Ocean Energy TechnologyOverviewPrepared for the U.S. Department of Energy Office of Energy Efficiency and Renewable EnergyFederal Energy Management ProgramJuly 2009DOE/

ContactsPrincipal Investigators:Kari BurmanPhone: 303-384-7558E-mail: [email protected] Walker, PhD PEPhone: 303-384-7531E-mail: [email protected] Management and Federal Markets GroupNational Renewable Energy Laboratory (NREL)MS 3011617 Cole BoulevardGolden, CO 80401Sponsor:U.S. Department of EnergyFederal Energy Management ProgramAcknowledgementsThis work was sponsored by the U.S. Department of Energy (DOE) Federal Energy Management Program(FEMP). Research regarding ocean energy resources, status of wave and tidal power technologies, andocean thermal energy conversion (OTEC) technologies was provided by Andy Walker, Walt Musial, andDesikan Bharathan at the National Renewable Energy Laboratory (NREL). Carol Fitzgerald, NRELLibrarian, provided research assistance. Kari Burman of NREL conducted research and prepared the report.Ocean Energy Technology Overviewi

Executive SummaryThis paper presents an overview of ocean energy technology as a source of renewable energy for U.S.Federal sites. It investigates ocean energy resources and new technologies under development to capturethat energy. These technologies span: Wave energyTidal energyMarine current energyOcean thermal energy conversion (OTEC)A brief history of the technologies is presented, as well as each technology’s commercial marketdevelopment status. Benefits and barriers to research and development are also examined along withvarious devices currently being validated in the field.Significant growth has occurred in the number of devices developed for ocean energy conversion since2003. Multiple countries are now becoming involved in technology research and development. As many ofthese technologies near commercial deployment, some governments are proposing market support policiesto reduce the current cost gap and help accelerate the rate of commercialization.Ocean energy resources are significant around the United States. New energy conversion devices couldhelp alleviate U.S. dependency on foreign oil while reducing Federal Government utility costs. Federalsites should take this opportunity to consider ocean energy development to generate renewable energy andhelp meet Federal mandates, such as the Energy Policy Act of 2005 (EPAct 2005) and the EnergyIndependence and Security Act of 2007 (EISA 2007).In general, Federal research and development funding for ocean energy technologies is increasing. Thereare several projects being sponsored by the Navy and other Federal entities. Support from nationallaboratories in testing new devices may help greatly in demonstrating design concepts and reliability ofnew devices. As long as progress is being made in the development of ocean energy technologies, theincreasing trend in Federal expenditures is likely to continue to rise.At the time of this report, few full scale commercialized ocean energy conversion systems have been tiedto the grid. A number of small prototypes are being tested, primarily in wave and marine currenttechnologies, and this number is growing. Technical and financial support from governments across theglobe may be crucial in moving new ocean energy technology from prototype to commercially viableproduct.Ocean Energy Technology Overviewii

Table of ContentsExecutive Summaryii1 Ocean undTechnology TypesResourcesBenefitsBarriers2 Wave Energy102.12.22.3101010OverviewResourcesEnergy Conversion Technologies3 Tidal and Marine Current Energy163.13.23.3161617OverviewResourcesEnergy Conversion Technologies4 Ocean Tidal Energy224.14.24.3OverviewResourcesEnergy Conversion Technologies2222225 Ocean Thermal Energy Conversion245.15.25.3242424OverviewResourcesEnergy Conversion Technologies6 Conclusion286.128Development SummaryReferencesOcean Energy Technology Overview30iii

