How students from the University of Minnesota built a solar car and what solar cars could mean for our future
Ivana Truong
On the scale of bad things that can happen to a solar car, a battery fire is the worst. Battery fires mean toxic fumes, dangerous byproducts and the possibility of “thermal runaway.” A phenomenon as frightening as the name, this means the lithium fire’s byproducts ignite, causing more cells to ignite, causing more byproducts to ignite, and on and on. Very quickly, you have a 1,500 degree chemical fire that can only be put out by smothering it with a truckload of sand.
If you’re lucky enough to have any part of the battery left after the fire, the cells are prone to spontaneously burst into flames, so they’re too dangerous to use. Rather than directly powering car systems, the solar panels mainly charge the battery, which then powers the car. Without a battery, the car — named Freya — couldn’t even start, let alone race.
“The battery starts on fire and your first thought is, we’re done. Our car is gonna be a pile of ash on the side of the freeway in Colorado,” said Kailey Johnson, a passenger in the car at the time of the fire.
Run entirely by students, the University of Minnesota Solar Vehicle Project designs, builds and races solar-electric cars. SVP is overwhelming at the best of times, but in summer 2021 before the race, building Freya became all-consuming. Until the week before the team left for the five-day, 900-mile race, it was a genuine question whether our team — of which I was a part of — could finish Freya in time.
From 1 p.m. to 11 p.m., you could walk into our St. Paul workshop and find at least a couple people working on the car. I also spent a few late nights at the workshop installing doors and working on the interior. By the time we were ready to leave for the race, the trash cans were filled with energy drinks consumed during all-nighters and we had a designated metal block for crushing the cockroaches that appeared after midnight. Quite literally, our blood, sweat and tears went into this car.
In the everyday building and designing of the car, sustainability rarely enters the picture.
However, ask any team member why they joined and what they want to do and sustainability never leaves the picture. Building a solar car from computer model to road-ready gives members an incomparable hands-on experience and the skills to innovate in a field that really matters. Transportation is the number one contributor to greenhouse gas emissions in Minnesota and makes up 29 percent of emissions nationally. While solar electric vehicles (solar EVs) are not a feasible solution now, engineers are continually improving the technology in creative ways.
There will probably never be a 100 percent solar-powered consumer car. Since the exterior of a car has an extremely limited surface area, there just isn’t the space for a solar array that produces enough power to drive even on cloudy days.
For these reasons, despite being about half the weight of a regular car, Freya still needs to supplement with external charging.
However, solar can provide extra power to EVs, increasing range and offering flexibility when there aren’t chargers nearby. A start-up called Lightyear aims to make solar-supplemented EVs more accessible. The company was founded by alumni of the Eindhoven University solar car team and they plan to release their second EV in 2022. Future solar arrays using different combinations of materials, textures and mirrors to improve solar cell efficiency could be used to make cars that are able to drive daily commutes on only solar power.
The day before the battery fire had been the best day of the race. In the morning, we had done our pre-race day rituals, involving praying to the sun and touching a sink basin the team brings to every race.
The whole day, we were making good distance, driving about 60 mph. Members were monitoring the estimated percentage of battery remaining, the state-of-charge (SOC). As the end of the day approached, it looked like we wouldn’t have enough charge to reach the next checkpoint. Still, the team captain made the call that we would try. Singing along to songs like “Here Comes the Sun’’ and “Mr. Blue Sky” the whole way for luck, the team drove through the beautiful hills of Colorado. While somehow reading at negative percent battery, Freya crested the last big hill before the stop and everyone knew we would make it.
Jacob Bunzel, the electrical engineering member watching our battery capacity, transmitted over the radio, “Watch out for wormholes opening up behind us. We are now below zero SOC! We’ve broken the laws of physics!”
We coasted into the stop in the last minutes of the race day and everyone ran out of their car towards Freya to celebrate.
When the battery burst into flames, a member from the following vehicle ran towards it with a fire extinguisher and put it out. With the fire put out so quickly and because the battery was outside the car, nobody was hurt and the car wasn’t damaged. Still, the battery was too dangerous to use or transport. Until well-past midnight, electrical members were disassembling the battery on the side of the freeway. Everyone was exhausted and knew it was impossible to continue the race without a battery.
The morning after the fire, instead of getting up at 6 a.m. and rushing to pack away tents, distribute lunches and check the car before heading to the starting point, we let each other sleep in and quietly gathered in groups to eat cold pizza from the night before.
While at the campsite, the electrical engineers went into the trailer where we stored our supplies and inspected a previous car’s battery pack. The old battery had hardware and battery cells that hadn’t been integrated with Freya’s software. Its condition was unknown because it had already been raced over 3,000 miles and the battery didn’t meet the current race regulations.
Retrofitting an old battery pack was a daunting task, but they got to work. After the race, while reflecting on the process, Bunzel said, “No matter what stage you are in building the solar car, someone makes a mistake and they keep going.”
By 1 p.m., the team drove to the local school where race officials had set up the next start point. Bunzel and several other members spent the whole morning and rest of the day coding and retrofitting the old battery to comply with race regulations. After speaking to race officials to clarify requirements and clear the electrical systems for driving, we were ready to head out the next day. About to depart for the final leg of the race, Freya was temporarily rechristened Feonix.
The next day we went slowly to conserve the lower-capacity battery and made it to the finish line. It wasn’t the finish any of us had pictured, but we celebrated the resiliency of our team and of Feonix, who rose, like her namesake, “Phoenix,” from the ashes to finish the race.