Solar car racing
Encyclopedia
Solar car racing refers to competitive races of electric vehicle
s which are powered by solar energy
obtained from solar panels on the surface of the car (solar car
s). The first solar car race was the Tour de Sol
in 1985 which led to several similar races in Europe, USA and Australia. Such challenges are often entered by universities to develop their students' engineering and technological skills, but many business corporations
have entered competitions in the past. A small number of high school teams participate in solar car races designed exclusively for high school students.
and the North American Solar Challenge. They are contested by a variety of university and corporate teams. Corporate teams participate in the races to give their design teams experience of working with both alternative energy sources and advanced materials. University teams participate in order to give their students experience in designing high technology cars and working with environmental and advanced materials technology. These races are often sponsored by government or educational agencies, and businesses such as Toyota keen to promote renewable energy sources.
team won this challenge for a 3rd time in a record average speed of 102.75 km/h over a distance of 3000 km, followed by the Australian Aurora (92.03 km/h) and the University of Michigan
(90.03 km/h). The increasingly high speeds of the 2005 race participants has led to the rules being changed for future solar cars starting in the 2007 race.
The 20th Anniversary race of the World Solar Challenge ran in October 2007. Major regulation changes were released in June 2006 for this race to increase safety, to build a new generation of solar car, which with little modification could be the basis for a practical proposition for sustainable transport and intended to slow down cars in the main event, which could easily exceed the speed limit (110 km/h) in previous years. The winner again was the Nuna 4 team averaging 90.87 km/h. The winner in the Adventure Class (driving under old rules) was the Ashiya University Solar Car Project team averaging 93.57 km/h.
The American Solar Challenge was sponsored in part by several small sponsors. However, funding was cut near the end of 2005, and the NASC 2007 was cancelled. The North American solar racing community worked to find a solution, bringing in Toyota as a primary sponsor for a 2008 race. Toyota has since dropped the sponsorship. The last North American Solar Challenge was run from June 13–21, 2010, from Dallas, Broken Arrow, OK to Naperville, IL. The race was won by the University of Michigan Solar Car Team. Michigan has won the race the last three times its been held, and six times out of the ten it has been held, establishing itself as the American dynasty of solar car racing.
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.
recognise a land speed record for vehicles powered only by solar panels. The current record is held by General Motors with their car Sunraycer. The record of 33 km/h was set in 1987.
The record takes place over a flying 1000 stretch, and is the average speed of 2 runs in opposite directions.
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 kilograms (55.1 lb) battery was removed so the vehicle was powered only by its solar panels. The record of 88.8 kilometres per hour (55.2 mph) was set on 7 January 2011 at the naval air base 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 (1,640.4 ft) stretch, and is the average of two runs in opposite directions.
in Canberra
.
The record was beaten by Dick Smith
and the Aurora Solar Vehicle Association
racing in the Aurora Q1
The current record was set in 2007 by the UNSW Solar Racing Team with their car Sunswift III mk2
, bicycle
, alternative energy
and automotive industries. Unlike most race cars, solar cars are designed with severe energy
constraints imposed by the race regulations. These rules limit the energy used to only that collected from solar radiation, albeit starting with a fully charged battery pack. Some vehicle classes also allow human power input. As a result optimizing the design to account for aerodynamic drag, vehicle weight, rolling resistance and electrical efficiency are paramount.
A usual design for today's successful vehicles is a small canopy in the middle of a curved wing-like array, entirely covered in cells, with 3 wheels. Before, the cockroach style with a smooth nose fairing into the panel was more successful. At lower speeds, with less powerful arrays, other configurations are viable and easier to construct, e.g. covering available surfaces of existing electric vehicles with solar cells or fastening solar canopies above them.
stores surplus solar energy produced when the vehicle is stationary or travelling slowly or downhill. Solar cars use a range of batteries including lead-acid batteries, nickel-metal hydride batteries (NiMH
), nickel-cadmium batteries (NiCd), lithium ion batteries
and lithium polymer batteries.
Power electronics may be used to optimise the electrical system. The maximum power tracker adjusts the operating point of the solar array
to that voltage which produces the most power for the given conditions, e.g. temperature. The battery manager protects the batteries from overcharging. The motor controller controls the desired motor power. Many controllers allow regenerative braking, i.e. power is fed back into the battery during decceleration.
