Energy | 12. April 2010 | posted by Jan Oliver Löfken

Energy question of the week: Is it possible to fly on nothing but solar power?

In cruise ships, electrical propulsion units – powered by diesel engines – are now standard equipment. Every day, buses with electric motors powered by fuel cells ply the streets of Hamburg. Now the first aircraft powered solely by electric motors are taking off. However, in the quest to find exciting, original and climate-friendly propulsion, are solar cells powerful enough to get an aircraft off the ground?

Yes - the Sun's energy is all it takes for a pilot to take to the skies. The latest example was provided recently by the solar-powered aircraft Solar Impulse, whose maiden flight lasted 87 minutes. On this aircraft, 12,000 solar cells arranged over the 63-metre wingspan capture enough sunlight to power four 10-horsepower electric motors. At a speed approaching 50 kilometres an hour, Solar Impulse took off from the military airfield of Payerne in the Swiss canton of Waadt and reached an altitude of almost 1,200 metres.

A flight around the world in 2012

Although this aircraft weighs only 1,600 kilograms, despite its enormous wingspan, it can carry only one person. But on a sunny day, a sufficient amount of surplus energy can be stored in batteries to keep the aircraft flying all through the night. The two project founders, André Borschberg and Bertrand Piccard, are already planning a round-the-world flight for their solar aircraft in 2012 – albeit with numerous landings.

DLR has made some important contributions to this aircraft. For example, the DLR Institute of Aerodynamics and Flow Technology in Braunschweig simulated the aerodynamics of Solar Impulse to establish its lift, and the strength of lateral forces imposed by gusting winds. "With this enormous wingspan, we are straying beyond the limits of familiar engineering experience. This is a great challenge for aerodynamics and structural components," states Martin Hepperle from the Institute. DLR work also included test bench studies by its Göttingen-based Institute of Aeroelasticity into structural response characteristics. Stationary vibration trials were performed to test the aircraft's ability to resist buffet (wing flutter) - Solar Impulse was required to demonstrate that it was sufficiently robust.

An aerodynamic model of Solar Impulse: pressure distribution with flow lines across the surface of a prototype. Photo: DLR. Top image: Solar Impulse/EPFL Claudio Leonardi.

Taking to the skies with fuel cells

DLR has its own electric aircraft. In July 2009, the DLR's research aircraft Antares DLR-H2 took off on its maiden flight, and became the first manned aircraft to become airborne, powered entirely by fuel cells. Unlike Solar Impulse, the Antares is capable of flying entirely independently of cloud cover and sunlight. This electrically-powered aircraft set an altitude record of 2,558 metres in November 2009 in the course of its 69-minute flight at an average speed of 115 kilometres an hour. Researchers at the DLR Institute of Technical Thermodynamics in Stuttgart have been planning further and longer test flights for the coming summer, and you will be able to read about these in a future edition of this Energy blog.

Other information on this topic:

DLR webcast: solar aircraft Solar Impulse - around the world on solar power

DLR is supporting this planned record-breaking flight for a solar-powered cross between a glider and an aircraft

The DLR Energy question of the week in 'The future of energy' Year of Science

The Federal Ministry of Education and Research (BMBF) has given the Year of Science 2010 the motto 'The future of energy'. For this reason the science journalist Jan Oliver Löfken will this year answer a question on the subject of energy in his blog each week. Do you have a question about how our energy supply might look in the future? Or do you want to know, for example, how a wave power plant works and how it can efficiently generate electricity? Then send us your question by email. Wissenschaftsjournalist Jan Oliver Löfken recherchiert die Antworten und veröffentlicht sie jede Woche in diesem Blog.


About the author

Energy journalist Jan Oliver Löfken writes among other things, for the Technologie Review, Wissenschaft aktuell, Tagesspiegel, Berliner Zeitung and P.M. Magazin on issues involving energy research and industry. For DLR, he answered the Energy question of the week during the Year of Energy 2010. to authorpage