Multirotor drones may one day be able recharge their batteries while out and about, instead of having to return to a charging station. They could do so via onboard ultra-thin solar cells, which have already been successfully tested on a small quadcopter.
One of the reasons we don't see drones in wider use now is because most of them can fly for only about 30 minutes before their battery runs out. This means they're typically limited to making round trips that are just 15 minutes each way – from their base to the destination and back.
One alternative involves having them stop at charging stations along their assigned routes as needed, but those stations would still have to be built, powered and maintained. Additionally, the drones would be limited to following flight paths that incorporated the stations.
That's where the new solar cells come in.
Created by scientists at Austria's Johannes Kepler University Linz, the lightweight, flexible cells are made of a semiconductor material known as perovskite, and they're less than 2.5 micrometers thick – that's just 1/20th the width of a human hair. And importantly, they're 20.1% efficient at converting sunlight into electricity, plus they boast a power output of up to 44 watts per gram.
In a proof-of-concept test of the technology, the scientists mounted a ring-shaped array of 24 of the cells on a commercially available CX10 miniature quadcopter, which was dubbed the Solar Hopper. The array made up just 1/25th of the augmented aircraft's total weight, with the cells themselves making up only 1/400th.
For one series of indoor trials – which were conducted under an artificial light source simulating sunlight – the drone was repeatedly kept hovering at half-throttle for 10 seconds, then landed and left to recharge for 30 minutes. It successfully completed six of these back-to-back "charge-flight-charge" cycles, and could conceivably have kept doing them indefinitely.
In another series of experiments, the Solar Hopper was once again hovered at half-throttle, but this time was left to do so until its battery ran out. These tests were conducted both with and without the solar array connected. It was found that when the array was connected, the flight time was extended by about 6%.
That's not a huge amount, but then again the technology is intended more for allowing drones to stop and recharge wherever sunlight is accessible, not for allowing them recharge while in flight. Additionally, the scientists point out that the figure would have been larger if the drone itself had been altered to be more energy-efficient.
And of course, the technology could have uses beyond the recharging of drones.
"Ultra-thin and lightweight solar cells not only have enormous potential to revolutionize the way energy is generated in the aerospace industry, there are also a wide range of applications that include wearable electronics, and the Internet of Things, that can also benefit from this new technology," says Christoph Putz, one of the study’s lead authors. "Lightweight, adaptable and highly efficient photovoltaics are the key to developing the next generation of self-sufficient energy systems."
A paper on the research, which was led by professors Martin Kaltenbrunner and Niyazi Serdar Sariciftci, was recently published in the journal Nature Energy.
Source: Johannes Kepler University Linz
