Cycloidal Wave Energy Converter

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The Cycloidal Wave Energy Converter (CycWEC) is a hydro-electric wave energy device that converts the energy of ocean waves to shaft power and subsequently electricity. It consists of one or two hydrofoils attached to a central shaft. The shaft then drives a generator, pump or other device utilizing the shaft power.

History

The CycWEC was invented by Dr. Stefan Siegel in 2005, and the first patents describing this technology were filed in 2006.[1] Initial scientific research was subsequently conducted under funding from the National Science Foundation starting in 2008.[2] The scientific research conducted at the United States Air Force Academy during this three year program included both numerical simulations as well as small scale two-dimensional wave flume experiments. Initial results were reported in scientific meetings as early as 2009.[3] Numerical simulations showed the ability to reduce the height of the incoming waves by more than 90%, and thus to extract more than 99% of the energy of the wave.[4] These were confirmed by experiments in a small 2D wave flume.[5] The encouraging results achieved during the basic scientific investigations led to the foundation of Atargis Energy Corporation by Stefan and Rina Siegel as well as Victor Korea in 2010. Atargis Energy subsequently received funding to conduct large scale wave tank tests from the United States Department of Energy in 2010.These were conducted in 2011 and 2012 at the Texas A&M Offshore Technology Research Center (OTRC) in Texas. Results were mixed. The device leaked and never produced power in 2011. After another year of development and continued leak problems, the WEC captured 370 watts of power in the 2012 tests. [6]

Operation

A Cycloidal Wave Energy Converter (CycWEC) is the adaptation of a Cycloidal Propeller to a different purpose, which is to extract energy from ocean waves. A cycloidal Propeller consists of one or more blades oriented parallel to a main shaft, and attached at a radius. While the geometry of a Cycloidal Propeller and a Cycloidal WEC looks identical, the purpose and mode of operation are entirely different. To convert waves into useful electrical energy, the CycWEC must synchronize with ocean waves, perfectly cancelling the wave by producing an anti-wave 180 degrees out of phase. In doing so, the CycWEC extracts the ocean energy to rotate a shaft which can drive a generator, converting the wave power into electrical power.

Cycloidal Turbines are sometimes seen as specialty wind turbines known as vertical axis wind turbines (VAWT). In the VAWT, the shaft is oriented vertically, and the turbine bears some resemblance to an eggbeater. While they can operate as efficiently as the more common horizontal axis wind turbines, economic considerations favor the latter. In the marine industry, Cycloidal Propellers have been used for many years as propulsion devices for tug boats and ferries, and are commonly known as Voith Schneider Propellers.

The CycWEC operates fully submerged in the ocean. For deep ocean waves the optimal CycWEC position is oriented such that the main shaft and hydrofoils are perpendicular to the incoming wave and parallel with the ocean surface. The hydrofoils are controlled by hydraulic actuation to adjust the blade pitch depending on the height of the incoming waves. In order to be useful as a wave energy converter, a Cycloidal WEC is synchronized to the phase of the incoming wave from which energy is to be extracted. This is achieved by an upwave surface elevation sensor. Algorithms to estimate wave direction as well as instantaneous phase and amplitude of the incoming wave are utilized to control both the main shaft power take off as well as the pitch of the wave energy converter blades. When this system is properly tuned, by accurate synchronization and pitch scheduling, an incoming unidirectional, irregular wave can be entirely terminated, where more than 99% of the wave energy is extracted.[4]

Potential

The CycWEC was conceived to address the main issues that all wave energy converter concepts are at present trying to address: High Cost of Energy, and difficulty surviving storms. The only two options to reduce the cost of energy are higher efficiency in extracting power from waves, and reduction of the cost of the device as well as its maintenance.

Efficiency

While small-scale laboratory tests have demonstrated more than 99% energy extraction in the inviscid limit,[4] another important property of the cycloidal wave energy converter is that the output is shaft power of almost constant torque throughout the wave cycle. This allows for a more efficient direct attachment of a generator, avoiding most of the power take off losses that exist with other wave energy devices.[7] The result is a very high efficiency of power conversion, which reduces the cost of energy.

Construction cost

The CycWEC uses hydrofoils that produce lift. This allows the blades to move faster than the water velocity, at the design point typically more than 10 times faster than the water velocity.[5] As power in a mechanical system is calculated to be Force times Velocity,[8] the faster moving CycWEC can create the same power output with a much smaller (hydrofoil) structure which reduces construction cost.

Storm Survival

The CycWEC wave energy converter operates fully submerged. In a storm, it can be further submerged below the tremendously energetic storm-driven wind and surface waves. This allows the CycWEC to survive where other wave energy devices may be destroyed due to loads induced by wind and breaking waves.

Challenges

As the CycWEC has at present only reached a Technology Readiness Level (TRL) of 4, many development challenges lie ahead. Some of these are:

  • Ensuring years of reliable operation of a novel device in a marine environment involves substantial effort in development and testing.[7]
  • The installation and production of the ocean floor mounted CycWEC is difficult and expensive.
    • Each device will have to be connected to the electric grid by means of an expensive sub-sea cable.[7]
    • A monopile or jacket foundation is required to anchor the CycWEC to the ocean floor.[1]
  • Interaction of the CycWEC with the environment, needs to be investigated in detail.
  • Noise generated by the CycWEC may disturb marine life[7]
  • A wave farm with many CycWEC devices may result in a loss of marine habitat[7]

See also

References

  1. 1.0 1.1 Template:US patent reference
  2. Air Force News 2008-08-20 Retrieved 2012-12-11
  3. NSF News 2009-11-18 Retrieved 2012-12-11
  4. 4.0 4.1 4.2 Applied Ocean Research: Deep ocean wave energy conversion using a cycloidal turbine (April, 2011).
  5. 5.0 5.1 Applied Ocean Research: Experimental wave termination in a 2D wave tunnel using a cycloidal wave energy converter (April, 2012)
  6. Houston Chronicle 2012-08-05 Retrieved 2012-12-11
  7. 7.0 7.1 7.2 7.3 7.4 Cruz, Joao (2008). Ocean Wave Energy: Current Status and Future Perspectives, p.409-411. Springer-Verlag, Berlin. ISBN 978-3-540-74894-6
  8. Mechanical Power Equation

External links