What is ocean renewable energy or marine renewable energy?

Ocean renewable energy or marine renewable energy are terms used to describe all forms of renewable energy derived from the sea including wave energy, tidal energy, ocean current energy, offshore wind, salinity gradient energy and ocean thermal gradient energy.

What is wave energy?

Wave energy describes energy generated from the power of waves near their surface. Several different types of wave energy conversion devices extract power from motion of waves. These include single point absorbers, such as the Finavera/AquaEnergy Aqua BuOY or Ocean Power Technologies’ Power Buoy, multiple point absorbers like Wavestar energy model and floating attenuator devices, like Ocean Power Delivery’s Pelamis. The power take off device within these systems converts the motion of the waves into electrical energy.

Wave power can also be captured through oscillating water columns, which trap waves in a column and change the air pressure in the upper portion which drives a turbine. Wavegen’s LIMPET, a shorebased OWC unit has been operating since 2000.

Wave power can also be captured through an overtopping device, which traps waves in a floating pool, which is then released through turbines to generate power. The Wave Dragon employs overtopping technology.

Where are wave resources in the United States?

In 2005, EPRI released a series of reports on wave energy potential in the United States, identifying resources off Alaska, Washington State, Oregon, Massachusetts, Hawaii and California as potentially attractive wave power sites. However, more extensive resource assessment is needed to fully understand the extent of wave resources in the United States.

Additional resources offering a simple explanation wave energy technology include this Wikipedia entry onWave Energy and from the British Wind Energy Association’s brochure, Why Marine?

What is tidal energy or tidal stream energy?

Today’s tidal stream projects differ from earlier concepts such as the 40 year old Rance Tidal Power Plant in France, which utilize a barrage to trap and release tidal flows. Tidal projects under development in the United States today do not rely on impoundments, and instead operate on a concept very similar to wind, with a tidal stream rather than wind driving turbines submersed in water. At present, Verdant Power has deployed the first of six tidal turbines in the East River which is generating electricity. Other companies developing tidal technologies include Marine Current TurbinesOpen Hydro and Ocean Renewable Power Company.

For more simple information on tidal energy, see this entry from PESWiki and the BWEA publication, Why Marine?

Where are tidal resources in the United States?

As with wave energy, EPRI also released a series of reports identifying sites in the United States and Canada with tidal potential. These sites are located in Maine, Washington, Bay of Fundy, Massachusetts and California. The EPRI report set off a gold rush of applications to FERC for preliminary permits to study tidal potential at most of the EPRI identified sites.
What is OTEC?

Ocean thermal energy conversion generates electricity from the temperature differential of cold subsurface sea water and warmer surface waters. For that reason, OTEC is best suited for tropical waters. Within the United States, an experimental OTEC plant has operated in Hawaii. For more resources on OTEC, consult OTEC News and Wikipedia entry on OTEC.
What is offshore wind?

Offshore wind is wind energy located offshore, typically in ocean waters, though the wind potential of the Great Lakes is also being explored in the United States. Because offshore winds are more powerful than onshore, offshore wind turbines are usually larger. At present, two offshore wind farms, Cape Wind and Long Island Power Authority have been proposed for the United States and are undergoing review by Mineral Management Service . But offshore wind has been operating in Europe for more than a decade. Most projects are located one to twelve miles from shore; mooring systems are currently under investigation which would allow for siting further off the coast in deep waters.

For more on offshore wind energy, visit these resources at
British Wind Energy Association or the American Wind Energy Association.

Why should we invest in marine renewables?

The beauty of marine renewables is that they are located near our nation’s coastlines and close to population centers, thereby reducing transmission costs. In addition, marine renewables provide an indigenous, emission free source of energy which will help fight global warming and wean our nation from dependence on foreign oil. As discussed in this Wave Energy White Paper prepared by MMS, the total average wave energy potential off U.S. coastlines is estimated as 2100 TWh/yr. Reduced for efficiencies and conversion losses, the more realistic generation figure is 252 TWh/yr or roughly the same amount of power currently supplied by traditional hydropower. Offshore wind resources on the Outer Continental Shelf have been estimated at 900,000 MW (seeMMS Whitepaper on Offshore Wind).