Some solar cars have complex data acquisition systems that monitor the whole electrical system, while basic cars show battery voltage and motor current. In order to judge the range available with varying solar production and motive consumption, an ampere-hour meter multiplies battery current and rate, thus providing the remaining vehicle range at each moment in the given conditions.
A wide variety of motor types have been used. The most efficient motors exceed 98% efficiency. These are brushless three-"phase" DC, electronically commutated, wheel motors, with a Halbach array
configuration for the neodymium-iron-boron magnets, and Litz wire
for the windings. Cheaper alternatives are asynchronous AC or brushed DC motors.
Solar cars usually have three wheels, but some have four. Three wheelers usually have two front wheels and one rear wheel: the front wheels steer and the rear wheel follows. Four wheel vehicles are set up like normal cars or similarly to three wheeled vehicles with the two rear wheels close together.
Solar cars have a wide range of suspensions
because of varying bodies and chassis. The most common front suspension is the double wishbone suspension
. The rear suspension is often a trailing-arm suspension as found in motor cycles.
Solar cars are required to meet rigorous standards for brakes. Disc brakes are the most commonly used due to their good braking ability and ability to adjust. Mechanical and hydraulic brakes are both widely used. The brake pads or shoes are typically designed to retract to minimize brake drag, on leading cars.
Steering systems for solar cars also vary. The major design factors for steering systems are efficiency, reliability and precision alignment to minimize tire wear and power loss. The popularity of solar car racing has led to some tire manufacturers designing tires for solar vehicles. This has increased overall safety and performance.
All the top teams now use wheel motors, eliminating belt or chain drives.
Testing is essential to demonstrating vehicle reliability prior to a race. It is easy to spend a hundred thousand dollars to gain a two hour advantage, and equally easy to lose two hours due to reliability issues.
Designing a solar array is more than just stringing a bunch of cells together. A solar array acts like many very small batteries all hooked together in series. The total voltage produced is the sum of all cell voltages. The problem is that if a single cell is in shadow it acts like a diode
, blocking the current for the entire string of cells. To design against this, array designers use by-pass diodes in parallel with smaller segments of the string of cells, allowing current around the non-functioning cell(s). Another consideration is that the battery itself can force current backwards through the array unless there are blocking diodes put at the end of each panel.
The power produced by the solar array depends on the weather conditions, the position of the sun and the capacity of the array. At noon on a bright day, a good array can produce over 2 kilowatts (2.6 hp). A 6 m2 array of 20% cells will produce roughly 6 kW·h (22 kJ) of energy during a typical day on the WSC.
Some cars have employed free-standing or integrated sails to harness wind energy. Many races, including the WSC
and NASC, consider wind energy to be solar energy, so their race regulations allow this practice.
and will need smaller lighter brake
s and other suspension
components. This is the virtuous circle when designing lightweight vehicles.
which can be usefully simplified to the performance equation
for long distance races, and values seen in practice.
Briefly, the left hand side represents the energy input into the car (batteries and power from the sun) and the right hand side is the energy needed to drive the car along the race route (overcoming rolling resistance, aerodynamic drag, going uphill and accelerating). Everything in this equation can be estimated except v. The parameters include:
Note 1 For the WSC the average panel power can be approximated as (7/9)×nominal power.
Solving the long form of the equation for velocity results in a large equation (approximately 100 terms). Using the power equation as the arbiter, vehicle designers can compare various car designs and evaluate the comparative performance over a given route. Combined with CAE
and systems modeling, the power equation can be a useful tool in solar car design.
This is significant to designers, who seek to maximize energy input to a panel of solar cells (often called an "array" of cells) by designing the array to point directly toward the sun for as long as possible during the race day. Thus, a south-north race car designer might increase the car's total energy input by using solar cells on the sides of the vehicle where the sun will strike them (or by creating a convex array coaxial with the vehicle's movement). In contrast, an east-west race alignment might reduce the benefit from having cells on the side of the vehicle, and thus might encourage design of a flat array.
Because solar cars are often purpose-built, and because arrays do not usually move in relation to the rest of the vehicle (with notable exceptions), this race-route-driven, flat-panel versus convex design compromise is one of the most significant decisions that a solar car designer must make.
