Dawn Levy, News Service (650) 725-1944; e-mail: [email protected]
Students race Route 66 in world's longest solar car challenge
Route 66 has seen faster cars. But few drivers have gotten their kicks along the historic road from Chicago and Los Angeles without a drop of gas. That changed July 15-25, when students from Stanford and 26 other institutions competed in the world's longest solar car race in a shining demonstration of the potential of renewable energy and electric vehicle technologies.
"The whole machine is doing 40 miles an hour off the power of a hair dryer -- about 1,000 watts," Stanford Solar Car Project leader Joel Segre said of one of the two Stanford cars that participated in the race. "If you convert that into efficiency, as in miles per gallon of gasoline, that's in the 800 to 1,200 miles-per-gallon range," the junior majoring in biomechanical engineering added.
Stanford was the only school to enter two vehicles in the American Solar Challenge, which was sponsored by the U.S. Department of Energy and its National Renewable Energy Laboratory, as well as companies EDS and Terion Inc. The first Stanford car, named the Third Degree Burner, competed in the stock class, which specifies lead acid batteries and prohibits arrays of photovoltaic, or solar, cells worth more than $10 per watt. That vehicle, which resembles a flat, red spaceship and took two years and $30,000 to build, took second place in its class with a completion time of 91 hours. The University of Arizona's Monsoon blew away competitors to take first place in stock class with a completion time of 70 hours.
Stanford's second car, the Backburner, a sleek three-wheeler, raced in the less stringent open class, which allows almost any battery type but restricts battery weight depending on chemistry considerations. Placing 18th with a completion time of 100 hours, the Backburner employed relatively inexpensive, used nickel metal hydride batteries. First place in open class went to the University of Michigan's M-Pulse, which took 56 hours to make the trip at an average speed of 40 miles per hour.
At 2,300 miles, the American Solar Challenge is the longest solar car race in the world, outdistancing the 1,882-mile trans-Australian route of the World Solar Challenge and the 1,300-mile Sunrayce '99 from Washington, D.C., to Orlando, Fla. Drivers have been racing solar cars since 1982.
How viable are solar cars?
Every day enough solar energy reaches Earth to meet the world's energy demands for a full year -- if only it could be harnessed.
Just as conventional batteries harness chemical differences to generate voltage, photovoltaic cells use special silicon wafers with two layers -- one that donates electrons, one that accepts electrons -- to create a difference in electrical potential.
"When sunlight hits a cell, it pings an electron off of the donor and it goes to the acceptor, and current flows," Segre explained. The electric current flows through a wire that connects to eight batteries storing a total of 96 volts to power the solar car's motor.
The solar cells are strung into seven independent arrays containing more than 100 solar cells each. But woe if one cell breaks, Segre said: "It's akin to the Christmas tree light effect."
Power consumption depends on vehicle speed. When the car moves slower than 40 miles per hour, batteries store the excess power generated by the solar arrays. At faster speeds, the car sucks juice from the battery.
The car also features "regenerative brakes," which "recycle" energy of motion that in conventional cars is lost during braking. Regenerative brakes trap significant power. Segre recalled a highlight of the race as the Third Degree Burner neared the finish line in Claremont, Calif.: "The driver was descending at 70 miles per hour from a beautiful mountain pass, passing traffic, getting 1,000 watts from the solar array and generating 5,000 watts from its regenerative brakes. So there we were, passing traffic and charging our batteries. Everyone was so excited, and the driver was howling into the radio."
Cost, not technology, remains the biggest deterrent to commercial viability, Segre said. Like computer chips, solar cells are made from silicon wafers requiring pure and exotic materials, and chip manufacturers demand top dollar. Whereas one silicon wafer is used to make one solar cell, that same wafer can be the precursor of many computer chips, each of which command a handsome price.
The Third Degree Burner's solar arrays cost more than $5,000. Some open-class teams ran solar arrays that put out triple the power but cost 100 times as much.
Light and strong, the chassis is the stuff of space shuttles and fighter jets. Its structure -- a Kevlar-based honeycomb sandwiched between carbon-fiber laminates -- yields an incredibly high strength-to-weight ratio. Formed on site from composite materials, the chassis weighs only 20 pounds but supports more than 800 pounds -- 350 pounds of batteries, 200 pounds of driver, 300 pounds of car parts.
