The hot air balloon is the oldest successful human-carrying flight technology. Hot air balloons have long fueled and consists of a bag called the envelope that is capable of containing heated air. The “balloon engine” uses solar energy to drive a giant hot air balloon as a “piston”, producing as much as 50Kw – enough energy to power 10 homes! Hot air balloons are able to fly to extremely high altitudes. Photo by Iceman

I would like to mention of a solar balloon. Solar airship is a hot air balloon which gains buoyancy by using only radiation from the sun; the balloons are generally made from black material, which helps them to heat up in the sunshine. This causes the air present inside the solar balloon to expand and reduce in density compared with the surrounding air. As such, the balloon functions like a hot air balloon. Usage at the moment is currently predominantly in the toy market, although it has been proposed that it be used in the investigation of planet Mars.

Some solar balloons are large enough for human flight. A vent at the top can be opened to release hot air for descent and deflation. Photo by Alex Jagendorf