Soaring on Sunshine

Battery technology has perhaps never been more important than it is today. As such, technological advancements in this area are sorely needed. As wearable electronic devices, electric cars, unmanned aerial vehicles, and so many other technologies mature, batteries are increasingly becoming the limiting factor. Without lighter, safer, and more energy-dense battery options, a great many otherwise transformative technologies will remain impractical for real-world use.

This problem is especially apparent when it comes to unmanned aerial vehicles and drones. Flight is inherently energy-intensive due to the need to generate lift and overcome drag. Drones, which rely on electric power for propulsion, must carry batteries that can provide sufficient energy to maintain flight while also being lightweight enough to avoid weighing down the craft. This creates a delicate balance between power capacity and weight, with the battery often being one of the heaviest components of the drone.

Since it is not clear if or when suitable batteries will be developed, a number of stopgap measures have been proposed. One of the most common solutions involves the creation of networks of charging stations, such that drones can land and charge themselves as needed, then continue on their mission. However, building out this sort of infrastructure is very expensive, and it limits the vehicles to staying within range of chargers in the network.

Rather than focusing on external charging networks, a team at the Johannes Kepler University Linz in Austria believes that drones should carry their own chargers. Their approach involves installing solar panels on top of drones, such that they can land when the batteries start to run low, wherever they may be, and top off their batteries before resuming the mission. Not only does this proposed solution lower the cost of keeping drones in the air, but it also extends their range indefinitely.

Typically, solar panels would not be a good choice for charging drones for a number of reasons. Chief among those reasons is the fact that the panels are heavy and add a lot of bulk that would negatively impact a vehicle’s aerodynamics — if they can get off the ground in the first place under the added weight, that is. But in this case, the researchers fabricated custom lightweight and flexible solar cells from a material called perovskite. At just 2.5 micrometers in thickness, these solar films can comfortably ride along on an aerial vehicle.

These perovskite-based solar cells are also excellent at converting light into electricity, with an impressive 20.1 percent efficiency. The total power output is fairly good as well at 44 watts per gram.

The power output may not be sufficient to get a large, heavy drone back in the air in a reasonable amount of time, but for special purposes, these solar cells might be the perfect solution. The researchers demonstrated that a CX10 miniature quadcopter, when fitted with an array of 24 solar cells, could be recharged in about 30 minutes. In a series of trials, the quadcopter was shown to take flight, then land to charge before returning to the air. Multiple such cycles were completed, but in principle, there is no limit to how far the drone could travel — as long as the sun is shining, anyway.

In the future, the team intends to explore how their novel solar cells might be used in wearable electronics, Internet of Things devices, and other applications.