A cm scale electret-based electrostatic wind turbine for low-speed energy harvesting applications

Abstract

This paper presents a small-scale airflow energy harvester built on an axial turbine architecture and exploiting an electret-based electrostatic converter. When the airflow velocity is high enough, the windmill starts rotating and creates a periodic relative motion between a stator and a rotor which induces variations of capacitance. These ones are directly converted into electricity thanks to the use of Teflon electrets charged at −1400 V which polarize the variable capacitors. We focus our study on a 4-blade axial turbine with a diameter of D=40 mm, a depth of W=10 mm, for a total volume of 12.6 cm 3 . This windmill has been tested with various blade angles and different types of electrostatic converters and output powers up to 90 μW at 1.5 m s −1 (7.5 μW cm −3 ) and 1.8 mW at 10 m s −1 (111 μW cm −3 ) have been obtained so far. The coefficient of power reaches C p =5.8% and among the small-scale airflow energy harvesters previously reported, this one has the lowest cut-in speed (1.5 m s −1 ).

Energy Harvesting Research: The Road from Single Source to Multisource

“…The working principle of electret‐based energy harvesters is similar to that of the conventional electrostatic ones but without the need for the external voltage source. There are two groups of electret materials—inorganic electrets, e.g., SiO 2 ‐based materials and polymer electrets, e.g., PTFE (also called Teflon), fluorinated ethylene propylene (FEP), CYTOP (amorphous perfluorinated polymer), parylene, etc. Inorganic electrets exhibit a high surface charge density but also an instability in the long term.…”

A methodology for low-speed broadband rotational energy harvesting using piezoelectric transduction and frequency up-conversion

“…An example is the micro-wind turbine. Perez et al presented a centimetre-scale electrostatic wind turbine for airflow energy harvesting [21]. The flow motion was converted to the rotation of turbine blades and electrets were mounted on the edges of blades as rotational components.…”

“…In terms of energy transduction for rotational energy harvesting, the dominant mechanisms are piezoelectric [19,15], electromagnetic [20,23] and electrostatic [21]. Their pros and cons are extensively investigated in vibration energy harvesting [10,24].…”

Nonlinear Analysis and Performance of Electret-Based Microcantilever Energy Harvesters

“…However, large softening behavior would prevent the pull-in instability, increase the level of the harvested power, and broaden the bandwidth. These observations give a deeper insight into the behavior of such energy harvesters and are of great importance to the designers of electrostatic energy harvesters.Energies 2019, 12, 4249 2 of 26 new technologies, it becomes viable to harvest power from ambient and aeroelastic vibrations [2-6], thermal energy [7,8], airflow [9][10][11][12], and ocean waves [13].Common energy-harvesting techniques employ piezoelectric [14][15][16][17][18], electromagnetic [19][20][21][22][23], electrostatic [24][25][26][27], and hybrid [28] conversion principles according to the type of application [29]. Electrostatic mechanism has advantages over other mechanisms where it is possible to work at low frequency and wide bandwidth [30].…”

“…To overcome this limit, electrostatic energy harvesters using electret (dielectric material with permanent polarization) have been fabricated and tested with different ambient vibration inputs, active surface areas, and electret potentials resulting in a wide range of output power [30].After introducing the first electrostatic current generator with two half-disk electrets in 1978 [32], many energy-harvesting structures have been fabricated and tested using electrets. A small-scale axial 4-blade turbine energy harvester was built using a cylindrical converter located all around the turbine [9]. An airflow energy harvester using flutter phenomenon and two parallel flat electret-based electrodes to convert flow-induced movements into electricity was demonstrated in [33].…”