Photograph by Harley Soltes, National Geographic
Published April 19, 2011
When 11 engineering students at Drexel University decided last year to enter a contest to design and build a super-fuel-efficient car, they knew that choosing to power their homemade vehicle with solar energy would increase their costs, their risks, and their aerodynamic drag.
They decided to go for it.
Their successful journey illustrates a truth that emerges to some degree from stories of all the 69 teams that competed in last weekend's Shell Eco-marathon Americas. Put enough young, smart folks together and ask them to focus on making a single vehicle, and the very barriers that have proven too steep for the big auto companies don't seem so insurmountable.
But the Drexel students—all graduating seniors who soon will be taking their skills into the job market—are part of a cadre who are convinced that they are entering a world demanding fundamental change in how we fuel transportation and the economy. "If you get in the energy field, eventually, you will be doing alternative energy," said Drexel electrical engineering student Asaf Erlich. "There's no way around that."
The Solar Choice
Only a handful of the 30 university and 18 high school teams from the United States and Canada who traveled to Houston for the competition chose to power their high-efficiency vehicles with solar cells. A far more certain path is to go with a traditional internal combustion engine, and then drive down gasoline or diesel consumption by making the car as light and as aerodynamic as possible. This year's winner, Université Laval of Québec City, constructed a sleek, white, bullet-shaped pod that cruised the six-mile track at 2,565 miles per gallon (1,090 kilometers per liter).
In contrast, the Drexel students knew that their homemade solar car would never be mistaken for a rocket. In order to produce as much energy as possible, their car would have to be wide.
"You want there to be a contour, so that you have a smooth flow of air over the car. We wanted a tapered edge," explained Shuiqiang Lin, the Drexel mechanical engineering student who led the finite element analysis to design the shape of the car. "But we wanted as large a body as possible to have as much area as possible for capturing the sunlight. But obviously, the size of the car poses a problem. That increases the cost, and time, and everything else."
But there was an inescapable logic in going with an electric motor, in the eyes of the students. The century-old combustion engine loses so much energy to heat that the best are only about 30 percent efficient, while good electric motors can achieve well over 90 percent efficiency in converting energy to motion. "That sounds like a lot better deal to me," said Erlich.
(Related Photos: Cars of Tomorrow at the Shell Eco-marathon)
So even though it's not easy to capture and store solar energy, the team decided the challenge was worth it.
Opportunities and Threats
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. David Ho, a mechanical engineering student from northeast Philadelphia, put together the team that included students from as close as the Philadelphia suburbs and as far away as Taiwan and Belarus. But what appealed to him about the project was the diversity of experience that would be required to work on a car. Mechanical and electrical engineers would have to work together. "That's the best thing about it," he said. "Trying to get people from all different disciplines."
The group asked Drexel associate professor Adam Fontecchio, associate dean for undergraduate affairs in the engineering college, to be one of their advisers on the project. A forward-thinking energy project made sense at the west Philadelphia school that was founded in 1891, when Pennsylvania was hub of the coal-powered Industrial Revolution. And Fontecchio was a logical choice because he was doing research into solar energy, including the possibilities of a paintable composite fluid that acts like solar cells.
The team had developed a briefing book, and presented Fontecchio with their plan. "It was one of the most impressive meetings I've ever had with a senior design student team," he recalled. But he didn't want them to just assume that a solar car was a good idea. He urged them to do a SWOT analysis, a method usually used in the business world for deciding whether to enter a product market. They had to list and consider their team's strengths and weaknesses, as well as the outside opportunities and threats.
As it turned out, the students identified many weaknesses. Unlike many of the competing teams in the Eco-marathon, who return year after year and have a chance to learn from past mistakes and perfect their vehicles, the Drexel students were starting from scratch. They did not have a working body shop. Other schools had over the years garnered huge corporate sponsorships, like Drexel's main solar competitors in the Eco-Marathon, Purdue University's team, which had support from Lockheed Martin, Exelon, GE Energy, and others. Purdue, they knew, was building a street-legal solar car that would cost about $100,000. Their budget for a prototype vehicle (not including all the safety features needed to actually drive on city streets) was about $3,000 to $4,000, they figured.
Still, the students felt the weaknesses were outweighed by the advantages they had in starting out fresh. "The opportunity was that if they succeeded," said Fontecchio, "it would be quite an impressive achievement."
From Computer to Reality
Before long, though, the project taught the students one of engineering's most heartbreaking lessons. Drexel mechanical engineering student Vince Tancredi sums it up this way: "You can design a lot more on the computer than it is actually feasible to make." Time, money, and contest rules prevented them from putting many of their ideas into the car.
