack with thousands of commodity lithium-ion cells could power a remarkably high-performance electric car, at a time when EVs were largely considered glorified golf carts. Over five years, Tesla built only 2,600 Roadsters, and their final price started at $109,000.
Lightyear plans to sell only 946 0s—because 9.46 trillion km is the distance light travels in one year, e.g. one light-year—at the substantial price of 250,000 euros ($249,200 USD). They will be manufactured in Finland by Valmet, a contract manufacturer that has built, among others, both Porsche Boxsters and the original Fisker Karma range-extended electric luxury sedan. The 81 million euros ($79.3 million USD) of funding it announced in early September should allow the company to get the 0 into production.
The Lightyear 2, which the company claims will arrive in late 2024 or early 2025 at a price of 30,000 euros ($29,400), will be the company’s volume model—akin to the Tesla Model S that went into production in 2012, four years after the Tesla Roadster arrived. But even Tesla didn’t try to cut its price by a factor of 10, so Lightyear has set itself an aggressive goal.
CEO and co-founder Lex Hoefsloots said the second vehicle will be a compact crossover akin to a Model Y. He notably didn’t deny the suggestion it would likely have to be built out of stamped steel, rather than the hand-laid carbon fiber of the Lightyear 0. They’re betting on batteries likely being cheaper by 2025, and photovoltaic cells more efficient. Hoefsloots and other execs declined to say anything further about the Lightyear 2, noting the company was still studying customer requirements for such a vehicle in both Europe and North America.
Biggest of Three
Lightyear is not the only company planning to bring a solar vehicle to market, but it’s the most ambitious, simply because its vehicle is the largest: a mid-size four-door sedan.
At the other end of the scale is a reboot of a United States startup that prototyped the ultra-efficient Aptera 2e two-seat, three-wheeled electric car in 2008 and 2009. It looked like nothing so much as a Cessna cabin sans wings and attracted a huge amount of attention. Version one of Aptera shut down in December 2011 while developing a four-wheeled vehicle amidst management upheaval and the Great Recession.
Now the original founders have brought Aptera back, with a battery-electric powertrain claimed to provide up to 1,000 miles of range from the largest (100 kWh) of four battery capacities, powering two or three 50-kW (67-horsepower) wheel motors. The latest Aptera has three square meters (32 square feet) of solar cells on its non-vertical surfaces, which it says generate up to 0.7 kilowatts. It says they will add up to 4 kWh a day, depending on geographic location. The ultra-aerodynamic, very light vehicle achieves up to 10 miles per kWh, so the solar cells can add up to 40 miles a day in the right conditions.
With 26,000 reservations in hand, the company told The Drive, “It is our goal to deliver a production-ready vehicle by the end of 2022 and ramp quickly in 2023.” Its first deliveries will be of a 400-mile, front-wheel-drive version. Aptera says, perhaps optimistically, that it hopes to scale production to a rate of 10,000 vehicles a year by the end of 2022.
Between the sleek Lightyear and the startling Aptera is the Sono Sion, another European startup aiming for ultra-efficient use of every electron. Its vehicle is a small, upright hatchback of a sort you see throughout European cities, but not so much in the U.S.
Started in 2012, the company has shown several concepts and prototypes of its vehicle. A year ago, it said it would fit a 54-kWh battery to what it now calls a “solar-supplemented electric car,” with photovoltaic panels on not only its roof and hood, but also the body sides (at least in a prototype shown in 2017). In April of this year, Sono said Finnish contract manufacturer Valmet—which is also building the Lightyear 0—would assemble the Sion, starting in the second half of 2023.
Sono Motors has no plans to sell the Sion in North America, but this fall it said it had received 20,000 reservations for the car, at an announced price of 29,900 euros ($29,300). It hopes to build 250,000 of them over seven years.
Photovoltaic Cells and Battery Cells
Photovoltaic cells have been with us for many decades, starting with their use on space satellites before 1960. Their efficiency has risen steadily to the point that they’re now mass-produced (largely in China) and usable both by individual homeowners for onsite generation and at a utility scale in fields of hundreds of acres. It’s still a five-figure project to cover the roof of your house in solar cells, but that installation produces considerably more electricity than it did 10 or 20 years ago.
The technology development of photovoltaics would be its own separate article (this is a good primer), but the important point to know is that today’s silicon-based solar cells convert 19 to 23 percent of solar energy. The theoretical maximum of those cells is no more than 28 percent, due to limitations on the wavelengths they can absorb.
Getting above that requires new types of photovoltaic cells, including those made of flexible organic materials. The Lightyear solar team noted that perovskite solar cells could boost that conversion ratio to 29 or 30 percent, automatically raising the energy produced per area by a quarter or more. Given the urgency of transitioning electrical generation to renewable and non-carbon-emitting sources, we can expect generous private and public funding to produce continuous advances in solar-cell efficiency and cost reduction.
Similarly, the cost-performance of battery cells improves by seven to 10 percent each year: their energy density increases for the same cost, or equivalent energy density costs less each year. That’s what’s taken us from 74-mile Nissan Leafs in 2011 to 520-mile Lucid Airs in 2021.
The combination of the two should create a virtuous circle, in which the possibility of cars that power themselves on sunlight grows ever closer. But even if solar cars can now do meaningful battery charging in sunny climes, two challenges remain.
On the Car? Or in a Field?
First, EVs remain pricey, and adding solar cells to them only exacerbates the problem. The Lightyear’s 60-kWh battery pack may now be average for the mid-size segment, but production EVs still aren’t yet price-competitive with their combustion-engine equivalents. The solar cells and their associated electronics likely add a further four figures of cost to the vehicle.
The second problem is that solar cells on the surface of a vehicle still can’t produce enough energy to power it—and they likely won’t any time soon. So why not simply put those solar cells somewhere else: on your roof, in a field, or in a “utility-scale” solar generation field of hundreds or thousands of acres of cheap solar arrays wired together?
At scale, it will inevitably be more cost-effective to keep your solar cells stationary rather than tying them to the cars whose batteries they recharge. So is a Lightyear showing off an impractical technology that’s as much about virtue signaling as actual energy efficiency? Certainly, the high-priced, low-yield solar panels on cars like Toyota Priuses and Fisker Karmas suggest that’s the case.
But I’m going to wait for the Lightyear 2 before I try to answer that question. Because if the company can really sell a four-passenger SUV that’s as slippery, as efficient, and can power itself to the same degree from the sun as its Zero—for $40,000—that may change the equation.
Especially for those drivers who can’t plug in at home each evening.
John Voelcker edited Green Car Reports for nine years, publishing more than 12,000 articles on hybrids, electric cars and other low- and zero-emission vehicles and the energy ecosystem around them. His work has appeared in print, online and radio outlets that include Wired, Popular Science, Tech Review, IEEE Spectrum and NPR's "All Things Considered."
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