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Home , Coriolis (project), Deep ocean water, Marine energy, Ocean current, Water column, Wave power

or collective redistirbution other or collective or means this reposting, of machine, is by photocopy article only anypermitted of with portion the approval The O of This article has been published in published been This has article Marine Renewable | Technology Development and Deployment

By Roger Bedard, Paul T. Jacobson, Mirko Previsic, Walter Musial, and Robert Varley , 2, a quarterly 23, Number The O journal of An Overview of Renewable

Energy Technologies ceanography S ociety. © 2010 by The O Abstract. Ocean energy is a term used to describe derived from and tidal/open-ocean energy the , including ocean wave energy, tidal and open- energy (sometimes resources. A small number of large called marine hydrokinetic energy), tidal barrages, offshore energy, and ocean companies are leading the commercial- ceanography S thermal and gradient energy. Shallow offshore wind is a commercial ization of offshore wind energy, ocean

technology (over 1,500 MW capacity installed in Europe). The technologies to convert thermal gradient, and salinity gradient ceanography S ociety. A the other ocean energy resources to , including deepwater offshore wind energy technologies. technology, albeit in their infancies, exist. These technologies are ready for full- P reserved. ll rights ociety. S scale prototype and early commercialization testing at sea. This paper highlights the Ocean Wave development status of various energy conversion technologies. Conversion Technologies end all correspondence to: [email protected] Th e O or

Ocean waves are generated by the influ- ermission is granted to in teaching copy this and research. for use article R Introduction plants: a 240 MW plant ence of the wind on the ocean surface, In the 1970s, the United Kingdom at LaRance, France; a 20 MW plant at which first causes ripples. As the wind had the most aggressive wave energy Annapolis, Nova Scotia, Canada; and continues to blow, the ripples become program in the world. Although the smaller plants in China and Russia. Tidal chop, then fully developed , and program contributed to important in-stream technology development has finally swells. In deep water, the energy research such as optimal control and been funded in Europe since the 1990s, in waves can travel for thousands of

tuning of wave conversion and DOE started its wave, tidal, and miles before it is finally dissipated ceanography S devices, it ultimately stalled as oil prices open-ocean current program in 2008. on distant . dropped and government funding Salinity gradient technology has received Many devices have been proposed to ociety, B PO stopped. The US Department of Energy attention in Europe, particularly in achieve the conversion of wave energy (DOE) funded an open-ocean current Norway and the Netherlands. into electricity. Various hydraulic or ox 1931, R

program in the 1970s, an ocean thermal Today, a large number of small pneumatic power conversion systems are epublication, systemmatic reproduction,

energy conversion (OTEC) program companies backed by government used, and in some cases, the mechanical MD 20849-1931, USA ockville, in the 1980s, and a wind program organizations, private industry, utili- motion induced by the wave energy is extending from the late 1970s to the ties, and venture capital are leading the converted directly to electrical power present, which includes a small offshore commercialization of technologies to (direct-drive). These devices can be wind component. There are a few generate electricity from ocean wave bottom-mounted or floating and vary .

22 Oceanography Vol.23, No.2 a

b

c d

Figure 1. (a) PowerBuoy (courtesy of Ocean Power Technologies), (b) WaveDragon (courtesy of WaveDragon), (c) Pelamis (courtesy of Pelamis ), and (d) oscillating terminator (courtesy of OceanLinx).