Designers can't just throw solar arrays atop conventional cars to convert them. Despite their cost, solar cells produce relatively small amounts of power. The reason solar cars can get away with such small power sources is that they are designed with efficiency -- rather than comfort or practicality -- in mind. Solar cars owe their extreme efficiency in part to their aerodynamics. They're short, flat and close to the ground. Adding rearview mirrors alone would double the drag of the car, Segre said: "That sort of attention to detail makes this car incredibly efficient but also incredibly impractical."
It's no surprise that the companies that recently came out with hybrid or electric cars -- GM/Saturn, Honda and Toyota -- have raced solar cars. "Solar cars are excellent testbeds," Segre said. "If you have inefficiency in the drive train, or some little rear view mirror that's not aerodynamic, it's going to show up." Contrast that with the average sport-utility vehicle, which is so inefficient to begin with that a less-than-aerodynamic rearview mirror escapes notice.
Solar cars also are hot. How hot? "Hot enough that I'm glad I'm too big to fit in the cockpit," said Segre, 6-foot-4. But students Scott Kohn, Ray Chen and Andy Gotterba were happy to take the driver's seat, sometimes for as long as six hours in heat topping 105 degrees.
It seems fitting then that all of Stanford's solar cars have had the root word "burner" in their names: 1993 saw the introduction of the Sunburner, followed by the Afterburner in 1995 and Afterburner II in 1997. The Third Degree Burner, which debuted in 1999, was raced in this year's stock class while the Backburner competed in the open class.
'On your mark, get set...'
The Stanford Solar Car Project is housed in an aluminum edifice on Stock Farm Road that is cheerily painted with a giant cardinal sun. A week before the race, the building was filled with exhausted but upbeat students working to troubleshoot problems that could turn Route 66 into the highway to hell.
Alumni of the Stanford Solar Car Project and the technical community, both at Stanford and beyond, have been hugely supportive. A week before the race, a student shorted out a $5,000 power supply necessary to charge the cars' batteries. Leonard Magelky of Dovebid offered to rent the students a replacement for just $150. The next day, after perusing the project website (http://www.stanford.edu/group/SSCP/index.htm), he decided he'd rather list his company as a sponsor, so he gave the students the power supply for free and offered to repair the old one at no charge.
Additional help came in the form of substantial cash donations from Google and Juniper Networks, a 15-passenger van from Ford, powerful computing tools from Compaq and Quantex, satellite phones and service from Globalstar and special funding from Stanford's student body.
Besides Segre, Kohn, Chen and Gotterba, project participants included Eloy Avila, Alan Amaya, John Cieslewicz, Alex Starns and Grace Liu, all of Stanford; Verity Pang of West Valley College in Saratoga, Calif.; and Ernie Avila of Elko High School in Elko, Nev.
"Safety first" was the rule of the road as the cars were preceded by a lead car and followed by a chase vehicle. Students in the lead vehicle communicated via radio with the race-car driver to alert him to potholes and hills or just help navigate Route 66, parts of which are unmaintained, and to direct him to checkpoints, which were often off the beaten path.
Students in the chase vehicle used laptop computers to model race performance and determine the optimal speed given cloudcover, elevation profile, wind speed and time of day. Satellite uplink to the web allowed them to view incoming weather systems and check the position of competing teams on the route. "After much pulling of hair and gnashing of teeth, we would eventually come out with a statement that the car should either speed up or slow down," Segre said.
The students' dedication paid off. The racing cars encountered no major setbacks, though flat tires were numerous. Solar car tires -- tubeless tires run at very high pressures -- are designed to minimize rolling resistance. When they heat up on hot pavement, the pressure inside increases, making them even more susceptible to popping. "The craterlike potholes of Route 66 don't help much either," Segre said. Nonetheless, Stanford's solar cars proved themselves viable highway vehicles. The Backburner has logged a top speed of 74 miles per hour, and the Third Degree Burner, 70 miles per hour.
Materials science and engineering Professor John Bravman, vice provost for undergraduate education, is faculty adviser for the project.
By Dawn Levy <