Renewable Ocean Energy

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Introduction and Background

Numerous studies have established that our reliance on fossil fuels (coal, oil, natural gas, gasoline) is a polluting and non-sustainable practice that has serious long-term repercussions (rising sea levels, acidification of the oceans, stronger and more frequent storms) for the earth (see Surfrider Foundation’s article on global Climate Change for more details). These changes are likely to be felt most strongly along our coasts. Breaking our reliance on fossil fuels will require development of a number of alternative sources of energy that are renewable and non-polluting.

The term "alternative energy" is typically used to describe sustainable means of generating electrical power that do not involve burning fossil fuels. Some people include nuclear power in the alternative energy category, but for this discussion we have excluded nuclear power due to environmental issues associated with the extraction and processing of uranium for fuel and disposal of spent fuel rods.

Alternative energy sources include solar, wind, waves, tides and geothermal energy. In some locations more than one technology is being considered. There are even proposals to utilize ocean currents such as the Gulf Stream or utilize the temperature differential between warm surface waters and colder waters deeper in the ocean to produce energy. Research into these areas has been going on for decades. For over 30 years, the Natural Energy Laboratory of Hawaii has been conducting research on the ocean thermal energy conversion (OTEC) process and its related technologies. More about OTEC.

For this paper we’ll confine our discussion to offshore utilization of wind, waves and tides to produce energy. These types of technologies are generally supported by environmentalists and environmental groups because they are sustainable (they don’t rely on a finite fuel source) and non-polluting. Because they don’t involve burning fossil fuels, they don’t generate carbon dioxide emissions and therefore don’t contribute to global warming.

Many marine-based renewable energy technologies are at relatively early stages of development, so there is little in the way of demonstrated effectiveness, cost, or environmental effects of large-scale ocean-based systems.

Despite the seemingly benign nature of wind, wave and tide-powered energy projects, some proposed offshore alternative energy projects have encountered opposition from local environmentalists, or at least concern about potential coastal/environmental impacts. In most cases these potential impacts are site specific, so a thorough understanding of the technologies and how the technologies might be adapted to a particular site is important. Provided below is a brief description of each of these technologies and a summary of environmental considerations (positive and negative) that have been raised regarding their implementation. We hope that this information will aid local environmental activists in their decisions and actions regarding proposed projects.


Most modern wind power is generated in the form of electricity by converting the rotation of turbine blades into electrical current by means of an electrical generator. A wind turbine can be thought of as an electric fan running in reverse.

Wind power is used in large scale wind farms for national electrical grids as well as in small individual turbines for providing electricity in isolated locations.

Wind energy is abundant, inexhaustible, widely distributed, clean, and mitigates the greenhouse effect.

Wind turbines are usually mounted on long vertical support structures extending up to a few hundred feet above sea or ground surface. The wind turbines are usually installed in a line or an array or a "wind farm" situated to catch prevailing strong wings.

Offshore wind turbines are considered to be less unsightly than onshore installations since they can be invisible from shore. Because there are fewer obstacles and stronger winds, such turbines don’t need to be built as high into the air. However, offshore conditions are harsh, abrasive, and corrosive, and it is more difficult to maintain a turbine in open marine waters than on land.

In areas with extended shallow continental shelves and sand banks (such as Denmark), turbines are reasonably easy to install, and give good service. The largest offshore wind turbines in the world are seven 3.6 MW rated machines off the east coast of Ireland about sixty kilometers south of Dublin. The turbines are located on a sandbank approximately ten kilometers from the coast that has the potential for the installation of 500 MW of generation capacity. As of 2006, the largest offshore wind farm was the Nysted Offshore Wind Farm at Rødsand, located about ten kilometers south of Nysted and thirteen kilometers west of Gedser, Denmark. The wind farm consists of seventy-two turbines of 2.3 MW, which produces 165.6 MW of power at rated wind speed. Three offshore wind farms in the United Kingdom are currently operating, North Hoyle (30 x 2MW), Scroby Sand (30 x 2MW) and Kentish flat (30 x 3MW). Another offshore wind farm, Barrow (30 x 30MW), is under construction. Under the energy policy of the United Kingdom further offshore facilities are feasible and expected by the year 2010.


Today, several offshore wind facilities are in the planning or permitting stages in the United States, including:

