The Alternative

• Solar powered cars are an obvious alternative to conventional gas-powered vehicles, as they do not create any dangerous, smog-forming emissions. They also run off of a completely renewable source: the sun. However, as of 2009, photovoltaic cells (technology used in solar powered cars) produce much less power and cost much more to develop than the internal combustion engine in fossil-fuel powered cars. This means that, currently, solar powered cars are not manufactured for consumers. Nearly all solar powered cars in existence have been designed solely to compete in solar powered car races. These races themselves are created to generate interest and research in the solar power field.
  
  

Photovoltaics

• A photovoltaic array
  
  Constructing a photovoltaic (PV) "array" is the first step in powering a solar car. Single PV cells are very small---roughly the size of a postage stamp. Multiple cells are combined, forming a "module." Modules are then connected to other modules to form an array. When you look at a solar panel, what you usually see is a PV array.
  
  

Doping

• Each PV cell contains two sheets of semiconductor material sandwiched together---usually "n-type" silicon on top (facing the sun) and "p-type" silicon below. Scientists use a process, called "doping," to replace some of the silicon atoms in each sheet with another type of atom. The "n-layer" is usually doped with phosphorus, the "p-layer" with boron. This leaves the n-layer with excess electrons (negative charge) and the p-layer with an electron deficiency (positive charge).
  
  

Photons and Electrons

• When the sun shines upon a PV cell, "photons" within the solar radiation free up electrons within the cell. The electrons surge from the n-layer, through a set of attached wires, to an electrical "load"---in this case, the car and its battery. The electrons travel through the load, powering it in the process, and exit through a set of wires that connect to the p-layer of the PV cell. There, absorbed photons keep the electrons free to travel from the p-layer to the n-layer and back out to the load. Thus, an electric car is powered by the sun.
  
  

The Mechanics

• The mechanics of a solar powered car are essentially the same as an electric one, but scaled down a bit to accommodate a smaller power supply. The main difference is that PV cells provide the electricity to power the car, instead of a pre-charged battery. However, solar cars do have a battery that can be charged by excess electricity generated by the PV cells. The battery is then used when solar radiation is unavailable (such as when it is overcast or during bad weather).
  
  

The Design

• Solar powered race car
  
  Most solar powered car designs include large PV arrays that dominate nearly the whole of the car's topside, due to the relatively low amount of power generated by PV cells. Most cars have only one or two small cockpits for passengers, in order to minimize weight and maximize array coverage; rear-wheel drive, with only one rear wheel or two placed close together, to minimize power usage; and an extremely aerodynamic design to minimize drag.
  
  

Performance

• According to speedace.info, one of the most extensive solar powered car info websites, most solar powered car engines are rated at 2 to 5 hp.
  
  The website for the Global Green Challenge (an Australian solar car race) claims that many solar-powered race cars can now travel in excess of 100 kp/h (roughly 62 mp/h). The challenge is making cars that can perform at that speed practical for the consumer.
  
  

For the Consumer

• The 2009 Toyota Prius comes with optional solar panels on the roof that supply power to the car's air conditioning. Toyota is also rumored to have green-lit development of a fully solar powered car that would eventually be available to the general population.