Solar vehicle

A solar vehicle is an electric vehicle powered by solar energy.

This is obtained from solar panels on the surface (generally, the top) of the vehicle. Photovoltaic (PV) cells convert the sun's energy directly into electrical energy. Solar vehicles are not practical day-to-day transportation devices at present, but are primarily demonstration vehicles and engineering exercises, often sponsored by government agencies.

By type

Solar Cars

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. Exceptions include solar-powered cars and utility vehicles.

Solar cars are often fitted with gauges as seen in conventional cars. In order 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 PV cells to convert sunlight into electricity. In fact, 51% of sunlight actually enters the Earth's atmosphere. 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%.

Solar array

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).

Cells,Modules,Arrays

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 and

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.

Races

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 3000 km. 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 North American Solar Challenge, previously known as the '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 North American Solar Challenge ran from August 13–21, 2008, from Dallas, Texas to Calgary, Alberta. The next race is expected to be run in the summer of 2010. You can see video of how University of Minnesota students built Centaurus I, one of the cars participating in the 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. 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.

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.

Solar bicycles and motorcycles

A solar bicycle or tricycle has the advantage of very low weight and can use the riders foot power to supplement the power generated by the solar panel roof. In this way, a comparatively simple and inexpensive vehicle can be driven without the use of any fossil fuels.

Solar photovoltaics helped power India's first Quadricycle developed since 1996 in Gujarat state's SURAT city.

The first solar "cars" were actually tricycles or quadricycles built with bicycle technology. These were called solarmobiles at the first solar race, the Tour de Sol in Switzerland in 1985 with 72 participants, half using exclusively solar power and half solar-human-powered hybrids. A few true solar bicycles were built, either with a large solar roof, a small rear panel, or a trailer with a solar panel. Later more practical solar bicycles were built with foldable panels to be set up only during parking. Even later the panels were left at home, feeding into the electric mains, and the bicycles charged from the mains. Today highly developed electric bicycles are available and these use so little power that it costs little to buy the equivalent amount of solar electricity. The "solar" has evolved from actual hardware to an indirect accounting system. The same system also works for electric motorcycles, which were also first developed for the Tour de Sol. This is rapidly becoming an era of solar production.

Solar ships

Japan's biggest shipping line Nippon Yusen KK and Nippon Oil Corporation said solar panels capable of generating 40 kilowatts of electricity would be placed on top of a 60,213 ton car carrier ship to be used by Toyota Motor Corporation.

Solar airplanes

The longest and highest altitude solar-powered (unmanned) airplane flight in August, 2008 used lithium-sulfur batteries for overnight energy storage.

Solar propelled spacecraft

A few spacecrafts that have been employed within the orbit of Mars have used solar power as an energy source for their propulsion system.

All current solar powered spacecraft use solar panels in conjunction with electric propulsion, typically ion drives as this gives a very high exhaust velocity, and reduces the propellant over that of a rocket by more than a factor of ten. Since propellant is usually the biggest mass on many spacecraft, this reduces launch costs.

Other proposals for solar spacecraft include solar thermal heating of propellant, typically hydrogen or sometimes water is proposed.

Another concept for solar propulsion in space is the light sail.

Practical applications

The Venturi Astrolab in 2006 was hailed as the world's first commercial electro-solar hybrid car, and it was originally due to be released in January 2008.

In May 2007 a partnership of Canadian companies lead by Hymotion altered a Toyota Prius to use solar cells to generate up to 240 watts of electrical power in full sunshine. This is reported as permitting up to 15 km extra range on a sunny summer day while using only the electric motors.

One practical application for solar powered vehicles is possibly golf carts, some of which are used relatively little but spend most of their time parked in the sun.

An inventor from Michigan, USA has built a street legal, licensed, insured, solar charged electric scooter. It has a top speed controlled at a bit over 30 mph, and uses fold-out solar panels to charge the batteries while parked.

A Swiss project, called "Solartaxi", has circumnavigated the world. The first time in history a solar powered vehicle has

gone around the world, covering 50000 km in 18 months and crossing 40 countries. It is a road-worthy solar car with a trailer, carrying a 6 m² sized solar array. The Solartaxi has Zebra batteries, which permit a range of 400 km without recharging. The car can also run for 200 km without the trailer. Its maximum speed is 90 km/h. The car weighs 500 kg and the trailer weighs 200 kg. According to team leader Louis Palmer, the car in mass production could be produced for 16000 Euro. Solartaxi has toured the World from July 2007 till December 2008 to show that solutions to stop global warming are available and to encourage people in pursuing alternatives to fossil fuel. Palmer suggests the most economical location for solar panels for an electric car is on building rooftops though, likening it to putting money into a bank in one location and withdrawing it in another.

Solar Electrical Vehicles is adding convex solar cells to the roof of hybrid electric vehicles.

Limitations and challenges

Fitting battery electric vehicles with solar cells would extend their range and allow recharging while parked anywhere in the sun. However, with present and near-term engineering considerations, it seems that the more likely place for solar cells will generally be on the roofs of buildings, where they are always exposed to the sky and weight is largely irrelevant, rather than on vehicle roofs, where size is limited. However, solar cell technology is starting to be used successfully in the powering of electric golf cars and utility vehicles. In the case of both building and vehicles, energy from rooftop panels can be stored in batteries for future use. While some inconveniences might cause challenges, there are limitations to using PV cell:

• Cost. While sunlight can provide a free clean source of energy, the creation of PV cells to capture that sunlight is expensive. In 2003, it was found that energy would cost $.30/kWh which is more than double that of residential electricity. These costs have dropped recently with Solar Panel costs coming down further and the reliability of the cells have much improved with thinfilm technology. The cost of Energy will depend on the place of operation as solar radiation differs from place to place.
• Lifetime. Even though sunlight has no lifespan, PV cells do. The lifetime of a solar module is approximately 30 years. Standard photovoltaics often come with a warranty of 90 % (from nominal power) after 10 years and 80 % after 25 years. However, in automotive purposes they need to be sealed well if meant to operate efficiently for decades in all weather conditions.

Plug-in hybrid and solar vehicles

An interesting variant of the electric vehicle is the triple hybrid vehicle—the PHEV that has solar panels as well to assist.

The 2010 Toyota Prius model will have an option to mount solar panels on the roof. They will power a ventilation system while parked to help provide cooling. An unconfirmed report in January 2009 stated that Toyota is working on an all-solar vehicle.