  • Cape Wind facility off the coast of Massachusetts. Developers filed for a permit from the U.S. Army Corps of Engineers in 2001 to build this 130-turbine facility slated to produce up to 420 MW. It is on the Outer Continental Shelf (OCS) (just beyond 5 km offshore), and it would be the largest offshore wind energy facility in the world. A court ruling in August 2010 apparently gave the project final approval and will allow construction to begin.
  • The Block Island Wind Farm is a 30-megawatt offshore wind farm to be located approximately three miles southeast of Block Island consisting of 5 turbines. The wind farm will be located entirely in Rhode Island state waters. The wind farm will generate over 125,000 megawatt hours annually, enough to power over 17,000 homes. Power will be exported to the mainland electric grid via the 21-mile, bi-directional Block Island Transmission System, a submarine cable proposed to make landfall in Narragansett, Rhode Island. More.
  • The Long Island – New York City Offshore Wind Project would be located in the Atlantic Ocean, approximately 13 nautical miles off the Rockaway Peninsula. It would likely be designed for 350 megawatts (MW) of generation, with the ability to expand it to 700 MW, giving it the potential to be the largest offshore wind project in the country.
  • A fifty-turbine facility off the Galveston, Texas coast. While this facility is not in the Northeast, where offshore winds are considered to be the strongest and other energy alternatives are lacking, its developers believe it will be successful because of the area’s experience with other offshore energy development and a more favorable state regulatory environment (Miller 2006). (State of Texas regulatory authority extends to 16 km off the coast, whereas other states’ authorities extend for 5 km.)
  • The Bureau of Ocean Energy Management (BOEM) has given the green light for Principle Power, Inc. to submit a formal plan to build a 30-megawatt pilot project using floating wind turbine technology offshore Coos Bay, Oregon. Principle Power, Inc. will seek to site its project within a 15-square-mile proposed lease area. The project is designed to generate electricity from five floating “WindFloat” units, each equipped with a six-megawatt offshore wind turbine. The turbines would be connected by electrical cables and have a single power cable transmitting the electricity to the mainland. The facility, sited in about 1,400 feet of water, would be the first offshore wind project proposed in federal waters off the West Coast and the first in the Nation to use a floating structure to support offshore wind generation in the Outer Continental Shelf. More info.

In September 2014 USA Today reported that 14 offshore wind farm projects had entered "advanced stages" of development. Two of the projects — Cape Wind in Nantucket Sound off the coast of Massachusetts and Deepwater's Block Island off Rhode Island (see above) — have moved into the initial stages of construction while the others have obtained a lease, conducted extensive studies or obtained a power purchase agreement. Nine are located on the East Coast.

Important differences exist between Europe and the United States regarding offshore wind environments. U.S. waters are generally deeper than those off the European coasts, and ocean conditions on the U.S. OCS are more severe than those in Europe. Thus, the technologies designed for European offshore environments will need to be modified to adapt to the harsher U.S. OCS conditions.

The U.S. Department of Energy Wind Program is committed to developing and deploying a portfolio of innovative technologies for clean, domestic power generation to support an ever-growing industry, targeted at producing 20% of our nation's electricity by 2030.

Environmental Considerations

Potential environmental concerns include impacts to views/aesthetics, noise, bird kills, interruption of shipping/boating routes, and blocking or diminishing the size of waves eventually reaching the coast.

Potential positive or negative impacts on the environment that may occur during operations are highlighted below.

  • Marine life. Foundations can act as artificial reefs with a resultant increase in fish populations from the new food supply. These increases in fish population may also have stimulating effects on bird populations in the area, which could promote collisions between birds and towers or rotors.
  • Migrating birds. In addition to potential collisions (bird strikes), it is possible that the birds would need to consume more energy to avoid collisions and maintain their orientation when navigating around the turbines. Tower illumination may also cause navigational disorientation for birds.
  • Interference with navigation for endangered and threatened species. Electromagnetic fields created by the electric cables running from the turbines and underwater noises and vibrations could affect orientation and navigational ability.
  • Potential alteration of natural environments and habitats. Underwater support pilings, anchoring devices, scour-protection materials, and electromagnetic fields could cause an increase or decrease in benthic communities, alter natural environments, and possibly affect migration patterns.
  • Emissions. Each unit of electricity generated from the wind that substitutes for a unit generated from fossil fuels helps reduce greenhouses gases, pollutants, and waste products that result from fossil fuel use.
  • Conflict with Other Sea Space Uses. Wind turbines on the OCS may interfere with commercial shipping and fishing and recreational boating. It is possible that wind turbine energy facilities may disrupt air traffic control and maritime radar systems.
  • Visual impacts for systems that are close to the shore. (At greater distances, visibility impacts are reduced.)
  • Noise. Newer wind turbine generators produce less sound than older turbines, but impacts of low frequency sound near the turbines on mammals would need to be investigated.

Wind turbines can kill birds, especially birds of prey. Siting generally takes into account known bird flight patterns, but most paths of bird migration, particularly for birds that fly by night, are unknown. Although a Danish survey in 2005 (Biology Letters 2005:336) showed that less than 1% of migrating birds passing a wind farm in Rønde, Denmark, got close to collision, the site was studied only during low-wind non-twilight conditions. A survey at Altamont Pass, California conducted by the California Energy Commission in 2004 showed that turbines killed 4,700 birds annually (1,300 of which were birds of prey). Radar studies of proposed sites in the eastern U.S. have shown that migrating songbirds fly well within the reach of large modern turbines. However, many more birds are killed by cars, and this appears to be a widely accepted cost.

Perceptions that wind turbines are noisy and contribute to "visual pollution" creates resistance to the establishment of land-based wind farms in some places. Moving the turbines offshore mitigates the problem somewhat, but offshore wind farms are more expensive to maintain and there is an increase in transmission loss due to longer distances of power lines. One solution to such objections is the early and close involvement of the local population, as recommended in the sustainability guidelines of the World Wind Energy Association - in the ideal case through community/citizen ownership of wind farms.