Since the solar cells they could afford were only 15 percent efficient in capturing sunlight and converting it into energy, they 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.
An even more practical problem was that their 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 would have to completely cut and shape and sand down the mold of their car by hand. 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 a moment of concern for them, and for me it was a nice teaching moment," recalled Fontecchio. "That's the reality of a handmade versus a mass-produced item." In the process of cutting the mold by hand, the size was off by mere fractions of an inch.
But the team readjusted the arrangement and covered their car front and back with rows of solar cells, all wired with redundancy in case something went wrong. To get their vehicle moving, they ordered an electric motor from China that was designed for bicycles. "People try to make bikes really light, really fast, and really efficient, so that's why the motor is almost perfect for this application," Erlich said.
Into the Competition
The Drexel students knew their car was working by the time they arrived with it in Houston, but it still was a nerve-wracking process taking it through the technical testing required by the Eco-marathon rules. The "Green Dragon," as it was called, after Drexel's school mascot, was actually more of a black carbon fiber wedge, with solar cells that occasionally glinted blue. After a long session at the measuring station, the car was given the go-ahead to race.
"They are close on everything," said retired Shell researcher Bobby Bowden, shaking his head as he wrote down their measurements. The car was only an inch away from being too wide for the competition and was a quarter inch away from being too tall. Team member Tancredi smiled and maintained the optimism that had become the group's trademark. "That's a good thing," he said. "It means we haven't wasted anything."
But once the team got into the line with the other student cars to make their first run, they realized that their joule meter, the device that measures how much energy their solar cells were generating, had stopped functioning. What had looked like the perfect cloudless day for a solar race soon became a sweltering hour under the relentless Houston sun. Instead of running the course, they raced to analyze and correct their circuitry before the track was closed for the first session, forcing them to wait until later in the afternoon, when the sun would be less optimal.
Drexel mechanical engineer John Toale, whose pride and joy was the design, build, and welding of the aluminum chassis inside the vehicle, had to walk away from the group in frustration, realizing there was nothing he could do to correct the problem. "The electrical guys are working on it," he said.
The group realized they had made their circuitry too complex, so they decided to simplify the wiring. By then they'd not only missed lunch but also the opportunity to race on Saturday as they reworked the electronics. By Sunday morning, the last day of the race, they were ready to run.
The Green Dragon had no problem making it around the track Sunday morning. The vehicle had not only solar cells but the storage and backup of an old battery that the students had found in the Drexel workshop and had stripped down and downsized for their vehicle (after checking with the battery company and determining it could be safely done, as long as they added a protection circuit). But the strict 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. In the angled early-morning sun, the Green Dragon was generating only 25 percent of the energy that the vehicle used on the course.
At noon, with high hopes and high sun, the Drexel team took the track again. This time, their solar cells, as confirmed by their now operational joule meter, produced 305 kilojoules of energy. The car used just 240 kilojoules to traverse the six-mile course. They had a valid run.
The Drexel students hoped to try again for an even better score, but later in the day, the wind picked up and blew one of the solar cells off their car's roof. Instead, they watched from the sidelines as the five other solar teams competing in the prototype car category, including Purdue University with the vehicle that had the only valid solar run last year, each cruised with their near-silent vehicles the ten laps of the course. But one after another, joule meter readings showed that none of the cars could break the barrier of producing more solar power than it used.
Drexel emerged as the only prototype solar car to turn in a valid run, enabling the team to take home the first prize of $1,500 in their category. (Purdue won the same prize for its car in the other race category, street-legal urban concept vehicles.)
Indeed, the inherent efficiency of the motor (as opposed to the combustion engine) was apparent in Drexel's result of 90 miles (144 kilometers) per kilowatt-hour. Using the standard that the U.S. Environmental Protection Agency has adopted for the new Chevy Volt, Nissan Leaf, and other electric vehicles, which equates 33.7 kilowatt-hours of energy to one gallon of gasoline, their result was the equivalent of 3,033 mpg (1,290 km/l).
Drexel's graduate student adviser, Pramod Abichandani, who accompanied the team to Houston and stood by through all the ups and downs of the weekend, was thrilled. "I'm going to give them a stellar report," he said, marveling at the problem-solving the students engaged in for their battery and their circuitry. "That is real-world engineering! To see undergraduate students do that is so great."
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.
"The grand winner is always the internal combustion category," 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."
Stumbling blocks like that didn't deter students like the members of Drexel's Green Dragon team. "You have to start somewhere," said Erlich.
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