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Across the Outback on Photons Alone

With Australia’s desert as its raceway, the World Solar Challenge illuminates some of the best electric-vehicle technology

13 min read
Nuna 4 solar car

Ray Runner: Blessed with a crystal-clear sky, the Nuna 4 solar car soaks up energy as it drives.

Photo: Hans-Peter van Velthoven

A legion of 38 solar cars gathers in State Square in Darwin, on the northern coast of Australia. The flat, rectangular bodies hug the ground like three-wheeled UFOs, their etherealness accentuated by their motors’ eerie, barely perceptible hum. Anxious racers neurotically swab their perfectly clean solar cells with feather dusters.

Helmeted drivers peer out through polycarbonate bubbles, waiting for their cue to lock down and dash across the continent. The vehicles are odd-looking and yet stately, not at all the giant cockroaches they have been mockingly described as in the past. Better to be a UFO, some are saying, than a cockroach.

The solar racers—a mix of university students and hobbyist-engineers—have converged in this remote tropical city for the ninth World Solar Challenge, the biennial transcontinental race that tests some of the world’s most innovative ideas in energy-efficient transportation on some of the planet’s most punishing terrain. On this humid October morning, ultracompetitive teams are polishing vehicles that easily cost more than US $2 million each, while others tinker with their homegrown labors of love.

At this Panasonic-sponsored event, the foremost eco-race on the planet, there’s tech intrigue and plenty of peculiarity. One team famously delivers its vehicle to each race in suitcases, and another team consists entirely of Japanese hairdressers. The University of Michigan contingent is here, as always, but this year it includes 100 support people, weather balloons, and an unpiloted aerial vehicle. Michigan and another group, Solar Team Twente, from the Netherlands, have each outfitted their vehicle with a system of mirrors that tracks the sun to concentrate light on some of the solar cells. Even in this race, no one’s ever put a solar concentrator on a car before, and its presence on these two has earned the teams cachet in the unofficial jostling for technical one-upmanship. Gossip swirls around Umicore Solar Team, from Group T, an engineering university in Leuven, Belgium, whose Umicar Infinity supposedly uses the most expensive—and powerful—triple-junction gallium-arsenide solar cells this side of low Earth orbit. Solar racers have been eyeing the Belgian vehicle even more warily since yesterday afternoon, when Umicar grabbed pole position in the qualifying heat at a nearby racetrack.

But it is the legacy of the Nuon Solar Team, from the Delft University of Technology in the Netherlands, that dominates the prerace chatter. Its Nuna cars have won the last three races, going back to 2001. On the other hand, no member of this year’s crew, other than its ex-astronaut advisor, Wubbo Ockels, has ever built a car before. And this past week hasn’t been kind to Nuna 4’s harried engineers, who have battled a temperamental motor controller and short-circuiting solar cells. It didn’t help when Ockels announced that no previous Nuna had faced so many prerace problems.

Standing there as spectators mill around the parked solar cars, Ivo Hagemans, of the Nuna team, notes: “Everyone says, you’ve already won three times, you have nothing to worry about. Well, no, no, I haven’t. Other people have. I have not.” He surveys the car moodily, his hands shoved in his pockets.

The rules are simple [see sidebar, "World Solar Challenge Race"]. Race across 3000 kilometers of the outback, driving from 8 a.m. to 5 p.m., until you get to Adelaide, on the southern coast. Your car’s only power source is a 6-square-meter solar array, which under bright sun puts out less than 2 kilowatts. If your idea of an efficient vehicle is a Toyota Prius, you’ve got to wrap your mind around an entirely different level of energy parsimony. Solar racers like to say that their cars run on as much energy as a hair dryer. By the time the winning car gets to Adelaide, it will have covered those 3000 km using roughly the same energy that an ordinary car gets by burning 7 liters of gasoline. The best cars travel about 90 km/h, though they are capable of going faster. “It’s performance racing,” says Michael Garland, a British university student freelancing as a member of Melbourne’s Aurora Vehicle Association team, another perennial contender. “It may be quirky and weird, but it’s top-notch engineering.”

