One of the great dreams of the alternative energy revolution is to create a car that runs totally on solar power. Unfortunately, with our present state of technological development, cars that run only on sunlight must remain a dream…for now. The principle behind a solar vehicle is to create enough energy to drive the car by converting sunlight into electricity through the use of photovoltaic cells. The problem is that the amount of energy available to run a vehicle depends on the surface area of the car itself. More surface area exposed to the sun means more sunlight and therefore more electricity, but it also means added weight. And added weight means more electricity is needed to move that weight. There is an optimal ratio of surface area to operating weight, and at the present time that ratio only allows for one person per vehicle. Most solar-only vehicles seen in competitions and at universities are basically glorified bicycles, with no room for passengers or cargo.
By putting batteries onboard the vehicle, additional stored energy is available for the motor, but once again the batteries contribute to the overall weight of the vehicle. There is also another problem to consider, however, if you leave the batteries off in order to conserve weight. If there are no batteries at all on the vehicle, then it can only operate when the sun is shining. This means that if you are out on a date in your solar car, you have to be home before sunset! And don’t even think about driving on a rainy day!
Races for total solar vehicles like the World Solar Challenge (www.wsc.org.au/) and the North American Solar Challenge (www.americansolarchallenge.org/) promote the use of solar vehicles by offering a yearly competition where the best and brightest (no pun intended) of solar engineers throughout the world can show their stuff. While the designs on these state-of-the-art solar vehicles are aesthetically pleasing, they leave a lot to be desired in terms of practical highway use. The main problem with having the solar cells attached directly to the vehicle is that photovoltaics work best when facing the sun. Since vehicles constantly move, the cells on these cars will very rarely be at an optimal angle for power generation. In terms of efficiency, if solar power cells were to be used at all, it would be better for them to remain in a stationary location facing the sun. So if solar-powered vehicles were to become a reality, it would be far more practical to charge the vehicle by leaving the solar panels at a fixed location. These solar panels would then have a hookup that could be attached to the car to charge the onboard battery pack when the vehicle is not in use.
Although the days of onboard photovoltaic vehicles are still a long way off in the future, that doesn’t mean that we can’t operate electric vehicles by using sunlight. It just means having the solar panels as a separate ‘filling station,’ no different from buying gasoline today.
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