For example, the 1990 and 1993 Sunrayce USA events were won by vehicles with significantly convex arrays, corresponding to the south-north race alignments; by 1997, however, most cars in that event had flat arrays to match the change to an east-west route.
that relays vehicle performance data to a following support vehicle, which can provide the vehicle's driver with an optimum strategy.
In addition, elevation changes over a race route can dramatically change the amount of power needed to travel the route. For example, the 2001 and 2003 North American Solar Challenge route crossed the Rocky Mountains (see graph at right).
Electric vehicle
An electric vehicle , also referred to as an electric drive vehicle, uses one or more electric motors or traction motors for propulsion...
s which are powered by solar energy
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
obtained from solar panels on the surface of the car (solar car
Solar car
A solar vehicle is an electric vehicle powered completely or significantly by direct solar energy. Usually, photovoltaic cells contained in solar panels convert the sun's energy directly into electric energy. The term "solar vehicle" usually implies that solar energy is used to power all or part...
s). The first solar car race was the Tour de Sol
Tour de Sol
The Tour de Sol in Switzerland was the first rally for solar powered vehicles. It was carried out annually from 1985 to 1993. The first event started on June 25 in Romanshorn on the Lake of Constance, and finished on June 30 in Geneva. 72 vehicles started in two classes; over 50 finished...
in 1985 which led to several similar races in Europe, USA and Australia. Such challenges are often entered by universities to develop their students' engineering and technological skills, but many business corporations
Corporation
A corporation is created under the laws of a state as a separate legal entity that has privileges and liabilities that are distinct from those of its members. There are many different forms of corporations, most of which are used to conduct business. Early corporations were established by charter...
have entered competitions in the past. A small number of high school teams participate in solar car races designed exclusively for high school students.
Distance races
The two most notable solar car distance (overland) races are the World Solar ChallengeWorld Solar Challenge
The World Solar Challenge is a solar-powered car race which covers through the Australian Outback, from Darwin to Adelaide.The race attracts teams from around the world, most of which are fielded by universities or corporations although some are fielded by high schools...
and the North American Solar Challenge. They are contested by a variety of university and corporate teams. Corporate teams participate in the races to give their design teams experience of working with both alternative energy sources and advanced materials. University teams participate in order to give their students experience in designing high technology cars and working with environmental and advanced materials technology. These races are often sponsored by government or educational agencies, and businesses such as Toyota keen to promote renewable energy sources.
Support
The cars require intensive support teams similar in size to professional motor racing teams. This is especially the case with the World Solar Challenge where sections of the race run through very remote country. The solar car will travel escorted by a small caravan of support cars. In a long distance race each solar car will be preceded by a lead car that can identify problems or obstacles ahead of the race car. Behind the solar car there wil be a mission control vehicle from which the race pace is controlled. Here tactical decisions are made based on information from the solar car and environmental information about the weather and terrain. Behind the mission control there might be one or more other vehicles carrying replacement drivers and maintenance support as well as supplies and camping equipment for the entire team.World Solar Challenge
This race features a field of competitors from around the world who race to cross the Australian continent. In 2005, the Dutch Nuna 3Nuna
Nuna is the name of a series of manned solar powered vehicles that won the World solar challenge in Australia four times in a row, in 2001 , 2003 , 2005 and 2007...
team won this challenge for a 3rd time in a record average speed of 102.75 km/h over a distance of 3000 km, followed by the Australian Aurora (92.03 km/h) and the University of Michigan
University of Michigan Solar Car Team
The University of Michigan Solar Car Team is a 501 non-profit organization at the University of Michigan in Ann Arbor. It is the most successful solar car team in North America, having won the North American Solar Challenge six times and is currently the defending three time Champion...
(90.03 km/h). The increasingly high speeds of the 2005 race participants has led to the rules being changed for future solar cars starting in the 2007 race.
The 20th Anniversary race of the World Solar Challenge ran in October 2007. Major regulation changes were released in June 2006 for this race to increase safety, to build a new generation of solar car, which with little modification could be the basis for a practical proposition for sustainable transport and intended to slow down cars in the main event, which could easily exceed the speed limit (110 km/h) in previous years. The winner again was the Nuna 4 team averaging 90.87 km/h. The winner in the Adventure Class (driving under old rules) was the Ashiya University Solar Car Project team averaging 93.57 km/h.