A race official looks at his wristwatch—8:00—and waves Umicar Infinity off the starting line. It glides down the street and out of sight. Then comes Aurora 101, the local favorite, accompanied by exuberant hoots from the crowd. And then Nuna 4, the weight of its celebrated predecessors pressing down on it.

Inside the Nuna, a panicked Oliver van der Meer gestures furiously at his tiny dashboard. He taps the pedal, but the car doesn’t budge. After a quick consultation, a dozen Dutch students in the team’s blazing orange shirts strip off the tape that holds the top shell, with the solar array, to the car’s carbon-fiber body. Solar cars navigate around them, drift up to the starting line, and disappear into Darwin. Six Nunans heave the top over van der Meer’s head.

It’s that pesky motor controller, which regulates the motor’s rotational speed and direction. Its Hall-effect sensors are producing a bizarre reading—the lights for both “drive” and “reverse” are lit on the console. In a brushless dc electric motor, which is what most high-end solar cars use, these highly specialized sensors track the position of the motor’s permanent magnet rotor. The team has seen this glitch before, but only in hot weather. It’s cool this morning, so what the heck? Someone runs to a support vehicle to fetch a spare—and less efficient—controller. “Anyone have a small screwdriver?” yells Vincent de Geus, the race strategist, over the spirited bleats of a local brass band.

Out comes the troubled controller and in goes the replacement. Some crew members reattach the top shell and swiftly tape over the edges, while the rest of the crew, visibly shaken, scurry to their chase vehicles.

With 27 solar cars now in front of it, Nuna 4 plunges into the race—straight into the chaos on leafy Mitchell Street and out to the first few kilometers of Stuart Highway, which it will ride all the way to Adelaide. Here the highway’s shoulder is a site of solar carnage, as a dozen teams facing early emergencies have pulled to the side of the road and ripped off the tops of their vehicles to poke and prod at misfiring components. The worst off is Michigan’s solar car, whose driver had braked late in the bumper-to-bumper traffic and hit a team vehicle, crumpling the car’s nose and damaging the steering system. Two rows of solar cells have been destroyed, and the driver is in tears.

The rest of the pack navigates through heavy traffic down the busiest stretch of Stuart Highway. Nuna 4 weaves easily between vehicles, overtaking solar racers and chase cars alike. Within 3 hours it’s in second place, ahead of Aurora 101 but behind the leading Umicar Infinity.

By midday, the highway thins to one lane, and signs of civilization dwindle to the odd roadhouse amid spotty clumps of spinifex grass. On either side, spindly eucalyptus trees poke out of the hard red earth. Every 20 minutes or so, a road train pulling three trailers bombs past, blasting the cars with strong side winds.

One of those trucks’ blasts dislodges the latch on Nuna 4’s canopy. The bubble top flies open, and van der Meer barely manages to grab it and pull it down. With one hand on the wheel and the other holding the canopy down, he can’t reach the regenerative brake anymore (which is a hand-operated toggle, unlike the foot pedal for the mechanical brake). The next 200 km become a battle between not braking, so as to not waste energy, and not cracking up. A cold sliver of air cuts at his neck while he drives.

So it is that the Nuna team makes its entrance into the outback. Around its convoy, dirty tendrils of smoke rise from patches of iron-tinged earth singed by recent fires. Where earlier local residents had lined the road to cheer them on, now only statuesque termite mounds—man-size piles of orange dirt—stand like mute sentries. The crippled racer rattles down the highway, its hollow body amplifying the reverberations to a deafening clatter. As another Nuna driver later describes it, ”It was like riding inside a giant guitar.”

