Pictures: Building the Perfect Solar Car

A Sunny Outlook

Photograph by Charlie Archambault, National Geographic

Electrical engineering student Mingming Liu takes the solar array outdoors in Drexel University's west Philadelphia neighborhood to test their power output with a voltmeter. Holding the array (not pictured) is mechanical engineering student Vince Tancredi. Building a car requires students from different engineering disciplines to work together. The students would be building their solar car not only for the Eco-marathon, but as the senior design project required of all Drexel students before they graduate.

Published April 22, 2011

Capturing Sunlight for Motion

Photograph by Charlie Archambault, National Geographic

Since the solar cells they could afford were only 15 percent efficient in capturing sunlight and converting it into energy, the Drexel students considered how much of an advantage it would be if they could incorporate panels that actually moved with the changing angle of the sun as the car circled the course on Houston's downtown streets. But such moving parts weren't allowed under the Eco-marathon rules.

As it turned out, their solar cells produced 305 kilojoules of energy on their competition run. The car used just 240 kilojoules to traverse the six-mile course--10 laps around the Discovery Green park in downtown Houston. That meant they had a valid run. Shell Eco-marathon rules for solar vehicles require that the car not be operating on the reserve battery power, but actually be generating enough solar energy to propel the car, or more. As it turned out, Drexel's car was the only entry among the five solar prototype teams to achieve this feat.  Purdue University reached the same milestone with a solar car it entered in another category, urban concept vehicles, and took home first prize for solar cars in that grouping. (In the Eco-marathon, urban concept cars must meet safety requirements to actually operate on city streets.)

Even though the efficiency of the Drexel car at its peak outstripped that of any of the internal combustion-powered vehicles at the Eco-marathon, it was not eligible for the grand prize, which is always an internal combustion car.

Shell's technical manager for the Americas race, Adrian Juergens, who works in the company's fuel research division, explained in an email: "The solar car works well as long as the sky is clear, i.e. the solar cars are dependent on the sun and the efficiency of the array panels." Those stumbling blocks didn't deter the solar competitors.

The winner of the race, Université Laval of Québec City, constructed a sleek, white, bullet-shaped pod that cruised the six-mile track at 2,565 mpg (1,090 km/l). It was the third consecutive win in the Eco-marathon Americas for the Canadian team.

(Related: "Breaking 2,500 mpg, Canadian Team Wins High-Efficiency Race")

Published April 22, 2011

Drilling into Design

Photograph by Charlie Archambault, National Geographic

Drexel mechanical engineering student Chun Yao Ker cuts aluminum in the machine shop for the chassis of his team's solar car in the Shell Eco-marathon Americas race.

Although the solar cells on the car roof will be getting the attention, constructing a sturdy, but lightweight supporting frame is crucial. "There are aspects of engineering that you don’t actually think about when you are doing the design," says Ker. "We have the body and we have the chassis, and both have to be manufactured at the same time, so there’s concurrent manufacturing going on. There are  idiosyncrasies and details you are not going to figure out your first time doing it. That’s part of engineering, part of study and learning."

Published April 22, 2011

Reinventing Wheeled Transport

Photograph by Charlie Archambault, National Geographic

Vince Tancredi, left, holds the chassis while fellow Drexel mechanical engineering student Chun Yao Ker checks the fit of the drive wheel, or motor, on the Green Dragon, the solar car the team built for the Shell Eco-marathon Americas.

The motor, ordered from China, was actually designed for an electric bicycle. "People try to make bikes really light, really fast, and really efficient, so that's why the motor is almost perfect for this application," said team member Asaf Erlich, an electrical engineering student (not pictured). To test the motor when it arrived, the students rigged it up to Erlich's bike and each took a spin around campus. But making sure it fit into their homemade car was the crucial step.

Published April 22, 2011

From Idea to Reality

Photograph by Charlie Archambault, National Geographic

Electrical engineering student Mingming Liu holds a diagram of how the solar arrays will be attached to the top of the Drexel University team's solar car.

What works on paper, however, doesn't necessarily translate to reality. When the solar cells they ordered arrived and they began to create the array that would cover the car, the measurements were off—even though the arrangement had fit perfectly as they calculated it on the computer. It was because the students' vehicle was so large they couldn't use any of the computer numerically controlled (CNC) milling machines that would be available to them at the school. Instead, they had to completely cut and shape and sand down the mold of their car by hand. In the process of cutting the mold by hand, the size was off by mere fractions of an inch.

"It was a moment of concern for them, and for me it was a nice teaching moment," recalled their adviser, associate professor Adam Fontecchio, associate dean for undergraduate affairs in the engineering college. "That's the reality of a handmade versus a mass-produced item."

But the team readjusted the arrangement and covered their car front and back with the rows of solar cells.

Published April 22, 2011

Hands-On Learning

Photograph by Charlie Archambault, National Geographic

Drexel engineering students Conjee Yeung, left, and Mingming Liu work on the soldering of a circuit board for their team's solar car.

"I think one of the most important things about this project is to have fun," says Yeung. "We get to test the components, the motor. We get to ride the motor--it’s pretty fun. I’m interested in putting cars together and building, that’s a plus for me. I don’t like sitting on a computer or doing calculations. I like the hands-on work."

(Related: "All-Girls Team Seeks Record in High-Mileage Marathon" and "Pictures: High School ‘ShopGirls' Design for the Prize")

Published April 22, 2011

An Aluminum Maze

Photograph by Charlie Archambault, National Geographic

Mechanical engineering student Chun Yao Ker prepares tubes to be welded onto the chassis of Drexel's solar car entry into the Shell Eco-marathon Americas.

Lightweight materials are crucial in building cars to compete in the high-efficiency vehicle race.

Published April 22, 2011

Black Wedge Dragon

Photograph by Charlie Archambault, National Geographic

Mechanical engineering student Shuigiang Lin sands the carbon fiber body of the Green Dragon, Drexel's solar car entry in the Shell Eco-marathon Americas.

Carbon fiber is a lightweight, strong material favored by many of teams in the Eco-marathon student design competition aimed at creating high-efficiency vehicles.

But when the car was complete, it looked more like a wide black wedge than a green dragon, with solar cells on the roof that occasionally glinted blue. Lin, who led the finite element analysis to design the shape of the car, explained that the car needed to have a contour, to cut down on aerodynamic drag. "But we wanted as large a body as possible to have as much area as possible for capturing the sunlight," he said. "But obviously, the size of the car poses a problem. That increases the cost, and time, and everything else."

The team's winning solar prototype vehicle measured in at only an inch away from being too wide for the competition rules, and a quarter inch away from being too tall. Team member Vince Tancredi (not pictured) maintained the optimism that had become the group's trademark. "That's a good thing," he said. "It means we haven't wasted anything."

Published April 22, 2011