Oscillating Water ColumnsAs of 2009, there are over 1000 wave energy conversion techniques which have been patented in Japan, North America and Europe [1]. Of all these technologies, oscillating water columns (OWCs) have one of the longest track records of deployment and grid-connected facilities have been operational now for over a decade. The first succesful implementation of this technology was the LIMPET wave power plant located on the coastline of the Isle of Islay. [2]
For more information on the LIMPET OWC device go to the 'Current Technologies' section of this website where you will find a short video presentation made by Voith Hydro Wavegen Ltd - the company that developed and operates LIMPET. |
Working Principles
OWCs are generally divided into two categories; fixed and floating. 'Submerged' devices which tap into more powerful deep water waves also exist but work on different principles, are fairly complex and have problems with mooring, access for maintenance and a requirement for long underwater cables. For these reasons, they have been omitted from this description.[3]
Both classes of OWC devices have their advantages and disadvantages but both fixed and off-shore devices work on the same principle. All systems are made up of the same basic elements: a collector chamber and a power take-off (PTO) system. The collector chamber is placed on the surface of the water in such a way that a column of air is trapped between the water and the collector. Incident waves cause the water column to oscillate which in turn forces the air in and out of chamber through an air turbine - usually a 'Wells Turbine'/Induction generator combination - generating electricity. An interactive animation below of a fixed OWC demonstrates its mechanics.
OWCs are generally divided into two categories; fixed and floating. 'Submerged' devices which tap into more powerful deep water waves also exist but work on different principles, are fairly complex and have problems with mooring, access for maintenance and a requirement for long underwater cables. For these reasons, they have been omitted from this description.[3]
Both classes of OWC devices have their advantages and disadvantages but both fixed and off-shore devices work on the same principle. All systems are made up of the same basic elements: a collector chamber and a power take-off (PTO) system. The collector chamber is placed on the surface of the water in such a way that a column of air is trapped between the water and the collector. Incident waves cause the water column to oscillate which in turn forces the air in and out of chamber through an air turbine - usually a 'Wells Turbine'/Induction generator combination - generating electricity. An interactive animation below of a fixed OWC demonstrates its mechanics.
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Fixed vs. Offshore OWCs
Floating Oscillating Water Column (Source: physics-edu.org)
Offshore OWCs - pictured left - have the advantage of using wave energy before the waves lose some of their energy through friction with the sea bed but also have a few disadvantages [4]. Their design and construction is more technical, they are difficult to install and require mooring, are prone to damage, require underwater cables to deliver electricity to shore and are more difficult to operate and maintain.
Fixed OWCs on the other hand recieve less energy from the waves but this effect can partly be compensated by wave energy concentration due to refraction or diffraction. have very high capital costs but are much better understood, easy to install, operate and maintain and are easily accessible.
Mainly though, this project is concentrated on fixed OWCs because floating OWCs are at an early stage of development and they work well on small scale as independent units but connecting enough of them to the grid to make them viable is a complex problem. At these early stages of development, difficulties should be minimised until a fuller understanding of the technology is achieved and attempting large-scale wave energy extraction at this stage of development seems unnecessary.
Fixed OWCs on the other hand recieve less energy from the waves but this effect can partly be compensated by wave energy concentration due to refraction or diffraction. have very high capital costs but are much better understood, easy to install, operate and maintain and are easily accessible.
Mainly though, this project is concentrated on fixed OWCs because floating OWCs are at an early stage of development and they work well on small scale as independent units but connecting enough of them to the grid to make them viable is a complex problem. At these early stages of development, difficulties should be minimised until a fuller understanding of the technology is achieved and attempting large-scale wave energy extraction at this stage of development seems unnecessary.