Energy Harvesting ‘Piezo-tree’ Concept
Researchers at the Cornell University have taken inspiration from nature and tried to imitate the swaying of tree branches. So what is the difference between natural swaying of trees and energy-harvesting tree created by Cornell University researchers? The flapping leaves developed in the laboratory generate energy which can be utilized by us. They are christened as the “Piezo-tree.” The synthetic leaves of the “Piezo-tree” are connected to a piezoelectric stem. The whole exercise till now appears to be low-cost, and easily scalable.
The movement of leaves is responsible for generating energy. They convert wind energy into electrical energy. The flapping motion of the leaves causes the instability of the aero-elastic system. The main constituent of the “Piezo-tree” is of Polyvinylidene Fluoride (PVDF) which is a flexible piezoelectric material.
The prototype behaves as a tree facing breeze. The Piezo-tree’s flexible plate and film oscillate just as a flag or leaf might flap in the wind. The flapping motion is generated due to instability of the aero-elastic system. Because the flexible piezoelectric material Polyvinylidene Fluoride (PVDF) can endure unpredictable wind strength. They have attached one edge of PVDF element to a cylinder bluff body and left the other edge free. When the breeze blows and touches this bluff body, it leads to a vortex-shedding. Then the periodic pressure difference forces the piezo-leaf to synchronously bend in the downstream of the air wake. The AC signal is gleaned from the flapping piezo-leaf that is working on a periodic bending model, and the electrical energy is then stored in a capacitor after rectifying it with a full-wave bridge.
However, Cornell University researchers were able to generate only about 100 pW because of the weak piezoelectric strain coefficient of PVDF. When the preliminary Piezo-Leaf Generator’s power level was not sufficient enough it was unable to drive even a common LED. Then, researchers attached a piece of plastic film to the end of the leaf along the direction of air flow. This move paid off. Now it showed around 100 times increase of power in the same condition. Researchers also tried various permutations and combinations. They had conducted a series of experiments. They utilized attachments of various shape, area, density and flexibility of plastic and polymer film. This threw out different results in the level of power.
When researchers were trying out different anatomical structure of their synthetic tree their design optimization studies showed that a particular vertical stalk, horizontal leaf arrangement would increase power output by an order of magnitude. This is a enormous, ten-fold progress over current leaf-stalk arrangements. The “piezo-tree” could be utilized as an efficient and exceptional power producer in a variety of environments. For practical and commercial purposes the researchers anticipate to build plant-like devices with hundreds or thousands of piezo-leaves.