North American Solar Challenge
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.The American Solar Challenge was sponsored in part by several small sponsors. However, funding was cut near the end of 2005, and the NASC 2007 was cancelled. The North American solar racing community worked to find a solution, bringing in Toyota as a primary sponsor for a 2008 race. Toyota has since dropped the sponsorship. The last North American Solar Challenge was run from June 13–21, 2010, from Dallas, Broken Arrow, OK to Naperville, IL. The race was won by the University of Michigan Solar Car Team. Michigan has won the race the last three times its been held, and six times out of the ten it has been held, establishing itself as the American dynasty of solar car racing.
The Dell-Winston School Solar Car Challenge
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. On 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. On even-numbered years, the race is a track race around the Texas Motor Speedway. Dell has sponsored the event since 2002.[1]South African Solar Challenge
The South African Solar ChallengeSouth African Solar Challenge
The South African Solar Challenge is an alternative fuel vehicle auto racing challenge in South Africa, with classes for hybrid vehicles, electric vehicles, solar vehicles, and biofuel-powered vehicles. The first challenge was run in 2008, and it will run every two years thereafter. The race...
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
Fédération Internationale de l'Automobile
The Fédération Internationale de l'Automobile is a non-profit association established as the Association Internationale des Automobile Clubs Reconnus on 20 June 1904 to represent the interests of motoring organisations and motor car users...
(FIA), World Wildlife Fund (WWF) making it the first Solar Race to receive endorsement from these 3 organizations.
Other races
- Formula-GFormula-GFormula-G or Turkish Solar Car Grand Prix is a solar car championship. The last race was done in Ankara, Turkey on 2007.The first and second positions in this year was held by the teams of Istanbul Technical University. The third place was held by Sakarya University. The 2006, and 2005 races were...
, a yearly track race in TurkeyTurkeyTurkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...
. - SuzukaSuzuka Circuit, Suzuka Circuit for short, is a motorsport race track located in Ino, Suzuka City, Mie Prefecture, Japan and operated by Mobilityland Corporation, the subsidiary of Honda Motor Co., Ltd..-Introduction:...
, a yearly track race in JapanJapanJapan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. - Phaethonhttp://www.phaethon2004.org, part of the Cultural Olympiad in GreeceGreeceGreece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
prior to the 2004 Olympics. - World Solar Rally2006 World Solar Rally in TaiwanThe 2006 World Solar Rally in Taiwan was a solar vehicle auto race held in September 2006 in Taiwan. Ten teams from five countries, most university-based, competed in a series of races around the island for the trophy.-Race:...
. - Eco-marathon Americas
Solar drag races
Solar drag races are another form of solar racing. Unlike long distance solar races, solar dragsters do not use any batteries or pre-charged energy storage devices. Racers go head-to-head over a straight quarter kilometer distance. Currently, a solar drag race is held each year on the Saturday closest to the summer solstice in Wenatchee, Washington, USA. The world record for this event is 29.5 seconds set by the South Whidbey High School team on June 23, 2007.Fédération Internationale de l'Automobile (FIA)
The FIAFédération Internationale de l'Automobile
The Fédération Internationale de l'Automobile is a non-profit association established as the Association Internationale des Automobile Clubs Reconnus on 20 June 1904 to represent the interests of motoring organisations and motor car users...
recognise a land speed record for vehicles powered only by solar panels. The current record is held by General Motors with their car Sunraycer. The record of 33 km/h was set in 1987.
The record takes place over a flying 1000 stretch, and is the average speed of 2 runs in opposite directions.
Guinness World Record
Guinness World RecordsGuinness World Records
Guinness World Records, known until 2000 as The Guinness Book of Records , is a reference book published annually, containing a collection of world records, both human achievements and the extremes of the natural world...
recognize a land speed record for vehicles powered only by solar panels. This record is currently held by the University of New South Wales
University of New South Wales
The University of New South Wales , is a research-focused university based in Kensington, a suburb in Sydney, New South Wales, Australia...
with the car Sunswift IV
Sunswift
The UNSW Solar Racing Team is a solar car racing team from the University of New South Wales. The team has built four cars since 1996...
