Vertical-stalk Flapping-leaf Generator for Wind Energy Harvesting

We study a parallelized flapping piezo-leaf generator for harvesting ambient wind energy and demonstrate an initial design. We fabricated prototypes in various configurations and performed a series of experiments to study performance trends. We propose a novel vertical-stalk L-shape design that exhibits improved output power density over horizontal piezoelectric configurations. While a significant power density performance gap still exists between the current state of piezoelectric devices and commercial wind turbines, their advantage remains in their robust solid-state, low-cost, low-maintenance and scalable construction. INTRODUCTION Renewable and sustainable energy research has attracted much attention with the increasing gap between the demand and supply of fuel in recent years. Researchers have been searching for a practical alternative to petroleum and coal for electrical power. Hydroelectric power stations and wind turbines are two of the most successful solutions in this field; however, even compared to hydroelectric energy, wind power is much more environmentally friendly. Nevertheless, there are some limitations of traditional wind power generators, namely, that using a large rotational turbine to harvest energy from the air requires significant financial and infrastructure investment, large real-estate area and long term commitment. The focus of our research is to investigate the principles and feasibility of the harvesting energy from the wind in constrained spaces such as around buildings, as an alternative to conventional rotary wind turbines. The central idea is to harvest energy from wind induced vibration instead of wind driven rotation. Much previous work has focused on using piezoelectric materials to convert mechanical vibration energy into electrical power. Anton, Paradiso, Priya and Sodano et al. [1] [2] [3] [4] reviewed recent devices and applications of piezoelectric materials based energy harvesters. Roundy et al. [5] [6] developed a vibration based piezoelectric generator with a beam configuration, and provided a model for estimating the output voltage and power with experimental validation. Shen et al. [7] developed cantilevered power harvesting prototypes with three types of piezoelectric materials: lead zirconium titanate ceramic (PZT), macro fiber composite (MFC), and Polyvinylidene Fluoride (PVDF). They compared the power generating capabilities of the three materials under large vibration amplitudes. A similar device and mathematic model of piezoelectric cantilevered generators has also been studied by Sodano et al. [8]. In order to harvest fluid induced energy, some researchers [9] [10] have designed a novel “energy harvesting eel” using PVDF, which could convert the flow energy to electrical power in oceans and rivers through a flow induced oscillating motion on the PVDF film, which followed bluff body. The model and experimental validations were both studied. Priya and Myers et al. [11] [12] designed and optimized a small windmill prototype to extract energy from airflow. They used a wind driven mechanism to bend a series of piezoelectric bimorphs transducers, with the wind driving the rotation of the small windmill. A variety of other piezoelectric and magnet materials based wind energy generation concepts were discussed in