Researchers from Austria’s Johannes Kepler University (JKU) Linz have developed ultra-thin, ultralight solar cells that can recharge a drone. When adequate sunlight is available, this solar module can generate 250 mW of power or 44 watts per gram. It’s not a lot of power, but the proof-of-concept is remarkable, allowing drones to operate more autonomously. The researchers developed and flew an autonomous hybrid-solar-powered drone, which they call the Solar Hopper, to test the performance of their solar cells. 

During the flight tests, the solar hopper was able to operate and complete multiple charge-flight-charge cycles just by using sunlight to charge its batteries.

“The solar hopper showcases how an energy-autonomous aerial vehicle can execute various tasks, such as large-scale mapping, surveillance, search and rescue, reconnaissance, etc. Upon completing its mission, the hopper recharges and begins anew, highlighting its ability to operate continuously without external power sources,” Christoph Putz, one of the researchers and a PhD student at JKU Linz, told ZME Science.

Perovskite solar cells for drones

While conventional solar cells are made of silicon, the ultrathin and ultralight cells powering the solar hopper are composed of perovskite. This is a calcium titanium oxide mineral that is used in LEDs, Li-ion battery applications, photodetectors, and lasers. 

In recent years, perovskite-based solar cells have also gained a lot of attention due to their potential for high-efficiency and low-cost manufacturing. A 2016 study suggests that while silicon cells cost 75 cents to produce one-watt power in ideal sunlight conditions, perovskite cells can achieve the same output for only 10 to 20 cents.

According to the researchers, these cells also offer numerous advantages over conventional silicon solar cells in the context of powering autonomous drones. 

For instance, perovskite solar cells can be fabricated in ultrathin layers, making them exceptionally lightweight without sacrificing power output. In fact, the solar cells on the Solar Hopper are 20 times thinner than a human hair.

Compared to silicon cells, they also offer a high power-to-weight ratio, making them ideal for applications where weight is paramount, such as aerial vehicles. Plus, they can perform well even in low-light conditions and therefore, are suitable for drones operating in variable lighting environments like cloudy or partially shaded areas.

Moreover, they can be manufactured on flexible substrates, making them lightweight and malleable to complex surfaces.

“By leveraging these advantages, perovskite solar cells offer a compelling solution for powering autonomous aerial vehicles, enabling longer flight times, increased operational range, and enhanced mission capabilities,” Putz said. 

Also, “The ultrathin solar cells are not exclusive to quadcopter drones; various aerial vehicles, including planes, blimps, and even wearable electronics like smartwatches, biosensors, or smartphones, can also leverage this technology for enhanced performance,” he added. 

The Solar Hopper flight tests

Solar Hopper is a hybrid-power quadcopter drone with a distinctive appearance, equipped with a circular frame featuring 24 interconnected perovskite solar cells. 

The entire solar module is 25 times lighter than the drone and the weight of the perovskite cells is only 0.25 percent of the aircraft’s total weight. So adding the circular frame to a drone doesn’t affect performance or stability during flight. 

The researchers conducted multiple Solar Hopper flight tests during which the drone recharged itself using the on-board solar module.

They found that Solar Hopper could fly for over two minutes and then be fully recharged in about 1.5 hours in the power-saving state, with communication switched off. Whereas in the ready-to-fly state, with all communication channels switched on, the drone took 3.5 hours to recharge. 

“In our study, we have demonstrated six flight-recharge-flight cycles without any indication of performance degradation. It’s worth noting that we haven’t optimized the drone itself for efficiency. Our aim was to demonstrate how an off-the-shelf product can be converted into an energy-autonomous drone simply by integrating our solar cells,” Putz told ZME Science.

To compare the change in flight time, the researchers also flew the solar hopper without the solar module. They noticed that when solar cells are on board, the flight time of the aircraft increases by nearly six percent.

This is just the beginning 

The results from the Solar Hopper flight tests show that we can fly drones using sunlight. It also suggests that ultralightweight perovskite solar cells can open new pathways of how solar cells can be integrated into new drone designs, extend their flight times, increase payload capacity, and enhance the overall performance of energy-autonomous aerial vehicles. 

Moreover, this technology has the potential to replace or augment various existing power sources across a range of applications. For instance, in emergencies such as natural disasters, ultrathin solar cells integrated into emergency shelters, communication equipment, or medical devices could provide a reliable source of electricity when traditional power sources are unavailable or disrupted. 

However, perovskite solar cell modules like the one utilized by the researchers still come with many limitations and are not ready for wide-scale usage. 

For instance, the current solar module design can only power small-scale drones, and can’t be used for large aerial vehicles. The cell recharging process is time-consuming.  

Putz and his colleagues are hopeful that with further research, they can improve the scalability, performance, and stability of their solar module, and make it feasible for use in large-scale drones and other applications. Elsewhere, researchers at Queen Mary University of London developed their own solar-powered quadcopter, a 70-gram aircraft that can fly for an average time of 3.5 min and recharge in approximately 68 min.

“Continued research efforts will focus on further enhancing the environmental stability and efficiency of ultrathin perovskite solar cells, ensuring their reliability for long-term use in various applications,” Putz told ZME Science.

The study is published in the journal Nature Energy.