in size, orientation, and distance from Overtopping Terminator sea surface then turns conventional low- . Four of the best-known offshore A terminator reflects or absorbs all of head hydro turbines that are coupled to technology concepts are introduced the wave energy—hence it “terminates” generators to produce electricity. below and depicted in Figure 1. the waves. One type of terminator is an overtopping device that uses a Linear Absorber or Attenuator Point Absorber floating reservoir structure, typically A linear absorber, sometimes called Devices that are small compared to a with reflecting arms to focus the wave an attenuator, is a device that is large typical (waves of interest energy (Figure 1b). As waves arrive, they compared to a typical wave’s length. The for energy production vary from 40 overtop the ramp and are restrained in linear absorber structure is oriented to over 300 m in length) are termed the reservoir. The due roughly parallel to the direction of wave “point absorbers.” Point absorbers are to the height of collected water above the propagation and is composed of multiple bottom-mounted or floating structures that absorb energy from all directions. Roger Bedard ([email protected]) is Private Consultant, Palo Alto, CA, USA. The power conversion system may take Paul T. Jacobson is Senior Program Manager, Marine and Hydrokinetic Energy Research, a number of forms depending on the Research Institute, Palo Alto, CA, USA. Mirko Previsic is President, Re Vision selected configuration. Figure 1a shows a Consulting LLC, Sacramento, CA, USA. Walter Musial is Principal Engineer, National Wind floating ; however, a point absorber Technology Center, National Renewable Energy Laboratory, US Department of Energy, could as well be a bottom-standing Boulder, CO, USA. Robert Varley is Program Manager, Lockheed Martin Company, device with an upper floater element. Manassas, VA, USA.

Oceanography June 2010 23 sections that rotate in pitch and yaw rela- system built into the coastline of the water to an onshore turbine that tive to each other. That motion is used Island of in Scotland in 2000 by generates electricity. to pressurize a hydraulic fluid, which (now part of Voith Hydro); In the area of testing and test facili- then turns a turbine that is coupled the second unit is located on Pico Island, ties, the US industry is to a generator to produce electricity. Azores, . In 2003, WaveDragon currently challenged by the lack of Figure 1c depicts a slackly moored, was the first offshore, grid-connected proper and standardized infrastruc- floating, hinged-contour linear absorber. wave power unit and was deployed in ture to deploy and test wave energy The four sections move relative to each a protected bay in Denmark due to its conversion devices in the open ocean. other, and this motion is converted subscale . However, progress is being made toward into electricity at each hinge point by a In 2004, Pelamis, the first full- the development of such facilities. The hydraulic power converter system. scale, grid-connected wave power Northwest National Marine Renewable unit deployed at sea, was installed at Energy Center (NNMREC), led by OSU, Oscillating Water Column the European Marine Energy Center will provide wave energy developers Terminator (EMEC), a wave test facility, in the UK. with test berths to perform field tests and An oscillating water column (OWC) Based on the successful EMEC testing, demonstrations of subscale and full-scale terminator is a conversion device that the first commercial sale of an offshore devices. Pacific Gas and Electric (PG&E) harnesses the motion of the ocean wave power plant was announced in will provide an undersea electrical waves as they push an air pocket up or May 2005 and the first 2.25-MW stage of grid connection called “WaveConnect” pull it down. This device is a partially that plant was deployed off the of several miles offshore of California and submerged chamber with air trapped Portugal in 2008.1 will connect wave energy converters above a column of water (Figure 1d). As In the United States, Ocean Power from multiple vendors to the PG&E waves enter and exit the chamber, the Technologies (OPT) was the first to (similar to the UK Wave water column moves up and down and deploy kilowatt-scale wave energy Hub funded by the UK government) and acts like a piston on the air, compressing converters off the of Hawai’i and provide for testing and evaluation of the and decompressing it to generate a New Jersey in 2005. Columbia Power devices for commercial deployment. reversing stream of high-velocity air in Technologies (CPT) and Oregon State Additional demonstration projects are an exit blow hole. This air is channeled University (OSU) were the first to deploy ongoing and planned in the UK, Ireland, through a turbine/generator to produce kilowatt-scale wave energy converters , Portugal, China, Japan, Australia, electricity. An OWC is also a type of off the west coast of the United States Canada, and the United States. If these wave terminator. in 2007 and 2008. OPT plans to deploy early demonstration schemes prove a 150-kW point absorber off the coast successful, medium-size wave farms with Status of Ocean Wave of Reedsport, Oregon, with construc- capacities up to 50–100 MW could be Energy Conversion tion starting in 2010. CPT’s next ocean deployed within the next five to ten years. Technologies deployment is planned for late 2010. Today’s wave energy conversion tech- The first nearshore surge-type wave Tidal and Open-Ocean nologies are the result of many years energy converter to deliver electricity Current Energy Conversion of testing, modeling, and development to the grid was the Technologies by many organizations. About 4 MW Oyster, which was mounted to the A tidal current (or hydrokinetic) of capacity has been installed to date at a depth of 10 m at EMEC turbine converts the in worldwide, primarily as engineering in late 2009. The surge from passing a moving of water to electricity. prototypes. The first shore-based, grid- waves moves a hinged flap, which drives The gravitational of the sun and connected wave power unit was an OWC a hydraulic piston to deliver high- the moon on ’s ocean causes sea

1 The major investor in the Pelamis project off the coast of Portugal declared bankruptcy in 2009. The three 750 kW Pelamis machines are now dockside and awaiting resolution of the financial situation.

