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A Nanotechnology Approach to Scavenging Wind and Solar Energy
By Michael Berger, Nanowerk M
ore than 60 research groups worldwide are now develop- ing variations of the tribo-
electric nanogenerator (TENG), which converts ambient mechanical energy into electricity for powering wearable electronics, sensor net- works, implantable medical devices and other small systems. Self-powered nanotechnology
based on these nanogenerators aims at powering nanodevices and nanosystems using the energy har- vested from the environment in which these systems are supposed to operate. This offers a completely new approach for harvesting mechanical energy using organic and inorganic materials.
The Harvest of the Future An interesting approach comes
from a group of Chinese scientists who propose to scavenge the large
amounts of wasted wind energy in cities. In a paper in the May 5, 2016,
While the hybrid solar cell/TENG device could be installed ideally on
rooftops, individual TENG arrays could be used anywhere to capture air movement.
online edition of ACS Nano (“Effi- cient Scavenging of Solar and Wind Energies in a Smart City”), they pro- pose a hybrid nanogenerator that consists of a solar cell and a TENG, which can be utilized to individually or simultaneously scavenge solar and wind energies. “In an equivalent device area of
about 120 by 22 millimeters (4.72 x 0.87 in.), the solar cell can deliver an
output power of eight milliwatts, while the corresponding output pow- er of the TENG can be up to 24 milli- watts,” says professor Ya Yang from the Beijing Institute of Nanoenergy and Nanosystems. “We have utilized a transformer to decrease the imped- ance of the TENG for achiev- ing the impedance matching between the solar cell and the TENG.” The team’s device struc-
ture incorporates a vibration film at the middle of the TENG that includes a Kap- ton film with two copper (Cu) electrodes on both sides, where the FEP (fluorinated ethylene propylene) film, as the triboelectric layer, was affixed on the copper elec- trode. Another two copper electrodes were joined on the top and bottom of the acrylic substrate, respectively, re- sulting in an air gap between the two copper electrodes. The TENG’s dimen-
sions are tiny: The thickness of both the Kapton film and FEP film is about 25 µm, and the thickness of the cop- per electrode is about 200 nm. The air gaps between the vibration film and the copper electrode on the acrylic substrate are 2 mm (0.079 in.), so that the height of air intake is about 4 mm (0.16 in.). While the hybrid solar cell/
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(a) A conventional wind turbine
generator. (b) Integrated solar cell units on the roof of a building. (c) Schematic diagram of rooftop hybridized nanogenerators. (d) Schematic of a hybridized nanogenerator. (e) Photo of a hybridized nanogenerator. (Photo cour- tesy of the American Chemical Society)
TENG device could be installed ide- ally on rooftops, individual TENG ar- rays could be used anywhere to cap- ture air movement, for example, at the outlet of air conditioning units. “The working of the TENG is
based on the wind-induced vibration of the middle Kapton/Cu/FEP films, resulting in periodic contact and sep- aration between the FEP and the top/bottom copper film as both the conductive electrode and the tribo- electric material,” explains Yang. “The output current of the TENG can reach 260 µA under a wind speed of about 15 m/s (33.55 mph). This out- put current decreases with increas- ing the loading resistance, resulting in that the largest output power of the TENG can be up to 26 milliwatts under the responding loading resist- ance of 1 MW.” For their experiments the team
used a homemade lithium-ion bat- tery with a titanium dioxide nan- otube array as the electrode material to store energy generated by the hy- brid nanogenerator. “Our research holds great prom-
focus on the following two aspects: to improve the stability of the hy- bridized device output, and to design a new management circuit for TENG to obtain higher current signals and voltage about 5V.”
Note from the editor: along with tri- boelectric nanogenerators, piezoelec- tric and pyroelectric nanogenerators convert mechanical energy or thermal energy into electricity. Triboelectric generators were first demonstrated in 2012 by Dr. Zhong Lin Wang at Geor- gia Institute of Technology. Since the technology’s debut, the output power density of these devices has increased by five orders of magnitude. They can be used to harvest energy from daily human motion, walking, vibration, mechanical triggering, rotating tires, wind, flowing water and many other activities. To learn more, read Dr. Wang’s paper on the technology at
http://nanoscience.gatech.edu/pa- per/2014/14_FD_01.pdf.
Contact: Nanowerk, LLC, 700
Bishop Street, 17th Floor, Suite 1700, Honolulu, HI 96813 Web:
www.nanowerk.com r
ise for practical applications to maxi- mize solar and wind energy scaveng- ing from city areas, for realizing some self-powered functions — such as sensors —in a ‘smart city’ environ- ment,” concludes Yang. “The next stages in our investigations will be to
August, 2016
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