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Ocean power, or marine and hydrokinetic (MHK) power, refers to a form of power generation that harnesses the kinetic energy of water, excluding hydropower.

Current and Potential Cost

No forms of MHK are in widespread usage today, but some have the potential to be affordable in the future.

Levelized cost of ocean energy. Sources: Carbon Trust [3], Energy Technologies Institute [8], Helfer et al. [10], IEA et al. [11], International Renewable Energy Agency ([12] and [13]), Khasawneh et al. [16], Neary et al. 2016 [22], Neary et al. 2014 [23], Ocean Energy Systems [24], OpenEI [26], Salvatore et al. [29].

Resource Base and Environmental Concerns

MHK technologies show the production potential worldwide and in the United States.

Production potential for MHK technologies worldwide and in the United States. World figures are from Helfer et al. [10] and Stenzel and Wagner [30] for osmotic power, Stenzel and Wagner [30] for osmotic power with ecological constraints, IRENA [15] for tidal, Lockheed Martin [18] for OTEC, Minerals Management Service et al. [20] for marine current, and Pelc and Fujita [27] for wave. US figures are from the Electric Power Research Institute [6] for river current, Georgia Tech Research Corporation [9] for tidal stream, Lockheed Martin [18] for OTEC, the US Department of energy for wave energy in the Continental US, and the Wave Power Technologies Office [33] for overall wave potential.

All MHK technologies show modest greenhouse gas impacts.

Greenhouse gas impacts of MHK technologies. Figures for wave from Sörensen and Naef [28], tidal current and tidal stream from Lewis et al. [17], and OTEC from Banerjee et al. [1].

Wave Power

Wave power refers to any technology that harnesses kinetic energy from ocean waves.

Achieving the full potential of wave energy will require more research and development. We estimate that $2.5 billion would be needed, the same that the U.S. Department of Energy spent from 1978 to 2014 on R&D on wind energy [4][31]. We estimate an additional $300 million of investment is needed to bring partial scale projects to full commercial scale [25]. Based on a learning rate such that doubling the deployment of wave technology should bring the price down by 15% [21], we estimate that $5.5 billion of public subsidy would bring wave technology to a price of 6 ¢/kWh, at which point it could compete in coastal electricity markets.

By focusing early commercialization on islands and other areas with expensive electricity, the needed subsidy might be reduced. To estimate the potential value of wave energy, we use a more conservative estimate of the production potential in the United States of 550 TWh per year, excluding Alaska [14]. We furthermore estimate that a mature wave industry could reduce the levelized cost of electricity by 0.5 ¢/kWh relative to other options, generating $2.75 billion of economic value per year.

More research is needed on ecological impacts. Wave capture devices could benefit marine life by serving as artificial reefs, while harmful impacts include noise and electromagnetic fields [5]. Deployment of wave energy must also take into account competition with other sea uses, such as shipping and fishing.

Tidal Power

Tidal power refers to any technology that harnesses the kinetic energy of water induced by tides.

Tidal technology has faced greater-than-expected engineering challenges, with costs in the UK of 46 to 53 ¢/kWh [3]. Only through a combination of research and development and learning-by-doing can tidal power achieve a cost of 16 ¢ or less [3].

Turbine blades and electromagnetic effects may harm the local environment [2]. Additionally, tidal power might disrupt the local ecology by altering the flow of water [34].

Ocean Thermal

An ocean thermal device (OTEC) harnesses the ocean's temperature differential for electricity production or to harvest cool water for a district cooling system. OTEC may be able to supply all of the world's electricity without disrupting the temperature profile of the oceans [12].

For electricity alone, OTEC will almost certainly be expensive, with capital costs for mature technology at least $7750/kW [19]. OTEC has the potential to create useful coproducts, such as cold water for district cooling systems or for tropical agriculture [19], nutrient pumping to support open-ocean mariculture [19], or fresh water [32]. The economic feasibility of OTEC may require accounting for coproducts [12][19][32].