Meanwhile, around midday, the Nuna team’s strategists realize they’ve got a problem. In their “mission control” vehicle, the three of them are monitoring the state of the racer’s lithium-polymer battery through the voltage and current readings sent over a wireless link from the solar car’s motor controller. They’ve tailored their strategy software to calculate speeds for a day that lasts from 8 a.m. to 5 p.m., but with the half-hour delay in the start and the corresponding shift in light conditions, their algorithm is off. De Geus, the chief strategist, manually calculates the speeds, scribbling on a pad of paper as the sun’s intensity wanes.

Short of crashing, the biggest disaster that can befall a solar team is draining the battery prematurely. The load on the battery is related to the drag on the car, and that drag increases with the square of the speed. Put another way, driving too fast for the conditions can do a team great harm. The strategists spend their time calculating, at 2-minute intervals, the optimal speed, taking into account variables such as how much driving they anticipate for the rest of the day and the near-term weather forecast.

Luckily for the Nuna team, the race rules and the staggered start let them recoup the time they squandered replacing the motor controller. As other cars pull off the road to mark the end of the first racing day, Nuna’s scouts speed ahead to find a suitable campsite—one with unobstructed western exposure that will let them use the remaining sunlight to top off the battery for tomorrow’s start.

Soon the convoy turns into a little clearing surrounded by brittle grasses. The sun starts to set, and desert flies emerge in swarms. As day one ends, the Nunans are behind the Belgian Umicar Infinity team, which has set up a bare-bones campsite 13 km ahead, butted up against tall grass a few meters off the shoulder. A few kilometers behind Nuna, Aurora 101 is doing the same. Flies clinging to their faces and shirts, the racers pitch their tents on the red gravel, tilt their solar arrays to catch a last few photons, and set up lights to examine their cars before bedtime.

Day 2 dawns, at 5:30 a.m., with the Dutch ex-astronaut sitting alone in the middle of Nuna’s dark campsite, strumming a few bars of “House of the Rising Sun” on his guitar. Sleepy, orange-clad figures emerge from the colony of canvas tents. They prop up the top half of the car’s body, with the solar array, as the first rays of the sun peek over the horizon. They roll up their sleeping bags, make Nutella sandwiches, and dust the insides of the car. “This is the day of truth,” says Ockels. “With an empty road and much less overtaking, we’ll see which team really is the best.”

One car from the convoy departs an hour early to collect weather data and report on road conditions—a euphemism for kangaroo roadkill. As 8 a.m. approaches, the day’s first driver, Joep Steenbeek, steps into the solar car and tightens his helmet strap. With less than 10 minutes left, the crew attaches the top, fastens cables, and tapes over the edges to smooth them against air resistance. The race official calls time, and the team waits for a looming road train to pass. The solar car slides onto the road, the motor singing its weird whine over the road train’s fading rumble.

The morning drive is smooth and sunny. Umicar Infinity coasts into the next of the race’s mandatory control stops, at Tennant Creek, 7 minutes before Nuna 4. (The control stops give reporters a chance to catch up with the solar cars and the teams an opportunity to check vehicles for wear and tear.)

But all is not well in Infinityland. An aluminum bolt holding the steering system in place has snapped, causing the rack-and-pinion gears to wear down and making steering nearly impossible. With no other option, the Belgians pull aside to repair their steering system and replace the bolt with a simple clamp, and Nuna 4 slips past them. “Yeah…aluminum was maybe not the best choice of material for that bolt,” says Niels Burez, who oversaw Umicar’s mechanics, with a gloomy smile. “If it wasn’t for these problems, we’d be passing Nuna, I’m sure.”

But then the weather takes a turn for the worse, as the vehicles speed into a storm brewing over Alice Springs—the midpoint of the race, and of Australia. Nuna’s suspension, strained by a persistent crosswind, finally gives in. The team stops to replace a collapsed shock absorber, surrendering 15 precious minutes. Then 80 km/h winds cause the car to yaw left so much that the left tire bursts. The unthinkable almost happens: Nuna nearly empties its battery while racing the setting sun to Alice Springs. It is forced to stop just 12 km north of the city. But when it gets there, the following morning, it is 1 hour 22 minutes ahead of the Belgian car.