Regarding impacts to waves, an environmental analysis of the proposed Scarweather Sands Offshore Wind Farm project in the UK indicated that there would be minimal (generally 0.1% to about 4%) reduction in wave heights along the area of coast in the "wave shadow" of the wind farm project (Environmental Statement prepared by United Utilities, January 2003).

Siting Constraints

In selecting OCS wind facility locations, developers will need to consider how candidate areas are already used to avoid potential conflicts. In addition to minimizing the types of potential environmental impacts identified above, potential siting issues that need to be considered include the following:

  • Shipping lanes
  • Excavation of raw materials in OCS areas
  • Existing areas used for disposal of dredged materials and other wastes
  • Pipelines
  • Commercial and recreational fishing areas
  • Low-flying aircraft flight patterns
  • Military operations and radar systems
  • Migration patterns for birds and mammals

Waves, Tides and Ocean Currents

In comparison to wind power, wave, tidal and ocean current power technologies are in their infancy. Wave-power or tidal-power generators have been tested near the shores of New Jersey, New York, Hawaii, Scotland, England and Western Australia. A handful of commercial projects are also in the works, including the world’s first "wave farm," being installed off the north coast of Portugal. A field of tidal turbines is also being built off the shore of Tromso, Norway.

In Massachusetts, Representative William D. Delahunt has proposed that the United States follow in Britain’s footsteps to build an ocean energy research center off the Massachusetts coast. TRC Environmental Corporation prepared a report Existing and Potential Ocean-Based Energy Facilities and Associated Infrastructure in Massachusetts (PDF) in 2006.

In Oregon, researchers in the College of Engineering at Oregon State University are developing technology that taps the motion of the ocean as a source of clean energy. Annette von Jouanne and Alan Wallace, OSU professors of electrical engineering, are designing, testing, and implementing a buoy prototype energy extraction system that would be anchored offshore in an energy wave park. Research shows that the Oregon coast near Reedsport is one of the best locations in the U.S. for such a park. The wave energy researchers utilize OSU facilities, which include the Motor Systems Resource Facility; the Energy Resources Research Laboratory, where researchers are developing turbine models; and the O. H. Hinsdale Wave Research Laboratory, home of a tsunami research facility. In January 2013 it was announced that the nation’s first utility-scale, grid-connected wave energy test facility will be located in Newport, Oregon. The new facility, called the Pacific Marine Energy Center, will test energy generation potential and the environmental impacts of wave energy devices, at an ocean site about five miles from shore. Subsea cables will transmit energy from the wave energy devices to the local power grid, and data to scientists and engineers at on-shore facilities.

In Florida, Florida Atlantic University (FAU) has been selected by the Florida Technology, Research and Scholarship Board to receive $5 million to establish The Florida Center of Excellence in Ocean Energy Technology. The Center will look at South Florida's ocean currents, specifically the Gulf Stream, as a potentially abundant renewable energy source. More on this. A new technology that is beginning to be studied is the use of underwater kites to extract energy from ocean currents. The U.S. Bureau of Ocean Energy Management (BOEM) has information on Ocean Current Energy. BOEM states:

"There are a number of different current technology concepts under development. Prototype horizontal axis turbines, similar to wind turbines, have been built and tested, and over the next 5 to 7 years would be the most likely commercial development scenario. Although ocean current technology is still in its early stages of development, several tidal and in-stream current turbine applications are near commercialization. These devices take advantage of the daily tidal cycles in near-shore ocean environments, or steady water flow from freshwater rivers."

A new and promising ocean current energy technology is the Ocean Energy Turbine being developed by Crowd Energy.


The total power of waves breaking on the world's coastlines is estimated at 2 to 3 million megawatts. In favorable locations, wave energy density can average 65 megawatts per mile of coastline. A 2011 report Mapping and Assessment of the United States Wave Energy Resource estimates that the total available wave energy resource along the nation's outer continental shelf is 2,100 terawatt-hours (TWh) per year.

Wave energy.jpg

Wave power projects generally utilize the up-and-down motion of a device floating in the ocean encountering ocean swells to generate electricity. Oregon Sea Grant has put together a nice graphic and primer on wave energy devices. Three general approaches to capturing wave energy are:

Floats or Pitching Devices

These devices generate electricity from the bobbing or pitching action of a floating object. The object can be mounted to a floating raft or to a device fixed on the ocean floor. One device that could be placed in this category is the bioWAVE ocean wave energy system from BioPower Systems. This technology is scheduled to be tested off the coast of Port Fairy, Australia by early 2013.

Here's a video of a wave energy plant in Brazil, reportedly the first wave energy plant in Latin America.

Oscillating Water Columns (OWC)

These devices generate electricity from the wave-driven rise and fall of water in a cylindrical shaft. The rising and falling water column drives air into and out of the top of the shaft, powering an air-driven turbine.

Wave Surge or Focusing Devices

These shoreline devices, also called "tapered channel" or "tapchan" systems, rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. Water flow out of this reservoir is used to generate electricity, using standard hydropower technologies.

Much of the early work on this technology was done by Dr. Stephen Salter, who developed a test device known as "Salter’s Duck." Wave power technologies can also be divided into four classes—attenuators, terminators, point absorbers and overtopping devices. Each of these classes of devices are described below, with some specific examples of pilot or commercial application cited.


