Fluttering polymer ribbons harvest electrical energy

A new low-cost nanogenerator that can efficiently harvest electrical energy from ambient wind has been created by Ya Yang at the Beijing Institute of Nanoenergy and Nanosystems of the Chinese Academy of Sciences and colleagues.

The team reports that the device achieves high electrical conversion efficiencies for breezes of 4–8 m/s (14–28 km/h) and say that it could be used to generate electricity in everyday situations, where conventional wind turbines are not practical.

As the drive to develop renewable sources of energy intensifies, there is growing interest in harvesting ambient energy in everyday environments. From breezes along city streets, to the airflows created as we walk, the mechanical energy contained in ambient wind is abundant.

The challenge is to harvest this every in an efficient and practical way. This has proven difficult using existing technologies such as piezoelectric films, which operate at very low power outputs.

Yang’s team based their new design around two well-known phenomena in physics. The first is the Bernoulli effect, which causes the fluttering of two adjacent flags to couple. If separated by a very small gap, the flags will flutter in-phase, while at slightly larger separations, they flap out-of-phase, and symmetrically about a central plane.

The second is the triboelectric effect – the familiar phenomenon behind the “static electricity” that is created when different objects are rubbed together and then separated – resulting in opposite electrical charges on the objects and a voltage between the two.

Two polymer ribbons

Using two polymer ribbons; one coated with a silver electrode, and the other with the polymer FEP, Yang and colleagues combined these phenomena to create a “Bernoulli effect-dominated triboelectric nanogenerator”, or B-TENG. When subjected to a parallel airflow, the out-of-phase fluttering of the ribbons causes them to touch and separate periodically; resulting in a build-up of charge which could be used to generate an output voltage.

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The researchers showed that their 3×8 cm device created usable electrical energy for wind speeds as low as 1.6 m/s, with conversion efficiencies exceeding 3.2% for speeds between 4–8 m/s.

The device’s practicality was demonstrated by using it to illuminating 100 LEDs in a series circuit; integrating it into a self-powering thermometer; and using it to charge a 100 µF capacitor to 3 V in 3 min. Together, these elements were incorporated into a self-powered pressure sensor for a pipeline, using lightweight and extremely low-cost materials.

Yang’s team now hope to improve the B-TENG’s efficiency to make it even more compact – potentially enabling its integration with everyday devices. At the same time, they also hope to scale-up the device to create kilowatt-scale generators, which could compete with traditional wind turbines.

If successful, the B-TENG could be used in applications ranging from wearable electronics, which can be charged by the airflow generated by walking; to clean power generation in biodiverse areas, where spinning turbines can be harmful to wildlife.

B-TENG is described in Cell Reports Physical Science.

Physics World

Journal Reference:

A Triboelectric Nanogenerator Exploiting the Bernoulli Effect for Scavenging Wind Energy

Summary:


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 μA, and 2.5 mW, respectively, with dimensions of 3 × 8 × 2 cm3 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 applications.

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