May 22 2010

Attenuators

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How does an attenuator work?

Attenuators are situated parallel to the force and direction of a wave. They are held in place by mooring on the seabed. The motion of the device from the crest and trough of the wave exerts force on a turbine that then feeds energy into the grid.

The Image below shows the inner structure of the most common attenuators design:

attenuator inside

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The Pelamis Wave Energy Converter:

Wave 2

 

Attenuator Wave

 

  • The Pelamis Wave Energy Converter is the result of many years of engineering development by Pelamis Wave Power. It was the world’s first commercial scale machine to generate electricity to the grid from offshore wave energy and the first to be used commercially (1).
  • The Pelamis device was developed in Scotland and was the first commercially viable wave energy attenuator device.
  • The Device was originally intended to produce 2.5 MW.
  • Real world applications showed the first devices in Portugal had a rated power 750 kilowatts.
  • A typical Pelamis ‘farm’ would span one square kilometer, providing 30 megawatts of power in an optimal setting
  • 20 megawatts is more likely for a location near North Carolina
  • The second generation of Pelamis devices, known as P2, has been tested in Orkney Scotland and shows considerable improvement over the first device.
  • The combined P2 test program – which also involves testing by an E.on-owned machine – has now accumulated 7500 grid connected operating hours, and exported 160MWh of electricity to the national grid. (1)
[youtube]http://www.youtube.com/watch?v=7TSmYmV23W0[/youtube]

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Anaconda Wave Energy Converter

]

source: http://www.guardian.co.uk/environment/2009/may/06/anaconda-wave-power

  • Instead of hinged segments, the Anaconda is made up of one large rubber tube.  Bulge waves form inside the tube when it is squeezed by a passing wave.   The action of the bulge waves turn a power-generating turbine at the far end of the device.
  • The full scale device was proposed to be about 200m in length and produce 1MW of power
  • Could have potentially been used in any area where wave power exceeds 25 KW/m  (5).
  • Cheaper to produce and easier to maintain than the hard-surfaced attenuators
  • The company Checkmate Seaenergy ltd., appears to no longer exist, casting doubt on the Anaconda’s viability.

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Potential for use worldwide and in the United States and North Carolina:

Optimal locations for the Pelamis wave energy device are circled on the map. Note that offshore of the United States East Coast there is potential for wave power.

Photo: http://hydropower.inel.gov/hydrokinetic_wave/pdfs/day1/09_heavesurge_wave_devices.pdf

The following graph is from a study which was conducted using buoys at various offshore locations to determine the amount of potential power which could be generated by a wave energy device such as the Pelamis.

Annual energy output (AEO) (in GWh) for 6 case studies and their respective capacity and capture width (represented as a number in the energy output bar) (3).

The following graph shows global wave power density estimates.  Based on current predictions, sites in the yellow to red range would likely be compatible with the Anaconda device (5).

Wave Power World Map

The following chart shows the wave power potentials for several states as determined in a 2004 study (6):

State

Wave Power

Density

Estimated Annual Energy Production

Assumed Capacity Factor

Maine

12.4 kW/m

1076 MWh

40%

Oregon

21.2 kW/m

1337 MWh

40%

Washington

26.5 kW/m

1587 MWh

40%

Hawaii

15.2 kW/m

1143 MWh

40%

Attenuators are a feasible technology in many areas, requiring less wave power than many other wave power converters, such as point absorbers.  One potential issue for wave energy in the future is the variability of the resource.  Wave power fluctuates seasonally and there may be some annual fluctuation, though in some areas this fluctuation is negligible (7.)  Wave attenuators have environmental impacts which are in line with other renewable energy devices (Boehlert and Gill.)

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Works Cited:

Munro, Alistair. “Year of Pelamis Wave Power Testing Hailed Success.” The Scotsman. 05/21/2013

Boehlert, George and Andrew Gill. “Environmental and Ecological Effects of Current Renewable Energy Technology: A Synthesis.” Oceanography (2010): 68-81. Electronic Document.

 

 

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4 responses so far




4 Responses to “Attenuators”

  1.   Bethyn Merrick-Nguyenon 29 May 2010 at 8:42 pm

    Honestly, sort of wanted to laugh when I first saw a picture. But you’ve been working hard to convince me otherwise, and I think its starting to work. It sounds like really neat energy harnessing process. And it looks the part too- futuristic, creative and bizarre- rock on water snake. There is little visual pollution from the shore, and minimal impact on the sea floor…its beginning to sound like a perfect technology. Increased efficiency and larger capacity would make this energy technology really awesome. Get going engineers!

  2.   mrrosson 31 May 2010 at 4:49 pm

    I am really fascinated by the Pelamis. It harnesses the ocean’s energy by mimicking wave nature. It seems like a very pure process with less environmental impacts than most systems we studied. I especially appreciate the way it can be installed and removed rapidly. My only concern is the use of the working fluid that is pumped through the hydraulic motors. I think I remember this fluid being some type of oil. My questions regarding Pelamis would be:
    How much fluid is used?
    What measures have been installed to prevent leaks?
    What would be done to contain this fluid in the event of a leak?

  3.   elizgon 31 May 2010 at 10:27 pm

    In response to Matt’s comment: good questions! Many of the issues that would be associated with hydraulic fluids have been mitigated in the design of the device. If you go to the environmental impacts page for the Pelamis there is more info on the biodegradable quality of fluids used in the motor.

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