Advances in solar cell technology can make drones a more powerful tool not only for the battlefield but also for civilian uses, such as firefighting, crop surveying and oil and gas field monitoring. A Silicon Valley startup called Alta Devices has been working with AeroVironment to engineer a drone that can stay airborne longer and carry out missions that are impossible before.

The result of the collaboration is a 13-pound prototype drone that can fly for 9 hours and 11 minutes, AeroVironment announced recently. The military contractor credited its new battery and Alta's solar technology for the feat. A drone similar to the one by AeroVironment typically can fly for one or two hours before it has to land and recharge, said Chris Norris, Alta's CEO. AeroVironment's new battery is good for three hours. By embedding Alta's ultra thin and highly efficient solar cells on the aircraft, the battery is able to recharge twice before daylight fades and keeps the drone in the air three times longer, Norris added.


Adding solar energy to the design could help AeroVironment win contracts. A drone that flies longer could carry out lengthier assignments and reduce its operating cost. Launched by hand (you fire up the motor, hold the drone up and then toss it into the air), the drone usually doesn't land gracefully. Its motor is designed to turn off when it reaches a certain altitude, and then it hits the ground and glides to a stop. More often than not, though, the impact causes some parts to break off.

"Landing is a traumatic event for these aircrafts," Norris said. Drone operators often bring many spare parts to the field. A drone that can stay in the air longer would be able to do more work before it has to land and undergo repairs. How much money the new design could save would depend on how much the advanced battery and solar cells adds to the price of the drone and the cost of operating and maintaining it.

Designing a solar-powered drone isn't just about slapping on as many solar cells as possible, though maximizing the use of the available space is certainly a key consideration. One factor to consider is the weight and efficiency of solar cells. The vast majority of the solar cells produced today are too thick and heavy or not terribly efficient for use by a drone, which needs to stay lightweight and nimble while carrying a camera or other equipment. Adding weight will require more battery power to operate. Alta's cells, made with gallium-arsenide, are 1 micron thick, compared with the common 180-micron silicon cells that you find in most of the solar panels on the rooftop today. Alta's cells also are more efficient at converting sunlight into electricity than thinner solar cells made with compounds such as copper-indium-gallium-selenide or cadmium-telluride.

Finding suitable surface areas to plant the solar cells is another design goal. The wings and tail are typically where the solar cells go. But cells can stick to the underside of the aircraft, too, in order to capture reflected light that is often available when the drone flies over a desert or snow, Norris said. He declined to disclose where Alta's cells are on the prototype Puma or how much electricity they could produce, citing the secretive nature of engineering drones with military use in mind.

"It all comes down to how much power they need, the flight characteristics relative to the sun, and how much the customers are willing to pay," Norris said.

Military isn't the only potential customer. There is a growing interest in using drones in agriculture, where the aircrafts could survey the crops and help farmers decide how much and where to administer pesticide, for example. Electric utilities also are interested in using drones to monitor the health of their transmission lines, particularly those located in remote areas, and to determine the extent of damage after a storm.