THE vehicles collect energy through photovoltaic solar cells which convert sunlight into electricity. This electricity is stored in a small battery pack which is used to drive an electric motor and in turn drive a wheel, normally through a chain or belt. Some vehicles are like bicycles that are solar assisted. The stored solar energy is used to "assist" the rider when going up hills or against a head wind. The most expensive and fastest vehicles are solar powered cars, which can cost millions of pounds to build and have top speeds of more than 140km per hour The best cars can travel more than 750km in one (sunny) day.
The design principles for a fast solar car are straightforward. Any losses in the electrical system, transmission and motor must be minimised. After this the two key areas are rolling resistance and aerodynamic drag. Rolling resistance is improved by reducing vehicle weight, good tyre selection and careful set-up of steering and suspension systems. Aerodynamic losses are governed by the car's frontal area, drag factor and speed. Aerodynamics become noticeable at speeds in excess of 60 km per hour and after that become increasingly dominant.