Attenuators are long multi-segment floating structures oriented parallel to the direction of the wave travel. The differing heights of waves along the length of the device causes flexing where the segments connect, and this flexing is connected to hydraulic pumps or other converters. The attenuators with the most advanced development are the McCabe wave pump and the Pelamis.

The McCabe wave pump has three pontoons linearly hinged together and pointed parallel to the wave direction. The center pontoon is attached to a submerged damper plate, which causes it to remain still relative to fore and aft pontoons. Hydraulic pumps attached between the center and end pontoons are activated as the waves force the end pontoons up and down. The pressurized hydraulic fluid can be used to drive a motor generator. A full-size 40-m prototype was tested off the coast of Ireland in 1996, and commercial devices are being offered by the manufacturer.

A similar concept is used by the Pelamis, which has four 30m-long by 3.5m-diameter floating cylindrical pontoons connected by three hinged joints. Flexing at the hinged joints due to wave action drives hydraulic pumps built into the joints. A full-scale, four-segment production prototype rated at 750 kW was sea tested for 1,000 hours in 2004. This successful demonstration was followed by the first order in 2005 of a commercial Wave Energy Conversion (WEC) system from a consortium led by the Portuguese power company Enersis SA. The first stage, scheduled to be completed in 2006, consists of three Pelamis machines with a combined rating of 2.25 MW to be sited about 5 km off the coast of northern Portugal. An expansion to more than 20-MW capacity is being considered. A Pelamis-powered 22.5-W wave energy facility is also planned for Scotland, with the first phase targeted for 2006.

Pelamis Wave Energy

The EPRI wave energy feasibility demonstration project has selected the Pelamis as one of the technologies for design, performance, cost, and economic assessment (Bedard et al. 2005). Sites for evaluation were selected off the coasts of Hawaii (15.2 kW/m average annual wave energy), Oregon (21.2 kW/m), California (11.2 kW/m), Massachusetts (13.8 kW/m), and Maine (4.9 kW/m). For systems at these sites scaled to a commercial level generating 300,000 MWh/yr, the cost of electricity ranged from about $0.10/kWh for the areas with high wave energy, to about $0.40/kWh for Maine, which has relatively lower levels of wave energy.


(No, this has nothing to do with the former Governor of California) Terminator devices extend perpendicular to the direction of wave travel and capture or reflect the power of the wave. These devices are typically installed onshore or nearshore; however, floating versions have been designed for offshore applications. The oscillating water column (OWC) is a form of terminator in which water enters through a subsurface opening into a chamber with air trapped above it. The wave action causes the captured water column to move up and down like a piston to force the air though an opening connected to a turbine. A full-scale, 500-kW, prototype OWC designed and built by Oceanlinx (2006) underwent testing offshore at Port Kembla in Australia, and a further project was planned for Rhode Island. The proposed project off Point Judith in Rhode Island ran into an economic glitch in October 2006 when it was learned that the Federal Energy Regulatory Agency (FERC) has a rule to force the company to pay existing power plants to compensate them for the electricity that they didn’t sell because of the free energy the Energetech would provide to customers during their pilot demonstration project. In July 2012 Oceanlinx received just under $4 million dollars in funding from Australia's Emerging Renewables Program. They are planning for a 1MW Wave Energy converter at Port Macdonnell, South Australia.

Terminator Schematic

In an Electric Power Research Institute (EPRI)-cosponsored study (Bedard et al. 2005), a design, performance, and cost assessment was conducted for an Energetech commercial-scale OWC with a 1,000-kW rated capacity, sited 22 km from the California shore. With the wave conditions at this site (20 kW/m average annual), the estimated annual energy produced was 1,973 MWh/yr. For a scaled-up commercial system with multiple units producing 300,000 MWh/yr, the estimated cost of electricity would be on the order of $0.10/kWh.

Another floating OWC is the "Mighty Whale" offshore floating prototype, which has been under development at the Japan Marine Science and Technology Center since 1987 (JAMSTC 2006).

Point Absorbers

Point absorbers have a small horizontal dimension compared with the vertical dimension and utilize the rise and fall of the wave height at a single point for WEC.

One such device is the PowerBuoy™ developed by Ocean Power Technologies (OPT). The construction involves a floating structure with one component relatively immobile, and a second component with movement driven by wave motion (a floating buoy inside a fixed cylinder). The relative motion is used to drive electromechanical or hydraulic energy converters. A PowerBuoy demonstration unit rated at 40 kW was installed in 2005 for testing offshore from Atlantic City, New Jersey.

OPT Power Buoy. Source: OPT

OPT also filed (July 2006) an application to the U.S. Federal Energy Regulatory Commission (FERC) for construction permission for a 50-megawatt (MW) wave power generation project in Reedsport, Oregon. This is the first request in the United States for such a power project on a utility-scale level. The company expects to install its ocean-tested PowerBuoy wave energy devices approximately 2.5 miles off the coast at a depth of 50 meters.