24 Oceanography Vol.23, No.2 Rotor Rotor Diameter a Blade b Gearbox Rotor Generator Diameter Rotor Nacelle Height Fixed Pitch Rotor Blade

Tower Gearbox Generator

Horizontal Axis Vertical Axis CONFIGURATIONS

c d

Figure 2. Tidal and open-ocean current energy conversion system configurations. (a) Axial and cross-flow turbines. (b) Axial turbine (courtesy of ). (c) Cross flow vertical turbine courtesy( of Lucid Energy). (d) Cross flow horizontal turbine courtesy( of Ocean Renewable Power Company).

level changes, which, in turn, give rise tidal barrage, they do not require a dam the water stream and may be any to strong tidal currents when the or impoundment. angle from horizontal to vertical with propagates through relative constric- Similar to wave energy conversion, respect to the ground tions. Open-ocean currents are the many devices have been proposed to 3. Non-turbines, including oscillatory vertical or horizontal movement of both accomplish the complex conversion hydrofoils, vortex-induced motion, surface and deep water throughout the of tidal and ocean current energy to and hydro venturi devices world ocean caused by forces2 electricity. It is helpful to introduce Figure 2 illustrates axial and cross-flow and thermal gradients. In the Northern these designs in terms of their physical types of turbines. Hemisphere, large circular ocean surface arrangements and energy conver- currents or gyres move clockwise, and sion mechanisms. Water turbines, like Status of Tidal In-Stream in the Southern Hemisphere, they rotate wind turbines, are generally grouped Energy Conversion counterclockwise. into three types: Technologies To convert tidal or open-ocean 1. Axial turbines in which the axis of The Marine Current Turbine (MCT) currents to electricity, energy conversion rotation is parallel to the water stream 300-kW experimental SeaFlow unit devices are placed in the flowing water and thereby horizontal with respect (Figure 2b) was installed in May 2003 stream where they harness the kinetic to the seabed and is the world’s first marine renew- power of the moving water. Unlike 2. Cross-flow turbines in which the able of significant size traditional hydroelectric generation or a axis of rotation is perpendicular to to be installed in a genuinely offshore

2 The Coriolis effect is an apparent that, as a result of Earth’s rotation, deflects moving objects (such as projectiles or air and water currents) to the right in the Northern Hemisphere and to the left in the Southern Hemisphere