1 Ocean Energy1.1 IntroductionThe Department of Energy’s (DOE) Federal Energy Management Program (FEMP) facilitates the FederalGovernment’s implementation of sound, cost-effective energy management and investment practices to enhance thenation’s energy security and environmental stewardship. FEMP works to reduce the cost and environmental impactof the Federal Government by advancing energy efficiency and promoting the use of distributed and renewableenergy at Federal sites. The overall goal is to lower Federal fossil-fuel energy consumption to reduce environmentaland national security risks. This goal is supported by renewable energy and energy efficiency mandates as set forthin the Energy Policy Act of 2005 (EPAct 2005), Energy Independence and Security Act of 2007 (EISA 2007), andother Federal regulations.Oceans cover 70 percent of the earth’s surface and represent an enormous amount of energy in the form of wave,tidal, marine current, and thermal resources. Though ocean energy is still in a developmental stage, researchers areseeking ways to capture that energy and convert it to electricity.EPAct 2005 provides the Department of the Interior (DOI) leasing authority to support production, transportation,and transmission of energy off the Outer Continental Shelf. This leasing authority provides jurisdiction over projectsthat produce alternative energy and can make use of existing oil and gas platforms in Federal waters.Marine technology was once considered too expensive to be a viable source of alternative clean energy, especiallycompared to already developed products such as wind and solar. However, with the increased price of oil and theissues of global warming and national security, U.S. coastal sites are looking to add ocean energy to their renewableenergy portfolios. This paper gives an overview of ocean energy technologies, focusing on four different types:wave, tidal, marine current, and ocean thermal energy conversion (OTEC). It outlines the operating principles, thestatus, and the efficiency and cost of generating energy associated with each technology.1.2 BackgroundOcean and marine energy refers to various forms of renewable electric energy harnessed from the ocean. There aretwo primary types of ocean energy: mechanical and thermal. The rotation of the earth and the moon’s gravitationalpull create mechanical forces. The rotation of the earth creates wind on the ocean surface that forms waves, whilethe gravitational pull of the moon creates coastal tides and currents. Thermal energy is derived from the sun, whichheats the surface of the ocean while the depths remain colder. This temperature difference allows energy to becaptured and converted to electric power.People have been fascinated with capturing ocean energy since the late 18th century. Monsieur Girard received thefirst recorded patent for wave energy conversion in 1799. The patented device consisted of a ship attached to shorewith waves driving pumps and other machinery. Only occasional attempts to harness the ocean’s energy were madebetween 1800 and the late 1960’s. However, in 1966, the largest tidal power station in the world was built in St.Malo, France [1]. This ocean tidal power station still operates today, producing 240 megawatt-hours (MWh) ofpower each year.Widespread attempts to harness ocean energy wax and wane with the price of oil. In 1973, an oil shortage crisisoccurred when the Organization of Petroleum Exporting Countries (OPEC) placed an embargo on shipments of oilto the U.S. and Europe. During that time, an engineer from Scotland, Stephen Salter, took the first steps to developan ocean-wave generator known as Salter’s Duck. The duck moves up and down with wave motion. A turbineconverts this movement to electrical energy. This single wave-conversion device produced six megawatts (MW) ofelectricity at a cost of nearly 1 per kilowatt-hour (kWh). The initial cost of wave power was considered too high,and the Salter Duck never made it to production [2].With fossil fuel prices increasing and expected to stay high in the future, the search for alternative energy resourcesis once again on the forefront. In the past few years, a growing interest emerged in ocean energy, and progress isbeing made to bring ocean energy technologies from development stages to the commercial market.Ocean Energy Technology Overview4

