A solar car is a solar vehicle for use on public roads or race tracks. Solar vehicles are electric vehicles that use self contained solar cells to power themselves from sunlight. Solar vehicles typically contain a rechargeable battery to help regulate and store the energy from the solar cells and capture kinetic energy from the vehicle during braking. Some solar cars can be plugged into external power sources to supplement the power of sunlight used to charge their battery.
Solar cars combine technology typically used in the aerospace, bicycle, alternative energy and automotive industries. The design of solar vehicles always emphasizes energy efficiency to make maximum use of the limited amount of energy they can receive from sunlight. Most solar cars have been built for the purpose of solar car races. However several prototypes of solar cars designed for use on public roads have been designed and built. As of November 2021, no solar cars have reached production, although several are planned to enter production in 2022.
Solar cars depend on a solar array that uses photovoltaic cells (PV cells) to convert sunlight into electricity. Unlike solar thermal energy which converts solar energy to heat, PV cells directly convert sunlight into electricity. When sunlight (photons) strike PV cells, they excite electrons and allow them to flow, creating an electric current. PV cells are made of semiconductor materials such as silicon and alloys of indium, gallium and nitrogen. Crystalline silicon is the most common material used and has an efficiency rate of 15-25%.
The first model solar car invented was a tiny 15-inch vehicle created by General Motors employee, William G. Cobb. Designated the Sunmobile, he displayed it in 1955 at the Chicago, Powerama convention. It was made up of 12 selenium photovoltaic cells and a small electric motor.
The solar array consists of hundreds of 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 six ways:
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).
To keep the car running smoothly, the driver must monitor multiple 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 thereby freeing the driver to concentrate on driving.
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. For example, the high speeds of 2005 race participants led to the rules being changed for solar cars starting in the 2007 race and 2014 also.
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 took place from July 6 to the 22nd, 2018 from Omaha, Nebraska to Bend, Oregon. 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 a 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, WGC (WSR/JISFC/WSBR) and the World Solar Rally in Taiwan. Suzuka and WGC 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 Sky Ace TIGA from the Ashiya University. The record of 91.332 km/h (56.75 mph) was set on 20 August 2014 at the Shimojishima Airport, in Miyakojima, Okinawa, Japan. The previous record was 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.
The first solar family car was built in 2013. Researchers at Case Western Reserve University, have also developed a better solar car which can recharge more quickly, due to better materials used in the solar panels.
Chinese solar panel manufacturer Hanergy plans to build and sell solar cars equipped with lithium-ion batteries to consumers in China. Hanergy says that five to six hours of sunlight should allow the cars’ thin-film solar cells to generate between 8-10 kWh of power a day, allowing the car to travel about 80 km (50 mi) on solar power alone. Maximum range is about 350 km (217 mi).
In June 2019 the solar-electric Lightyear One was announced. Designed by former engineers from Tesla and Ferrari, the car’s hood and roof are composed of solar panels. The vehicle also charges on regular electric power as well as fast-charging stations. In September 2021, the company Lightyear was reported to have raised enough money to bring the vehicle to limited production, at a cost of €149,000, delivering the first units in 2022.
In August 2019, Aptera Motors announced a funding campaign for a solar-powered, very efficient "Never Charge" EV, the Aptera, with up to a 1000 mile range. That funding campaign was successful and the Aptera prototype was shown and the EV launched on December 4, 2020.
In July 2020, the German car manufacturer Audi signed an MOU with an Israeli start-up Apollo-Power for development plan to incorporate the company proprietary lightweight flexible panels into Car parts. Apollo-Power's Agenda is to turn every car in the world to become Solar.
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