Oceanography June 2010 25 location. The site is 1 km off the coast of be installed in 2010. studies indicated that a 10,000 MW North Devon, UK. US tidal device developers are chal- installation would produce a very small In the United States, Verdant Power lenged by the lack of proper and stan- reduction in the speed installed an array of six 35-kW grid- dardized infrastructure to deploy and with no significant adverse side effects, connected water turbines in the tidal test tidal energy conversion devices in but indicated that more comprehensive studies were needed. In 2005, the Florida Atlantic University (FAU) Center for Ocean There are many types of ocean energy, Energy Technology (COET) in Dana and this is an active area of research , Florida, began a research program to investigate ocean currents as and development with considerable a resource, feasible ways of generating “lo ng-term promise. from ocean currents, and environmental and ecological interactions. FAU also is developing a platform to support ocean energy East River in New York in early 2007. the tidal passages. The Maine Maritime technology demonstration, validation, This experimental project is now” Academy has proposed a small-scale and development. complete and Verdant Power has applied test facility, and NNMREC’s tidal to the Federal Energy Regulatory energy branch at the University of Offshore Wind Energy Commission for a license to install Washington is developing plans for a Conversion Technologies 30 tidal turbines in that same location. full-scale test facility. Offshore, the blow stronger In 2008, MCT installed the largest In addition, a number of in-stream and steadier than they do onshore. tidal in-stream device to date, a dual, tidal demonstration projects are ongoing Consequently, high-wind resource areas 16-m-diameter rotor SeaGen machine and planned in the UK, Italy, Korea, are present just a few miles from many rated at 1.2 MW in Strangeford Narrows Canada, and the United States. If these of the world’s largest urban load centers. in Northern Ireland, an environmentally early undertakings prove successful, Offshore-wind-generated electricity can sensitive site. arrays up to 1–10 MW in capacity be used to bring low-carbon energy to OpenHydro of Ireland installed the could be deployed within the next many of these cities without the need first tidal in-stream turbine at the EMEC five to ten years. to build long-distance transmission tidal test facility in 2007. The turbine is lines over land. an experimental 300-kW, 6-m-diameter Status of Open-Ocean A wind turbine converts the kinetic device that can be lowered for testing Current Energy Conversion energy in the wind to electricity. The and raised above the water line for Technologies major components are a rotor (hub inspection and servicing on a pair of In 1977, Aerovironment Inc. conducted and blades), a gearbox, a generator, monopiles. OpenHydro is also testing preliminary studies to determine the and a tower (Figure 3). During the past a gravity base foundation at EMEC. environmental effects of an array of two decades, land-based wind energy A 1-MW, 10-m-diameter OpenHydro turbines producing 10,000 MW on the technology has seen a tenfold reduc- machine was installed in late 2009 at Gulf Stream and the surrounding land tion in cost and is now competitive the Nova Scotia Minas Passage Tidal areas. The program became known as with fossil and nuclear for electric Demonstration project site, and two the Coriolis Program, reflecting the fact power generation in many areas of the other 1-MW class machines—one that it is the Coriolis effect that causes United States and the world. The offshore from Marine Current Turbines and the intensification of the North Atlantic wind resource is complementary to the other from Clean Currents—will gyre near the Florida . These the onshore wind resource, and both

26 Oceanography Vol.23, No.2 shallow- and deepwater wind resource Although offshore service records promise for providing alternatives to the use is necessary for full offshore wind have not been any better than onshore, conventional monopiles, particularly and deployment. offshore turbines in the future must in deeper water, but higher costs could Offshore wind turbines evolved from be designed for higher reliability and preclude the widespread deployment of onshore wind technology using similar lower maintenance costs. They will be deepwater systems. rotors and energy conversion systems. equipped with more advanced condi- Wind turbines are arranged in arrays However, several offshore components tion monitoring, engage more efficient that take advantage of the measured and systems are different from those maintenance planning, and be designed prevailing wind conditions at the site. used in land-based systems. Machines to accommodate in situ repair. Offshore Turbine spacing is usually chosen to placed at sea are not constrained by the machines have different substructures minimize aggregate power plant power same transportation and installation than onshore turbines, requiring ocean losses, interior plant turbulence, and the limits as onshore machines even though engineering skills acquired from the oil cost of cabling between turbines. The the cost of deploying large vessels at sea and gas industry. Most installations are has a power distribution grid is high. The infrastructure and logistical fixed to the bottom in water depths of that begins by connecting the outputs support are significant portions of the 5–25 m, but new designs are extending of the individual turbines at 480 V to system cost for a large offshore wind the technology into deeper . The 690 V through a turbine farm, so offshore machines tend to be most common substructure is the mono- to a distribution voltage of about 34 kV. larger than land-based turbines. A larger pile—a large, thick-walled steel tube (up The electric distribution system collects output capacity per unit maximizes the to 60 mm thick and 6 m in diameter). the power from individual turbines at an value of the infrastructure, including The monopile foundation requires electric service platform (ESP), or substa- the cost of foundation and turbine massive hammers to drive the pile into tion, that provides a common electrical installations, vessels, maintenance, the seabed and special crane vessels for interconnection for all the turbines in the decommissioning, and energy capture lifting the turbine and tower into place. array. At the ESP, the voltage is stepped potential. Most offshore turbines are now Gravity-base foundations are also used up to about 138 kV and brought into between 3 MW and 5 MW (compared as an alternative to avoid the need for a phase; then the power is transmitted to land-based turbines that range from large pile-driving hammer or to accom- through a number of buried high-voltage 1.5 MW to 3.0 MW), and there are modate areas where piles cannot be subsea cables to shore, where an inter- several designs underway in the 5-MW reasonably driven. Multipile foundation connection point sends the power to the to 10-MW range. systems such as tripods are also showing grid. Once onshore, the voltage may need

Figure 3. Offshore ocean wind energy conversion.

