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October 7, 2013
Sun-powered speed: Stanford's student-built solar car to race across Australian outback
The all-student Stanford Solar Car Project has taken its latest solar-powered racecar, Luminos, to Australia to test its mettle in the Bridgestone World Solar Challenge.
By Bjorn Carey
Members of the Stanford Solar Car Project joined competing teams from around the world at a special media event at the Hidden Valley Sports Complex in Darwin, Australia, on Oct. 4. (Photo: Mark Shwartz, Stanford University)
The 2,000-mile drive across the Australian outback is on some of the world's most grueling roads. In many places, the single-lane highway that traverses the center of the continent is barely better than a dirt road, peppered with potholes and bumps. Drivers must also stay out of the way of "road trains" – 200-ton trucks towing up to four trailers – and the occasional wandering herd of cattle or emu.
It's a place where fire tornadoes – literally tornadoes that have sucked up a wildfire – are not an uncommon sight.
The trip is difficult enough on its own, but a team of Stanford engineering students is attempting to do it in a hand-built car without using a drop of fuel.
Luminos, the teams' lightweight, teardrop-shaped car, is topped with solar panels that generate all the electricity the car needs for its trans-Australian trip.
The sleek racer is the latest vehicle designed by the Stanford Solar Car Project, an independent group of students that has been building and racing solar-powered racecars since 1989. The students are pitting Luminos against more than 40 other teams of solar cars in this year's Bridgestone World Solar Challenge.
The race, which runs north to south from Darwin to Adelaide, is held every two years as an effort to spur innovation in high-performance, efficient solar-powered car design. The Stanford team finished 11th in the race in 2011, in large part because the team attempted too many high-reward technological risks, which ultimately led to numerous glitches during the race.
With Luminos, project director Wesley Ford, '13, who graduated this year with a degree in economics, said the team aimed to maximize efficiency, but never at the cost of reliability.
Thus far, that approach is paying off. After two days of driving and nearly 1,000 miles into the race, the team is sitting in fourth place. It's the top American entry and is trailing only the perennial top finishers.
A souped-up solar car
The group designed and built its own electric motors, which convert solar energy to horsepower with 97-percent efficiency, easily topping the 93-percent efficiency rate offered by the best off-the-shelf units. Narrow wheels and tires specially designed for solar-car racing reduce the car's road resistance, and bicycle-style disc brakes provide lightweight, superior braking power.
The handcrafted carbon fiber body is light and nimble, yet exceptionally sturdy. Weighing in at just 375 pounds, it's a cinch for a couple of students to tip on its side at the end of the race day, orient the solar panels to the horizon and soak up the final rays of the setting sun.
Wind tunnel testing at a facility typically reserved for NASCAR teams showed that the car's low profile and smooth lines give it less than half the aerodynamic drag of a cyclist.
The team's proximity to, and relationship with, Silicon Valley companies creates a mutually beneficial opportunity for the students to get their hands on cutting-edge, and even prototype, materials, while providing extreme-usage feedback to the companies.
For example, the car's thin plastic solar modules are layered with a prototype plastic material from 3M that has microscopic prism-like ridges on its surface; this reduces reflection and allows the solar units to absorb more light when the sun is low on the horizon, said Greg Hall, a Stanford senior majoring in computer science and the engineering team leader.
"It also reduces the aerodynamic drag of the car a little bit," said Hall. "It's a cool double-benefit material."
All these design elements are for naught, though, without careful race-day energy management. Although Luminos has easily topped 80 mph in road tests, it will need to stick to speeds in the 50-mph range to both stay below the speed limit – this is mandated, and there are time penalties for exceeding posted speed limits –and conserve the car's stored energy.
A group of students will follow Luminos in a trail car equipped with computers that show the solar car's real-time energy collection and expenditures. The trail crew will analyze the data to make sure that the car is running at top speeds when sun exposure is at its greatest, while still banking enough energy to keep the car zipping along when the sun is low on the horizon, or if clouds come out.
"They'll run the data through their computers, and radio me with the best speed to set the cruise control to preserve the battery," said Jason Trinidad, a prospective mechanical engineering major and one of the drivers. "Then I just have to keep the car on the road."
This is no simple feat. The front wheels of normal cars are slightly toed-in, which makes it easier to keep the car in a straight line. This set-up increases drag, however, so Luminos' wheels are set in parallel, causing the car to jitter around more than usual.
"You have to pay constant attention to the road, and make lots of continuous, small adjustments," Trinidad said. "It's grueling, but fun."
Winning isn't everything
The students take pride in being one of the few teams in the world that isn't directed by a faculty member or full-time researcher. Teams with this type of year-round leadership typically focus on perfecting a particular design, with students providing incremental improvements from year to year.
The Stanford Solar Car Project takes a less restrictive approach.
"We try to build a radically new car every two years," Ford said. "Generation to generation, we see a lot of innovation and ideas coming from the students as we take the best new technologies and try to integrate them into a new design."
Starting from scratch doesn't necessarily lead to consistent top finishes – it limits the amount of pre-race testing – but Ford said it provides a more engaging experience for students.
"By starting fresh, we get to see the whole process, from the early stages of laying out the design, all the way up to manufacturing the parts, body and electronics, testing them, and revising those designs," Ford said. "You get the full experience of integrating a system from the ground up, and we find that this really complements our academic experience."
Starting from scratch requires a much greater time commitment from students, said Hall, who has been involved in the project since before he started at Stanford. But the level of engagement and the one-on-one mentoring he receives from professors and from team alumni – many of whom are now involved in the solar or automotive industries – keeps him coming back for more.
Running a two-year project with a million-dollar budget produces challenges that simply can't be replicated by weeks-long classroom exercises, Hall said. Building a solar car puts students face-to-face with the same types of computer science, mechanical engineering and electrical engineering challenges that industrial engineers must overcome.
"I feel like I've done professional-grade work for my entire time as an undergrad," Hall said.
"The true value goes beyond doing well," Hall said. "I mean, that's how you measure performance, but at the end of the day it's about the great engineers that we put out. We're assured that each of the engineers we put out into the world will really know a lot about designing high-efficiency vehicles."
For more Stanford experts on solar energy and other topics, visit Stanford Experts.