A Hamburg-based company, Thermodyna, has developed an air-conditioning system that uses only the sun’s heat to produce hot or cool air as required.

The core of the system is a Schukey motor. For cooling, a solar panel uses the sun’s heat to produce steam which is converted into mechanical energy. This drives a pump which sucks damp, warm air out of the room, compresses it and then allows it to expand. According to Thermodyna, the process can cool the air to around 20 degrees Celsius.

"There are no electronics and hardly any components," says Thermodyna boss Volker Bergholte. The company plans to begin selling the units in 2010.