This summer, engineering students from across the nation will compete to see who can best harness the power of the sun and win a solar-powered race cross-country.
The race, a balance of speed and efficiency known as the American Solar Challenge (ASC), kicks off next week with qualifying rounds in Texas. Dedicated undergraduates from NUsolar, a Northwestern University McCormick School of Engineering student group, will take the car they designed and built down south to give the challenge their best shot.
We caught up with NUsolar’s president, fourth-year mechanical engineering student Phil Dziedzic, to learn more about the ASC, their car, and the team’s priorities off the race track.
Let’s start with the ASC. How do you qualify?
Before you’re allowed to begin the cross-country journey, you must complete a series of tests in a process called “scrutineering.” Some of these tests are stationary, where the officials inspect the car’s mechanical and electrical systems to ensure that everything meets the standards set by race officials. Others tests are dynamic, where we prove the car's ability to brake, its agility, and its stability at high speeds.
To qualify the drivers on your team, they need to demonstrate that they can exit the car quickly in an emergency – from being fully strapped-in to having both feet on the ground – in ten seconds. We’ll try to qualify four drivers total.
These tests culminate in the actual race qualifier, known as the Formula Sun Grand Prix (FSGP). While the cross-country ASC is held every other year, the track-based FSGP takes place annually. It is a race around a track in Texas, and teams must complete a certain number of laps before moving on to the ASC. Your starting position in the ASC is based on how fast you finished your laps.
In years without the ASC, the FSGP itself is the main event. Last summer, NUsolar proudly took third place.
Once your car and your team qualifies, you move directly on to the ASC. Tell me about the race.
The race is 1200 miles, starting in Tulsa, Oklahoma, and ending in Naperville, Illinois. It takes place on real roads—secondary highways—so we travel in a convoy with a car in front and in back of the solar car.
It’s kind of like the Tour de France. Teams stop at checkpoints and stage stops each night over the course seven racing days. The times from each leg of the race are added together. We start each day around 9:00 AM, and end at 6:00 PM. Each driver can only drive for six hours at a time. Ideally, there would only be one driver swap each day, but more realistically something will go wrong and we’ll need to pull over to fix it, so we’ll swap drivers at that point.
Even with six-hour legs, it’s rough. We definitely don’t design the cars for comfort. The cabin is pretty compact, pretty tight, and there’s no radio or air conditioning. Everything has to be powered by the battery pack.
Tell me more about the car, and how it works.
The car is completely electric. It runs on a 96-volt DC motor that is 97% efficient. The motor is powered by a battery pack that uses 520 lithium ion cells (the same batteries used in laptops and cell phones), because they’re light-weight and energy-dense. Finally, the outside of the car is covered by 468 solar cells made of mono-crystalline silicon (cut from single crystal of silicon) that are all 21% efficient. The sun hits the array [of solar cells] and generates electricity, which goes into the battery and powers the car.
How long can you drive the car before recharging?
The faster you go, the more energy you use. Without a chance to plug-in to charge, the car can run at about 30 mph for between three and four hours. The sun helps you, but you’re usually using part of your battery power because the sunlight is never ideal. Solar cells want direct sunlight, so throughout the day you get less and less power depending on the angle of the sun.
[When designing the outside of the car], you really have two options. You can have a flat array, where the top of the car is flat (which works best for the solar cells), or you can curve it for aerodynamics. It’s a balancing act—an optimization project.
In the 2008 race, we drove about 30 mph for the majority of the time. Our strategy this year is to go a little faster – about 45 mph – where possible.
The ASC is just one of NUsolar’s priorities. What else do you focus on?
First and foremost, we offer undergraduate students training to become professional engineers. We get real hands-on experience on an advanced and complex design project—we build, problem-solve, fix things, and move on. That’s our most important goal.
But another big goal is outreach—to teach the community about alternative energy. We bring the car to middle schools, high schools, companies, museums, and green events to show that solar is a reliable and viable form of energy.
After this year’s race, what’s next for NUsolar?
We’re already finalizing designs for our next car (the sixth NUsolar car), and we plan to start construction in the fall. We have some clever ideas to give us a better competitive advantage for the race next summer.
Can you share any of these?
One of the things we need to fight is aerodynamic drag. Our plan is to make the next car about three times more aerodynamic, which will make it more efficient.
Interested in keeping up NUsolar on their trip across the country? You can follow the team’s Twitter feed, which will be updated throughout the trip, on their blog here.