. Its 25 kilograms (55.1 lb) battery was removed so the vehicle was powered only by its solar panels. The record of 88.8 kilometres per hour (55.2 mph) was set on 7 January 2011 at the naval air base in Nowra, breaking the record previously held by the General Motors
General Motors
General Motors Company , commonly known as GM, formerly incorporated as General Motors Corporation, is an American multinational automotive corporation headquartered in Detroit, Michigan and the world's second-largest automaker in 2010...
car Sunraycer
Sunraycer
The Sunraycer was a solar powered race car designed to compete in the world's first race featuring solar-powered cars. This race is now called the World Solar Challenge. The Sunraycer, a joint collaboration between General Motors, AeroVironment, and Hughes Aircraft, won the first race in 1987 by a...
of 78.3 kilometres per hour (48.7 mph). The record takes place over a flying 500 metres (1,640.4 ft) stretch, and is the average of two runs in opposite directions.
Australian Transcontinental (Perth to Sydney) Speed Record
The Perth to Sydney Transcontinental record has held a certain allure in Solar Car Racing. Hans Tholstrup (the founder of the World Solar Challenge) first completed this journey in The Quiet Achiever in under 20 days in 1983. This vehicle is in the collection of the National Museum of AustraliaNational Museum of Australia
The National Museum of Australia was formally established by the National Museum of Australia Act 1980. The National Museum preserves and interprets Australia's social history, exploring the key issues, people and events that have shaped the nation....
in Canberra
Canberra
Canberra is the capital city of Australia. With a population of over 345,000, it is Australia's largest inland city and the eighth-largest city overall. The city is located at the northern end of the Australian Capital Territory , south-west of Sydney, and north-east of Melbourne...
.
The record was beaten by Dick Smith
Dick Smith (entrepreneur)
Dick Smith, AO is an Australian entrepreneur, businessman, aviator, and political activist. He is the founder of Dick Smith Electronics, Dick Smith Foods and Australian Geographic, and was selected as the 1986 Australian of the Year.-Electronics:In 1968, Dick Smith founded electronics retailer...
and the Aurora Solar Vehicle Association
Aurora Solar Car
The Aurora Vehicle Association is a group of volunteers who are dedicated to achieving and demonstrating extreme efficiency in transport. Aurora was started in 1980 by building high-fuel-efficiency petrol-powered vehicles. Between 1983 and 1985 Aurora held the world record for fuel economy at...
racing in the Aurora Q1
The current record was set in 2007 by the UNSW Solar Racing Team with their car Sunswift III mk2
Vehicle design
Solar cars combine technology used in the aerospaceAerospace
Aerospace comprises the atmosphere of Earth and surrounding space. Typically the term is used to refer to the industry that researches, designs, manufactures, operates, and maintains vehicles moving through air and space...
, bicycle
Bicycle
A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....
, alternative energy
Alternative energy
Alternative energy is an umbrella term that refers to any source of usable energy intended to replace fuel sources without the undesired consequences of the replaced fuels....
and automotive industries. Unlike most race cars, solar cars are designed with severe energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
constraints imposed by the race regulations. These rules limit the energy used to only that collected from solar radiation, albeit starting with a fully charged battery pack. Some vehicle classes also allow human power input. As a result optimizing the design to account for aerodynamic drag, vehicle weight, rolling resistance and electrical efficiency are paramount.
A usual design for today's successful vehicles is a small canopy in the middle of a curved wing-like array, entirely covered in cells, with 3 wheels. Before, the cockroach style with a smooth nose fairing into the panel was more successful. At lower speeds, with less powerful arrays, other configurations are viable and easier to construct, e.g. covering available surfaces of existing electric vehicles with solar cells or fastening solar canopies above them.
Electrical system
The electrical system controls all of the power entering and leaving the system. The battery packBattery pack
A battery pack is a set of any number of identical batteries or individual battery cells. They may be configured in a series, parallel or a mixture of both to deliver the desired voltage, capacity, or power density...
stores surplus solar energy produced when the vehicle is stationary or travelling slowly or downhill. Solar cars use a range of batteries including lead-acid batteries, nickel-metal hydride batteries (NiMH
NIMH
NIMH or NiMH may refer to:*Nickel-metal hydride battery, a type of rechargeable battery*National Institute of Mental Health, a part of the United States National Institutes of Health...