Potential environmental impacts of OTEC include the release of CO2 in quantities comparable with other renewable energy sources and the risk of the leakage of working fluids [19].

Osmotic Power

An osmotic, or salinity-gradient, power plant harvests the potential energy in the pressure difference between fresh and salt water, where fresh water rivers meet the ocean. An osmotic power plant runs at nearly full capacity and could serve as reliable base load power. Improvements in membrane technology, driven by water desalination, have improved prospects for osmotic power in recent years. The industry expectation is that a membrane power density of 5 W/m2 is needed to produce osmotic power profitably at 7-13 ¢/kWh, and this has been achieved by several designs in the laboratory [10].

More research is needed on the environmental risks of osmotic power. Concerns include eutrophication, water temperature changes, and discharge of chemicals [10].

River Current

River current power harnesses the kinetic energy of water flowing in a river. River current differs from hydroelectric power in that no dam is used to build a reservoir or impede the flow of water. River current power poses the risk of collisions between marine animals and turbine blades, as well as electromagnetic effects, but the wildlife and ecological impact should be less than conventional hydropower [7].

Marine Current

Marine current power harnesses the kinetic energy of oceanic currents. As with river current power, marine current power poses risks from turbine collisions and electromagnetic effects [2]. Additionally, it is uncertain what effect widespread usage of marine current power would have on ocean currents [20].

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[1] Banerjee, S., Duckers, L., Blanchard, R. "An overview on green house gas emission characteristics and energy evaluation of ocean energy systems from life cycle assessment and energy accounting studies". Journal of Applied and Natural Sciences 5(2), pp. 535-540. 2013.

[2] Baring-Gould, E., Christol, C., LiVecchi, A., Kramer, S., West, A. "A Review of the Environmental Impacts for Marine and Hydrokinetic Projects to Inform Regulatory Permitting: Summary Findings from the 2015 Workshop on Marine and Hydrokinetic Technologies, Washington, D.C.". National Renewable Energy Laboratory. July 2016.

[3] Carbon Trust. "Accelerating Marine Energy". July 2011.

[4] Coggins, A. "Policy Strategies for Advancing the Marine and Hydrokinetic Energy Industry". Masters Thesis, Humboldt State University. May 2013.

[5] DG Environment News Alert Service. "Marine ecosystem impacts of wave energy installations". European Commission. May 2010.

[6] Electric Power Research Institute. "Assessment and Mapping of the Riverine Hydrokinetic Energy Resource in the Continental United States". 2012.

[7] Electric Power Research Institute. "Fish Passage Through Turbines: Application of Conventional Hydropower Data to Hydrokinetic Technologies". Report by Electric Power Research Institute (EPRI), pp. 56. 2011.

[8] Energy Technologies Institute. "Tidal Energy: Insights into Tidal Stream energy". 2015.

[9] Georgia Tech Research Corporation. "Assessment of Energy Production Potential from Tidal Streams in the United States, Final Project Report". June 2011.

[10] Helfer, F., Lemckert, C., Anissimov, Y. "Osmotic Power with Pressure Retarded Osmosis: Theory, Performance and Trends - a Review". Journal of Membrane Science 453, pp. 337-358. March 2014.

[11] International Energy Agency, Nuclear Energy Agency, Organization for Economic Co-Operation and Development. "Projected Costs of Generating Electricity: 2015 Edition". September 2015.

[12] International Renewable Energy Agency. "Ocean Thermal Energy Conversion - Technology Brief". June 2014.

[13] International Renewable Energy Agency. "Salinity Gradient Energy - Technology Brief". June 2014.

[14] Jacobson, P. "Mapping and Assessment of the United States Ocean Wave Energy Resource". Electric Power Research Institute. December 2011.

[15] Kempener, R., Neumann, F. "Tidal Energy: Technology Brief". International Renewable Energy Agency. June 2014.

