"Micro-energy" invention scavenges the wind that turbines miss

Scientists in China have designed a nanogenerator that uses the wind power literally left behind in your wake.

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Wind is one of the Earth's most abundant natural energy resources, but harvesting every last wisp of energy from it can be tricky. Large, industrial wind turbines are expensive. They are also the frequent target of NIMBY-ism — the noise and look of such turbines isn't exactly "scenic."

As an alternative, scientists are looking to develop miniature generators that harvest ambient energy from the air instead. This could be as simple as harnessing the breeze created in the wake of a runner, for example.

Now, a team of scientists from China has just demonstrated the most efficient nanogenerator yet, making use of simple physical principles to generate enough power to light-up 100 LED bulbs with a gently blowing 3.4 mph breeze.

Detailed in a study published Wednesday in the journal Cell Reports Physical Science, the researchers explain that their nanogenerator — which looks a bit like a hair-dryer with a clear tube attached at the front — works by utilizing both the triboelectric effect and Bernouilli effect. The first describes what happens when you rub a balloon on your hair and static electricity causes it to stick, and the second refers to the fact that the faster air flows through something the less pressure it experiences. When just the right velocity of air passes through their generator, a pair of flapping films are pushed together and pulled apart to create an electric charge.

Senior author on the paper and researcher at the Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Ya Yang, said in a statement that a generator like this represents an opportunity for low-cost, mobile harvesting of wind energy

"Our goal is to solve the issues that the traditional wind turbines can't solve," says Yang. "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."

This out-of-phase dance between the two thin films creates enough energy to charge 100 LED lightbulbs.

Yang et al. / Cell Reports Physical Science

As the wind blows — To make their device, the researchers created a pair of laminated films using a combination of ferroelectric polymer and fluorinated polymer, both previously studied for their abilities to collect electric charges.

The researchers hung the films beside each other in clear plastic tubing, and then tested how they would react as different air velocities flowed around them. They found that the films exhibited four distinct states: stable with no contact, out-of-phase flapping, in-phase flapping, and chaotic flapping.

When looking at the amount of voltage created during these different scenarios, the team found that out-of-phase flapping generated the greatest voltage, thanks to a combination of the greatest number of surface area contact points and the greatest amplitude between the films when pulled apart.

These two then films, called B-TENG, create electricity by smashing together and pulling apart in a breeze.

Yang et al. / Cell Reports Physical Science

The generator performed its best at wind speeds of 8.9 to 17.9 mph (4 - 8 m/s) — equivalent to a fast jog or a speedy bike ride, the study suggests. But, the researchers say they were able to generate electricity from just the wind coming off someone waving their arms, too.

With this energy, they could power 100 LED lightbulbs, as well as a temperature and pressure sensor, the researchers report.

Going forward, Yang highlights two goals. One, the team hopes to miniaturize the generator to smaller than a coin so that it can be integrated into hand-held electronics, like a cell phone. If they succeed, it might be possible in the future to charge your phone with the same wind created from reaching your 10,000 steps.

Yang also wants to work towards sizing the technology way up.

"I'm hoping to scale up the device to produce 1,000 watts, so it's competitive with traditional wind turbines," he says. "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."

Abstract: Wind energy is one of the most cost-effective energy sources available today. Some techniques have been developed to scavenge wind energy, but making use of lower flutter velocity while maintaining high conversion efficiency remains challenging. Here, we report a triboelectric nanogenerator composed of two interacting triboelectric films with four flapping modes, enabling an effective work wind velocity as low as 1.6 ms-1 and a high conversion efficiency of 3.23%, which, to our knowledge, are better than previously reported values of wind energy scavenging. The output performance of B-TENG can be determined by device size and flow velocity; the optimized device exhibits an output voltage, current, and power of 175 V, 43 mA, and 2.5 mW, respectively, with dimensions of 3 x 8 x 2 cm ^3 at a flow velocity of 8 ms-1. The B-TENG may pave the way for future wind scavenging devices for a range of point-of-use Q2 applications.

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