Oceanography June 2010 27 to be increased again for power plants development is expected in the near Currently, installed capital costs for larger than 500 MW. For smaller arrays future from countries like Germany, offshore projects are 1.5 to 2.0 times that are closer to shore, the distribution where the first commercial offshore wind higher than for land-based wind grid can extend to the shore for direct farms are in process. All told, the EU turbines. Factors that contribute to the connection to a substation and grid expects offshore wind development to additional costs include marinizing the system, eliminating the need for an ESP. surge with offshore wind installations turbines for operation at sea, incorpo- The offshore ESP also provides a generating 150 GW by 2030. rating higher-reliability components, and central service facility for the wind farm, In the United States, interest in the at-sea location (e.g., expensive instal- which may include helicopter landing offshore wind is growing rapidly, lation vessels, logistics of working at sea, pads, a wind farm control room with although no offshore wind turbines longer power cable to distribution points supervisory control and data acquisi- have yet been installed. Over 2,000 MW ashore). In addition, operation and tion (SCADA) monitoring stations, a of offshore wind projects are moving maintenance costs are about three times hoist crane for smaller components, a through the permitting process and higher than for land-based systems. This rescue boat, a communication station, may come online by 2015. Most projects higher cost is partly because accessibility firefighting equipment, emergency are located in the North and Central to turbines is more difficult. External diesel backup generators, and staff Atlantic because the conditions are more severe and are more and service facilities, including emer- has a more gradual drop (compared difficult to measure and characterize. gency temporary living quarters for to the Pacific). This gentle slope allows Furthermore, extreme wind and wave maintenance workers. placement of turbines in federal waters loads combine to add substantial uncer- (> 3 nm from shore) while still taking tainty to the nascent design methods Status of Offshore advantage of relatively mature shallow- used for turbines and substructures. Wind Energy Conversion water technology. In addition, some New technologies to allow floating Technologies projects are being proposed in Texas deepwater deployments have been By the end of 2008, there were (between Galveston and Mexico) as conceptualized, and engineering design 1,471 MW of offshore wind energy well as the Great Lakes, and some states tools are well developed. In June 2009, collected worldwide with an expected have proposed projects in state waters the Norwegian oil company Statoil 420 MW added by projects in 2009. to give themselves greater local control launched the first full-scale floating The European Union estimates that and to speed up the permitting process. wind turbine. This 2.3-MW demon- stration turbine was deployed on a floating spar buoy, and constituted a major industry milestone. Ocean energy technology developers have a variety of conversion technologies at Ocean various stages of development. Conversion Technologies OTEC is the extraction of “ via a engine operating across the difference between warm over 1,100 MW of new offshore wind Canada has several projects planned as surface ocean water and cold deep ocean capacity will be added in 2010. China well. Pacific” winds exceed Atlantic winds water. In the tropics, surface water is also in the process of constructing in strength in many places, but offshore can exceed 26.7°C (80°F). its first 100 MW offshore wind farm wind has not garnered as much enthu- At ocean depths of 915 m (3,000 ft), near Shanghai. European projects are siasm from western US states due to the more or less, water temperatures are located mostly in the UK, Denmark, the difficulty of installing turbines in the usually less than 4.4°C (40°F). This Netherlands, and Sweden, but strong deeper waters. temperature differential can drive

