What if your umbrella could charge your phone? That speculative tech just got a bit closer to reality now that scientists have designed a small, highly efficient electricity generator that can create enough charge with a single droplet of tap, rain, or seawater to power 100 LED light bulbs.
The researchers hope that, alongside solar and wind power, the approach can help tackle the world’s energy crisis. Obviously, generating electricity with water is nothing new. But the study, published on Wednesday in the journal Nature, looked at how a unique connection between the water droplets and the generator interface increased the generator’s overall power.
By coating their droplet generator in a material with a near-permanent electric charge, the team observed that their generator was able to slowly collect charge from continuously falling droplets and store it until reaching its capacity. This allowed the generator to more efficiently convert the droplet's energy. From just a single droplet the generator was able to generate enough power to light up 100 small LED light bulbs, and with four droplets it could power 400.
While similar water droplet experiments have also demonstrated the ability to transform water into energy in a similar way, the authors write that the instantaneous power created by their coated generator was thousands of times higher than previous approaches that lacked the coating.
“The significance of this technology is the much enhanced electric power per falling rain droplet, which makes the device much more efficient to convert energy from a falling droplet to electricity,” said Xiao Cheng Zeng, a co-author on the study and professor of chemistry at the University of Nebraska-Lincoln
The generator's high efficiency didn’t come from just the coating alone. When looking closer at their generator, the team noticed that the generator experienced no peak in electric output when droplets initially hit the coated surface. It was only when the droplet began to spread out upon impact that the peak occurred. The team discovered that the droplet spreading and touching an aluminum electrode on the interface’s surface joined previously disconnected parts of the interface and created a closed circuit. The authors write that the droplet acted as the resistor while the surface coating acted as the capacitor.
This connection allowed for the coated surface to store charge from continuously falling droplets and then release that charge at peak electrical power when the droplets spread and connect the two ends of the circuit.
While this study looked at how droplets falling from only centimeters above the generator would behave, the study’s lead author and professor of mechanical engineering at the City University of Hong Kong, Zuankai Wang, said that their design is generic enough to be used in other scenarios as well.
“Our design is generic, which means the design can be extended to harvest energy of a water wave and even enclosed water inside a tube. It does not have to use the impinging droplet,” says Wang.
Wang said that the technology still has obstacles to overcome (for example, electrode corrosion) before their technology could be moved beyond the lab, but that he hopes within five-years to have a large scale proof-of-concept.
Correction: This article previously misstated how many LED bulbs four droplets of water can power. We regret the error.