University Students Race to Advance Solar Car Technology
For several decades, teams of students from universities around the world have been competing to build the best solar car, gaining valuable skills and building relationships along the way.
Electric vehicles (EVs) continue to gain popularity, yet issues around charging speed, range, and accessibility are still deterrents to wider acceptance. What if an EV could charge simply by being in the sun? Thousands of university students from around the world have been exploring exactly that through solar car competitions. The two main challenges are the Bridgestone World Solar Challenge in Australia, a 3,000+ kilometer north to south race across the outback, and the American Solar Challenge, a 1,500-2,000 mile race from Tennessee to Wyoming.
Luke Granger, an electrical and computer engineering student at the University of Illinois Urbana-Champaign, and Nihal Singh Gulati, a sophomore dual aerospace and electrical engineering/computer science major at UC Berkeley, are gearing up to race at the 2024 American Solar Challenge in July. Granger has been on the Illini Solar Car team for three years and is currently the team’s race manager. Gulati is the electrical sub-team lead for CalSol. Their teams have 60-80 active members who are regularly working on the car’s design or systems each week. “Everything from start to finish, at least in our team, is designed, built, tested, and raced by undergraduates. It’s a widely diverse group of people from all different colleges and majors. We have quite a few engineers but we also have people in architecture, physics, early childhood education, kinesiology, and business. Anybody can join the team,” Granger said.
Illini Solar Car vehicle, University of Illinois Urbana-Champaign
Team members have many opportunities for hands-on learning of new skills. “We have sub teams for dynamics, for the shell of the car, for battery, and solar. We have people who specialize in composites and in welding of the roll cage. These are all skills that we’ve gained through the club, which is sort of the amazing thing,” said Gulati.
Illini Solar Car makes a new car about every two years. “There’s no requirement for the competition to make a new car. However, the regulations are constantly adapting, so some things that you designed your car for in the past might be against safety or other regulations in the future,” he said.
CalSol vehicle, UC Berkeley
Design considerations
The first design consideration is aerodynamics. The surface of the car must also be as smooth as possible to minimize drag. Teams typically opt for one of two shapes: bullet or catamaran. The Illini Solar Car vehicle is a single-seater bullet design. It is narrow, with a very long tail to maximize aerodynamics while accommodating a four-square-meter solar panel array. The CalSol car is an asymmetrical catamaran design, with the driver on one side.
The next decision is the number of wheels. “The primary benefit of three wheels is that you lose the weight of all that suspension for a fourth wheel, as well as the need for another set of brakes and all that goes with that,” said Granger.
Minimizing weight and maximizing power and efficiency factor into every aspect of the design. “We optimize for lightness of the car, we optimize for aerodynamic drag, we optimize for maximum solar power coming in and battery capacity. When you’re recovering this little power, every kilogram of weight matters. Every bit of loss from the electrical system matters,” said Gulati.
Another consideration concerning efficiency is the impact of anything that covers the solar cells. On these competition vehicles, the cells are completely exposed to maximize efficiency. Glass or plastic or film of any kind adds protection and would be necessary in a production vehicle, but reduces efficiency.
The build phase
The teams rely on industry partners to construct their cars. “Our vehicle shells have to be laid up in carbon fiber. First, we need a giant foam mold, and that requires a giant CNC [computer numerical control] machine to create the shape of the car. We do our carbon fiber layup by hand and bring it to a company called Flying S in central Illinois that bakes and cures the shell,” said Granger. “Then the car is wrapped for aesthetics and to smooth out any imperfections in the surface of the carbon fiber to improve the aerodynamics. The carbon fiber isn’t perfectly smooth like you’d see on actual racecars, but we do the best we can with students.”
Phoenix Contact supplies components to multiple solar car teams. Shown here are some of the most requested items. (L to R) SACC-DSIV-M12MS-5CON-L 90 – Device connector rear mounting, MC 1,5/16-STF-3,5 – PCB connector, SAC-5P-M12MS/ 1,0-920/M12FS – Bus system cable, and SAC-5P-M12T/2XM12 VP – T distributor.
Phoenix Contact connectors are used for the CAN bus that does all the communication between the different driver systems. “One of the unique quirks of our car is instead of having an accelerator pedal, we have an electronic encoder on our steering wheel. The driver moves that encoder, which tells the PCB inside the steering wheel what message to send back to the motor controller over that CAN bus to control the car,” Granger said.
Illini Solar Car used Molex MicroFit connectors for the low voltage connections for all the ancillary systems like the lights and the horn, and anything that uses a low voltage wire. An emergency stop throughout the vehicle allows them to cut all power if necessary. “Our boards all have Molex SL connectors. We crimp them ourselves,” said Gulati. Andersen Power connectors, available from RS, are used for high voltage connections, like the battery disconnect, the motor disconnect, and the solar array disconnect.
Driving innovation
The underlying goal of these competitions is to push innovation in this field, Granger said. The single-occupant vehicles, such as the one made by Illini Solar Car, are mainly engineering proof-of-concept. The multi-occupant vehicles in the race are also scored on practicality; they are bigger and resemble cars you would see on the road, Granger explained. They can charge off the wall as well as with the solar panels. Solar alone doesn’t yet have the efficiency to provide highway speed for driving to work and back every day. The most likely way to use solar in the near term is to supplement EV charging. “As we continue the research, we can potentially find something that works even better than silicon cells. Once we can get something where the energy density is high enough on the roof of your car to extract enough energy from the sun to just drive whenever and wherever, that’s when we can start to see it roll out into mainstream.”
Areas for innovation are the battery chemistry, higher efficiency motor controllers, and maximum power point trackers, which convert the solar energy into energy the battery can use. “Because solar fluctuates, and therefore, what voltage and what current you’re going to get, you want to optimize for the point where you’ll get the most power,” Granger said.
Running on solar power
The engineering challenges and requirements of a solar car vary greatly from an internal combustion engine. “When racing a solar car, you’re very much constrained by power. Gasoline has extremely high energy density that will get you where you need to go and you can hit really high speeds with it because you don’t need to worry too much about the energy consumption. Input from the solar panels is going to be a lot less than what a traditional car might run on,” Gulati said.
Typically, the big question with solar is what happens when there is no sun? “We are a solar electric car, but basically, it is like an electric vehicle on the road today. We still have a battery and the same kind of motor. The difference is we take our energy from the sun rather than from the wall, so our battery is smaller than what you would see in an EV because we’re constantly charging. On a sunny day, we can travel 30 to 40 miles per hour and get all our power from the solar panel without discharging the battery. When there are clouds, we have a few hours to drive on that battery pack. We have some buffer to continue to drive without peak sunlight or even at night,” said Granger. “The battery also allows the car to go faster than is possible just from the sun. The car can go up to 67 miles per hour, but in the way we have it configured, the sun can’t supply that much power. The battery offsets that.”
Solar panels mounted on houses or other stationary surfaces are angled to get the most sun. Accomplishing this on a moving vehicle, can be a little trickier. “We have a lot to think about because you want to shade the solar cells the least amount of time possible,” said Gulati. “In the American Solar Challenge, we’re going to be driving east to west, so the sun will more often be on our left. Our driver sits on the right side of the car to avoid shading parts of the cells. When we stop the car we have special stands that will prop the solar panel up at an angle such that we’re at the optimal power generation angle.”
Watch: The YouTube Original BWSC Documentary
Watch: The American Solar Challenge: Road race across the Oregon Trail
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