The teams trickle into this odd oasis, corralled by race officials who had decided that the half-day lag between cars was bad for press coverage. Wearing a floppy hat and wraparound sunglasses, veteran solar racer Alain Chuzel examines a few vehicles in the blinding sun. Chuzel, from Phoenix, has a company, SunCat Solar, that encapsulates solar arrays for racers. Encapsulation protects the arrays from airborne pebbles and debris, which can crack cells. Because a string of cells performs only as well as the weakest in the sequence, protecting an array from damage is of utmost importance.

Usually, solar cells have minor defects, Chuzel explains. Depending on what’s needed, “one man’s junk is another man’s gold.” Once cells are selected, they are arranged in strings and coated in special materials to make them sturdy enough to bend over a car body and withstand flying pebbles.

Hans Gochermann, who has a solar-technology company in Germany, adds another step to each encapsulation. The fanciest solar cells—mostly rejects from the International Space Station, he says—are no more than 31 percent efficient, and there’s an art to squeezing as much energy as possible out of those brittle semiconductor slices. He encapsulated the top three teams’ arrays by texturing the cell surface with matte 5-micrometer-wide pyramids. When light hits the surface, some of it is reflected. But instead of allowing light to bounce away, the pyramids deflect some of the rays back onto other pyramids, giving the photons a second chance to be soaked up and increasing the array’s power by 4 percent. The technique is particularly effective with the oblique rays of morning and evening.

Cell encapsulation is but one of several cutting-edge microindustries that have emerged to cater to solar racing. Looking for the most efficient motor controllers on the planet? You’ll find them here, most of them made by Tritium, of Woolloongabba, Australia. Tritium’s motor controller—a lightweight three-phase 20-kW inverter with supposedly unprecedented power density—came from the company employees’ own solar car experience, at the University of Queensland. The controller has a cruising efficiency of 98.3 percent, so very few of the car’s scanty supply of watts get wasted. Tritium is hoping that, having locked up the solar car market, it can now branch out into electric vehicles and grid-connected photovoltaics.

This wouldn’t be the first solar-car spin-off to become something bigger. The builders of Honda’s solar cars, which dominated the races in the early 1990s, later designed the Honda Insight, the first mass-produced hybrid car. General Motors’ solar car, also from that era, morphed into the company’s first electric effort, the EV 1. True, it was pulled from the market peremptorily, prompting conspiracy theories and a major motion picture. And mass-market success has also so far eluded New Generation Motors, an American company licensing Australian technology, whose astoundingly efficient wheel motors—at best 95 percent—are used by most solar racers.

“These are literally the engineers of the future, as in, they’re ahead of their time,” says Steven Camilleri of In Motion Technologies, another race alumnus now trying to sell uniquely efficient, lightweight motors born during his solar racing days. “The world isn’t ready for us,” Camilleri concludes. [See “Motor Maniac,” in this issue, for a profile of Camilleri.]

Early the next morning, the cars are released back onto the road. Some thin clouds scuttle across the sky, and an east-blowing crosswind continues to badger the teams.

“You have to look carefully at a cloudy sky,” says Hagemans, the Nunans’ logistics guru. Teams may adjust their speed to go faster through the cloudy parts and slow down in sunny patches, to give the battery pack more time to charge.

Dust storms periodically shatter the monotony of the drive. Sticks dance in the middle of the road, and seconds later a shroud of dust slams Nuna 4, throwing it off its course. A harrowing second later, the driver regains control.

