Small wind energy harvesting

Abstract

For most large scale construction projects these days, the use of remote electronic sensors is almost mandatory when it comes to monitoring the structure for maintenance works after completion. The problem with current models of electronic sensors is that most are run by an exhaustible power supply, such as batteries. Furthermore, when it comes to changing the batteries, this in itself presents a potential problem if the sensor is embedded deep inside the structure.

Hence, the development of a self powered sensor is not only environmentally sustainable, it also makes the task of maintaining a building easier and potentially cheaper. Modern technology has opened up many avenues of harvesting the environment for energy. The focus of this project is to combine both wind power and piezoelectric materials to develop a self powered remote sensor. The idea is to make use of the ambient surrounding wind in the building(eg, air conditioning vents, underground MRT tracks) and to convert this wind into electricity using the properties of piezoelectric materials. Basically, piezoelectric materials convert mechanical energy into electricity through the direct piezoelectric effect when the material is deformed.

Currently, most piezoelectric harvesters (PEHs) are basically 'flapping' cantilevers. They generate electricity by sticking pieces of piezoelectric material to the cantilever, and through environmental influences(wind in this case), get the cantilever to deflect. This deflection generates electricity through the direct piezoelectric effect. The problem with this is that most PEHs currently work within a single degree of freedom. That is to say, they are only efficient at the resonant frequency where the deflection is the greatest. However, piezoelectric energy harvesters based on galloping do not have the problem of narrow bandwidth (which should be feasible at lower effective wind speed ranges). In addition, the self-excited and self-limiting characteristics of galloping make it a promising aeroelastic phenomenon that can be exploited to obtain structural vibrations for energy harvesting purpose.

Improving the performance of small wind energy harvesters involves 2 parts, namely : Reducing the cut-in wind speed and enlarging the power output. This project shall explore ways to improve the power generation capabilities using multi-modal techniques, which is essentially altering the shape and stiffness of the cantilever beam to accommodate another degree of freedom.