Solar Car Designs Race Toward `Market' Goal
BOSTON — SOLAR cars are no longer just for show.
Races between ultralightweight cars impractical for daily use have prodded great leaps in technology for use in a variety of other applications.
Four areas where solar-car designers have consistently striven to improve efficiency are batteries, motors, motor controllers, and solar arrays.
* "Batteries are the Achilles heel of the electric car," says Robert Wills, of Northeast Sustainable Energy Associates, which sponsors a solar race every year. Currently, the batteries are so heavy and produce such limited power that the cars deliver very few miles for each charge of the batteries and develop little power. This severely restricts the cars' marketability, he notes.
"If we could achieve twice the energy-to-weight ratio of the best [conventional] lead-acid batteries," he says, electric vehicles "would be easily marketable."
Car companies are working on a nickel-metal-hydride battery that should have two to four times the energy of conventional batteries, Dr. Wills says. When these become commercially viable, they may appear in everything from lap-top computers to rechargeable hand-tools to electric and internal-combustion cars.
* Motors, too, have come a long way since the early days of solar-car racing. A number of companies have developed specialized electric motors for portable installations that are being used in many solar race cars.
"The biggest technology improvement with our motors is that they are brushless," so they are lighter, have less friction, and require no maintenance, says Kevin Barnes, project manager for solar and hybrid electric-vehicle programs with Unique Mobility of Golden, Colo.
"Where our motors shine is any place where limited power is [available], and some degree of mobility is needed," Mr. Barnes says. He notes that the motors are used in a planned BMW electric car, an electric hybrid bus under development for Ontario, Canada, and wheelchairs.
* Another technological need electric cars have spotlighted is for controllers to run electric motors at varying speeds. Until now, Wills points out, industrial electric motors have been run at full speed based on the cycle of alternating current, then a valve has been installed, for example to cut the flow of a water pump to the needed amount. The speed of an electric-car motor, on the other hand, needs to be variable along with traffic conditions.
"By putting variable-speed drives on motors," Wills says, "we could save enormous amounts of energy in industry."
* Electric cars using solar charging need to take maximum advantage of the sun in a variety of conditions. The problem, says Anita Rajan, president of Solectria Corporation of Arlington, Mass., is that power from solar cells depends on temperature as well as light. More light hitting the cells increases the current they produce, but higher temperature lowers the voltage.
To equalize these restrictions, solar cars use a maximum-power point tracker to maintain the cells' peak efficiency. (In addition to solar-assisted electric cars, Solectria produces power trackers and its own brushless motors and motor controllers.)
The power trackers also have applications in stationary water pumps and in solar power for homes, Wills says.