Racing with the Sun
MIT students’ solar-vehicle team makes a strong showing down under.
Deep in the Australian outback on a warm October morning, 14 MIT students and alums climbed out of their sleeping bags at 6 a.m. to get ready for another day of hard driving, in convoy, down endless flat stretches of straight, hot, dusty roads. One car took the lead to create a buffer against other traffic, and a van brought up the rear to monitor the group’s progress.
In between these ordinary vehicles, a futuristic car built by a small student-run team made its way more than 3,000 kilometers, from Darwin to Adelaide, powered solely by the sun. Looking like something imported from a sci-fi fantasy, the low-slung single-seater was covered from stem to stern with shiny black photovoltaic panels–about 600 solar cells connected in six arrays. And inside, under a plastic bubble canopy reminiscent of a fighter jet, a driver tried to maintain an ideal speed calculated by the team in the chase vehicle on the basis of constantly updated estimates of how long the battery power would last. Despite the pressure–and temperatures as high as 110 °F–the drivers loved every minute of it.
“You have to hit yourself over the head every night and say, ‘I’m in the middle of Australia racing a solar car!’ ” says team member Maddie Hickman ‘11. “You can’t comprehend how you ended up there.” The team passed flocks of emus (and mobs of kangaroos en route to the race), and every night the deep, quiet darkness of the remote desert was lit by unfamiliar stars.
The members of the MIT Solar Electric Vehicle Team (SEVT) had spent two years designing, building, and testing to earn the right to compete in the weeklong 2009 World Solar Challenge, the world’s longest race of solar vehicles. And on these isolated roads, their intimate familiarity with every detail of their car–named Eleanor, after one in the movie Gone in 60 Seconds–helped them make it to the finish line. More than half the teams did not.
The rules let teams drive only from 8 a.m. to 5 p.m. But they could start charging the batteries earlier, so each team rose with the sun to set up the solar panels. “At 8 a.m., we’d jump in our cars and get off as fast as possible,” says Hickman. And at 5:00 p.m., they’d set up the arrays again to catch all the light they could before sundown.
The first day, everything went smoothly for the MIT team. But on day two, when they pulled over for a routine switch of drivers, Eleanor hit a rock. One of the special high-pressure tires immediately went flat. And as they started to change it, a lug nut jammed.
“We pulled off the entire hub–something we had never practiced,” says team member Chris Pentacoff ‘06, an iRobot engineer who was a driver for MIT in the 2003 and 2005 races. “But we had practiced taking everything apart, and we had spare parts of everything. We just swapped the hub and were back on the road in about 20 minutes.”
MIT’s team is “usually one of the smallest teams, if not the smallest, in terms of number of people, and in the lower tier in terms of the funding we get,” says Pentacoff. “But we’re generally regarded as the most resourceful.” That reputation was enhanced in 2005, when MIT’s vehicle suffered a rollover. “Most people thought we were completely out of the running,” he says, and yet the team made improvised repairs and finished the race in sixth place.
Last year, MIT’s team was one of only two that designed and built their own electric controllers, the interface between the solar cells and the car’s array of batteries. The amount of energy that solar cells capture varies with the time of day, the angle of the sun, and the amount of cloud coverage. The controllers track the output of the cells and the level of charge in the batteries, maximizing the amount of energy stored in the batteries without overcharging them. The custom-built units helped the car capture solar energy more efficiently, says graduate student Robert Pilawa ‘05, MEng ‘07, who designed the controllers and oversaw the construction of 14 of them (six used in the car, plus eight spares). The overall efficiency of the MIT controller is 98.5 percent, he says; a standard commercial controller is significantly heavier and only 90 to 95 percent efficient. While that doesn’t sound like much of an improvement, the team calculated that its controllers shaved off 30 to 40 minutes overall–and in some years, even a few minutes would mean the difference between first and second place.
The custom controllers proved crucial at the end of the third day. “Our battery pack ran completely empty,” Pilawa says. There were still about two hours of sunlight when the day’s racing was done, but because the battery was so low, the relay that activated the controllers wouldn’t turn on, and they couldn’t begin charging. Once again, they improvised: “One of the people who designed the battery pack and I were able to literally hot-wire it to bypass the relay. It was enough to jump-start it, just for a few seconds.” A commercial controller might not have survived the spike in power, he says, but theirs came through unscathed.
MIT’s SEVT, started by James Worden ‘89 after he competed in the Swiss Tour de Sol in 1986, is believed to be the world’s oldest such team. (As a freshman, Worden commuted to campus from Arlington in an electric car he’d built in high school; he and his wife, Anita Rajan Worden ‘90, went on to found a solar-vehicle company called Solectria.) It has competed in six of the 10 World Solar Challenge races in Australia, and this year’s performance ranked among its best ever: out of the 39 teams that registered, and the 32 teams that actually raced, it was one of only 14 that finished, coming in second in its division (for cars using silicon solar panels) and sixth overall. With a shape that gives it a drag coefficient of just 0.11 (regular cars range from 0.24 to 0.50), it can reach 90 miles per hour, though the team conserved power during the race by limiting speeds to an average of 55.
Eleanor will be superseded by a new vehicle that the team is designing for the 2011 race. And after more than two decades, solar cars are not even close to being commercially viable. Still, Pentacoff believes developing the technology is worth the effort. “Even if solar cars aren’t going to be practical, a lot of the components will be,” he says. “It’s a great test bed, and the technology could be applied to a lot of other things.” Battery management systems and power trackers designed for solar cars are already being adapted for other applications, including the control of stationary solar array systems.
It’s also a great experience that teaches team members hands-on lessons about design, fabrication, improvisation, and the handling of various materials, such as the composites they used to build the car’s sleek, lightweight body. And they get training on the fly in organization and fund-raising. “I learned a lot more through the solar car than a lot of my classes,” Pentacoff says. “It teaches about how things are made, how to make them cheaper and easier. You have a limited amount of materials and you have to figure out how to make do. It produces a lot of creativity and ingenuity.”
And of course, it builds powerful bonds among the team members, who celebrated reaching the finish line in Adelaide’s Victoria Square by jumping into a public fountain. “Hanging out in the outback, you get pretty tight with the team,” says Hickman.
But above all, it’s a thrill to design and build a car from scratch and put it to the test. “We do it,” Pentacoff says, “because it’s fun.”
See video and photos of Eleanor in the outback:e_SFlbtechnologyreview.com/Eleanor