The buoys proposed for the coast of Oregon would extend about 15 feet above the water - and the wave park eventually would have four rows of 50 buoys for a total of 200. The park would take up 1.5 square miles of ocean - 1/2 mile wide by 3 miles long. The buoys could generate enough electricity to power about 2,000 homes Initially the project is projected to generate a total of 2 MW, but approval for the full-scale project will generate 50 MW from the wave power plant. The company has already consulted key stakeholder groups about its plans and will continue to work closely with these groups over the initial stages of the project. Gov. Ted Kulongoski supports the project. He has organized an Oregon Solutions team to help streamline the process. Port of Umpqua Commissioner Keith Tymchuk and state Sen. Joanne Verger, D-Coos Bay, co-chair the group.

According to the company, a key strength of the PowerBuoy system is its compact nature and low visual impact. OPT's wave energy converter consists of a vertically oriented column or cylinder that absorbs the rising and falling motion of ocean waves to cause the buoy mechanics to move freely up and down. This movement in turn drives an electric generator that creates usable on-site power or power that can be cabled away to a nearby mainland location. OPT's PowerBuoy technology was cited in recent U.S. Congressional hearings in support of increasing funding for ocean energy demonstration programs. U.S. Representative Jay Inslee (D-WA) proposed an amendment to the Deep Ocean Energy Resources (DOER) Act, which would increase the funding for ocean energy demonstration programs such as this one from $6 million to $20 million per year. Unfortunately, after years of planning and financial investment, OPT announced in April 2014 that they had abandoned plans to develop a wave energy project off Reedsport, Oregon. More on this.

Testing in the Pacific Ocean is also being conducted, with a unit installed in 2004 and 2005 off the coast of the Marine Corps Base in Oahu, Hawaii. A commercial-scale PowerBuoy system is planned for the northern coast of Spain, with an initial wave park (multiple units) at a 1.25-MW rating. Initial operation was expected in 2007.

The AquaBuOY™ WEC being developed by the AquaEnergy Group, Ltd. (2005) is a point absorber that is the third generation of two Swedish designs that utilize the wave energy to pressurize a fluid that is then used to drive a turbine generator. The vertical movement of the buoy drives a broad, neutrally buoyant disk acting as a water piston contained in a long tube beneath the buoy. The water piston motion in turn elongates and relaxes a hose containing seawater, and the change in hose volume acts as a pump to pressurize the seawater. The AquaBuOY design has been tested using a full-scale prototype, and a 1-MW pilot offshore demonstration power plant is being developed offshore at Makah Bay, Washington. The Makah Bay demonstration will include four units rated at 250 kW placed 5.9 km (3.2 nautical miles) offshore in water approximately 46 m deep.

Australian company Carnegie Wave plans to commission a “commercial scale” installation near Perth in 2014, using a fully submerged device that uses wave power to pump water to shore for conversion to electricity. In fact, in early 2015 it was announced that the world’s first grid-connected wave power station had been activated off the coast of Western Australia (WA). The company says its system is “different from other wave energy devices as it operates under water where it is safer from large storms [and corrosion] and invisible from the shore”. The round, submerged buoys are tethered to seabed pump units, which are installed at a depth of between 25 and 50 meters. Waves crashing into the buoys drive the pumps, which push pressurized seawater through a pipeline beneath the ocean floor to an onshore hydroelectric power station. Here, the high-pressure water drives a turbine and generates electricity.

Another company, M3 Wave, plans to install a new device just off the Oregon coast during summer 2014. M3 will be using a pressure-based device, sitting out of sight on the ocean floor. As a wave passes over it, air inside the device is pushed by pressure changes from one chamber to another, spinning a turbine to generate electricity.

The Sotenäs Wave Energy Project off the coast of Sweden is an ambitious initiative consisting of a total of 420 energy-capturing buoys. When finally completed, the €25 million park will provide a total output of about 10 MW, installed over an area of some 0.8 km2 - making it the largest full-scale demonstration project of its kind anywhere in the world, as well as the first ever multiple unit wave power plant. In December 2015, the project achieved a major milestone in the development of the first 1 MW of the Plant, when 120 tons of subsea generator switchgear was deployed in cooperation with Norwegian company Cecon Contracting and connected to the Swedish National Grid along a 10 km subsea cable. This was closely followed by the connection, in late January 2016, of several six meter diameter buoys to corresponding linear generator Wave Energy Converters (WECs), signalling the final stage of bringing each unit on line. The Sotenäs Wave Power Plant uses the motion of waves to directly drive a WEC. It is made up of a unique design consisting of a direct coupled linear wave energy generator that is attached to the sea bed using a concrete gravity mounting plate and connected via a line to a buoy positioned on the surface of the sea. The theory is that the motion of the buoy perfectly matches the up and down movements of the waves - in the process, also enabling the WEC to generate electricity and eliminating the need for a complicated mechanical transmission system. The WECs themselves are connected to a series of marine substations, which are capable of transmitting an alternating current directly to the onshore grid. Read more.

Other point absorbers that have been tested at prototype scale include the Archimedes Wave Swing (2006), which consists of an air-filled cylinder that moves up and down as waves pass over. This motion relative to a second cylinder fixed to the ocean floor is used to drive a linear electrical generator. A 2-MW capacity device has been tested offshore of Portugal.