), nickel-cadmium batteries (NiCd), lithium ion batteries
Lithium ion battery
A lithium-ion battery is a family of rechargeable battery types in which lithium ions move from the negative electrode to the positive electrode during discharge, and back when charging. Chemistry, performance, cost, and safety characteristics vary across LIB types...
and lithium polymer batteries.
Power electronics may be used to optimise the electrical system. The maximum power tracker adjusts the operating point of the solar array
Photovoltaic module
A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...
to that voltage which produces the most power for the given conditions, e.g. temperature. The battery manager protects the batteries from overcharging. The motor controller controls the desired motor power. Many controllers allow regenerative braking, i.e. power is fed back into the battery during decceleration.
Some solar cars have complex data acquisition systems that monitor the whole electrical system, while basic cars show battery voltage and motor current. In order to judge the range available with varying solar production and motive consumption, an ampere-hour meter multiplies battery current and rate, thus providing the remaining vehicle range at each moment in the given conditions.
A wide variety of motor types have been used. The most efficient motors exceed 98% efficiency. These are brushless three-"phase" DC, electronically commutated, wheel motors, with a Halbach array
Halbach array
A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side...
configuration for the neodymium-iron-boron magnets, and Litz wire
Litz wire
Litz wire is a type of cable used in electronics to carry alternating current. The wire is designed to reduce the skin effect and proximity effect losses in conductors used at frequencies up to about 1 MHz...
for the windings. Cheaper alternatives are asynchronous AC or brushed DC motors.
Mechanical systems
The mechanical systems are designed to keep friction and weight to a minimum while maintaining strength and stiffness. Designers normally use aluminium, titanium and composites to provide a structure that meets strength and stiffness requirements whilst being fairly light. Steel is used for some suspension parts on many cars.Solar cars usually have three wheels, but some have four. Three wheelers usually have two front wheels and one rear wheel: the front wheels steer and the rear wheel follows. Four wheel vehicles are set up like normal cars or similarly to three wheeled vehicles with the two rear wheels close together.
Solar cars have a wide range of suspensions
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
because of varying bodies and chassis. The most common front suspension is the double wishbone suspension
Double wishbone suspension
In automobiles, a double wishbone suspension is an independent suspension design using two wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The shock absorber and coil spring mount to the wishbones to control...
. The rear suspension is often a trailing-arm suspension as found in motor cycles.
Solar cars are required to meet rigorous standards for brakes. Disc brakes are the most commonly used due to their good braking ability and ability to adjust. Mechanical and hydraulic brakes are both widely used. The brake pads or shoes are typically designed to retract to minimize brake drag, on leading cars.
Steering systems for solar cars also vary. The major design factors for steering systems are efficiency, reliability and precision alignment to minimize tire wear and power loss. The popularity of solar car racing has led to some tire manufacturers designing tires for solar vehicles. This has increased overall safety and performance.
All the top teams now use wheel motors, eliminating belt or chain drives.
Testing is essential to demonstrating vehicle reliability prior to a race. It is easy to spend a hundred thousand dollars to gain a two hour advantage, and equally easy to lose two hours due to reliability issues.
Solar array
The solar array consists of hundreds (or thousands) of photovoltaic solar cells converting sunlight into electricity. Cars can use a variety of solar cell technologies; most often polycrystalline silicon, monocrystalline silicon, or gallium arsenide. The cells are wired together into strings while strings are often wired together to form a panel. Panels normally have voltages close to the nominal battery voltage. The main aim is to get as much cell area in as small a space as possible. Designers encapsulate the cells to protect them from the weather and breakage.Designing a solar array is more than just stringing a bunch of cells together. A solar array acts like many very small batteries all hooked together in series. The total voltage produced is the sum of all cell voltages. The problem is that if a single cell is in shadow it acts like a diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
, blocking the current for the entire string of cells. To design against this, array designers use by-pass diodes in parallel with smaller segments of the string of cells, allowing current around the non-functioning cell(s). Another consideration is that the battery itself can force current backwards through the array unless there are blocking diodes put at the end of each panel.
The power produced by the solar array depends on the weather conditions, the position of the sun and the capacity of the array. At noon on a bright day, a good array can produce over 2 kilowatts (2.6 hp). A 6 m2 array of 20% cells will produce roughly 6 kW·h (22 kJ) of energy during a typical day on the WSC.