1.3 Technology TypesFour types of ocean energy conversion exist: wave energy, tidal energy, marine current energy, and ocean thermalenergy conversion.Wave EnergyWave energy is generated by the movement of a device either floating on the surface of the ocean or moored to theocean floor. Many different techniques for converting wave energy to electric power have been studied.Wave conversion devices that float on the surface have joints hinged together that bend with the waves. This kineticenergy pumps fluid through turbines and creates electric power. Stationary wave energy conversion devices usepressure fluctuations produced in long tubes from the waves swelling up and down. This bobbing motion drives aturbine when critical pressure is reached. Other stationary platforms capture water from waves on their platforms.This water is allowed to runoff through narrow pipes that flow through a typical hydraulic turbine.Wave energy is proving to be the most commercially advanced of the ocean energy technologies with a number ofcompanies competing for the lead.Tidal EnergyThe tidal cycle occurs every 12 hours due to the gravitational force of the moon. The difference in water height fromlow tide and high tide is potential energy.Similar to traditional hydropower generated from dams, tidal water can be captured in a barrage across an estuaryduring high tide and forced through a hydro-turbine during low tide. To capture sufficient power from the tidalenergy potential, the height of high tide must be at least five meters (16 feet) greater than low tide. There are onlyapproximately 20 locations on earth with tides this high. The Bay of Fundy between Maine and Nova Scotia featuresthe highest tides in the world, reaching 17 meters (56 feet). This area has the potential to produce 10,000 MW [3].Current EnergyMarine current is ocean water moving in one direction. In the U.S., it is found primarily off the coast of Florida.This ocean current is known as the Gulf Stream. Tides also create currents that flow in two directions. Kineticenergy can be captured from the Gulf Stream and other tidal currents with submerged turbines that are very similarin appearance to miniature wind turbines. As with wind turbines, the constant movement of the marine currentmoves the rotor blades to generate electric power.Ocean Thermal Energy ConversionOcean thermal energy conversion, or OTEC, uses ocean temperature differences from the surface to depths lowerthan 1,000 meters, to extract energy. A temperature difference of only 20 C (36 F) can yield usable energy.Research focuses on two types of OTEC technologies to extract thermal energy and convert it to electric power:closed cycle and open cycle. In the closed cycle method, a working fluid, such as ammonia, is pumped through aheat exchanger and vaporized. This vaporized steam runs a turbine. The cold water found at the depths of the oceancondenses the vapor back to a fluid where it returns to the heat exchanger. In the open cycle system, the warmsurface water is pressurized in a vacuum chamber and converted to steam to run the turbine. The steam is thencondensed using cold ocean water from lower depths [3].1.4 ResourcesOcean energy has great potential as a renewable energy resource for the U.S. Tidal current and wave potential aloneare estimated to produce approximately 400 terawatt-hours per year (TWh/yr) or 10 percent of the national energydemand [4]. The Electric Power Research Institute (EPRI) performed an energy resource study in 2005 and 2006that examined seven locations in North America. The estimated wave resource was found to be approximately 2,100TWh/yr (Figure 1). EPRI also studied tidal energy in North America [4] and found the power potential to be 6.6TWh/yr (Figure 2).Ocean Energy Technology Overview5

Alaska 1,250 TWh/yrWA, OR, and CA440 TWh/yrHawaii330 TWh/yrNew England / MidAtlantic 110 TWh/yrFigure 1: Preliminary Estimate of U.S. Coastal Wave Energy Resources (60-meter Depth and Greater than 10 kW/m)Courtesy of the Electric Power Research InstituteOcean Energy Technology Overview6

Knik Arm, Alaska1 TWh/yrAdmiralty, Washington1.7 TWh/yrTacoma, Washington0.9 TWh/yrWestern Passage, Maine0.9 TWh/yrGolden Gate, California2.1 TWh/yrFigure 2: Estimated Tidal Energy Resources in the U. S. for Selected Tidal PassagesCourtesy of the Electric Power Research InstituteOcean current resources in the U.S. are found primarily off the southern coast of Florida in the Gulf Stream. Thisresource has a very high energy density compared to other renewable energy sources, such as wind. Sea water ismore than 800 times denser than air [5]. Thus, a 12 mile per hour (mph) marine current generates the equivalentamount of force that is contained in a constant 110 mph wind [6]. The total amount of ocean current energyresources worldwide is estimated to be 5,000 GW. Capturing 1/1000th of the energy produced in the Gulf Streamcould provide Florida with 35 percent of its demand [6].Marine energy also includes thermal energy potential. OTEC requires a temperature difference of at least 20 C. Intropical and subtropical latitudes between 24 north and 24 south of the equator, ocean water varies by 20 C fromthe surface to 1,000 meters down. The estimated potential power from thermal energy resource worldwide is 10,000TWh/yr [3]. Table 1 provides a summary of estimated ocean power resources [7].Form of Ocean EnergyTidesWavesTidal (marine) currentThermal gradientEstimated Global Resource (TWh/yr)300 80,000800 10,000Table 1: Estimated Ocean Power ResourcesCourtesy of IEA-OES 2006 Policy ReportOcean Energy Technology Overview7