Overtopping Devices

Overtopping devices have reservoirs that are filled by impinging waves to levels above the average surrounding ocean. The released reservoir water is used to drive hydro turbines or other conversion devices. Overtopping devices have been designed and tested for both onshore and floating offshore applications. The offshore devices include the Wave Dragon™ (Wave Dragon 2005), whose design includes wave reflectors that concentrate the waves toward it and thus raises the effective wave height. Wave Dragon development includes a 7-MW demonstration project off the coast of Wales and a pre-commercial prototype project performing long-term and real sea tests on hydraulic behavior, turbine strategy, and power production to the grid in Denmark. The Wave Dragon design has been scaled to large sizes, with a span of more than 200 m across the reflector arms and a capacity of approximately 24 MW.

The WavePlane™ (WavePlane Production 2006) overtopping device has a smaller reservoir. The waves are fed directly into a chamber that funnels the water to a turbine or other conversion device.

Basic research to develop improved designs of WEC devices is being conducted in regions such as near the Oregon coast, which is a high wave energy resource (Rhinefrank 2005).

The Wave Hub project (technology not yet specified) is being proposed for the north coast of Cornwall, England.

Environmental Considerations

Conversion of wave energy to electrical or other usable forms of energy is generally anticipated to have limited environmental impacts. However, as with any emerging technology, the nature and extent of environmental considerations remain uncertain. The impacts that would potentially occur are also very site specific, depending on physical and ecological factors that vary considerably for potential ocean sites. As large-scale prototypes and commercial facilities are developed, these factors can be expected to be more precisely defined.

Potential environmental impacts include withdrawal of wave energy from the ecological system, interactions with marine life, noise, bottom impacts from anchors, and visual appearances. Environmental impacts from cable landings may be a concern, as are electrical and magnetic energy imparted into seawater. A wave energy facility could also pose a threat to navigation.

The following environmental considerations require monitoring:

Visual appearance and noise are device-specific, with considerable variability in visible freeboard height and noise generation above and below the water surface. Devices with OWC and overtopping devices typically have the highest freeboard and are most visible. Offshore devices would require navigation hazard warning devices such as lights, sound signals, radar reflectors, and contrasting day marker painting. However, Coast Guard requirements only require that day markers be visible for 1 nautical mile (1.8 km), and thus offshore device markings would only be seen from shore on exceptionally clear days. The air being drawn in and expelled in OWC devices is likely to be the largest source of above-water noise. Some underwater noise would occur from devices with turbines, hydraulic pumps, and other moving parts. The frequency of the noise may also be a consideration in evaluating noise impacts.

Reduction in wave height from wave energy converters could be a consideration in some settings; however, the impact on wave characteristics would generally only be observed 1 to 2 km away from the WEC device in the direction of the wave travel. Thus there should not be a significant onshore impact if the devices were much more than this distance from the shore. None of the devices currently being developed would harvest a large portion of the wave energy, which would leave a relatively calm surface behind the devices. It is estimated that with current projections, a large wave energy facility with a maximum density of devices would cause the reduction in waves to be on the order of 10 to 15%, and this impact would rapidly dissipate within a few kilometers, but leave a slight lessening of waves in the overall vicinity.

Little information is available on the impact on sediment transport or on biological communities from a reduction in wave height offshore. An isolated impact, such as reduced wave height for recreational surfers, could possibly result. An environmental analysis conducted for the Wave Hub project mentioned above indicates a worst case scenario of up to a 13% reduction in wave height along a small section of the north coast, with more likely scenarios showing up to a 5% reduction in wave height.

The U.K. organization Surfers Against Sewage (SAS) have looked into the Wave Hub project and have issued the following statement:

Since being asked to provide input into the project almost 3 years ago, SAS have pushed heavily to get the impact the Wave Hub will have on the surf investigated. The first of these, an independent peer reviewed study conducted by the University of Exeter is now in the public domain. SAS have been acknowledged by the Authors of this paper for their input. The research concludes that a realistic scenario for the wave hub would produce an average change in significant wave height at the shoreline of 1 cm or less. SAS believes that any slight reduction in wave height will be unnoticeable by surfers. This view is backed by the peer reviewed paper which states:

"There is little cause for concern that effects introduced by the Wave Hub will be felt by shoreline users of the sea. This, along with worst case scenario modeling carried by Halcrow, suggests the impact of the Wave Hub will be minimal."

There is still some concern within the surfing community about future wave farm developments. SAS feels that future developments will need to be assessed by the surfing community on a case by case basis in an objective manner.

Marine habitat could be impacted positively or negatively depending on the nature of additional submerged surfaces, above-water platforms, and changes in the seafloor. Artificial above-water surfaces could provide habitat for seals and sea lions or nesting areas for birds. Underwater surfaces of WEC devices would provide substrates for various biological systems, which could be a positive or negative complement to existing natural habitats. With some WEC devices, it may be necessary to control the growth of marine organisms on some surfaces.

Toxic releases may be of concern related to leaks or accidental spills of liquids used in systems with working hydraulic fluids. Any impacts could be minimized through the selection of nontoxic fluids and careful monitoring, with adequate spill response plans and secondary containment design features. Use of biocides to control growth of marine organisms may also be a source of toxic releases.

Conflict with other sea space users, such as commercial shipping and fishing and recreational boating, can occur without the careful selection of sites for WEC devices. The impact can potentially be positive for recreational and commercial fisheries if the devices provide for additional biological habitats.