The heat, the dust, and the battering force solar car designers to balance robustness and weight against low drag and rolling resistance. This year, the race’s organizers required the cars to be a shade more practical. As a result, the vehicles now have smaller arrays, normal upright seats, and ordinary steering wheels. A German entrant, Bochum University of Applied Science’s SolarWorld No. 1, with three wheels and a platypus front end, almost looks like something you’d take to pick up a few groceries. But its commodious form makes it seem bloated next to the sleek, anorexic top performers, and during the race it dawdles behind the lead cars, averaging 73 km/h. By contrast, the team proudly reports that Nuna 4 was the most aerodynamic vehicle ever tested at the wind tunnels run by DNW, a German-Dutch aerodynamics-testing facility. The Aurora 101 car also excelled aerodynamically, with a record of its own at Monash University’s wind tunnel, near Melbourne.

The Nuna convoy flies through Coober Pedy, an opal-mining town with a spectacularly lunar landscape. The wind never lets up, and that afternoon they pop the left tire four times. Each change takes less than 3 minutes for the well-practiced team, but it is clear the suspension is in peril. That night, they rebuild the left suspension, change tires, and vacuum everything in sight.

It is to be the Nuna crew’s last night under the outback’s starry skies. The next day they push—hard—to reach the outskirts of Adelaide by the 5 p.m. official cutoff. The Belgians are about 40 minutes behind them. It is a solid lead, but not an unbreakable one, and Infinity is technically a faster car. Just one small breakdown, or one miscalculation, could blow the race.

The sunset fills the enormous sky with radiant colors. The air is chilly, and the team builds a fire with a few scraps of wood they scavenge from the blank landscape. A half-dozen skeletal trees stand out in silhouette against the purple sky, improbable signposts of a greener time. The students string colored lights around the campsite and blast dance music into the deaf, endless desert.

“Southbound road train, this is Nuna solar car team, can you hear us?” a voice crackles over CB radio channel 40. “We’re from the Netherlands. What’s your speed?”

“Oh, hi, solar car! Are you the front-runners?” comes the brittle reply.

“Yes, and we’d like to pass you after the next hill.”

“Oh, right, no worries.”

It’s Thursday afternoon. The landscape is quickly turning hilly. In the Nuna chase car, strategist de Geus can’t believe how the battery is holding up. “I’d set the speed at 90 and check,” he later recalls. “The battery seemed fine, so I increased it to 95. It was still fine, so we went up to 100, then 105—wow! So we just kept going.” It’s as auspicious a start as they could have hoped for.

A few hours later, Stuart Highway cuts through Port Augusta, population 14 000, at the head of Spencer Gulf. The wispy car darts into gaps in overtaking lanes and tears past dense lines of traffic. At 4:15 p.m., Nuna is speeding along at exactly the speed limit, 110 km/h, pushing through rolling farmland toward Adelaide. The race is now against time: Umicar is nowhere in sight, but 5 p.m. is alarmingly near.

They make it. At 4:55 p.m. Nuna 4 slides across the finish line first. It averaged 91 km/h over the whole race, slower than the previous three Nunas but still remarkable considering the new vehicle restrictions these team members had to contend with. As the racer comes to a stop, the students tumble out of the support vehicles. They look around, whoop, and hug each other awkwardly. Then they start cheering for real as the truth hits home: they’ve won. They’ve saved their legacy. With champagne erupting from bottles, they drench their solar array, but no one cares.

Neither this car, nor anything like it, will blend into everyday life anytime soon. But these young engineers have pulled off a wonderful and improbable feat. They’ve built something outlandish and complex with little more than their own hands, some fairly simple tools, and some institutional blessings.

“The concept of a commercial solar car is completely ridiculous,” reflects Sidd Bikkannavar, a race official. “But seeing them gives some people hope that a different future might exist, that there might be an alternative way of doing things.” On this parched landscape, in a place where mammals have pouches and eucalyptus trees are known to explode, perhaps the idea of a different future is not so crazy after all.

To Probe Further

Click here to watch video footage of the race.

The two books considered the bibles of solar racing are Speed of Light: The 1996 World Solar Challenge by David M. Roche et al. (1997) and The Winning Solar Car: A Design Guide for Solar Race Car Teams by Douglas R. Carroll (2003).


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