1.5 BenefitsThe increasing price of oil and fossil fuels along with the growing concerns of global warming has sparked interestin renewable energy in the U.S. and around the world. The search for clean, sustainable energy to generateelectricity is again in the forefront of the news, and the race to develop ocean power at a competitive price isimportant.Coastal areas in the U.S. have high population densities, requiring large electrical energy demand. Ocean energy isavailable to these coastal areas, which also contain a high density of Federal sites. Figure 3 shows Federal sitelocations and indicates what types of ocean energy technology are applicable. Green highlights indicate militarybases, light blue highlights indicate Department of Defense (DOD) facilities, and dark blue highlights indicatecivilian facilities.Tidal Current &Wave EnergyWave EnergyWave Energy & OTECTidalCurrentEnergyMarineCurrentEnergyFigure 3: Map of U.S. Federal Sites and Applicable Ocean Energy TechnologiesCourtesy of Pacific Northwest National LaboratoryAnother benefit is size. As discussed in the previous section, ocean energy resources are significant and have a highpower density for generating electricity. This allows ocean turbines to be smaller than wind turbines.1.6 BarriersMultiple barriers exist for ocean energy technologies, such as gaining site permits, the environmental impact oftechnology deployments, and grid connectivity for transmitting the energy produced.PermittingA number of Federal agencies play a role in ocean energy permitting. EPAct 2005 specifies the following Federalagency roles: DOE Office of Energy Efficiency and Renewable Energy (EERE)– Ocean energy, wave, and hydrokinetic technology developmentOcean Energy Technology Overview8

DOI Minerals Management Service (MMS)– Designated lead agency to permit non-extractive energy facilities (including waves on the OuterContinental Shelf)– Siting activities in collaboration with the DOD Corps of Engineers– Navigation obstructions in Federal water ways (Section 10 Permit)– Water quality and approval of most transmission lines Federal Energy Regulatory Commission (FERC)– Power supply contract approvals– Defined powerhouse under Federal Powers Act of 2003 for wave and tidal National Oceanic and Atmospheric Administration (NOAA)– Siting in and around protected areas (marine sanctuaries)– Specific legislation for OTEC (not active)Permitting and obtaining Federal approval to install ocean energy projects can be cumbersome. Permitting is one ofthe key factors delaying the deployment of ocean energy. Progress has been made to allow the pilot testing of newtechnologies on a smaller scale before going through the full permitting process.Environmental ImpactMarine technologies are new, unproven, and their cumulative environmental impacts are not known [8]. Thoughocean energy systems are expected to have little negative impact on the environment, the technologies are too newto gauge all factors. Prolonged studies are needed.Transmission LinesAvailability of transmission lines impacts how fast ocean energy can be commercialized. Planning for upgrades withutility companies should be a part of overall ocean energy projects.Ocean Energy Technology Overview9

