Hot Topic- Ocean-Based Renewable Energy
Ocean-Based Renewable Energy

The European Union (EU) has committed to producing 20% of its energy from renewable sources by 2020. This has led countries such as Sweden, Ireland, Germany, and Denmark to be pioneers in developing a variety of technologies to harness and deliver energy. Systems associated with winds, waves, and tides produce underwater noise, the effects of which are being studied.

Offshore wind turbines at Barrow Offshore Wind off Walney Island in the Irish Sea.
Offshore wind turbines at Barrow Offshore Wind off Walney Island in the Irish Sea. Image credit: Andy Dingley

Several countries have come together to examine the environmental effects of marine energy development through Annex IV, a collaborative partnership among member nations of the International Energy Agency’s Ocean Energy Systems. The objective was to gather expert data and current research on marine energy technologies and make them widely accessible through Tethys, an online clearinghouse database that consolidates a variety of information, including journal articles, images, and research updates, on the environmental effects of marine renewable energy technologies. In addition to providing broad access, emphasis was placed on creating a collaborative space or commons for interaction among researchers, developers, regulators, and stakeholders to further the development of marine renewable energy and the study of its effects.

Wind energy is increasingly being used as an alternative energy source, and offshore wind power has become one of the fastest growing energy technologies. Winds tend to be stronger and more uniform at sea than on land. In addition, there are large, potentially productive areas available offshore. The potential effects on marine life of the sound generated by the construction and operation of wind farms need to be considered when siting wind turbines. Construction operations produce intense sounds that may affect marine animals over short durations. However, operation of wind farms could result in long-term increases in ambient noise, which could cause masking that might affect animal feeding and reproduction. More studies on the effects of wind farms are needed, particularly as new turbines are designed.

Like offshore winds, ocean waves contain a tremendous amount of energy that can potentially be harnessed. However, waves, and the power they may generate, have inherent variations caused by wave to wave timing, sea state conditions, weather conditions, and seasonal changes. Wave energy converters (WECs) harness kinetic energy from the surface motion of ocean waves and convert it to electricity. They may also extract energy from pressure fluctuations below the water surface; wave motion causes the water level to rise and fall, causing an underwater pressure differential on a WEC device (or the water column) relative to its base (or the seafloor). WECs come in a variety of shapes and sizes, differing in the way they harness energy, the water depth at which they are deployed, and their location (shoreline, near-shore, offshore).

A wave attenuator, a type of wave energy converter (WEC)
A wave attenuator, a type of wave energy converter (WEC). The device captures energy from the relative motion of the two arms as a wave passes. Image credit: Aquaret (http://www.aquaret.com).
Another WEC: a submerged pressure differential device.
A submerged pressure differential device. These technologies capture energy from pressure changes as a wave moves over the top of the device, causing it to rise and fall. Image credit: Aquaret (http://www.aquaret.com).


Tides offer another potential source of renewable energy. Tidal power has an advantage in that tides are more regular than solar, wind, and wave conditions. Tidal-based energy technologies use dams, gates, fences, and/or submerged turbines to capture the movement of incoming and outgoing tides and produce electricity from the movement of water. In areas where tidal movements are large, underwater turbines can be used to capture the kinetic motion of the tides to produce electricity.

A horizontal axis turbine, used for tidal energy production.
Horizontal axis turbines. These tidal devices are similar to wind turbines. The turbine is placed in the water and tidal action (ebb and flow) causes the rotors to rotate around the horizontal axis and generate power. Image credit: Aquaret (http://www.aquaret.com).

Similar with the issues related to the development of wind turbines, the potential effects of underwater sound generated by the construction, operation, and decommission of wave- and tidal-based systems need to be considered. Many tidal devices closely resemble conventional hydropower and wind turbine systems. Thus, manufacturers of tidal energy devices can look to other turbine technologies for research and development insights. WECs have no close counterpart among current technologies, and there are many different designs to consider. This leads to challenges when characterizing and assessing the potential environmental and biological impacts of energy production using WECs.

Although initial deployments and early stage tests have been conducted for some ocean-based renewable energy systems, data about their potential effects is lacking. Few tidal and wave technologies have been adequately characterized to describe the sounds they produce, including their amplitude and frequencies. As these technologies are further developed, scientists are investigating potential marine mammal interactions with installed systems, effects of the underwater noise they produce, marine habitat alterations by the physical structures, and changes in water flow. Effects have the potential to vary greatly depending on system designs, stage of deployment (installation vs. operation), deployment location, animals and habitats present, and the scale of deployment (individual devices vs. large systems operating day and night). In addition, at the broader spatial scale of marine planning, ambient noise assessments provide baseline information on the marine species utilizing areas scheduled for ocean-based renewable energy development and can help predict potential effects when systems are operational.

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References

  • Copping, A., Battey, H., Brown- Saracino, J., Massaua, and M., Smith. 2014, "An international assessment of the environmental effects of marine energy development." Ocean and Coastal Management. 99, 3-13. 
  • Copping, A., Smith, C., Hanna, L., Hoyt Battey, H., Whiting, J., Reed, M., Brown-Saracino, J., Gilmam, P., Massaua, M. 2013, "Tethys: Developing a commons for understanding environmental effects of ocean renewable energy." International Journal of Marine Energy.4-5, 41-51. 
  • Frid, C., Andonegi, E., Depestele, J., Judd, A., Rihan, D., Rogers, S., Kenchington, E. 2012, "The environmental interactions of tidal and wave energy generation devices." Enivronmental Impact Assessment Review. 32(1), 133-139. 
  • H. Lund and B.V. Mathiesen. 2009, "Energy System analysis of 100% renewable energy systems – the case of Denmark in years 2030 and 2050." Energy 34(5) 524-531. 
  • Patricio, Sofia. 2012, "Underwater Noise Effects from Wave Energy Devices on Marine Mammals: A Possible Approach." In: The Effects of Noise on Aquatic Life, Advances in Experimental Medicine and Biology. A.N. Popper and A. Hawkins (eds.) Volume 730. Pp 505-507. 
Additional Resources

  • "Aquatic Renewable Energy Technologies (Aqua-RET)" (Link)
  • "European OWC Wave Power Plant on the Island of Pico/Azores." (Link)
  • UMass Dartmouth, "New England Marine Renewable Energy Center." (Link)
  • Bureau Of Ocean Energy Management, "Ocean Current Energy." (Link)
  • Oregon Wave Energy Trust, "Ocean Energy." (Link)
  • "Tethys." (Link)
  • TETHYS: Wave, "The Marine and Hydrokinetic (MHK) Environmental Impacts Knowledge Management System (KMS)" (Link)
  • Ocean Energy Systems, "What is Ocean Energy? Waves." (Link)