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"  Last week the Solar Impulse, a Swiss plane designed to fly around the world powered only by solar panels, flew for the first time. Aviator and scientist Bertrand Piccard, the man behind the project, sees it as the next great adventure in flight, and Solar Impulse is an appealing poster child for renewable energy. But this technology also has real applications, from traffic management to data network infrastructure. Solar aircraft look absurdly underpowered. Solar Impulse has the wingspan of a Boeing 747-400, but the engine power of around eight horsepower is comparable to a motor scooter. Its cruising speed of about 45 mph is not much better either. Solar cannot replace jet engines, but has the edge in endurance. With the aid of batteries for night flying, the Solar Impulse will fly for five days at a time. The military have long been aware of the potential of solar flight. Unmanned spy drones like the Global Hawk have a flight endurance of more than 30 hours, but as far back as 1983 an unidentified U.S. intelligence agency commissioned work on a classified drone known as HALSOL (for High ALtitude SOLar) which would extend flight time to weeks.  The solar technology of the 1980&amp;#039;s was not up to the task, but HALSOL was later resurrected by the Ballistic Missile Defense Organization (BMDO). Under a project called Raptor/Talon, BMDO envision a fleet of long-endurance drones circling enemy territory, ready to shoot down ballistic missiles with miniature Talon missiles. Again, the technology was not mature enough. In 1993 HALSOL was declassified and turned over to NASA.   NASA continued development of solar aircraft in conjunction with plane maker AeroVironment. In 2002 they demonstrated how a solar aircraft could act as a &amp;quot;communications satellite&amp;quot; from sixty thousand feet, broadcasting a television signal and carrying communications.  The Pentagon&amp;#039;s latest solar development is the Zephyr, designed by QinetiQ North America under a $44 million contract. This 70-pound drone has unofficially broken endurance records with a three-and-a-half day flight, but the ultimate goal is flying for three months at a time. QinetiQ brags Zephyr&amp;#039;s low cost and long endurance are ideal not just for military but also for civilian missions, such as disaster relief, ocean monitoring and weather research. The Zephyr could even act as a communication relay, bringing instant broadband network capability. Pegasus, a European solar aircraft partnership, sees even more potential, suggesting applications including pipeline checking, flood management, urban mapping and forest fire risk assessment. All that is needed is for the technology to grow. And judging from Solar Impulse&amp;#039;s test flight, solar aircraft technology is maturing nicely.  "^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.popularmechanics.com/flight/a5551/solar-powered-plane-potential/>