More Information on Wave Energy

A good Primer on Wave Energy Devices has been prepared by Oregon Sea Grant.

More information on wave energy can be found at Surfrider Foundation's Ocean Energy blog (now included in the Coastal Blog).

NEWS - In August 2013 the U.S. Department of Energy announced $16 million for seventeen projects to help sustainably and efficiently capture energy from waves, tides and currents. Together, these projects will increase the power production and reliability of wave and tidal devices and help gather valuable data on how deployed devices interact with the surrounding environment. Here is a list of the 17 projects.

A Wave Energy Test Site (part of the Hawaii National Marine Renewable Energy Center) exists at Kaneohe Bay, Oahu, Hawaii. At least three full-scale wave energy converters, all intended to produce significant grid power when deployed in arrays, are now in line to be tested in Hawaii.

The Northwest National Marine Renewable Energy Center is funded by the U.S. Department of Energy to facilitate the development of marine renewable energy technologies -- primarily wave and tidal -- via research, education, and outreach. Established in 2008, NNMREC is a partnership between Oregon State University (OSU) and the University of Washington (UW). In 2011 NNMREC’s research agenda expanded to include offshore wind energy technology as well. The Pacific Marine Energy Center (PMEC) is the name of NNMREC’s marine energy converter testing facilities located around the Pacific Northwest region. Much of PMEC is still in the early planning stages. Ultimately PMEC will facilitate testing of a broad range of technologies being produced by the marine energy industry. On the OSU campus, PMEC includes scaled laboratory testing at the Wallace Energy Systems and Renewables Facility and the wave tanks at the O.H. Hinsdale test facility. On the UW campus, testing is supported at the Harris Hydraulics Laboratory’s current flume and small-scale wave flume. For intermediate scale wave energy devices, UW supports open water testing in Puget Sound and in Lake Washington. For a full scale wave energy resource, the North Energy Test Site (NETS) can accommodate devices up to 100kW connected to the Ocean Sentinel, and larger devices if no grid emulation or connection is required. The grid-connected site currently under development (initially referred to as "PMEC") will be referred to as the South Energy Test Site (SETS). SETS will serve as the utility-scale wave energy test facility for the US, and is expected to be available for device testing in 2016. Over time, there are plans to add other wave and current test facilities to the PMEC portfolio to create a global hub for marine renewable energy development.

To help developers navigate the regulatory process, the California Ocean Protection Council published permitting guidance for ocean renewable energy projects in December 2011. And in August 2013, U.S. senators Ron Wyden, D-Ore., and Lisa Murkowski, R-Alaska, introduced the Marine and Hydrokinetic Renewable Energy Act of 2013, which would promote the development of and streamline permitting for marine renewable technologies. On January 20, 2014, the European Commission released a two-step Blue Energy Action Plan under which the EU will first convene stakeholders to identify and propose solutions to challenges facing the marine renewables industry and then develop a strategic road map by 2016 to guide the sector toward commercialization.

Why has wave power lagged behind wind and solar power as an alternative energy source? This article by Dave Levitan provides some insights. Another article published in Business Week in December 2014 discusses the cruel realities of trying to build, install and operate machinery that will withstand a harsh environment of salt water, storms, and powerful currents.


Tidal power is a means of electricity generation achieved by capturing the energy contained in moving water mass due to tides. Two types of tidal energy can be extracted: kinetic energy of currents between ebbing and surging tides and potential energy from the difference in height (or head) between high and low tides. The former method - generating energy from tidal currents - is considered much more feasible today than building ocean-based dams or "barrages," and many coastal sites worldwide are being examined for their suitability to produce tidal (current) energy.

The extraction of potential energy involves building a barrage and creating a tidal lagoon. Barrages are used to close off a basin for trapping a water level inside them. The basic elements of a barrage are caissons, embankments, sluices, turbines and ship locks. Sluices, turbines and ship locks are housed in caisson (very large concrete blocks). Embankments seal a basin where it is not sealed by caissons. The barrage traps a water level inside a basin. Head is created when the water level outside of the basin or lagoon changes relative to the water level inside. The head is used to drive turbines. In any design this leads to a decrease of tidal range inside the basin or lagoon, implying a reduced transfer of water between the basin and the sea. This reduced transfer of water accounts for the energy produced by the scheme.

In Eastport, Maine the Ocean Renewable Power Company (ORPC) TidGen Cobscook Bay tidal energy project was launched in July 2012. Harnessing the power of the massive tidal shifts in Cobscook Bay, an inlet connected to the much larger Bay of Fundy, the project is the first in the U.S. to receive a FERC license, negotiate a power purchase agreement, and install and operate a power-producing tidal generator. More info.

The Federal Energy Regulatory Commission (FERC) previously gave the go-ahead to a feasibility study for a kinetic energy tidal power project on Little Machias Bay in Maine by Tidewater Associates. Other companies interested in exploring tidal energy projects in this area include Verdant Power LLC and Maine Tidal Energy Co., based in Washington D.C. Verdant Power has been trying for years to erect a small field of tidal turbines in New York’s East River. The project, with a $1.5 million underwater sonar system to continuously monitor for fish around the turbines, may get started in fall 2006.

