by Terri Bartling
Imagine a solar-powered electric vehicle, it almost appears to be floating, barely touching the road's surface. As it passes, all that is heard is the faint "hum" of an electric motor, the "whir" of spoked wheels and the "whoosh" of rushing air through its aerodynamic design. Sound a little far-fetched? Think again.
Chad Travnicek, son of Gary and Janice Travnicek of rural Bal-
ed build just such a car. lent at the South Dakota
_ __ Mines and Technology at Rapid City, Chad was also a' member of the support crew for the Solar Rolar, SDSM&rs first, entry in the USA Sunrayce. The competition is designed to challenge science, mathematics, and engineering students and foster scientific innovation and creativity across North America.
In January 1994, 65 colleges submitted their proposal, detailing their solar car project. Forty collegiate teams would be selected for USA Sunrayce 95, the third such event. A panel of event sponsors evaluated each proposal and selected the 30 highest ranking teams. These seeded teams would automatically gain entrance to the race provided they could meet a minimum performance requirement. The other ten slots would be awarded during a pre-race qualifying event.
SDSM&Ts team, dubbed the South Dakota Solar Motion Team, would consist of over 100 students, from freshman to graduate students, by the time the proposal was submitted, financing was secured and the vehicle was built. SDSMT, divided into three major groups; logistics, financing, and engineering, met with faculty advisors on a regular basis but decisions were ultimately made by the students.
Tb defray the cost of the solar cells, the largest expenditure for
the project, the team instituted an Adopt-a-Cell program. Individual sponsors could make contributions in Increments of $20 to adopt a solar cell. In exchange, the sponsor's name was written inside the shell, directly beneath their adopted cell and they received a Solar Rolar T-shirt.
Their proposal was one of only 6 new teams selected as a seeded team to the race. This means that the Solar Rolar team had to displace a team that had already competed in a previous Sunrayee.
Students spent from ten to well over 40 hours a week working on various aspects of the project. "Many teams have members that take a year off from classes to participate. I don't think anyone at SDSM&T did that, but we tried to take a lighter load," said Chad. "A couple of teams also drove cars that had been built by a sponsor instead of student teams."
How does a solar-powered car work? Energy from the sun, in the form of solar radiation, hits-the photovoltaic array, commonly referred to as solar cells or a solar panel, and is converted to electrical energy, called solar insolation. The energy is fed into a controller that channels the electrical energy to a brushless DC motor to drive the vehicle, or to batteries to store the energy. If one were to think of the electrical energy as 'gas," th* batteries act as a "gas tank" and tfie solar cells are the "gas station,1 providing a constant
Below, the Solar Rolar, without the solar cell canopy. Five of the eight batteries are housed in the rectangular box located between the wheels. The other three batteries are mounted on the driver's side of the car.
At right, SDSM&T President Dr. Richard Gowen waves the green flag as the Solar Rolar starts the race in Indianapolis on June 20.
flow of "gas' as long as the sun is out.
Because solar-powered vehicles can use electricity generated by the solar cells instead of depending on power from batteries that must be recharged by plugging into an available power outlet like electrical cars, the batteries are only used to supplement power to the solar-powered vehicle. Obviously, on the days when the sun doesn't shine, the batteries are used as the primary source of power.
On a sunny day, the solar cells on the Solar Rolar will generate a maximum of about 1000 watts, which is approximately the power needed to run a typical hair dryer. Given the vehicle's aerodynamic properties, Solar Rolar will need about 1800 watts to operate at 55 miles per hour. The remaining 800 watts will be^drawn from the batteries.
At the end of each day's route, the team will use the remaining daylight to recharge Solar Rolar's batteries, replacing all of the energy consumed during that day's course.
That's the scenario for a sunny day...however, anyone can design a solar-powered car that can run on a sunny day.
On a cloudy -day, instead of direct, concentrated sunlight, the energy from the sun decreases and becomes diffused. The Solar Rolar has cells mounted on the side skirts so that on a cloudy day,
when the solar insolation decreases to 30% of that on a sunny day, the solar cells on the Solar Rolar will still produce approximately 60% of its peak power.