28 Oceanography Vol.23, No.2 a Rankine thermodynamic cycle to OTEC generate electricity. The ideal Carnot effi- ciency of this small temperature differ- ential is very low. For a system operating TURBINE Ocean Surface between 26.7°C (80°F) and 4.4°C (40°F), the maximum theoretical efficiency is VAPORIZERCONDENSER only 7.4% and real efficiencies will be less. Regardless, Carnot efficiency is not WATER WATER the true measure of OTEC feasibility IN OUT 15°C 10°C because “” is free. OTEC has been technically demon- Depth: 1000 Meters strated as a feasible method to generate electricity. Figure 4 depicts a closed-cycle OTEC system whereby the working WATER fluid is recirculated within the system. Working Fluid: Ammonia IN 5°C Warm surface ocean water boils a pres- surized working fluid in the vaporizer. Figure 4. Illustration of ocean thermal energy conversion. The vapor expands through a turbine to drive a generator and produce electric power. The expanded vapor is converted primary disadvantage of the open-cycle when that organization was acti- back to a liquid in the condenser using system is the very large size and limited vated in January 1975. Two industry cold, . The working capacity of the turbine. teams developed conceptual designs fluid pump returns the liquid back to It is possible to combine the flash under the NSF program. the vaporizer to complete the cycle. evaporation and condenser of an open- Ammonia is one OTEC fluid used cycle system with a closed-cycle system Status of Ocean Thermal because of its thermal properties. Cycle to produce electric power and desali- Energy Conversion efficiency may be boosted by super- nated water. This combination is referred Technologies heating, reheating, and similar strategies to as a hybrid cycle. In 1979, a Lockheed team demonstrated used in steam cycles, though the cost of The ocean is the solar collector in an net power production from an at-sea the added complexity must be offset by OTEC power system. Because this large closed-cycle OTEC system with the any performance gains. ocean thermal mass remains relatively operation of Mini-OTEC off the coast of An open-cycle OTEC system uses constant in temperature, an OTEC Hawai’i. This plant generated approxi- warm surface ocean water as the power plant provides power mately 50 kW of gross power with about working fluid. The warm ocean water generation capability that is very attrac- 15 kW of net power. In 1980, DOE is introduced into a vacuum chamber tive to utilities. deployed OTEC-1, a converted Navy whereby a portion of the water flash Modern-day OTEC studies were tanker moored in waters off Hawai’i, to evaporates. The low-temperature, supported by the National Science test heat exchangers and other compo- low-pressure steam (relative to most Foundation’s (NSF) Research Applied nents of a closed-cycle OTEC plant and existing power plants) expands through to National Needs program, partly to investigate the environmental effects the turbine to drive the generator. The in response to the increase in fossil- of an ocean-stationed OTEC plant. expanded vapor is converted back to fuel costs (notably oil) in late 1973. Support for OTEC development waned a liquid in the condenser using cold Government direction of the program in the early 1980s when the administra- deep ocean water. The condensed liquid moved to the Energy Research and tion sought to eliminate DOE just as is available as desalinated water. The Development Administration (ERDA) the agency’s program was about to fund

