May 22 2010
How it Works
An oscillating water column (OWC) is a wave energy converting technology that can be installed onshore preferably on rocky shores; nearshore in up to 10m of water; or offshore in 40-80m deep water. The device consists of a large wave capture chamber, a platform for an air turbine, a lip, wing walls, and an air chamber. When waves approach the device, they enter under the partially submerged lip that traps air in a piston type system, forcing the air upwards through the air turbine. This pressure forces the turbine to spin, which is how the energy is harnessed by the waves. As the waves retreat, air enters back into the air chamber from the other side of the turbine.
The Wells Turbine
OWC utilize turbines that can be divided into two different groups: turbines with fixed pitch blades and turbines with variable pitch angle blades. The conventional Wells turbine along with axial and radial impulse turbines can be included in the first group. The second group includes the Denniss-Auld turbine (Gareev, 2011).
The Wells turbine is the most common turbine in the air chamber. It spins when air is pushed up through and pulled back into the column. This turbine has the ability to constantly spin in one direction regardless of air flow direction, which allows for optimal energy harvesting (“Islay LIMPET,” 2002).
There are several other kinds of air turbines found in OWC: impulse turbines, radial turbines, and the Denniss-Auld turbine. A company in Australia called Oceanlinx has improved upon their Denniss-Auld turbine naming it the airWAVE. It is claimed to be more efficient than any turbine on the market (Takao and Toshiaki, 2012).
Where in the World?
It has already been established that the OWC prefers rocky shores for onshore/nearshore devices, but they also require a consistent and strong wave climate. Typically, the higher the latitude (above 30 degrees) the better the location for an OWC. Also western shores are best due to the directional patterns of waves (Carbon Trust, 2010). There have been installations in several places around the world: Scotland, India, Australia, Portugal and Japan. Unfortunately North Carolina is not the best location for onshore oscillating water columns. The best locations in the United States can be found in the upper northwest, in Oregon and Alaska. The northeast coast in New England also serves as a decent location, but the northwest has at least 4X greater energy potential. However, there are no OWC projects in the United States at this time.
Oceanlinx is an Australian company leading the way in wave energy designs. They have already demonstrated their knowledge in OWC with several test sites. Port Kembla, off the coast of Sydney, Australia, has housed both greenWAVE and blueWAVE technology. GreenWAVE technology refers to the nearshore OWC while blueWAVE OWC are located in deep ocean. The greenWAVE Mk1 OWC operated from 2005 to 2009 as Oceanlinx’s first full-scale prototype. Its blueWAVE project, called Mk3–Pre Commercial, operated from February 2010 to March 2010, and was one of the first floating deep sea OWC to be connected to the grid.
Installed Capacity and Economics
The LIMPET, which is the OWC located on the coast of Islay, Scotland, is currently operating as a prototype at 75kW. However, the facility is able to work at a full capacity of 500kW . This is the generating capacity that makes wave energy economically viable and able to compete in the commercial market (Carbon Trust, 2010) The site in India built as a nearshore OWC is operating at 150kW. The Mk3-PC built by Oceanlinx was rated to 2.5MW. The stark differences depend on the construction, air turbine, and wave energy available. Wave energy is currently quite expensive operating at 14 cents per kWh. This is due partly to the expensive installation costs and technology development. Eventually as wave energy become more wide spread the cost will be lowered to a price comparable to wind energy.
The environmental impacts of OWC do not appear to be as great as other renewable devices installed in the ocean, and are certainly cleaner than nonrenewables. A Life Cycle Assessment of OWC calculated that the carbon emissions over 25 years, including construction, installation, operation and decommissioning, would be 24 grams of carbon dioxide (Oceanlinx, 2012). OWC do not have any moving parts underwater, meaning no organisms will get caught inside of a turbine. Several issues that have been discussed regard the visual aspect of having an OWC onshore or right offshore: it would destroy the view and would generate noise pollution. However, if located in deep sea, it would be far enough offshore so it could not be seen or heard. The OWC itself will operate as an artificial reef to increase the marine species in an area.
Carbon Trust. Shoreline and Nearshore OWC Wave Energy Devices. Rep. N.p.: n.p., 2010. Docstoc. Web. 25 July 2012.
Drew, B., A. R. Plummer, and M. N. Sahinkaya. “A Review of Wave Energy Converter Technology.” Rev. of Wave Energy Converter Technology. Proceedings of the Institution of Mechanical Engineers 16 June 2009: 887-902. Web of Science. Web. 22 July 2012.
Gareev, Andrei. Analysis of Variable Pitch Air Turbines for Oscillating Water Column (OWC) Wave Energy Converters. Thesis. University of Wollongong, 2011. N.p.: n.p., n.d. Print.
“Islay LIMPET Wave Power Plant.” The Queen’s University of Belfast, 2002. Web. 24 May 2010. <http://www.wavegen.co.uk/pdf/LIMPET%20publishable%20report.pdf>.
“Oceanlinx | Wave Energy Technology.” Oceanlinx | Wave Energy Technology. N.p., n.d. Web. 22 July 2012. <http://www.oceanlinx.com/>.
Takao, Manabu, and Toshiaki Setoguchi. “Air Turbines for Wave Energy Conversion.” International Journal of Rotating Machinery (n.d.): n. pag. Hindawi Publishing Corpoation. Web. 22 July 2012.
Webb, Ian, Chris Seaman, and Gordon Jackson. Oscillating Water Column Wave Energy Converter Evaluation Report. 4 Feb. 2005. Raw data. The Carbon Trust, n.p.
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