2 Wave Energy2.1 OverviewWave energy is captured by devices that are stationary or move up and down with the frequency of waves. Energyconversion devices also capture waves in reservoirs by overtopping the device and channeling sea water through ahydro turbine to generate electricity. Wave height and frequency determine wave energy. Section 2.3 discussescategories of wave technology and current technology development in more detail.2.2 ResourcesFigure 4 maps the kilowatt per meter (kW/m) crest length of wave energy around global coastlines. The crest lengthis measured from one crest, or peak, to the next.Note that wave energy increases as latitudes increase north or south. Latitudes greater than 40 generate the highestenergy. The largest wave energy in the U.S. is found in Alaska, reaching 67 kW/m. Conversely, there is virtually nowave energy in the Gulf Coast.Hawaii10-15 kW/mFigure 4: Wave Energy Levels in kW/m Crest LengthCourtesy of the European Ocean Energy Association2.3 Energy Conversion TechnologiesWave energy technology is rapidly growing and varies widely in application of conversion devices. Energyconversion devices can be situated on or off shore.Four categories of wave energy technology exist: attenuators, point absorbers, overtopping terminators, andoscillating wave column (OWC) terminators. Point absorbers and attenuators capture wave energy as they are placedin the path of the wave. Attenuators are situated parallel to the waves and energy is captured over the surface area.Point absorbers are moored to the sea bed or float near the surface, collecting wave energy from all directions.Terminators restrain wave motion and capture energy through long arms. OWC terminators capture water from anopening into a partially submerged platform and let that water rise in an air column. The air is compressed, whichdrives a turbine to generate electricity.Table 2 outlines devices, applications, and projects in development for each wave energy technology.Ocean Energy Technology Overview10

Table 2: Wave Energy TechnologyCompany:AWS Ocean EnergyProduct Name:Archimedes WaveswingProduct Website:http://www.awsocean.comCompany:Renewable Energy HoldingsProduct Name:CETOProduct Website: - PointAbsorber:Developed in 2004, thisdevice is a buoy moored tothe seabed. Waves moveover a submerged air-filledupper casing and pushagainst the fixed cylinder.Air inside the cylinder iscompressed, serving as apoint absorber. Thecompressed air drives ahydraulic system andgenerator set to convert thewave energy to electricity.Technology - PointAbsorber:Moored to the seabed andcompletely submerged,movement produces highpressure sea water that isdelivered to shore throughpipes. The high-pressuresea water can bedesalinated with reverseosmosis and used to drivethe on-shore hydro-turbine.There is no need forunderwater cabling or highvoltage transmission.CETO will operate inwaters between 15-50meters below breakingwaves.Ocean Energy Technology OverviewProjects:Test Performance:Pilot power plant installedoff the coast of Portugalin 2004. Power plant inPortugal was designed totest technology at fullscale but was notdesigned as a long-termdemonstrator.Pilot plant delivered wavepower to the Portuguesegrid at predicted levels (250kW).Pre-commercial 250 kWprototype to be tested inScotland (EMEC).Pre-commercial 250 kWdevice is planned fortesting during 2009 and2010 at Orkney’sEuropean Marine EnergyCenter (EMEC) inScotland.Projects:First CETO wave energyconversion device wastested in WesternAustralia in January 2008.The technology is scalableand the commercial systemwill be in excess of 1 MW.Figure 5: Archimedes WaveswingCourtesy of AWS Ocean EnergyTest Performance:Produced sustained highpressure sea water greaterthan 1,000 pounds persquare inch (psi) duringtesting.CETO is the only waveenergy technology thatproduces fresh waterdirectly from sea water.Commercially availabilityexpected in 2009.Figure 6: CETOCourtesy of Renewable Energy Holdings11