Oceanography June 2010 29 a pilot plant demonstration. Limited OTEC is the capital cost of the system. freshwater generates a voltage over DOE funding survived to support OTEC systems exploit a low-energy each membrane, and the total potential a test program for heat exchanger resource and therefore need to of the system is the sum of the poten- performance, material corrosion, and move large amounts of ocean water to tial differences over all membranes. biofouling, as well as separate programs generate utility-scale electric power. It is important to remember that the process works through differences in ion instead of an electric field, which has implications for the type Except for shallow-water offshore wind, of membrane needed. In RED, as in a ocean energy technologies are still in an fuel cell, the cells are stacked. A module emerging stage of technology development, with a capacity of 250 kW is the size of a shipping container. “where land-based wind technology was With PRO, is pumped into approximately 15 to 25 years ago. a chamber that is separated from a freshwater by a semi-permeable membrane. As a result of the osmotic pressure difference between the two focused on alternative cold-water pipe Each of the major OTEC subsystems , water diffuses through the designs and gimbal attachments during must together” in the most cost- membrane into the seawater chamber, the 1980s and 1990s. effective manner to generate economi- thereby diluting the seawater and A number of small companies cally viable cost of electricity. Beaudoin increasing its volume. Pressure compen- promote OTEC technology. These et al. (2010) addresses OTEC commer- sation in the chamber spins a turbine to companies include Makai Ocean cialization barriers. generate electricity. Figure 5 is an artist’s Engineering, Ocean Energy and conception of a PRO plant at . Engineering Systems International, Sea Salinity Gradient Energy International (now OTEC Conversion Technologies Status of Salinity International), Marine Development When a river runs into the ocean and Gradient Energy Associates, and Offshore Infrastructure freshwater mixes with seawater, huge Conversion Technologies Associates. Over the past three years, amounts of energy are unleashed. Salinity Salinity gradient technologies are Lockheed Martin Corporation has gradient power, or , is the being developed for commercial use restarted its OTEC efforts and, with energy retrieved from the difference in in the Netherlands (for RED) and some of these companies, is developing the salt concentration between seawater Norway (for PRO). an OTEC pilot plant and a commer- and river water. Two practical methods A new proposal to improve a cial plant design. DOE has recently for this are reverse electro dialysis (RED) 75-year-old dike, the Afsluitdijk, in the supported OTEC development under and pressure-retarded osmosis (PRO). Netherlands could make it the world’s its Advanced Water Power Project in Both processes rely on osmosis3 with leading site for generating power using the Wind and Program ion-specific membranes. RED technology. The Afsluitdijk is a Office. The Naval Facilities Engineering With RED, a salt solution and 32-km-long (20-mile-long) causeway Command (NAVFAC) awarded freshwater pass through a stack of that was constructed in part to dam an OTEC contract last year to the alternating cathode and anode exchange off the Zuiderzee inlet of the North Lockheed Martin team. membranes. The chemical potential Sea, turning it into the massive fresh- The primary barrier to entry for difference between saltwater and water lake, the IJsselmeer. The lake

3 Osmosis: of fluid through a semi-permeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of solute on both sides of the membrane.

30 Oceanography Vol.23, No.2 periodically discharges water because Summary 10 to 15 years away from large-scale rivers and streams continually feed it, For ocean wave and tidal/ocean current commercial development. The which makes it an ideal location for the hydrokinetic technology, only several United States has yet to deploy an RED saltwater power plant. dozen devices have progressed to offshore wind system. Statkraft of Norway has been devel- rigorous subscale laboratory wave-tank Eight countries active in OTEC oping osmotic power since 1997 with a or tow-tank model testing. Only a couple research and development have launched view to achieving cost-effective osmotic of dozen have advanced to short-term or are planning a number of projects: power production, making it the world (days to months) tests in natural waters. France, the UK, the Netherlands, leader in the development of PRO tech- And only a few devices have progressed Sweden, Norway, Japan, Taiwan, and nology. The world’s first osmotic power to long-term (> 1 year) testing of full- the United States. There are about plant was opened in November 2009 at scale prototypes in natural waters. The 100 nations and territories with access to Tofte, outside Oslo, Norway. This plant first commercial wave energy plant was OTEC thermal resources. has been in development for more than realized in 2008 in Portugal, and the first Two countries, the Netherlands and a year. It will have a limited production commercial tidal current plant or ocean Norway, have active R&D programs in capacity (designed for 10 kW but initially current plant has yet to be realized. salinity-based . operating at 2–4 kW) and is intended Shallow-water offshore wind is a There are many types of ocean energy, primarily for testing and development commercial technology with almost and this is an active area of research purposes. The aim is to be capable of 1,500 MW of capacity installed in and development with considerable constructing a commercial osmotic Europe. Deep-water offshore wind long-term promise. Ocean energy power plant within a few years’ time. is an emerging technology, probably technology developers have a variety of conversion technologies at various stages of development. The time period needed for these technologies to progress from concept to deployment of a long- term, full-scale prototype in natural waters is on the order of 5 to 10 years. Except for shallow-water offshore wind, ocean energy technologies are still in an emerging stage of technology development, where land-based wind technology was approximately 15 to 25 years ago. It is too early to know which technologies will turn out to be the most cost-effective, reliable, and environmentally sound, which may differ by location.

Reference Beaudoin, G., D. Robertson, R. Doherty, D. Corren, B. Staby, and L. Meyer. 2010. Technological challenges to commercial-scale application of marine renewables. Oceanography 23(2):32-41.

Figure 5. Artist’s conception of a pressure-retarded osmosis (PRO) plant placed at sea level. Courtesy of Statkraft

Oceanography June 2010 31