Design of a Point Absorber Type wave energy conversion device



Angus Tai



Index

Introduction

Design

Actual Model

Results

Conclusion



Introduction

With oceans covering over 71% of the Earth’s Surface, and 53% of the nation’s population living near the coastal area, wave energy can be a significant source of electricity to coastal areas. With the density of waves greater than that of air, there is 15-20 times more available energy per square meter than wind or solar; fewer wave energy converter installments is needed to capture the same amount of energy than wind and solar, making wave energy one of the least expensive of renewable energy sources and with a high yield. For instance, one study showed that the potential of accessible wave energy in the UK is around 700kWh/yr, almost double the electricity consumption of the UK, although practically only a portion of the accessible wave energy can be captured. Wave energy also minimizes environmental impact. Unlike wind turbines which may be a noise or visual nuisance, most wave energy conversion devices are located offshore, and generally have a low profile. Wave energy devices are barely visible and will have little to no impact on coastal residents and the environment.  Moreover, electrical output from wave energy is more predictable than wind energy, because waves continue to travel and transmit energy once created; therefore wave energy converter devices can be better optimized to maintain a steady and high output.  

Despite its apparent benefits, wave energy devices have been slow to develop into efficient energy device. In 1982, the Department of Energy in UK struck down a wave energy converter – the Salter Duck when the development of the device was almost to a completion. A report prepared by the British Atomic Energy Authority headquarters claimed that wind energy has more potential than wave energy, thus most renewable energies funding shifted to develop wind energy  and put a halt to the development of wave energy. However, wave energy conversion devices have become more practical as more technological obstacles have been overcome. Some Wave energy conversion devices (WECD) are already in small scale commercial electricity generation and more devices are expected to follow.



Design

Currently WECD designs are highly engineered products with numerous advance technology. It is unlikey to build a small scale yet workable WECD from ground up with a one man team and limited time. Previous coastal engineering students had built some tidal or wave energy model that is not capable of producing any electricity, so the objective here is to build a simple WECD that has capability to show signs of producing electricity.

The resultant design is one that closely resmebles a point absorber type WECD but lack all the complicated hydraulic system, instead the hydraulic system is replaced by a linear generator. The design is base on the principle of Faraday's law of induction. When a magnet slide back and forth through a selonoid, a current is induced inside the wire of the solenoid.

This design is composed of two parts. The upper part is a tube with a solenoid attached to a buoyance unit which rise and fall with wave motion. Another part consist of a magnet inside the tube, the vertical location of the magnet is to be maintained still in water by two counter force: weight of the magnet  and the buoyancy force of the floating piece attached to the magnet.
 
 
video here....

Advantage of this design:

 

Drawback of this design:


Actual Model





A demonstration of horrible craftsmanship.
A Faraday Flashlight "as seen on TV" was modified to make a home-made WECD. The final product deviate from the original design because no foam is small enough yet still have sufficient buoyancy to support the weight of the magnet. A rigid pole is attached to the magnet. The end of the magnet has a foam to make it float. The device did not line up perfectly vertically, the device is

Results

The device is placed inside a bathtub subjected to waves generated with a food tray.

video here ...

Unforturnately, the LED did not lite up after a few trials. A few observation were made during the testing:
I also placed the magnet and the upper proportion of the unit into the water and shake it manually to observe the effect of water. The LED did lite up normal for a brief moment; however, the LED became dimmer at the same effort after a while.

Conclusion

This little experiment demonstrates how difficult it is to construct a proper WECD. The possible reasons why the device did not work may due to:
Building a WECD requires extensive knowledge in multi displane - including but not limited to