(CN) — Scientists have built a portable wind “turbine” to harness the power of a slight breeze. In the future, they plan to build a full-size version that may even compete with traditional wind turbines.
Imagine a small device hanging from your backpack that could power your phone or laptop, even after nightfall. While typical wind turbines require strong gusts to spin those giant rotor blades, this nanogenerator, called the B-Teng, could potentially power your electronics using only the gentle breeze whipped up by an evening walk.
Wind speeds drastically diminish as you move further inland, creating a marked drop-off in efficiency for standard wind turbines as you move away from shore. They’re also large, noisy, expensive and particularly dangerous for birds, making them unviable for use near national parks or nature preserves.
The new “tiny turbine” created by researchers is comprised of two thin strips of plastic that flap together inside a tube. This flapping generates an electrical charge, much like rubbing a balloon against your head, called the triboelectric effect, which gets stored in a capacitor.
Researchers detail this novel design in a new study published Wednesday in the journal Cell Reports Physical Science.
"You can collect all the breeze in your everyday life," said senior author Ya Yang of the Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, in a statement. "We once placed our nanogenerator on a person's arm, and a swinging arm's airflow was enough to generate power."
Instead of relying on the heavy winds required by traditional turbines, this new design can generate power from wind as weak as 3.6 miles per hour, but performs best with wind speeds between nine and 18 miles per hour. While it is not a true turbine, its conversion efficiency of 3.23% dwarfs previous attempts by scientists at wind scavenging.
Thanks to the low-cost materials it’s built from, it could also prove to be orders of magnitude cheaper per unit of energy generated. At 1 inch, by 3 inches, by 0.75 inches cubed, the diminutive design generates 175 volts of electricity, producing 2.5 mW of power. That’s enough to charge a small gadget, or in the authors' case, 100 LED light bulbs and a thermometer.
"Our intention isn't to replace existing wind power generation technology. Our goal is to solve the issues that the traditional wind turbines can't solve," Yang said. "Unlike wind turbines that use coils and magnets, where the costs are fixed, we can pick and choose low-cost materials for our device. Our device can also be safely applied to nature reserves or cities because it doesn't have the rotating structures."
The amount of power generated by the B-Teng depends on exactly how the two pieces of plastic flap together. Depending on how the winds blow, its fluttering can be grouped into four possible states: stable (no contact), out-of-phase flapping, in-phase flapping and chaotic. Out-of-phase flapping is the sweet spot for energy generation, so the goal is to encourage that type of movement.
The two films move in phase at lower wind speeds and move chaotically at higher speeds. When the distance between the two films increases, they begin to flap out-of-phase, hitting peak efficiency. Increase wind speeds further and they enter a chaotic state, where the triboelectric generator effect drops off and electricity generation ceases.
The gist being that higher wind speeds don’t always equate to greater power output because the key factor is how the two pieces of film flap in tandem.
“As the wind velocity increased, the fluttering motion became chaotic, and irregular fluttering could also be observed that unpredictably decreased the effective contact area, which is the reason for the lower electricity output. The results showed that the movement frequency of B-TENG increased as the wind velocity increased from 4 ms¯¹ to 15 ms¯¹, a vital element of the increase in electricity output,” the study states.
The authors plan to build two subsequent versions of the B-Teng, one larger and one smaller. Yang hopes an even tinier device could be combined with small electronics such as a phone to provide a constant power supply.
He is also interested in creating a large version to rival standard wind turbines for use in areas where a standard turbine isn’t practical.
"I'm hoping to scale up the device to produce 1,000 watts, so it's competitive with traditional wind turbines," Yang said. "We can place these devices where traditional wind turbines can't reach. We can put it in the mountains or on the top of buildings for sustainable energy."
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