We've heard about "solar-powered" quadcopters before, in which their battery is charged by ground-based photovoltaic panels. Now, however, engineering students have built a copter that draws its power directly from onboard solar cells, apparently allowing it to stay airborne as long as the sun is shining.

Developed by a student team from the National University of Singapore (NUS), the drone is built mainly from carbon fiber, tipping the scales at just 2.6 kg (5.7 lb). It has no onboard battery or other energy-storage system, but is instead equipped with an array of 148 silicon solar cells, giving it a total surface area of approximately 4 square meters (43 sq ft).

Under the supervision of associate professor Aaron Danner, eight successive groups of students have been working on the project since 2012. Although a drone that combined solar and battery power was flown in the past, this is NUS' first one to rely solely on direct solar power.

So far, it has been flown by remote control up to an altitude of over 10 meters (33 ft). As it's equipped with a GPS system, it can reportedly also fly autonomously.

It is hoped that this proof-of-concept model could ultimately lead to solar-powered quadcopters that might serve as power-providing "flying solar panels" at disaster sites, or that could be used for tasks such as surveillance and photography. For some applications, the addition of an integrated battery would let the aircraft keep flying at night or in cloudy conditions.

"Our aircraft is extremely lightweight for its size, and it can fly as long as there is sunlight, even for hours," says Danner. "Unlike conventional quadcopter drones, our aircraft does not rely on onboard batteries and hence it is not limited by flight time. Its ability to land on any flat surface and fly out of the ground effect in a controlled way also makes it suitable for practical implementation."

You can see the drone in flight, in the following video. And although it's being called Asia's first fully solar-powered quadcopter, a student team from Queen Mary University of London claimed to have built one five years ago.