A solar car is a solar vehicle used for land transport.
Solar cars combine technology typically used in the aerospace, bicycle, alternative energy and automotive industries. The design of a solar vehicle is severely limited by the amount of energy input into the car. Most solar cars have been built for the purpose of solar car races. Since 2011 also solar-powered cars for daily use on public roads are designed List of solar cars (with homologation).
Solar cars are often fitted with gauges as seen in conventional cars. To keep the car running smoothly, the driver must keep an eye on these gauges to spot possible problems. Cars without gauges almost always feature wireless telemetry, which allows the driver's team to monitor the car's energy consumption, solar energy capture and other parameters and free the driver to concentrate on driving.
Solar cars depend on photovoltaic cells to convert sunlight into electricity. Unlike solar thermal energy which converts solar energy to heat for either household purposes, industrial purposes or to be converted to electricity, PV cells directly convert sunlight into electricity. When sunlight (photons) strike PV cells, they excite electrons and allow them to flow, creating an electrical current. PV cells are made of semiconductor materials such as silicon and alloys of indium, gallium and nitrogen. Silicon is the most common material used and has an efficiency rate of 15-20%.
The solar array consists of hundreds of photovoltaic solar cells converting sunlight into electricity. In order to construct an array, PV cells are placed together to form modules which are placed together to form an array. The larger arrays in use can produce over 2 kilowatts (2.6 hp).
The solar array can be mounted in several ways:
- horizontal. This most common arrangement gives most overall power during most of the day in low latitudes or higher latitude summers and offers little interaction with the wind. Horizontal arrays can be integrated or be in the form of a free canopy.
- vertical. This arrangement is sometimes found in free standing or integrated sails to harness wind energy. Useful solar power is limited to mornings, evenings, or winters and when the vehicle is pointing in the right direction.
- adjustable. Free solar arrays can often be tilted around the axis of travel in order to increase power when the sun is low and well to the side. An alternative is to tilt the whole vehicle when parked. Two-axis adjustment is only found on marine vehicles, where the aerodynamic resistance is of less importance than with road vehicles.
- integrated. Some vehicles cover every available surface with solar cells. Some of the cells will be at an optimal angle whereas others will be shaded.
- trailer. Solar trailers are especially useful for retrofitting existing vehicles with little stability, e.g. bicycles. Some trailers also include the batteries and others also the drive motor.
- remote. By mounting the solar array at a stationary location instead of the vehicle, power can be maximised and resistance minimized. The virtual grid-connection however involves more electrical losses than with true solar vehicles and the battery must be larger.
The choice of solar array geometry involves an optimization between power output, aerodynamic resistance and vehicle mass, as well as practical considerations. For example, a free horizontal canopy gives 2-3 times the surface area of a vehicle with integrated cells but offers better cooling of the cells and shading of the riders. There are also thin flexible solar arrays in development.
Solar arrays on solar cars are mounted and encapsulated very differently from stationary solar arrays. Solar arrays on solar cars are usually mounted using industrial grade double-sided adhesive tape right onto the car's body. The arrays are encapsulated using thin layers of Tedlar.
Some solar cars use gallium arsenide solar cells, with efficiencies around thirty percent. Other solar cars use silicon solar cells, with efficiencies around twenty percent.
The battery pack in a typical solar car is sufficient to allow the car to go 250 miles (400 km) without sun, and allow the car to continuously travel at speeds of 60 mph (97 km/h).
The motors used in solar cars typically use less power than a toaster, about 2 or 3 horsepower, yet solar cars can attain the same speed as a typical family car (100 miles per hour (160 km/h)).
The two most notable solar car races are the World Solar Challenge and the North American Solar Challenge, overland road rally-style competitions contested by a variety of university and corporate teams.
The World Solar Challenge features a field of competitors from around the world who race to cross the Australian continent, over a distance of 3,000 kilometres (1,900 mi). Speeds of the vehicles have steadily increased. So, for example, the high speeds of 2005 race participants led to the rules being changed for solar cars starting in the 2007 race.
The American Solar Challenge, previously known as the 'North American Solar Challenge' and 'Sunrayce USA', features mostly collegiate teams racing in timed intervals in the United States and Canada. This race also changed rules for the most recent race due to teams reaching the regulated speed limits. The most recent American Solar Challenge ran from July 14-21, 2012, from Rochester, New York to St. Paul, Minnesota. The next race is expected to be run July 21-28, 2014 from Austin, Texas to St. Paul, Minnesota.
The Dell-Winston School Solar Car Challenge is an annual solar-powered car race for high school students. The event attracts teams from around the world, but mostly from American high schools. The race was first held in 1995. Each event is the end product of a two-year education cycle launched by the Winston Solar Car Team. In odd-numbered years, the race is a road course that starts at the Dell Diamond in Round Rock, Texas; the end of the course varies from year to year. In even-numbered years, the race is a track race around the Texas Motor Speedway. Dell has sponsored the event since 2002.
The South African Solar Challenge is an epic, bi-annual, two-week race of solar-powered cars through the length and breadth of South Africa. Teams will have to build their own cars, design their own engineering systems and race those same machines through the most demanding terrain that solar cars have ever seen. The 2008 race proved that this event can attract the interest of the public, and that it has the necessary international backing from the FIA. Late in September, all entrants will take off from Pretoria and make their way to Cape Town via the N1, then drive along the coast to Durban, before climbing the escarpment on their way back to the finish line in Pretoria 10 days later. In 2008 the event was endorsed by International Solarcar Federation (ISF), Fédération Internationale de l'Automobile (FIA), World Wildlife Fund (WWF) making it the first Solar Race to receive endorsement from these 3 organizations.
There are other distance races, such as Suzuka, Phaethon, and the World Solar Rally. Suzuka is a yearly track race in Japan and Phaethon was part of the Cultural Olympiad in Greece right before the 2004 Olympics.
Guinness World Records recognize a land speed record for vehicles powered only by solar panels. This record is currently held by the University of New South Wales with the car Sunswift IV. Its 25-kilogram (55 lb) battery was removed so the vehicle was powered only by its solar panels. The record of 88.8 km/h (55.2 mph) was set on 7 January 2011 at the naval air base HMAS Albatross in Nowra, breaking the record previously held by the General Motors car Sunraycer of 78.3 kilometres per hour (48.7 mph). The record takes place over a flying 500 metres (1,600 ft) stretch, and is the average of two runs in opposite directions.
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- List of solar car teams
- List of solar cars (with homologation)
- Electric boat
- Frisian Solar Challenge
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