Solar Electric

Electric vehicles use electric motors instead of an internal combustion engine to provide motive force. Solar-powered vehicles (SPVs) use photovoltaic (PV) cells to convert sunlight into electricity. The electricity goes either directly to an electric motor powering the vehicle, or to a special storage battery. PV cells produce electricity only when the sun is shining. Without sunlight, a solar-powered car depends on electricity stored in its batteries.

Since the 1970s, inventors, government, and industry have invested their time, skill, and knowledge to develop solar-powered cars, boats, bicycles, and even airplanes.

In 1974, two brothers, Robert and Roland Boucher, flew an extremely lightweight, remote-controlled, pilotless aircraft to a height of 300 feet. It was powered by a PV array on the wings. In 1975 an improved version flew to 17,000 feet. (The U.S. Air Force funded the development of these aircraft with the hope of using them as spy planes.) In the early 1980s, Paul MacCready and his son developed a sun-powered plane, which crossed the English Channel at an average speed of 50 mph and a height of 12,000 feet. NASA supported the development of the "Pathfinder," a remote-controlled, 100 foot long "flying wing" weighing less than 600 pounds. It is almost completely covered by a thin-film PV array. This PV system produces electricity to operate small motors, propellers, and flight control devices that move and steer the craft. The Pathfinder, with its ability to fly to altitudes as high as 80,000 feet, could be the precursor to solar-powered aircraft that can stay aloft for months as alternatives to space-based remote sensing satellites.

Perhaps Ed Passerini built the first totally solar-powered car in 1977. It was small, lightweight, and cost relatively little. Solar cars equipped with advanced technology have been built with the backing of large automobile manufacturers, including General Motors (GM), Ford, and Honda.

Because solar cells produce electricity only when the sun is shining, SPVs are not practical for daily use. Most SPVs with built-on PV arrays are used only as research, development, and educational tools, and/or to participate in the various SPV races held around the world. These races, such as the World Solar Challenge (Australia), the Tour de Sol (Switzerland), the American Tour de Sol, and the American Solar Cup, serve as proving ground for new solar vehicle technologies, and help expose the public to the idea of solar energy as a power source. Students, engineers, and other inventors throughout the world compete in these races, often setting new records for distance, speed or fuel efficiency.

PV cells are being used in some prototype EVs to extend their driving range. These are often referred to as solar-assist electric vehicles. In the case, the vehicle receives only a small amount of their electricity from solar energy, and uses conventional methods of recharging batteries.

Although solar energy is an unlimited resource, it is not always available when it’s needed. To convert and store solar energy, an array of PV cells can be built onto the vehicle body itself, or fixed on a building or a vehicle shelter to charge the electric vehicle’s battery while it is parked.

SPVs that have a built-on PV array differ from conventional vehicles (and most EVs) in size, weight, and shape. The car must be extremely efficient. Lightweight structural materials, such as aluminum or lightweight composites, improve performance. They are usually built to carry very little – one or two people. Some use no batteries; others use lightweight silver-zinc batteries. The chassis of GM’s Sunraycer, a prototype SPV that has won many solar car races, weighs only 14 pounds; the entire shell weighs less than 100 pounds; and the total weight of the vehicle, without the drive, is 390 pounds. While most developers use crystalline silicon PV cells, GM has used more efficient and more costly gallium arsenide cells.

A large amount of surface area is needed on the car to rely one hundred percent on solar power. The Sunraycer has a 90-square-foot curved solar array integrated into the teardrop-shaped body of the car. John Mitchell Systems designed an SPV with a PV array integrated into two vertical airfoils. These act as a sail to provide aerodynamic thrusts. (In tests, the vehicle achieved 30 miles per hour suing wind power alone.) Ford and other auto companies have designed tiltable arrays that track the sun.

Because an SPV has few moving parts, service requirement are less than for conventional cars. An SPV does not have an internal combustion engine, liquid fuel tank, fuel lines, carburetor, spark system, muffler, or pollution-control equipment. No timing belts, water pumps, radiators, fuel injectors, or tailpipes are required. No tune-ups, emissions-control adjustments, oil changes, or oil filter replacements are needed.

Lightweight silver-zinc batteries are expensive and need to be recycled after only a few charging cycles. Nickel-metal-hydride batteries may last up to 100,000 miles.

The primary safety concern with the development of a prototype vehicle or vehicle altered by hobbyists – as the majority of SPVs are – is that of design and an ability to adequately test the vehicle. If meant for road use, the final design must be road worthy. Proper attention must be paid to all aspects of vehicle design, including steering, suspension, breaks, rollover protection for the driver, proper seatbelts and seating, properly secured motors and batteries, and adequate chassis strength and durability. All prototypes and modified vehicles must be properly tested before operating on-road.

As with all electric vehicles, lethal levels of electricity may be present in the battery pack, so it should be treated with the same caution and respect as a full fuel tank in an internal combustion vehicle.

The first American Solar Cup was held in September 1988 in Visalia, California, with the winning car clocking speeds up to 85 mph. Electric vehicles are very quiet.

A vehicle completely covered with solar cells receives only a small amount of solar energy each day, and converts an even smaller amount of that to useful energy. State-of-the-art PV cells are only about 20 efficient.

The efficiency of solar cars is measured in watt-hours per mile, instead of miles per gallon. Efficient vehicles have traveled a mile on less energy than a 100-watt light bulb consumes in one hour. (For a gasoline-powered car to achieve comparable efficiency, it would need to get 500 miles per gallon.)

To store solar-generated electricity, some SPVs use silver-zinc batteries, which have both advantages and disadvantages when compared with lead-acid batteries. Silver-zinc batteries are lighter, are more efficient, and accept higher rates of charging. They are very expensive, however, and may be charged and discharged (cycled) only a few times before they become unusable and require recycling.

Of all vehicle types, those relying on solar energy have the least impact on the environment. Since there is no internal combustion engine and no combustion takes place, there are no emissions. Added emissions are not produced by power plants, since SPVs do not rely on utility-generated electricity.

Thanks to the Northeast Sustainable Energy Association (NESEA) for providing this information.

To learn more about electric vehicles, visit the Electric Vehicle Association of the Americas. Easy Breathers also has a profile of electric vehicles expert Michael Hackleman.