Jul 25 2012

Point Absorbers: The Technology and Innovations

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Point Absorbers – How they Work

The point absorber is a type of wave energy device that could potentially provide a large amount of power in a relatively small device, compared to other technologies.  While there are several different designs and strategies for deploying these types of devices, they all work in essentially the same manner.  Point absorbers are relatively small compared to wave length, and may be bottom mounted or floating structures.  The conversion of power in the system can take many forms, depending on the conformation of the device (Bedard and others, 2010).  The vertical motion of the buoy is utilized to alternate the compression of a gas or liquid in some form of container, converted into rotational movement of the power generator, or converted in other similar ways (Minin, Valeriy, and Grigoriy Dmitriev, 2007).  The relative motion between the wave-activated float on the sea surface and the seabed structure activates a power takeoff system (Wan Nik WB and others).

New Projects from Ocean Power Technologies

Probably the best known of the point absorber devices is the PB150 PowerBuoy©, developed by Ocean Power Technologies (OPT). The PB150 is a floating structure with a low surface profile while inside, a piston-like structure oscillates as the device bobs with the movement of the waves. This motion drives a generator to produce electricity, which is sent to the shore by an underwater cable.  OPT is currently developing the PowerTower©, a system with a 500 kW capacity, that when completed is expected to drive the OPT system into a higher level of commercial and utility-scale product capability. The US Department of Energy (DOE) along with the UK Government, have begun funding several stages of the PB500 PowerTower development program (oceanpowertechnology.com).  In Coos Bay, Oregon, OPT plans to install a PB500 wave farm system in the coming years. If completed, the Coos bay project is expected to be the largest wave energy park in the world, capable of supplying 275,000 MW annually to the grid.


Currently, the PB150 model is operational and has been tested successfully in many areas, with other operational sites in progress. One such site is located in Reedsport.  While there are many proponents of the project, some resident and conservationists in the Reedsport area have concerns about what the devices will do to the environment. In the spring of 2010, OPT dropped the first installation of the project, a 200-ton, 80-foot tall test buoy off the coast north of Reedsport, “smack in the middle of some of Oregon’s most productive crab grounds,” according to Portland Monthly. There is fear that the wave farm could disrupt the booming crabbing industry, whales that frequent the area and fish and/or mammal navigation (Gewin,Virginia).  To lay rest to these types of concerns, numerous studies have been conducted in the past few years. The physical presence of wave energy devices “can lead to localized changes in water movement energy and turbulence…which can cause benthic sediment scouring and resultant habitat changes” and the within the water column, increased and changing turbulence could, potentially, result in prey and predator aggregation (Boehlert and Gill, 2010).  The project itself is currently in the Environmental Assessment and permitting phase, and therefore the validation of these arguments will soon be confirmed or rejected.  Research from 2008 by Boehlert and others assessed the wave energy potential as well as environmental impacts of wave energy devices in the Pacific Northwest, more than almost any other area on theUScoast.  While there were many sides to consider, the research suggested that the resource available in that area was substantial, and that vast amounts of environmental impact could be mitigated through thorough spatial planning; buoys should not be placed in sensitive areas, generally closer to shore than 40 m depth (Boehlert and others, 2008).  The plans for the Reedsport project place it 2.5 miles off the coast, which will hopefully limit negative impacts on the ecology of the area.

PowerBuoy PB150 design Curtesty of oceanpowertechnologies

An additional site for OPT PB150 and PB500 installations include a large system off the coast of Portland in the state of Victoria, Australia. This project is in the permitting and consent applications process and a balance for financing is being sought.  Wave energy across the continental shelf reduces the estimates for offshore wave energy withdrawal; however the wave energy resource on the Southern Australian margin remains considerable (Hemer, M. A., and D. A. Griffin).  This utilization of a renewable energy source would significantly reduce Australia’s green house gas emissions as at the moment, approximately 50% of Australia’s GHG emissions are contributed from electricity generation (Yusaf, Talal, 2011).

Other Point Absorber Technology

OPT is not the only company investing in point absorber technology.  Wavestar and AWS Ocean Energy are experimenting and implementing wave farms at sites around the globe.  Wavestar for instance installed a one-half scale 600 kW machine in Hanstholm, Denmark that has been on the grid since February 2012. The company website provides a near-real time video of the device, along with data and archives of the devices output.  “Waves run the length of the machine, lifting 20 floats in turn. Powering the motor and generator in this way enables continuous energy production and a smooth output (wavestarenergy.com).”  Production at the company continues, as the plans for a 6 MW machine are in the makings.


 The Wavestar point absorber system.


Bedard, Roger, Paul T. Jacobson, et all. “An Overview of Ocean Renewable Energy Technologies.” Oceanography 23.2 (2010): 22-31. The Oceanography Society, June 2010. Web. 22 July 2012. <https://sakai.unc.edu/access/content/group/2d0d2285-281e-481c-94fd-0029b847533f/Readings/bedardandothers_2010_oretoverview.pdf>.