Some cars have employed free-standing or integrated sails to harness wind energy. Many races, including the WSC
World Solar Challenge
The World Solar Challenge is a solar-powered car race which covers through the Australian Outback, from Darwin to Adelaide.The race attracts teams from around the world, most of which are fielded by universities or corporations although some are fielded by high schools...
and NASC, consider wind energy to be solar energy, so their race regulations allow this practice.
Aerodynamics
Aerodynamic drag is the main source of losses on a solar race car. The aerodynamic drag of a vehicle is the product of the frontal area and its Cd. For most solar cars the frontal area is 0.75 to 1.3 m2. While Cd as low as 0.10 have been reported, 0.13 is more typical. This needs a great deal of attention to detail.Mass
The vehicle's mass is also a significant factor. A light vehicle generates less rolling resistanceRolling resistance
Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball or tire rolls on a flat surface, in steady velocity straight line motion. It is caused mainly by the deformation of the object, the deformation of the surface, or...
and will need smaller lighter brake
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
s and other suspension
Suspension (vehicle)
Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car's roadholding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants...
components. This is the virtuous circle when designing lightweight vehicles.
Rolling resistance
Rolling resistance can be minimised by using the right tires, inflated to the right pressure, correctly aligned, and by minimising the weight of the vehicle.Performance equation
The design of a solar car is governed by the following work equation:
which can be usefully simplified to the performance equation
for long distance races, and values seen in practice.
Briefly, the left hand side represents the energy input into the car (batteries and power from the sun) and the right hand side is the energy needed to drive the car along the race route (overcoming rolling resistance, aerodynamic drag, going uphill and accelerating). Everything in this equation can be estimated except v. The parameters include:
| Symbol | Description | Ford Australia | Aurora | Aurora | Aurora |
|---|---|---|---|---|---|
| Year | 1987 | 1993 | 1999 | 2007 | |
| η | Motor, controller and drive train efficiency (decimal) | 0.82 | 0.80 | 0.97 | 0.97 |
| ηb | Watt-hour battery efficiency (decimal) | 0.82 | 0.92 | 0.82 | 1.00 (LiPoly) |
| E | Energy available in the batteries (joules) | 1.2e7 | 1.8e7 | 1.8e7 | 1.8e7 |
| P | Estimated average power from the array (1) (watts) | 918 | 902 | 1050 | 972 |
| x | Race route distance (meters) | 3e6 | 3.007e6 | 3.007e6 | 3.007e6 |
| W | Weight of the vehicle including payload (newtons) | 2690 | 2950 | 3000 | 2400 |
| Crr1 | First coefficient of rolling resistance (non-dimensional) | 0.0060 | 0.0050 | 0.0027 | 0.0027 |
| Crr2 | Second coefficient of rolling resistance (newton-seconds per meter) | 0 | 0 | 0 | 0 |
| N | Number of wheels on the vehicle (integer) | 4 | 3 | 3 | 3 |
| ρ | Air density (kilograms per cubic meter) | 1.22 | 1.22 | 1.22 | 1.22 |
| Cd | Coefficient of drag (non-dimensional) | 0.26 | 0.133 | 0.10 | 0.10 |
| A | Frontal area (square meters) | 0.70 | 0.75 | 0.75 | 0.76 |
| h | Total height that the vehicle will climb (meters) | 0 | 0 | 0 | 0 |
| Na | Number of times the vehicle will accelerate in a race day (integer) | 4 | 4 | 4 | 4 |
| g | Local acceleration due to gravity variable (meters per second squared) | 9.81 | 9.81 | 9.81 | 9.81 |
| v | Calculated average velocity over the route (meters per second) | 16.8 | 20.3 | 27.2 | 27.1 |
| Calculated average speed in km/h | 60.5 | 73.1 | 97.9 | 97.6 | |
| Actual race speed km/h | 44.8 | 70.1 | 73 | 85 |
Note 1 For the WSC the average panel power can be approximated as (7/9)×nominal power.
Solving the long form of the equation for velocity results in a large equation (approximately 100 terms). Using the power equation as the arbiter, vehicle designers can compare various car designs and evaluate the comparative performance over a given route. Combined with CAE
Computer-aided engineering
Computer-aided engineering is the broad usage of computer software to aid in engineering tasks. It includes computer-aided design , computer-aided analysis , computer-integrated manufacturing , computer-aided manufacturing , material requirements planning , and computer-aided planning .- Overview...
and systems modeling, the power equation can be a useful tool in solar car design.