Company:Pelamis Wave Power(PWP)*Product Name:PelamisProduct Website:*Formerly Ocean PowerDeliveryCompany:Finavera Renewables*Product Name:AquaBuoyProduct Website:*Formerly AquaEnergyTechnology - Attenuator:Semi-submerged structurecomposed of cylindricalsections linked byhydraulic joints. Rampumps resist wave motionin the joints that in turnpump high-pressure oilthrough motors. Thehydraulic motors drivegenerators to produceelectricity. Each device is140 meters long and 3.5meters in diameter withthree wave energyconversion modules.Technology - PointAbsorber:A moored buoy floats onthe surface of the waves.As the buoy moves up anddown, sea water inside a25-meter (82-foot) tubedrives a piston that thendrives a hose pump. Seawater inside the elongatedhose becomes pressurizedand is released to drive thePelton turbine. Underwatertransmission lines transmitelectric energy to shore.The AquaBuoy must bedeployed where waterdepth is greater than 50meters (164 feet).Ocean Energy Technology OverviewProjects:PWP is working on threefull scale trials with theinitial one deployed inPortugal summer 2008:2.25 MW Agucadourawave project off the coastof Portugal for Enersisand Babcock & Brown.3 MW project underdevelopment off the coastof Orkney for ScottishPower Renewables.5 MW wave station forCornwall, UnitedKingdom, as part of theCornwall Wave Hub.Projects:1 MW project in MakahBay, Washington,pending a FERCenvironmental impactstudy.2 MW project with 200MW planned for Figueirade Foz, Portugal.5 MW wave energydevice off Ucluelet,British Columbia, grantedan investigative permit.20 MW wave energyproject off Western Cape,South Africa.200 MW wave park underdevelopment in Coos Bay,Oregon. FERC granted apreliminary permit forthis project.Test Performance:The multiple PWP units inAgucadoura make up theworld’s first multi-unitcommercial wave farm tiedto Portuguese grid.Each Pelamis is capable ofgenerating 750 kW with anexpected average of 25-40%of this power beingcontinuously generated.Cost:Estimated (2004) 2 millionto 3 million per device.Figure 7: PelamisCourtesy of Pelamis Wave PowerTest Performance:Each 40-ton AquaBuoy israted for up to 250 kW.Unfortunately, the prototypedevice failed before powertests were complete,springing a leak that causedthe pump to malfunctionafter only one month ofdeployment. The AquaBuoysank off the coast ofOregon. The test wasintended to measure poweroutput of the AquaBuoy 2.0.No reports from this testhave been released.Figure 8: AquaBuoyCourtesy of Finavera RenewablesCost:The cost for the project inMakah Bay, Washington,including grid connectioncable and four AquaBuoys,was 3 million (2004).12

Company:Ocean Power TechnologiesProduct Name:PowerBuoysProduct ology - PointAbsorber:Converts wave motion intoelectricity with a mooredbuoy that floats freely upand down in the water. Astructure with a pistonmoves as the PowerBuoybobs in the waves. Thismovement drives a turbineand electric generator.Projects:1 MW wave parkdeployed for the U.S.Navy in Oahu, Hawaii.5 MW wave station forCornwall, UnitedKingdom, as part of theCornwall Wave Hub.1.25 MW commercialwave power station offthe Spanish coast.Agreement signed withIberdrola. Still indevelopment.100 MW project in CoosBay, Oregon. Applicationfiled with FERC forpermits.Company:Voith Hydro*Product Name:LimpetProduct Website:*Wavegen is a whollyowned subsidiary of VoithSiemens Hydro PowerGenerationTechnology Overtopping Terminator:Secured on shore, theLimpet is an inclinedOscillating Water Column(OWC). An air chambercaptures wave energy froman opening in the bottom.Water compresses the airas it moves up the column,which turns a turbine at thetop. The turbine spins thesame direction no matterthe air direction.Ocean Energy Technology Overview2 MW to 50 MW wavepark near Reedsport,Oregon. Agreementsigned with PacificNorthwest GeneratingCooperative (PNGC)Power.Projects:The Limpet prototype hasbeen installed since 2000on the island of Islay inScotland.Test Performance:PowerBuoys installed inHawaii and New Jerseyrated at 40 kW each.Operational 2005 inAtlantic City, New Jersey.Demonstrated feasibility ofwave power in New Jersey.Testing and grid connectiondeployed for the U.S. Navyin Kaneohe Bay, Hawaii.Completed extensiveenvironmental assessment.Demonstrated wave powerfor use at US Navy bases,worldwide.Figure 9: PowerBuoyCourtesy of Ocean Power Technologies, Inc.Test Performance:The Limpet on Islay hasthree chambers thatgenerate a combinedaverage of 100 kW.Typical ratings for shorewave energy stations are100 kW to 500 kW per unit.Figure 10: LimpetCourtesy of Voith Hydro13