[16] Khasawneh, Q., Tashtoush, B., Nawafleh, A., Kan’an, B. "Techno-Economic Feasibility Study of a Hypersaline Pressure-Retarded Osmosis Power Plants: Dead Sea Red Sea Conveyor". Energies. November 2018.

[17] Lewis, A., S. Estefen, J. Huckerby, W. Musial, T. Pontes, J. Torres-Martinez. 2011: Ocean Energy. In IPCC Special Report on Renewable Energy Sources and Climate Change Mitigation. [O. Edenhofer, R. Pichs-Madruga, Y. Sokona, K. Seyboth, P. Matschoss, S. Kadner, T. Zwickel, P. Eickemeier, G. Hansen, S. Schlömer, C. von Stechow (eds)], Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

[18] Lockheed Martin Mission Systems & Sensors. "Ocean Thermal Extractable Energy Visualization, Final Technical Report". October 2012.

[19] Masutani, S., Takahashi, P. "Ocean Thermal Energy Conversion". From Encyclopedia of Ocean Sciences, J.G. Webster, ed., John Wiley & Sons, Vol 19, pp. 93-103. 1999.

[20] Minerals Management Service, Renewable Energy and Alternate Use Program, U.S. Department of the Interior. "Technology White Paper on Ocean Current Energy Potential on the U.S. Outer Continental Shelf". May 2006.

[21] Mirko Previsic, Contributing Authors: Jeff Epler, Maureen Hand, Donna Heimiller, Walter Short, and Kelly Eurek. "The Future Potential of Wave Power in the United States". Prepared by RE Vision Consulting on behalf of the U.S. Department of Energy. August 2012.

[22] Neary, V., Kobos, P., Jenne, D., Yu, Y. "Levelized Cost of Energy for Marine Energy Conversion (MEC) Technologies". Conference: Proposed for presentation at the EPI's 6th Annual Energy Policy Research Conference (EPRC) held September 8-9, 2016 in Santa Fe, NM, U.S.A. August 2016.

[23] Neary, V., Lawson, M., Previsic, M., Copping, A., Hallett, K., LaBonte, A., Rieks, J., Murray, D. "Methodology for Design and Economic Analysis of Marine Energy Conversion (MEC) Technologies". Conference: Proposed for presentation at the GMREC 2014 held April 14-17, 2014 in Seattle, WA. April 2014.

[24] Ocean Energy Systems. "International Levelised Cost Of Energy for Ocean Energy Technologies". An International Energy Agency technology initiative. May 2015.

[25] Offshore Renewable Energy Catapult. "Financing solutions for wave and tidal energy". November 2014.

[26] OpenEI. "Transparent Cost Database". Accessed May 11, 2019.

[27] Pelc, R., Fujita, R. "Renewable energy from the ocean". Marine Policy 26(6), pp. 471-479. November 2002.

[28] Sörensen, H, Naef, S. "Report on technical specification of reference technologies (wave and tidal power plant)". New Energy Externalities Developments for Sustainability. November 2008.

[29] Salvatore, J. et al. "Cost of Energy Technologies". World Energy Council, with Bloomberg New Energy Finance. 2013.

[30] Stenzel, P., Wagner, H. "Osmotic power plants: Potential analysis and site criteria". 3rd International Conference on Ocean Energy. October 2010.

[31] U.S. Department of Energy. "Department of Energy FY 2015 Congressional Budget Request". (see p. 7 for FY 2013 and 2014 figures).

[32] Vega, L.A. "Economics of Ocean Thermal Energy Conversion (OTEC): An Update". Offshore Technology Conference 2010, OTC 21016, Houston, Texas, 3-6 May.

[33] Water Power Technologies Office, Office of Energy Efficiency & Renewable Energy, U.S. Department of Energy. "Marine and Hydrokinetic Resource Assessment and Characterization". Accessed August 9, 2019.

[34] Wolf, J., Walkington, I., Holt, J., Burrows, R. "Environmental impacts of tidal power schemes". Proceedings of the Institution of Civil Engineers-Maritime Engineering 162(4), pp. 165-177. 2009.