Only two things matter when building a race car powered by the sun: maximizing efficiency and minimizing weight. Everything else is secondary when the goal is crossing a continent using just enough energy to power a hair dryer.

All the top teams in the esoteric sport of solar racing embrace this "less is more" ethos to a degree that would please Colin Chapman. But the University of Michigan, arguably America's best team, has taken it to fanatical levels in a relentless drive to win the World Solar Challenge in October.

The biennial sprint across Australia is the oldest and most prestigious race of its kind, the Daytona 500 or Monaco Grand Prix of solar racing. No American team has won the 1,800-mile race since General Motors' Sunraycer led the inaugural run in 1987. The University of Michigan Solar Car Team is determined to end the drought. It has spent more than $1 million building Quantum, its most advanced solar car ever.

"It's the ultimate electric vehicle," said Chris Hilger, a junior chemical-engineering major who is the team's business manager. "At its heart, it's an electric vehicle that uses top-of-the-line technology, from the batteries to the motor to the communications. It just happens to be solar."

Quantum is the team's 11th car since its inception in 1989. Construction started by stripping the previous car, Infinium, to the last bolt and weighing everything. Infinium brought U of M its third consecutive (and sixth overall) victory at the American Solar Challenge last year, but it weighed 500 pounds. The team set out to trim every extraneous ounce from Quantum.

To start, it used modeling software to determine how much stress the car and its components are subjected to. That brought a startling discovery.

"We were significantly over-engineering the car," Hilger said.

Everything about Infinium was stronger and heavier than necessary. With that in mind, the team set about designing slimmer, lighter parts. No one will say just what Quantum weighs, but the target was 320 pounds.

"It's very light," is all Hilger would say.

Secrecy is common in solar racing, a highly competitive sport where a four-day race can come down to minutes. Top teams spend $1 million or more building their cars. U of M is gunning for the defending champions from Tokai University in Japan and the Nuon Solar Team of Delft University, the Dutch team that won the four previous races.

Given the intense competition, Hilger was equally coy discussing the three-wheeler's drivetrain. Three wheels are the norm in solar racing because they offer less rolling resistance. A hub-mounted motor from CSIRO drives the rear wheel, generates "a few horsepower" and is 98 percent efficient.

"It's one of the most efficient motors in the world," Hilger said.

The car is covered with 6 square meters [65 square feet] of silicon solar cells, somewhere between 600 and 800 in all, and they generate "something less than 2 kilowatts of power," Hilger said.

"We can cruise at 60 mph on less than 2 kilowatts," he said.

The car features a lithium-polymer battery to keep things moving when the clouds roll in. Regenerative braking sends energy back to the pack. Hilger wouldn't say how big a battery Quantum has, but said 5 kilowatt-hours is the norm in solar racing. Everything is bolted to a carbon-fiber monocoque and covered with carbon-fiber bodywork. Major components are aluminum or titanium.

The body was designed with help from Exa Corp., which provided the CFD needed to make the car as slick as possible. Hilger's keeping mum on the car's drag coefficient, but top-tier solar racers are in the super-efficient 0.07-to-0.1 range. To put that in perspective, the General Motors EV1 was 0.195, and the current-generation Toyota Prius is 0.25.

The car, which is 16 feet long, 3.5 feet tall and 6 feet wide, ran under its own power for the first time April 8. No one's put the hammer down yet, but Hilger says Infinium could do 105 mph on a track. That's well above the 50 to 60 mph the cars average in a race, but it speaks to the level of engineering involved.

Top-level cars like Quantum are exquisitely engineered. The team received help from some of the best engineering firms in the world. The list includes Ricardo, which worked with McLaren to develop the engine in the MP4-12C supercar, and Roush, which has a hand in everything from tuning to NASCAR racing. Each of the Big Three automakers is a sponsor, and they're very interested in what the team is up to, because a solar car is simply a highly efficient electric vehicle.

"Through working with this team we have access to cutting-edge research that the team is employing, which helps us learn as we develop our own products," Mark Fields, executive vice president of Ford, told Wired.com. "The technology that the team works with – the lithium-ion batteries, how you manage thermal energy – is hardwired into our electrification strategy going forward."

The team finished the car months ahead of schedule, leaving plenty of time for fine-tuning. Quantum will compete in the Formula Sun Grand Prix at Indianapolis Motor Speedway next month, where it will be thoroughly shaken down before heading to Australia in October.

"We think we can refine and improve the car by going through it with a fine-tooth comb to shave more weight and find more efficiency," Hilger said.

Competing Down Under will require more than getting in and mashing the accelerator. Solar races are a marathon, not a sprint, and the defending champs finished the 2009 race in 29 hours, 49 minutes at an average speed of 63 mph. There is a tremendous amount of strategy involved as teams manage their energy and keep an eye on the weather: Michigan's team includes a meteorologist.

"Being able to predict cloud cover will give you a huge advantage, so you can plan ahead and manage your energy," said Spencer Quong of of Quong & Associates, an advanced-automotive-engineering consultancy. He founded the UC-Berkeley Solar Vehicle Team in 1990. "But if you have enough sunlight and you can gather more sunlight than you can use, your foot is on the floor."

You can bet the guy behind the wheel of Quantum will have his foot to the floor. The team is supremely confident of its chances, and determined to bring the trophy home in October.

"I think we have a better chance of winning that we've ever had in the past," Hilger said.

Top photo: Team members AJ Trublowski, Cole Witte (yellow T-shirt), Chris Hilger and Caitlin Sadler (from left) install a temporary top on Quantum. (Scott Soderberg/University of Michigan.)

The team tests Quantum at General Motors' Milford Proving Grounds. That's Jonathan Meed with the computer. Driver Ryan Mazur and Gerald Chang (center) are testing the steering wheel. Photo: Scott Soderberg/University of Michigan

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