Race route considerations
The directional orientation of a solar car race route affects the apparent position of the sun in the sky during a race day, which in turn affects the energy input to the vehicle.- In a south-to-north race route alignment, for example, the sun would rise over the driver's right shoulder and finish over his left (due to the east-west apparent motion of the sun).
- In an east-west race route alignment, the sun would rise behind the vehicle, and appear to move in the direction of the vehicle's movement, setting in the front of the car.
- A hybrid route alignment includes significant sections of south-north and east-west routes together.
This is significant to designers, who seek to maximize energy input to a panel of solar cells (often called an "array" of cells) by designing the array to point directly toward the sun for as long as possible during the race day. Thus, a south-north race car designer might increase the car's total energy input by using solar cells on the sides of the vehicle where the sun will strike them (or by creating a convex array coaxial with the vehicle's movement). In contrast, an east-west race alignment might reduce the benefit from having cells on the side of the vehicle, and thus might encourage design of a flat array.
Because solar cars are often purpose-built, and because arrays do not usually move in relation to the rest of the vehicle (with notable exceptions), this race-route-driven, flat-panel versus convex design compromise is one of the most significant decisions that a solar car designer must make.
For example, the 1990 and 1993 Sunrayce USA events were won by vehicles with significantly convex arrays, corresponding to the south-north race alignments; by 1997, however, most cars in that event had flat arrays to match the change to an east-west route.
Energy consumption
Optimizing energy consumption is of prime importance in a solar car race. Therefore it is useful to be able to continually monitor and optimise the vehicle's energy parameters. Given the variable conditions, most teams have race speed optimization programs that continuously update the team on how fast the vehicle should be traveling. Some teams employ telemetryTelemetry
Telemetry is a technology that allows measurements to be made at a distance, usually via radio wave transmission and reception of the information. The word is derived from Greek roots: tele = remote, and metron = measure...
that relays vehicle performance data to a following support vehicle, which can provide the vehicle's driver with an optimum strategy.
Race route
The race route itself will affect strategy, because the apparent position of the sun in the sky will vary depending various factors which are specific to the vehicle's orientation (see "Race Route Considerations," above).In addition, elevation changes over a race route can dramatically change the amount of power needed to travel the route. For example, the 2001 and 2003 North American Solar Challenge route crossed the Rocky Mountains (see graph at right).
Weather forecasting
A successful solar car racing team will need to have access to reliable weather forecasts in order to predict the power input to the vehicle from the sun during each race day.See also
- List of solar car teams
- Race the SunRace the SunRace the Sun is a 1996 comedy-drama movie starring Halle Berry and James Belushi. The plot is loosely based on the true story of the Konawaena High School Solar Car Team, which finished 18th in the 1990 World Solar Challenge and first place among high school entries.-Plot:A new science teacher at...
- South African Solar ChallengeSouth African Solar ChallengeThe South African Solar Challenge is an alternative fuel vehicle auto racing challenge in South Africa, with classes for hybrid vehicles, electric vehicles, solar vehicles, and biofuel-powered vehicles. The first challenge was run in 2008, and it will run every two years thereafter. The race...
- Tour de SolTour de SolThe Tour de Sol in Switzerland was the first rally for solar powered vehicles. It was carried out annually from 1985 to 1993. The first event started on June 25 in Romanshorn on the Lake of Constance, and finished on June 30 in Geneva. 72 vehicles started in two classes; over 50 finished...
- Hunt-Winston School Solar Car Challenge
- The Quiet Achiever, the world's first solar-powered racecar
External links
- Howstuffworks.com: How solar cars work
- Solar Decathlon Web site.
- Solar cars in inventors.about.com
- American Solar Challenge on solar cars article
- World Solar Challenge website
- North American Solar Challenge 2005
- International Solar Car A - Z
- The Dell-Winston Solar Challenge
- South African Solar Challenge
- http://web.ew.usna.edu/~bruninga/APRS-SPHEV.html
- National Museum of Australia BP Solar Trek vehicle The Quiet Achiever