Lizzie Hayes, of Nayland College, asks :-

Is it realistic that cars will eventually be replaced with solar-powered cars?

Richard Duke, an electrical engineer at the University of Canterbury, responded.

At sea level on the earth the total incident solar power is about 120,000,000,000,000 kilowatts. The present population of the earth is just under 6 billion people and so about 20 million watts of solar power is available to each person. Thus it seems that there should be plenty of solar power for everyone. However we must remind ourselves that this 120,000 billion kilowatts is spread over the entire surface of the earth. So on a bright sunny day the earth receives at best about 1 kilowatt for every square metre of area.

An average small car's bonnet, roof and boot area typically totals less that six square metres and the efficiency with which incident solar energy can be converted into electric energy by a solar cell is only around 15 per cent. Thus if these areas were covered in solar cells the obtainable electric power is only about 0.9 kW (1 kW per square metre x 6 square metres x 0.15). Compared to an average small car which has a petrol engine capable of delivering 60 to 200 kW, the solar powered car appears to be an unlikely alternative. Of course electric energy can be stored in batteries to be used at some later time and most experimental solar cars around the world use various types of batteries for this purpose.

Batteries are however heavy, expensive and take a long time to charge from solar cells. Thus the totally solar powered production car is unlikely to be built. We are more likely to find solar cells used to power accessories, such as ventilation fans.