Sun Racer Set to
Soak in the Gold


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Photo: Ford

Its top speed is 125 miles per hour, its emissions are zero, and it gets an infinite number of miles to the gallon.

Because there are no gallons, other than gallons of sunshine.

Meet Nuna6, a road-worthy, solar-powered racecar, lighter and more efficient than ever before.

Nuna6's predecessors 1 through 4 triumphed in Australia's World Solar Challenge race four times in a row. But in 2009, Nuna5—like all the Nuna's, a product of a team of students out of Delft University of Technology in the Netherlands—was defeated by Japan's Tokai Challenger. A quarter of the solar panels had stopped producing energy and the car was at a standstill for several hours. Despite that, Nuna5 came in second.

Nuna6

The Nuna6 is targeting a first place finish in the 2011 World Solar Challenge in Australia.
Photo courtesy of Nuon Solar Team.

This year, they're going for the gold. Or the blue, if we're talking ribbons. Despite Nuna5's already extreme lightness and efficiency when cutting through air (it weighed 341 pounds and had 12 times less aerodynamic resistance than a typical sedan), the designers of Nuna6 have managed to lower overall drag by 10%.

Ironically, the gains are due to a change in the rules that was intended to make things greener—and tougher. Solar cells come in several flavors. Silicone cells are the kind you see on rooftops, backpacks, or calculators. Gallium cells, however, can convert a greater percentage of sunshine to energy. Currently, though, they are much more expensive than silicone. Prior to this year, teams could use whatever solar cell they could afford. Now the World Solar Challenge's ruling body has altered the rules so that teams have to choose between three square meters of Gallium or six of silicone. The hope was that the change would nudge innovation in the direction of something that might actually be usable one day.

Nuna6

The Nuna6 in wind tunnel.
Photo courtesy of Jorrit Lousberg.

The Delft students chose silicone because the price allowed them to buy enough to create a tight mosaic on the surface of the car. "The solar panel was where we could ditch area," explains Bruno Moorthamers, who's studying aerospace engineering at Delft and is one of Nuna6's designers and drivers. "Solar cells have little corners cut out of the cells—each corner is effectively area you have to take with you. But it's not useful; it doesn't gain you more energy. The silicone cells are cheaper, so we could buy more, cut them up and put them back together."

Other innovations helped get the drag down too. A new carbon fiber "weave" used on the latest Formula 1 racers keeps the vehicle light, and a sleek composite resin from DSM helps encourage laminar flow. The team nickel-and-dimed the aerodynamics wherever they could, making the driver's compartment even smaller than those of previous Nunas. "We squeezed the driver area, losing comfort, which is not important for the race," notes Moorthamers.

Nuna6

Nuna6 with the Nuon Solar Team from Delft University of Technology.
Photo courtesy of Jorrit Lousberg.

The smaller swath of cells combined with the other advantages reduced drag by 10%. The vehicle now produces approximately the same amount of drag as a truck's side view mirror at 62 miles per hour.

Of course, system failure, not drag, was the reason Nuna5 didn't win the 2009 race. "Reliability is an extremely important factor—maybe even the most important factor after the design is finished," says Moorthamers. "Our electrical system has been heavily changed. We used fewer electrical components—the less you have, the less can fall out."

However reliable, fast, and environmentally sound the Nuna6 is, it will be some time before the rest of us get to drive anything like it. "For a usable solar car, which is safe for four people, and  that you can drive to the mall—maybe another 30 years," says Moorthamers, who hopes to pursue such a possibility in his academic research. "But I can imagine, for example, Jay Leno buying one now."

Michael Abrams in an independent writer.

The vehicle now produces approximately the same amount of drag as a truck's side view mirror at 62 miles per hour.

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October 2011

by Michael Abrams, ASME.org