The zero-fuel aeroplane, Solar Impulse.

Pilot Bertrand Piccar with his friend and business partner Andre Borschberg  designed the zero-fuel aeroplane, Solar Impulse.

Solar Impulse has covered some 30,000km in its quest to become the first plane to circle the world using no fuel, just the energy from the Sun.

Their plane is wider than a 747 jumbo jet but weighs just 2.3 tonnes, which poses some unique challenges:

• The aircraft is very sensitive to the weather conditions
• But its solar cell and battery efficiency is very high
• This means it can stay aloft for many days and nights
• The pilot is permitted only catnaps of up to 20 minutes
• The cockpit is little bigger than a public telephone box

Sourc:http://www.bbc.com/news/science-environment-36867613