1) At present the major challenge with utilizing the solar energy is the high cost of the PV cells. However, in future as the use of the PV cells for various applications increase, cost of manufacturing technology for PV cells is sure to come down. This will promote greater use of the PV cells and continuous sliding down of the prices. The solar car will become affordable cost wise in the next five years or so.
2) Another major challenge is the number of PV layers required for producing sufficient amount of electricity to drive the car. Again with advancements in the technology the silicon chips can be developed that are able to produce more electricity in from smaller area.
3) Then another challenge with solar cars is that PV cells will generate electricity only during daytime. To overcome this problem the PV cells can be designed to collect maximum solar energy so it fulfills all day and night requirements of the car.
When these things happen the solar cars will bring major changes in the shapes and sizes of the car. The scene of the airplane like looking cars running swiftly on the roads will become common. It will be just like airplane running on the roads. The sitting posture in such cars will be similar to the pilot sitting in the fighter plane. And when this happens who knows one day this car will start flying too!