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.