Maine Tidal Energy is owned by Oceana Energy Corp. Oceana is pursuing potential tidal energy projects at eight sites along the coasts of the United States, including the "The Chops" section Kennebec River in Maine, Vineyard Sound off Martha’s Vineyard in Massachusetts and in San Francisco Bay, California. The project in the Kennebec River has already brought opposition from several groups, including the Friends of Merrymeeting Bay, who are concerned that rotating blades in the submerged tidal energy system could injure, kill or block passage of species such as the short-nosed sturgeon, seals and eels (see below).

Nationwide, at least 22 tidal energy projects are under review by FERC. Over the past two years, the agency has issued preliminary permits for 11 projects in Florida, New York, California, and Washington. This year (2006), it received 11 more applications for projects in the Northeast, Pacific Northwest, and Alaska.

Environmental Considerations

Tidal power projects, since they are typically built right on the coast, can potentially have significant impacts on the coast and on coastal resources.

The placement of a barrage into an estuary has a considerable effect on the water inside the basin and on the fish. Lagoons, on the other hand, could be used for fish or lobster farming, adding to their economic viability.

Turbidity (the amount of matter in suspension in the water or how cloudy the water is) decreases as a result of smaller volume of water being exchanged between the basin and the sea. This lets light from the Sun to penetrate the water further, improving conditions for the phytoplankton. The changes propagate up the food chain, causing a general change in the ecosystem.

As a result of less water exchange with the sea, the average salinity inside the basin decreases, also affecting the ecosystem. Again, lagoons do not suffer from this problem.

Estuaries often have high volume of sediments moving through them, from the rivers to the sea. The introduction of a barrage into an estuary may result in sediment accumulation within the barrage, affecting the ecosystem and also the operation of the barrage.

Once again, as a result of reduced volume, the pollutants accumulating in the basin will be less efficiently dispersed. Their concentrations will increase. For biodegradable pollutants, such as sewage, an increase in concentration is likely to lead to increased bacteria growth in the basin, having impacts on the health of the human community and the ecosystem. The concentrations of conservative pollutants will also increase.

Fish may move through sluices safely, but when these are closed, fish will seek out turbines and attempt to swim through them. Also, some fish will be unable to escape the water speed near a turbine and will be sucked through. Even with the most fish-friendly turbine design, fish mortality per pass is approximately 15% (from pressure drop, contact with blades, cavitation, etc.). This can be acceptable for a spawning run, but is devastating for local fish passing in and out of the basin on a daily basis. Alternative passage technologies (fish ladders, fish lifts, etc.) have so far failed to solve this problem for tidal barrages, either offering extremely expensive solutions, or ones which are used by a small fraction of fish only. Research in sonic guidance of fish is ongoing.

There have been proposals to combine tidal and wind power and install tidal stream turbines on the bases of offshore wind turbines. The hybridization of wind and wave energy could enhance cost competitiveness with onshore wind facilities because of synergies that include single permitting; shared foundation/mooring infrastructure; shared deployment and operation maintenance with common facilities, equipment, and personnel; and higher capacity. However, marine-based renewable energy technologies are all at relatively earlier stages of development than offshore wind, so such amalgamated facilities are not imminent.


There appear to be several potentially viable ocean-based alternative energy technologies that do not rely on petroleum products and directly produce no air, water or solid waste emissions. In spite of these positive environmental considerations, each of the aforementioned technologies (wind, waves, tides) may have site-specific environmental considerations that should be thoroughly evaluated before a full-scale system is constructed. Most of these technologies, particularly those based on generating electric power from waves or tides, are in the early stages of commercial development and will likely go through the small demonstration project phase before any large-scale facilities are constructed.

Additional Resources

The U.S. Department of Energy’s Marine and Hydrokinetic Technology Database provides up-to-date information on marine and hydrokinetic renewable energy, both in the U.S. and around the world. The database includes wave, tidal, current, and ocean thermal energy, and contains information on the various energy conversion technologies, companies active in the field, and development of projects in the water.

The website was developed by NOAA and the Bureau of Ocean Energy Management (BOEM) to support offshore renewable energy development.

BOEM's Jan/Feb/March 2012 newsletter focuses on renewable ocean energy. There are articles on:

  • BOEM’s Renewable Energy Program: Smart Initiatives Lead to Offshore Progress
  • Roundup of State Activities
  • BOEM and Partners to Study Offshore Renewable Energy
  • Collaboration Pursues Answers to a Sea of Development Questions Evaluating Potential Visual Impacts on Historic and Cultural Resources

Surfrider Foundation has developed a Policy on Renewable Ocean Energy.

Surfrider Foundation published a series of articles on ocean energy during 2009 in the publication Making Waves. These articles covered a general introduction, Offshore Oil and Gas Drilling, Wave Energy Development, Liquified Natural Gas, Offshore Wind Power and Energy From Tides and Currents.

Surfrider also maintains blogs on the subjects of Ocean Energy, Ocean Protection and Offshore Oil Drilling.

This article is part of a series on the Ocean Ecosystem looking at the various species of plants and animals which depend on a healthy coast and ocean environment, and the threats that can be posed to them by human activity

For information about laws, policies and conditions impacting the beach ecology of a specific state, please visit Surfrider's State of the Beach report to find the State Report for that state, and click on the "Beach Ecology" indicator link.