A robust marine renewables energy industry can help create jobs, revitalize abandoned shipyards and improve the economies of coastal communities. And marine renewables also provide opportunities for technology exports to other nations.

The private sector has already started to recognize the benefits of marine renewables, and in the past year, many large institutional companies have acquired or made investments in marine renewable technologies.

What are the costs of marine renewable technologies?

Naturally, costs vary with the type of technology. The MMS Whitepaper on Offshore Wind states that where once the cost of offshore wind was around forty cents/kWH, over the past twenty years, costs have dropped to between 4 and 6 cents/kwh. By 2012 and beyond, DOE envisions 5 MW and larger machines generating power for 5 cents/kWh.

Cost estimates are more difficult for wave and tidal, which in contrast to offshore wind, lack operational history. For wave, costs have been estimated as between 9 and 16 cents/kWh, far more favorable than the 40 cents/kWH that offshore wind cost “out of the box.” For instream tidal, the EPRI reports predicted costs as low as 6 to 9 cents/kWH because tidal power’s similarities to wind allow it to benefit from the advancements already made by wind and potentially share economies of scale.
Are there environmental effects associated with marine renewables?

As with any development, marine renewables may have some environmental impacts, though they are expected to be minimal. For offshore wind, extensive eight year studies from Denmark show that offshore wind projects have virtually no impacts on birds, surrounding marine life or area tourism. In the United States, offshore wind has generated controversy because of potential visual or aesthetic impacts.

For tidal projects, possible effects include interference with fish migration, fish entrainment or interference with natural tidal patters through extraction of energy from tidal flows. For wave projects, similar concerns exist with regard to interference with fish or marine mammal migration (because wave systems are closed, entrainment is not an issue), reduction of wave height and release of lubricants used within wave systems. Again, effects are expected to be minimal and developers have expressed willingness to monitor projects, gather data on effects and apply adapative management techniques to deal with effects if observed.

What is adapative management?

Adaptive resource management is a process of decision making used in the face of uncertainty, with an aim to reducing uncertainty over time via system monitoring. Adaptive management involves monitoring a system and adapting it, through operational changes, to address any environmental effects observed. Adaptive management is an optimal mechanism for siting wave and tidal projects because it provides a system for gathering data and learning about effects in real world condition and making necessary changes.
If the private sector is investing in marine renewables, why does the industry need government support?

Marine renewables require government support to create a level playing field with other forms of renewable energy. The financial community often evaluates the viability of a potential technology by the level of federal support it receives. At present, wave and tidal power are not eligible to receive production tax credits, investment tax credits or 5 year accelerated depreciation, thus relegating them to “second class citizenship” in the view of the financial community.

Moreover, few other renewables are subject to the extensive environmental regulatory requirements, particularly at the pilot or pre-commercial phase, as marine renewables. Estimates show that the environmental costs associated with the permitting of small marine renewables projects (under 1 MW or 8 units or less) comprises as much as 40 percent of the overall project cost. Subsidizing the costs of studies, which will benefit the public at large, will help accelerate deployment of marine renewables project while ensuring that the environment remains protected.

Finally, the costs of marine renewables remains high. In part, costs will decrease as the industry grows and creates economies of scale. But as in the wind industry, costs can also be reduced through government funded projects that research ways to streamline fabrication, develop best practices for O&M and standards for evaluating technologies. In addition, government funded resources assessments can help identify optimal sites, where developers will get the “biggest bang for the buck” from available resources.

Additional Resources:

DOE prepared a report on the state of the marine renewables technology pursuant to the requirements of the Energy Independence and Security Act, with this full  list of companies and status of their projects.

For an additional overview of the current state of the industry, see this interview with EPRI Ocean Energy group leader, Roger Bedard at Inside Greentech.

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