It may not look like something you'd take onto the local freeway, but the car in the above picture can easily hit highway speeds, running on nothing but solar power. It's the newest vehicle, called Infinium, to be produced by the University of Michigan's solar car team. That team drove Infinium's predecessor, Continuum, to a ten-hour margin of victory in the 2,400-mile North American Challenge last year, and is planning on racing its newest vehicle in the World Challenge in Australia later this year.

We talked with Alex Dowling, the team's strategy director, about everything that goes into solar racing. The mere fact that there's a strategy director involved should hint that driving a solar car involves a lot more than simply having the fastest car on the course. The students on the Michigan team handle everything from meteorology to clearing roadkill from the race course—and that's just on race days.

The evolution of solar cars

Dowling said that, when solar racing first started, cars weren't getting all that much power from the sun to the wheels. As a result, aerodynamics really didn't matter all that much, while catching the sun did, so cars had all sorts of elaborate mechanisms for getting as much of their solar cells into the sunlight as they could. As things grew more efficient and the cars picked up speed, aerodynamic issues came to dominate—teams would build an efficient shape, and build the panels into that, catching as many rays as they could. This ushered in what Dowling called the "rolling poptart" era of racing vehicles.

What changed next wasn't the approach, but the rules. Starting with the 20th anniversary edition of the race in 2007, things had to get a bit more car-like, with an upright driver's seat and an actual steering wheel, and solar panels were limited to covering six square meters of the vehicle's surface. This appears to have ushered in something akin to a pregnant poptart, one that, with driver and ballast, weighs in at about 300kg (660 lbs).

With one major exception, the components of the car are simply exotic versions of familiar items. The solar cells aren't silicon—Dowling said that current silicon is in the area of 20 percent efficiency. Instead, they use a triple-junction gallium-arsenide cell of the sort that typically powers a satellite; these yield efficiencies above 25 percent. The car also has some batteries to smooth over bumps in the solar power, although those take up less than 30kg of the car's weight. Using lithium polymer cells, those can pump out about six kilowatt hours, which will keep the car running for three hours at highway speeds.

Those of you who can do basic math have probably recognized that this means the car runs on engines that draw two kilowatts of power, a number that Dowling compared to the draw of an industrial microwave oven—which you may have encountered while nuking a frozen burrito at your local 7-Eleven. It does that using a lightweight, highly efficient engine that was developed by an Australian research agency; the engine itself is integrated into the wheels of the vehicle.

"To a first-order approximation, the engine is the electrical system," Dowling told Ars. Nevertheless, the car has a series of low-powered embedded boards to distribute power, monitor performance, and handle communications, running on the sort of network that's typically used in current-generation autos. Although these don't add up to a major power draw, they involve lots of customization, and are fairly sophisticated. The team has made them so that they can be reprogrammed remotely and, if that doesn't work, they can swap them out at the next scheduled break point. During the North American challenge, where it took the team 50 hours to get from Plano, Texas to Calgary, it suffered only 20 minutes of downtime.

The previous model, the Continuum, shown with a car for scale. Image: UM Solar Car Team

Moving beyond the car

But, as we mentioned earlier, a lot goes into racing a solar car beyond the car itself. "As the speed increases you're starting to look at 50, 60mph; there's a considerable amount of power consumed by each additional mile an hour," Dowling said. "There's a trade off between energy and time." To determine how best to expend the vehicle's energy budget, including the power in its batteries, the team has developed software that models the vehicle's performance.

To provide the raw material for that model, the team relies both on performance measurements of the vehicle (which, since they built it, they definitely have) and field data from the route of the challenge. The team uses a commercial high-precision GPS system that can typically provide locations at 10cm precision. Prior to the race, the team drives the whole route, producing a three-dimensional profile for their models. This also gives them a chance to note some of the road features that may play into strategic decisions, like speed limits, sharp turns, and the like.

The model also takes meteorological inputs, which help it figure out how much power the car is likely to have to work with. But, since "nobody really forecasts for the middle of Australia," as Dowling put it, the Michigan group brings along its own meteorological team, and has been known to launch its own weather balloons ahead of some races.

On race day, the race team deploys several vehicles beyond the car doing the actual racing, and integrates all their data and locations into "something like an amateur fleet management system that a trucking company might deploy," Dowling said. To keep them all on the same page, they set up their own network, using cellular signals in the US, and satellite communications when in Australia.

The weather team drives about forty miles ahead of the vehicle and, in addition to the weather data, marks road hazards like potholes and debris on their map. For the smaller debris, like roadkill kangaroos in Australia, a scout team that has a shorter lead over the racing vehicle stops and clears them, updating the shared map accordingly. Immediately behind the solar car is the chase vehicle, which houses the strategy team. All of that generally keeps the racing vehicle speeding through checkpoints and stage stops.

A real-world opportunity

Dowling said that the Michigan team is entirely student run—there are faculty advisors, but they primarily perform administrative duties and help ensure that the project meets safety requirements. At any given time, there are roughly 40 students that are willing to put 10 hours or more into the work, performing work that includes fundraising, speaking about the project to high school students, working on the hardware and software, etc. Since the entire team turns over every few years due to graduation, the project has to have a pretty strong appeal in order to drag people away from all the other options college life provides.

For Dowling, the experience adds depth to the classroom experience. "It has been three years of immense technical management and learning experiences," he said. "It's both an educational opportunity and a sanity check on classroom material—you're likely to trust something once you've gone out in the field to use it."

So, although some of the technology behind the solar car isn't likely to show up on the roads any time soon—and some of it is already there—the students will be taking the experience they get into their careers, which will undoubtedly involve fields that are far more diverse than the automotive industry.