Company:Aquamarine PowerProduct Name:OysterProduct Website: Overtopping Terminator:Uses the movement of aflap (12 meters by 18meters). When waves comein and out to drive anoscillating wave surgeconverter, or pump, thepump delivers highpressure water to drive atypical hydroelectricgenerator located on shore.Projects:Pilot testing started in2008 off the Orkney coastin Scotland.Test Performance:Each Oyster can produce300 kW to 600 kW peakenergy depending onlocation.Figure 11: OysterCourtesy of Aquamarine PowerCompany:Wave DragonProduct Name:Wave DragonProduct Website:http://www.wavedragon.netTechnology Overtopping Terminator:Captures waves in its longwings and focuses thewater over the top to forma reservoir above sea level.Released water is forcedthrough hydro-turbines thatgenerate electricity. Thereservoir contains 1,500 to14,000 cubic-meters ofwater. Device width is upto 390 meters.Projects:Prototype deployed in2003 off the coast ofNissum Bredning,Denmark, that has so fargenerated electricity formore than 20,000 hours.7 MW device to bedeployed in 2011 offPembrokeshire, Wales, tobe tested 3 to 5 years.Test Performance:Rated generated power isbetween 1.5 MW and 12MW depending on waveclimate.Cost:Estimated (2004) 10million to 12 million forthe 4 MW device.Figure 12: Wave DragonCourtesy of Wave DragonOcean Energy Technology Overview14

Company:Oceanlinx*Product Name:Oscillating Water Column(OWC)Product Website:*Formerly EnergetechTechnology – OWCTerminator:Oceanlinx patentedoscillating water column(OWC) technology. Aswaves pass the Oceanlinxdevice, water enters frombeneath the column andcompresses the air insidethe chamber. Thiscompressed air drives theturbine located in anarrow tapered part of thecolumn.The Oceanlinx OWC canbe deployed on theshoreline or in waterdepths of up to 50 meters.Projects:450 kW prototype powerpurchase agreement withIntegral Energy in PortKembla, New SouthWales, Australia.5 MW facility letter ofintent signed withCornwall, UnitedKingdom, as part of theCornwall Wave Hub.1.5 MW signedmemorandum ofunderstanding withRhode Island.Test Performance:Each OWC produces 100kW to 1.5 MW dependingon wave climate.Cost:Estimated (2004) 2.5million to 3 millionFigure 13: Oscillating Water ColumnCourtesy of Oceanlinx2.7 MW wave generatormemorandum ofunderstanding signedwith Hawaii.1.5 MW under contractwith GPP, Namibia.Ocean Energy Technology Overview15

3 Tidal and Marine Current Energy3.1 OverviewTidal current is created from the gravitational pull of the moon and sun. Tidal current moves in two directions andreverses four times per day. Tidal current energy conversion devices are the most common of the two ocean currenttechnologies. Tidal turbines are similar to wind turbines but can be made smaller due to the high energy density ofwater.Marine current refers to water that moves continuously and is driven by the motion of the ocean from solar heatingand wind near the equator. Marine current moves in one direction with relatively constant flow.3.2 ResourcesFigure 14 shows available tidal current resources [9]. Figure 15 shows available marine current resource. Thehighest resource for tidal current in the U.S. is located in the upper northeast, northwest, and Alaska. The highestU.S. resource for marine current is primarily in the Gulf Coast around the tip of Florida. Energy conversion from theGulf Stream could potentially supply Florida with 35 percent of its electricity needs [6].Figure 14: Global Distribution of Mean Tidal RangeCourtesy of the Electric Power Research InstituteOcean Energy Technology Overview16

Figure 15: Major Ocean CurrentsCourtesy of National Oceanic and Atmospheric Administration3.3 Energy Conversion TechnologiesOcean current energy conversion devices are submerged in sea water and capture energy from the ocean similar tothe way wind turbines capture energy from the wind. Ocean water is

Energy Management and Federal Markets Group . National Renewable Energy Laboratory (NREL) MS 301 . 1617 Cole Boulevard . Golden, CO 80401 . Sponsor: U.S. Department of Energy . Federal Energy Management Program . Acknowledgements . This work was sponsored by the U.S. Department of Energy (DOE) E