Hot wheels: follow a fleet of solar cars as they zoom past kangaroos in Australia's wild Outback

Science World, April 16, 2007 by Judith Jongo-Cohen

Australia is home to colonies of koalas and mobs of kangaroos, and soon it will host a squadron of race cars. On October 25, 2007, dozens of sleek vehicles will rev their engines and begin a cross-country race (see race map, right). For a large part of the 3,000 kilometer (1,864 mile) journey, the cars will speed through the Outback. Navigating through this immense desert--where desolate roads are dotted with signs warning of camel and kangaroo crossings--may be daunting enough, but these race cars will be making the trip without using a single drop of gasoline. Impossible? Not during Australia's Panasonic World Solar Challenge (WSC).

The WSC is the largest solar-car race in the world. To fuel the trip, the vehicles will soak up sunlight and convert its energy into electricity. Held every two years, the WSC attracts teams of university students and engineers from private companies around the globe. The first race took place in 1987, with the winning car crossing the finish line in roughly 45 hours. In 2005, the winner clocked in at 29 hours and 11 minutes. What will it take to win the 20th anniversary race this fall?

SUN CATCHERS

As racers charge through the Outback, they might catch a glimpse of giant termite mounds rising like headless tree thinks from the desert sand. But there's no time to stop and snap photos. A car's driver and the support team that will be accompanying the car in separate vehicles are too busy making sure that the race vehicle is running smoothly and its solar-energy-capturing functions are operating properly.

To capture the sun's energy, the top of each car is decked with a solar array, or panels made up of approximately 3,000 photovoltaic cells (see Nuts & Bolts, p. 14). When sunlight hits the array, negatively charged particles called electrons flow through the cells. These moving electrons create electrical energy that flows to the car's motor. Any energy not used immediately by the motor to move the car is stored in batteries. These batteries are the same as the rechargeable kind used in laptops. But while a laptop's battery pack contains only six batteries, "our solar car [battery pack] has 640 of them," says Alex Hayman, a member of the Massachusetts Institute of Technology team, which placed sixth in the 2005 race. Batteries provide a race car with a needed boost on cloudy days, when the solar array might not produce enough energy to power the vehicle's motor.

At 5:00 p.m., the race clock officially stops for the night, and the teams set up roadside camps. They use the downtime to make car repairs and to charge their cars' batteries some more. To capture the maximum amount of the fading sunlight, a team lifts off its car's top and positions the solar array toward the sun. However, the team must watch for sudden willy willys. These whirling "dust devils" can blow away an array or pummel the delicate cells with debris.

SPACE CRUISERS

Outback campers must also be alert for scorpions and venomous snakes, and "the flies are all over your face," says Hayman. But at 8:00 a.m., any thoughts of creepy creatures disappear; the race clock officially starts ticking again. The drivers hit the road in their spaceship-like cars. These cars' sleek shapes not only look cool, but they actually help the cars optimize power.

Under peak sunlight conditions, the solar array can provide a vehicle with about as much power as a hairdryer. To run on such a meager power supply, solar cars must be aerodynamic. A sleek shape allows air molecules to flow smoothly over a car. By reducing air resistance, or air molecules rubbing against the car, there is less drag. With less energy used to fight this slowing force, more energy is available to propel the car.

Another way to conserve energy is to keep the car lightweight. Since the more massive a car is, the more energy it takes to move it, most solar race cars weigh less than 180 kilograms (400 pounds). That's less than half as much as a gas-fueled two-seater sports car. To achieve this, solar cars are made of lightweight but tough materials such as Kevlar, a material used in bulletproof vests. Also, every part of the car must have an essential purpose. That means there are no hood ornaments or bulky stereo speakers.

Stripped down and streamlined, solar-powered cars have an average cruising speed of 100 kilometers (60 miles) per hour, says David Fewchuk of Melbourne, Australia's Aurora team, which finished second in the 2005 race.

FLASH TO THE FUTURE

Winning the WSC is the dream of all the teams, but a deeper motivation drives racers. "We believe in developing solar energy for practical purposes--to reduce harm to the environment and to people's health," says Meghan Cartwright, a member of Canada's Queen's University team. Solar-powered vehicles, unlike traditional gas-guzzling cars, do not spew air pollutants such as carbon dioxide. This gas is a leading contributor to global warming.

Today, most people don't drive environmentally friendly, sun-fueled cars because they are very expensive to build. But thanks in part to technological advances made by WSC racers, some motor companies are beginning to test for ways to effectively incorporate solar power into cars. For example, companies have tested hybrid cars that use solar energy to supplement other energy sources, such as gasoline--or even wind. "I believe that someday, solar-powered cars [for the public] will become a reality," says Jonathan Mash, a member of the Queen's University team.