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Small-Scale Wind Energy Harvesters for Structural Health Monitoring

By Scott Beressers

Research interest include: wind and vibration energy harvesting, piezoelectric and magnetoelectric non-linear effects, drivetrains, biomimetic airfoil design, induction machine design, and continuum fluid dynamics.
Current projects include:

  • Development of “contact-less” piezoelectric-based wind turbine
  • Application of small-scale, conventional wind turbine
  • Design and fabrication of mid-scale, duct-augmented wind turbine for residential uses

 

“Contact-less” Piezoelectric Wind Turbine
Conventional wind turbines rely on electromagnetic generators for electro-mechanical energy conversion.  While electromagnetic generators are highly matured and efficient for larger-scale power generation, they are limited by several factors including high cogging torque and high rotational speeds.  In low altitudes (below 50 ft from ground) and in areas with low average wind speeds, conventional wind turbines are not able to operate consistently at high rotational speeds. Hence, piezoelectric materials have explored as a low-torque, low-rotaional speed alternative for electro-mechanical energy conversion in wind turbines.  In the case of small-scale (blade swept area below 5 in2) wind turbines, the more continuous operation from using piezoelectric materials can offset the corresponding decrease in efficiency from switching away from electromangetic generators.  In the “contact-less” wind turbine concept, the effectiveness of using piezoelectric materials is increased by using alternating-poled, permanent magnets to excite the piezoelectric materials; hence, there are no frictional losses from contact between some mechanical actuator and the piezo’s.  The efficiency of wind turbine configuration can be further increased through performing detailed blade design, using high “d31” piezoelectric materials, and designing for resonance.

   

1st generation (left) and 3rd generation (right) “contact-less” wind turbine prototypes. Figure 1. 1st generation (left) and 3rd generation (right) “contact-less” wind turbine prototypes.

Small-scale Wind Turbine
While piezoelectric-based wind energy harvesters offer certain advantages for low power generation, conventional, electromagnetic wind turbines are a highly developed and matured technology.  It is for this reason the development of a scaled-down version was investigating; yielding the first prototype designated Small-scale Wind Energy Portable Turbine (SWEPT).  The prototype was developed using conventional, horizontal-axis wind turbine design techniques and is the most efficient prototype to-date.  However, the limitations of cut-in wind speed and lack of scalability still exist.  Further explorations into utilizing electromagnetic technology will include: bio-inspired airfoil design, custom-tailored direct-drive generator design, and duct augmentation.
   

Small-scale wind energy portable turbine (SWEPT) is the first prototype for small-scale wind energy harvesting; developed based on conventional, electromagnetic wind turbine technology Figure 2. Small-scale wind energy portable turbine (SWEPT) is the first prototype for small-scale wind energy harvesting; developed based on conventional, electromagnetic wind turbine technology

Residential, Duct-Augmented Wind Turbine
The third research area being investigated in wind energy harvesting is a “middle-scale”, duct-augmented wind turbine for use in residential areas.  While using these “middle-scale” (often referred to as “small-scale” within the wind turbine industry) are not a new area of research, there has been an increased interest in alternative energy solutions for the average consumer.  Unfortunately, there are number of issues with residential wind turbines that push consumers to look towards solar as an alternative.  Among these are excesive noise and limited usability due to low wind speeds.  It was, therefore, determined that the use of a duct or “shroud” placed circumferentially, around the blade rotor may not only reduce noise and lower cut-in wind speed, but also improve the overall performance of the turbine.  While such a duct may be infeasible on the full-sized, industrial models, the relative cost of the duct compared to the traditional components of a residential wind turbine is greatly reduced.  Thus far, our investigations have included basic CFD evaluations of the duct design, the use of a multi-stage rotor, and the implementation of a direct-drive generator.  The overall goal is to provide a wind turbine capable of producing 1-10 W of power at a cut-in wind speed of 3-5 mph.

   

Cocept model of purposed duct-augmented wind turbine for residential use.  The blade diameter will be 1 meter. Figure 3 . Cocept model of purposed duct-augmented wind turbine for residential use. The blade diameter will be 1 meter.