Wave Powered Suction Turbine
Introduction: The Need for Alternate Energy Sources
In today’s world, the development of sustainable energy sources is coming to the forefront of issues to stop the damage to our planet. Wind farms and solar panels tend to dominate thought when thinking of sustainable energy sources, but one of the most underutilized and prevalent sources of sustainable energy is the world’s oceans. As most of the world is covered by the seven oceans, and also large gulfs and inland seas, it seems like a logical choice to powering our world renewably.
The Potential of the Wave Powered Suction Turbine
One technology that has been getting a lot of attention from sustainable energy initiatives is that of the wave powered suction turbine. This technology is one of the first viable power sources that taps into the boundless resource of dynamic bodies of water. It is estimated that ocean waves can ultimately provide up to 2 terawatts of electricity which is close to the 1.9 terawatts generated by the world today.   The waves utilized by the suction turbine devices are formed by wind which in turn is created as a result of density gradients in the air created by the heating effect of the sun, and therefore constitutes the wave powered suction turbine as a sustainable form of energy production. 
How It Works
An oscillating water column inside of a a large, cavernous container, open on the bottom side and half submerged into a highly active wave location is the functioning piston-cylinder of the wave powered suction turbine. As can be seen in Figure 1, as the waves roll by and the water level rises in the empty box, the air occupying the space is displaced and forced through the opening and through the subsequent turbine and generator setup. As the wave continues to pass through the box or as the water recedes from the coastline, the water level falls and air returns through the turbine passage because of the vacuum created in the box. A Wells turbine design allows for the turbine rotation direction to remain constant and independent of the direction of the air flow; this is accomplished by turbine blades with variable pitch that result in slower turbine speeds but increased turbine torque, thus the turbine will run continuously with each passing wave. 
|FIGURE 1. Operation of a Wave Powered Suction Turbine, courtesy of European Marine Energy Centre and Wavegen|
The steadiness of the electrical power output can be unpredictable, and has been part of the systems commercial drawbacks. Because the electrical grid is set at a certain frequency, a lot of conditioning is needed to get the generator in sync with the grid and this aspect of the system remains in the development stages.  Sensors to predict the frequency and amplitude of incoming waves are being utilized to increase the effectiveness of the system for given conditions. The Oceanlinx design, as seen in Figure 2, is capable of generating peak commercial power outputs between the range of 100kW to 1.5MW.
|FIGURE 2. Oceanlinx Design and Image, courtesy of Oceanlinx. |
Wavegen, a subsidiary of Voith Siemens Hydro Power Generation Company, has designed and implemented a Land Installed Marine Powered Energy Transformer (LIMPET) that is affixed to the coastline and can therefore undergo maintenance and connect to the power grid with less difficulty than the Oceanlinx design.  Figure 3 is a picture of the LIMPET design by Wavegen, and an animation of the design in action can be seen here (scroll through the tabs in the bottom right corner). Similar principles of the Wavegen design drive the Oceanlinx open water anchored design.
|FIGURE 3. Land Installed Marine Powered Energy Transformer in Scotland, Courtesy of EarthFuture.com.|
Areas with adequate wave activity and of high interest to the technology include northeastern and northwestern United States, Scotland, Canada, southern Africa and Australia.  These units can be used alone or on wave farms where multiple units are connected to deliver the needs of a community located near the coastline. Also, it has been proposed that wave farms can provide erosion control by acting as a breakwater.
Current Status of Wave Power Suction Turbine
At current, wave powered suction turbines are not a very commonly used power source. One system that is in use is a LIMPET located in Islay, a part of Scottish Highlands. LIMPET, since the year 2000, has been supplying 0.5MW of power to the local community.  Also, the Islay Wave Bus, powered by LIMPET, is the first wave powered electric bus in the world. 
A project is underway to bring wave energy, in the form of LIMPET or its Wavegen counterpart OSPREY, to the Faroe islands. This project is a collaboration between Wavegen and SEV, an energy company in the Faroe islands. 
The EMEC, European Marine Energy Centre, has an oscillating water column at their Billia Croo, Mainland Orkney test site. The Orkney site was selected because it receives continuous Atlantic waves of up to 15m in height. It also has a large professional community whose focus is on renewable and sustainable energy. The EMEC hopes to one day find renewable power solutions for the European continent using one of its most untapped resources for power, the Atlantic Ocean.  A chart of wave intensity can be seen in Figure 4.
|Figure 4: Wave Intensity Around the World in kW per meter of crest. Courtesy of Ocean Power Delivery.|
There are several projects that are underway by Oceanlinx to bring wave power to Australia, the United Kingdom, Namibia, and the United States of America. In Portland, Victoria, Australia, the advanced permitting stage has been reached for the largest wave energy project currently in development in the world. This plant will consist of eighteen 1.5 MW wave power units, similar to that shown in Figure 2, that will produce a combined 27MW of power. Also, in Namibia, a contract has been signed with the GPP, a part of the South African Utility SELCo for a 1.5MW. It is planned for this unit to be followed by 10 more units in the future. 
|Figure 5: Oceanlinx Wave Farm Proposal, Courtesy of Oceanlinx|
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- D. Greaves
- A. Layton
- M. Neely