SPECIAL! SCIENCE CONTESTS: Sunrayce '93
Will your next car run on the power of the sun? It's possible, argue the college students who harnessed the sun's energy to compete in Sunrayce '93. Student engineers and scientists from 34 colleges and universities designed and built solar-powered cars, then raced them from Texas to Minnesota. Teams had just seven days to make the 1,102-mile trip, a rigorous challenge when sunlight is the only source of power, and a stormy day can create disaster. The winning strategy in this race is ultimately keyed to the weather.
Notes & Discussion
Activity: The Ultimate Zeppelin
Report From the Field: Betsy White, University of Michigan
NOTES & DISCUSSION
- For participating students, Sunrayce '93, sponsored by the U.S. Department of Energy, capped a two-year engineering program. What design challenges and limitations did they face? (Among others: designing the shape of the car to minimize weight and reduce drag; deciding where to mount the solar panels for maximum energy gain; figuring out how to use available energy.)
- Explain and illustrate how a solar car works. (Photovoltaic cells on the car collect and convert energy from the sun into electric energy stored in batteries.) How is it different from an electric car? (Electric cars run on batteries that are recharged by electricity.) What is the main disadvantage? (Sunshine is not always available.) What are some of the advantages? (It requires no gasoline; is nonpolluting; can travel thousands of miles on the energy of a hair dryer.)
- First place winner Maize & Blue from the University of Michigan went on to race across the harsh Australian Outback in the 1993 World Solar Challenge, in which solar-powered vehicles a distance of 1900 miles in average heat of over 110 degrees F.
- Brainstorm other current and potential uses of solar power and other sources of renewable energy. Would you drive an electric or a solar-powered car? Why or why not? What are the energy issues involved?
ACTIVITY: THE ULTIMATE ZEPPELIN
Design and build a lighter-than-air vehicle that is solar-powered, self-propelled and self-guided. Then race it against other vehicles. Your challenge is to put a new spin on lighter-than-air vehicle (LTAV) locomotion. You will need a helium tank for the activity. "The Ultimate Zeppelin" is completely open-ended and relies on your innovation. References on the physics of flight will be helpful. Make sure to review the parts of a lighter-than-air vehicle, including the envelope, rudder and gondola.
LTAVs have fascinated people since 1709, when Father Bartolomeu de Guismao of Portugal flew the first model hot-air balloon. LTAVs can be filled with hot air or helium. Their unique property of floating in air is explained by thermal expansion and gas density differences. Hot-air balloons move with air currents, while airships (blimps) use gasoline-powered engines.
Here is a list of suggested materials. You do not have to use all of them; you may wish to add others.
- plastic trash bags
- dry cleaner bags
- packaging tape
- rubber cement
- glue gun
- white glue
- solar cell(s)
- electric motor(s)
- propeller(s) or small fan blade(s)
- light-duty electrical wire
- balsa wood or foam core board
- rubber bands
- ballast (sand, lead shot, etc.)
- plastic straws
- hair dryer
- The LTAV envelope must be gas-tight and may be any shape with a volume of up to 0.5 cubic meters. It must have a fill tube that can accept either hot air from a hair dryer or helium from a pressurized bottle. A name or logo must be clearly printed on two sides of the envelope.
- The LTAV must have a frame and/or gondola to hold solar cells, motor(s) and ballast. The frame must have a moveable rudder.
- A "tether" must be attached to the underside of the LTAV. The tether can only be touched before launch or if the LTAV goes out of control.
- The LTAV must be powered by solar cell(s), motor(s) and propeller(s).
- The course should be no longer than 50 meters nor shorter than 25.
- Competition requires 3 flights per heat. LTAVs must start separated by a space of 5 meters. The best time in any of the 3 flights of a heat wins.
- You may make adjustments during flights. The audience must remain still during flights since air currents can affect speed and direction.
- If it is necessary to touch the tether after launch, you automatically lose that one flight of the heat. Touching someone else's tether disqualifies you from the competition.
- Used ballast must be collected and stored for proper disposal.
- The fastest flight time of the last heat wins the competition.
- Test your design often.
- Use hot air for testing purposes, helium for the competition.
- If a design doesn't work, scrap it and redesign.
- Select a wide open area for your competition. A gym is ideal. If you hold the competition outside, allow for breezes and winds. A still day would be perfect.
- Hint: the smallest, lightest, most compact design will probably win the race.
- Suggested Reference: Consult The Way Things Work by David Macaulay (Houghton-Mifflin, 1988).
- Use "The Ultimate Zeppelin" activity to introduce Archimedes' principle, density, thermal expansion and the physics of flight. You can also use the story to launch discussions of the sun and solar energy.
- Compare contemporary cars with a typical solar-powered vehicle. For example, first place winner, the Maize & Blue, weighs 500 lbs. and operates on 3 horsepower. The cars in Sunrayce '93 ran about 143 miles per day; how far is that in km? At an average speed of 30 miles per hour, how long would it take a solar car to travel that distance?
REPORT FROM THE FIELD: BETSY WHITE, UNIVERSITY OF MICHIGAN
Betsy White, a member of one of the Sunrayce teams profiled on Frontiers, is a sophomore at the University of Michigan, where she's studying to be a mechanical engineer. She's taking this semester off to go with the team to Australia, where Maize & Blue-named for the school colors-faces a tough challenge. "For the race in Australia, we have solar cells that are more efficient than those we were allowed to use for Sunrayce," explains Betsy, "but they're not as efficient as some of the competition, which includes corporate teams like Honda and Toyota R&D from Japan."
In Australia Betsy is working on team communications and logistics. While in the U.S., she acquired the all-important radios, which are used to maintain communication with the driver. "We need constant communication to plan strategy and to make sure everything is going OK," Betsy explains. "We also use radio modems to transmit voltage and current data through telemetry between the car and our chase van."
Betsy first became involved in the Sunrayce program because she was interested in working with solar cells, and decided to attend a meeting of the project's power team. "At the meeting, they said they needed someone to buy diodes. I raised my hand and said, 'I'll do it if you tell me what they are.' So I worked on getting the diodes and finding a sponsor for them, and then spent a lot of time soldering the solar cells for the Sunrayce car."
She plans to stay involved in the project until she graduates and is already working on the team that will design the next solar-powered car. "In addition to the engineering challenges, I've learned a lot of people skills," says Betsy, "such as how to call up people at corporations and ask them for materials and financial support for the project. These people are more than willing to help, and the contacts can help with future job leads. Overall, it's a great experience."
Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.