The Solar Rolar will pay an aerodynamic penalty for this additional cell space on a sunny day, but hopes to be compensated by improved performance on cloudy days.
Since each team will be trying to maximize the amount of energy produced from the same amount of sun, the energy management strategy used by each teams plays an important factor in who wine the race. A team meteorologist will be responsible for predicting the amount of energy that can be produced each day. Foul weather will certainly have a tremendous impact on the strategy used by each team.
As a mechanical engineering student. Chad joined the solar motion team just after the proposal had been submitted. Working in a rented building, about 20 miles from campus, they used large blocks of styrofbam to build a mold for the belly pan and nose cone of the Solar Rolar. A mold, made from lumber, was used to design the shell, the part of the car that the solar cells are attached to.
The molds were waxed and then draped with two layers of carbon-fiber mesh. After resin was applied to the mesh, a layer of 3/8"
high-temp foam Vas added, followed by an additional two layers of mesh. The mold was baked to ^harden the resin and then the parts of the car were ready to be painted.
The design and shape of each car varies from the Solar Rolar to a round design that looks like a space ship to a shape that looks more like a helicopter or a beetle. Some of the vehicles have three wheels while others have four wheels.
Optimum aerodynamics and the placement of the solar cells were considerations used to design the body shape of the Solar Rolar. Analyses also included the effect of strong croeswinds on the overall vehicle drag as well as vehicle stability.
About 800 test miles were put on the car after it was built. This is very important for the team to be able to successfully compete with their solar-powered car. "I think this had a lot to do with the low amount of maintenance required on our car. We had to change a tire on the road once and that was about it," commented Chad.
In mid-June, 1995, over 45 cars arrived in Indianapolis to meet performance standards and vie for the ten remaining slots to enter the race. ^
Only 38 cars' passed the
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Bcrutineering and gathered at the starting line for the USA Sunrayce 95 on June 20. The victor would be the solar-powered car completing the official course, from Indianapolis, IN to Golden, CO, with the lowest cumulative elapsed time. The race schedule covered about 122 miles each day, '„ 'arriving in Golden on June 29. ' A typical day on the race route begins at 5:30 am. Around 6:00 am, team members push the car out of the impound area into a grassy field and put the shell on the charging rack to catch a few morning rays. The rack is turned and titled towards the sun to receive the maximum amount of radiation. The solar cells are •prayed with distilled water to keep them cool and increase their efficiency in generating power.
While the shell is charging, team members make any necessary repairs and take turns Having breakfast.
At 8:15 am, the drivers meet with race officials to hear about changes to the race route and information on road construction.
The team includes four drivers, working in pairs with an exchange at the mid-day break. On
their off day, they travel ahead to scout out the next day's course.
An all-team meeting follows in which overall standings and official results of the previous day are handed out. Other announcements, such as a car drop-
i ping out of the race, are made at
I this time.
1 Ifs now 8:30 am. Time for the support crew to gas up vehicles and buy groceries for the mid-day break. The other two meals of the day are provided by the race coordinators.
At 9:45 am, the car is pushed or driven to die an area near the start line to await their turn. Lead and chase vehicles must also be ready in line or the trio forfeits its position and drops to the back of the line. On the first day, start-
The shell of the Solar Rolar is placed on a charging rack everymorningandafternoon. The rack is tilted to catch the maximum rays as teammate Zach Spencer sprays distilled water on the cells to cool them and make them more efficient.
The Solar Motion Team tyfts the solar cell canopy off the Solar Rolar to prepare for another day in the Sunrayee 95.
ing positions were determined by performance during the qualifying race rounds of the previous week.
The cars advanced to the start line in one-minute intervals, led by California State Polytechnic University at Pomona at 10:00 am. Solar Rolar was the tenth car to leave Indianapolis led by a scout vehicle and followed by the chase van, as were all the solar-powered cars.
Connected by radio, the scout or
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Copyright 1995, Gregory Times Advocate. The original work may be protected by U. S. copyright law (Title 17, United States Code), which governs reproduction, distribution, public display, and other uses of protected works. Some uses may be legal with permission from the copyright holder if the use is fair use or within another legal exemption. The user of this work is responsible for compliance with the law.
Devereaux Library. South Dakota School of Mines and Technology.