Boehlert, George W., and Andrew B. Gill. “Environmental and Ecological Effects of Ocean Renewable Energy Development.” Oceanography 23.2 (2010): 68-81. The Oceanography Society, June 2010. Web. 22 July 2012. <https://sakai.unc.edu/access/content/group/2d0d2285-281e-481c-94fd-0029b847533f/Readings/boehlertandgill_2010_synthesisenergyandenviron.pdf>.

Boehlert, G. W, G. R. McMurray, and C. E. Tortorici (editors). 2008. Ecological effects of wave energy in thePacific Northwest.U.S.Dept. Commerce, NOAA Tech. Memo. NMFS-F/SPO-92, 174 p.

Gewin, Virginia. “The Next Wave.” Portland Monthly. Saga City Media, Inc, Nov. 2010. Web. 22 July 2012. <http://www.portlandmonthlymag.com/travel-and-outdoors/articles/the-next-wave-november-2010/1/>.

Hemer, M. A., and D. A. Griffin. “The Wave Energy Resource Along Australia’s Southern Margin.” Journal Of Renewable & Sustainable Energy 2.4 (2010): 043108. Academic Search Complete. Web. 15 July 2012.

Minin, Valeriy, and Grigoriy Dmitriev. “Prospects for Development of Non-conventional and Renewable Sources of Energy on the Kola Peninsula.” Bellona Foundation (2007): n. pag. Bellona Foundation. BellonaMurmansk, 2007. Web. 22 July 2012. <http://www.bellona.org/reports/Clean_energy_Kola>.

“Projects.” Wave Star. Wavestar – Unlimited Clean Energy, n.d. Web. 22 July 2012. <http://wavestarenergy.com/>.

Utility Scale Systems. Ocean Power Technologies, n.d. Web. 22 July 2012. <http://www.oceanpowertechnologies.com/>.

Wan Nik, W. B. and others. “Wave Energy Resource Assessment and Review of the Technologies.” International Journal of Energy and Environment 2.6 (2011): 1101-112. IEEF. Web. 22 July 2012. <https://sakai.unc.edu/access/content/group/2d0d2285-281e-481c-94fd-0029b847533f/Readings/WanNokandothers_2011_wavereviewoftechandresource.pdf>.

Yusaf, Talal, Steven Goh, and J.A. Borserio. “Potential Of Renewable Energy Alternatives In Australia.” Renewable & Sustainable Energy Reviews 15.5 (2011): 2214-2221. Academic Search Complete. Web. 22 July 2012.

Videos: youtube – oceanpowertechnologies and wavestarenergy

38 responses so far

38 Responses to “Point Absorbers: The Technology and Innovations”

  1.   mcmatton 06 Dec 2012 at 7:23 pm

    Could this also work by the bobber going up and down to spinning a generator at the sea floor?

  2.   ldubbson 06 Dec 2012 at 7:36 pm

    Yes, mcmatt, that type of device is also considered to be in the point absorber class. The European Marine Energy center has a great resource that describes the characteristics of different wave device classes. The website is: http://www.emec.org.uk/marine-energy/wave-devices/. Have fun exploring!

  3.   sarathon 29 Jan 2013 at 6:23 am

    What is the cost of point absorbers?

  4.   ldubbson 29 Jan 2013 at 2:17 pm

    Thanks for your question, Sara. Costs of point absorbers will vary, but the first commercial utility scale wave farm in the US, the Reedsport Wave Power Station in Oregon, consisting of 10 150 kW PowerBuoy point absorbers is estimated to cost $64 million for a total capacity of 1.5 MW. Read more at their website: http://www.power-technology.com/projects/reedsportwavepowerst/

  5.   in adult videoson 23 Apr 2013 at 4:49 am

    Wow, this post is good, my sister is analyzing these
    things, so I am going to inform her.

  6.   Matt Ron 07 Jul 2014 at 10:17 pm

    So I had a question about this technology and the possibility of combining it with other green technologies to leverage not only reduced capital expenditure costs, reduced environmental impact, but also possibly increased efficiencies on the technologies themselves?

    It seems like there are three technologies that have similar capital outlay requirements or at least could have synergies for one another.

    Ocean based Wind Towers – Turbines
    -Large Infrastructure for stability
    -Large Electrical Infrastructure to convert energy / transmit electricity to land
    -Large maintenance costs due to difficulty of location

    Ocean based Solar Arrays
    -Large Infrastructure for stability – mooring
    -Large Electrical Infrastructure to convert energy / transmit electricity to land
    -Large maintenance costs due to difficulty of location

    Point Absorber Bouy

    -Large Infrastructure for stability – mooring
    -Large Electrical Infrastructure to convert energy / transmit electricity to land
    -Large maintenance costs due to difficulty of location

    All of these technologies have similar requirements for operation and have similar environmental downsides so the negative impacts would be minimized. If these technologies were used in combination it would seem that the overall fixed and maintenance cost per watt could be lowered as these would be shared across these methods.

    There may even be other synergies that would be realized if this method were used. When turbines are sunk in the water this creates turbulence which has the potential to increase the amount of energy gathered from bouy techology.

    Any ideas if such an installation has been investigated for the possible synergies in these methods?

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