Principles of the Oscillating
Water Column (OWC)
 
(Images courtesy of Wavegen) Cutaway diagram of Islay shoreline wave energy device, UK
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How it works continued...
Another notable example of an OWC is the Mighty Whale. It is the worlds largest offshore floating OWC and was launched in July 1998 by the Japan Marine Science and Technology Center. This prototype, moored facing the predominant wave direction, has a displacement of 4,400 tons and measures 50m long. The Mighty Whale has three air chambers that convert wave energy into pneumatic energy. Wave action causes the internal water level in each chamber to rise and fall, forcing a bi-directional flow over an air-turbine to generate energy. The resulting electricity is supplied mainly to the nearby coastal areas. Storage batteries onboard ensure that electricity is available even during periods of reduced wave activity. It is projected that a row of such devices could be used to supply energy to fish farms in the calm waters behind the devices, and aeration/purification of seawater [7]. Another promising type of wave energy power plant is a shoreline-based system called the Tapered Channel (Tapchan). The principle here is capital intensive yet has potential due to its ruggedness and simplicity. A tapering collector funnels incoming incoming waves in a channel. As the wave travels down the narrowing channel it increases in height till the water spills into an elevated reservoir. The water trapped in the reservoir can be released back to the sea similar to conventional hydroelectric power plants to generate electricity [1]. The advantage of this particular system lies in its ability to buffer storage which dampens the irregularity of the waves. However, the Tapchan system does require a low tidal range and suitable shoreline topography -limiting its application world-wide. A demonstration prototype of this design has been running since 1985 and plans are under consideration to build a commercial scale plant in Java [8]. |
The "Mighty Whale" is the world's largest offshore floating wave energy device (Source: CADDET Renewable Energy Newsletter) |
Advantages
The primary advantages of wave energy power plants are the following: onshore wave energy systems can be incorporated into harbor walls and coastal protection, thus reducing the cost of such systems, and providing dual use; create calm sea space behind wave energy systems for the development of mariculture or other commercial and recreational uses; long-term operational life time of plant; provides a non-polluting and inexhaustible supply of energy. |
| The concept of TAPCHAN
is an adaptation
of traditional hydroelectric power production [12]. 
(Copyright Boyle, 1996) |
Disadvantages
The primary drawbacks of tidal power plants are the following: high capital costs for initial construction [9] to resist exposure to strong wave forces, storms, and corrosion [10]; wave energy is an intermittent resource [2]; requires favorable wave climate. The highest concentration of wave energy occurs between the latitudes 40° and 60° in each hemisphere, which is where the winds blow most strongly. Latitudes of around 30° of the equator due to the regular trade winds may also be suitable for exploitation of wave energy [11]; offshore wave energy systems require investment power transmission cables for electrical connections to shore [11]; degradation of scenic ocean front views from wave energy devices located near or on the shore, and from onshore overhead electric transmission lines [10]; potential interference with other uses of coastal and offshore areas such as navigation, fishing, and recreation if not properly sited [2]; by reducing the height of waves they may affect beach processes in the littoral zone [2]. |
| An example of the duel
purpose of a wave energy barrage
incorporated into a harbor wall for coastal protection. 
(Image courtesy of Wavegen) |
Conclusions
Ocean waves have the potential to contribute up to one TW to the global energy supply. The problems associated with the intermittence of wave energy can be smoothed by integration with the general energy supply system. Many different wave power plants, some of them multi-purpose, have been proposed, assessed, and cost-estimated [9]. With the development of large-scale demonstration and commercial power plants underway, wave energy will begin to play an increasing role in complementing other renewable and conventional energy technologies to meet global needs. |
| Archimedes Wave Swing- generates electricity by
drawing
energy from sea swells. It is a simple system of connected air chambers utilising a flywheel effect, using the heave of the sea to produce electrical energy. 
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References
1. Thorpe, T.W. 1998. Chapter 15: Wave energy, In:
Survey of Energy
2. Charlier, R.H. and Justus, J.R. 1993. Ocean Energies:
Environmental,
3. DOE/CE-0258. 1989. U.S. Department of Energy Information. 4. McCormick, M.E. 1981. Ocean Wave Energy Conversion,
5. Seymour, R.J. (Ed.) 1992. Ocean Energy Recovery: The
state of
6. Wavegen website: http://www.wavegen.co.uk/ 7. Ogiyama, H. 1999. The Mighty Whale, CADDET
8. Ross, D. 1997. Wave Power, In: Renew, Issue 109, Network
9. Falnes, J. and Lovseth, J. 1991. Ocean wave Energy,
Renewable
10. Shaw, R. 1982. Wave Energy: A design challenge,
Ellis Horwood
11. Burnham, L., Johansson, T.B., Kelly, H., Reddy, A.K.N. and
12. Boyle, G. (ed.) 1996. Renewable Energy, Power for a Sustainable
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