SOLAR VEHICLES

First Solar Power Car - July 2004 marked the 20th anniversary since Greg Johanson and Joel Davidson set The First Guinness World Record for a 100% solar powered car. In 1984 the solar electric vehicle was retired and taken apart, but the solar array is still producing electricity for an off-grid home.
(adapted from the June 1986 in Photovoltaics International magazine)
To demonstrate the principles of a solar electric car at an open-air fair, Greg Johanson wired some Photovoltaic (PV) cells onto a toy electric train. Seeing the attention this little solar train got as it sped around its track, we thought that a solar vehicle would attract more interest in PV. That's what inspired us to build our first solar energy car.
Our first vehicle was a lightweight three-wheeler with a 1/2 horsepower, 60V, DC motor. Five small, 20 amp-hour, 12V batteries wired in series were used for motive power. Five 35W solar modules, mounted like a canopy, charged the batteries. The vehicle could travel over 40 mph (64 km/h); under 30 mph (48 km/h) it was actually fun to ride. Under direct solar power in full sun, the vehicle would go 6 mph (9.6 km/h).
All the time and money put into the vehicle was lost when it was stolen one evening, but we had been bitten by the solar power car "bug." We wanted to build something bigger and better and different than the battery-powered vehicles that were fairly commonplace. Our experience and all the solar powered car information we had indicated that a solar-only solar powered car was possible.
After research and discussions with bicyclists and engineers, we sketched plans that built on the design ideas developed by members of the International Human Powered Vehicle Association compromises had to be made to accommodate the solar array. The Sunrunner solar power car, our aptly named vehicle, was designed for speed, but we wanted the array to double as a portable power plant for more practical demonstrations.
Construction proceeded slowly as we were paying for the project out-of-pocket with no sponsor or grant. We used lightweight chrome-molly steel for Sunrunner's frame. The design provided enough flex to eliminate the need for suspension hardware. We used wheels designed for tandem racing bicycles and light-weight wheelchairs. No batteries were used on Sunrunner; the solar array would be the entire power plant.
As the speed run would be a straight track, high speed maneuvering was unnecessary, so Sunrunner was designed with a larger turning radius, simplifying mechanics. Our experience with the solar electric car taught us to design for the open, quiet roads in the desert, not the city. There are no restrictions on experimental vehicles, but city driving is out. The danger of an accident caused by curious drivers and onlookers was too great. Every time we took Sunrunner on the street, traffic would stop and people would stare.
Our first brakes were racing bicycle disc brakes which worked too well. They locked the wheels on our lightweight vehicle, causing tire burn-through. We compromised and used bicycle caliper brakes, which we jokingly called "slower-downers."
The power train was a simple one-wheel chain and sprocket drive from the motor shaft to one axle. We used the same model 1/2 horsepower motor as our first vehicle because it was so efficient. Our experience with the motor on solar powered water pumping systems and our first solar power car indicated that it would give us the best performance.
For power, we used 24-44W 1 x 4 ft (305 x 1219 mm) PV modules with no metal frames, back sheets or interconnect boxes to minimize weight. The array was connected in series parallel for nominal 60V operation. Early street testing was a problem as the motor did not have the starting torque necessary to get us across intersections in traffic. In addition, terminal velocity would not be reached until we traveled 5/8 mile (1 km). Again, it was time for a design compromise.
We changed to a less efficient 1 horsepower motor. A dc-to-dc converter was used for the vehicle which changed the current/voltage of the array to provide high current and low voltage needed to get the motor started. Once rolling, the converter would shift to higher voltages.
For the lowest drag coefficient, the driver should be recumbent, face forward, stomach down. We opted for a more conventionally seated recumbent position, giving the driver better visibility, more comfort, and somewhat better safety. Lying back in the solar array solar energy car, speeding along close to the roadbed was a wonderful feeling.
To transport the solar electric vehicle, we modified a boat trailer by extending the frame 5 feet (1.5 m) and adding a plywood deck to which Sunrunner was strapped. Also on the deck were 16 golf cart type deep cycle batteries and a 2500 watt inverter. The combined solar vehicle array and trailer provided approximately 5 kWh/day of electricity with 16 kWh battery storage for loads up to 2.5 kW. The batteries and the inverter were not a part of the solar powered car, but were used for demonstrations.
Time and money were running out. Solar electric car testing was limited to one or two days per month on the relatively quiet desert roads near Palmdale, California. Friends were always willing to give a hand in exchange for a ride. Cruising along in the solar energy car at over 30 mph (48 km/h) with a safety car in front and behind was fantastic.
The solar electric vehicle performed as predicted. Wind resistance was not a factor as the frontal area was very small. Drag from the top and bottom surface of the solar array did affect speed, but nothing could be done about it. The tires were inflated to 120 pounds per square inch (psi) so the solar powered car rested on only 4 square inches (25.8 sq cm) of tire-to-road, reducing resistance significantly.
It was time for clocking by an official independent timer. The International Human Powered Vehicle Association, official timer for DuPont's award for the first bicycle to reach 65 mph (104.6 km/h), was willing and available. Unfortunately, the track they used was in one of the smoggiest places in Los Angeles. To make things worse, their timing device was set up right after two underpasses and the track was one-way going into a 12 mph (19.3 km/h) head wind.
Although conditions were far from optimal, on July 1, 1984, at Bellflower, California in 70% of full sun light, Sunrunner was driven by Mary Anne Reynolds, achieving 24.7 mph (39.8 km/h). This speed was well under our near 40 mph (64.36 km/h) desert runs, but was officially clocked by independent observers needed to submit result to the Guinness Book of World Records. The 1986 edition of the Book of Records listed Sunrunner as the world's fastest "Solely Solar Powered Vehicle."
During 1984 and 1985, we had an open invitation to race any other solar powered car on land or in the air, but no one accepted our challenge. By 1986, a few other people had gotten into the fun of solar power car activities. Peter Rubie had an aborted attempt at a cross-country run. Art Boyt made a cross-country run, although his vehicle used battery storage. In Europe, Mercedes Benz spent a lot of money to build a racer. The solar electric car craze had caught on.
Sunrunner solar energy car appeared at energy trade shows and outdoor exhibits. We couldn't afford to participate in international shows, but Sunrunner was on television and in movies worldwide. Expo 86 organizers showed Sunrunner on a 360 degree dome screen in a film on travel. In keeping with the travel theme, Expo organizers thought a solar powered car would make a good exhibit. Greg jumped at the chance to build another solar vehicle for the Vancouver Expos. The third solar power car had 12 PV modules, six deep-cycle batteries and a 2 horsepower series wound motor. Batteries give it a range of 40 miles (64 km). It took the solar array three days to recharge the batteries, but batteries gave the vehicle "punch." It could "lay rubber" and go over 60 miles per hour (96 km/h).
The Future of Solar Electric Vehicles looks bright. With the increase in fuel prices we are approaching cost effectiveness at $ 3.50 per gallon. With the advent of the Hybrid vehicles it looks like a great entrance point for additional energy inputs such as solar energy. It may not be only source of energy but today it can be 10-20%, tomorrow 20-40% and as oil and fuels become harder to recover and more costly to its users options must be found. For those who choose to think ahead and try to set a example of hope for the future we offer a real option today with the Pruis PV Kit to make a small 10-20% step in the right direction. They maybe baby steps but they are in the right direction and if we are lucky enough to show some real demand for such a product some car mfg. might take notice and make it a real option off the showroom floor.