Ocean Energy

Generating technologies for deriving electrical power from the ocean include tidal power, wave power, ocean thermal energy conversion, ocean currents, ocean winds and salinity gradients. Of these, the three most well-developed technologies are tidal power, wave power and ocean thermal energy conversion. Tidal power requires large tidal differences which, in the U.S., occur only in Maine and Alaska. Ocean thermal energy conversion is limited to tropical regions, such as Hawaii, and to a portion of the Atlantic coast. Wave energy has a more general application, with potential along the California coast. The western coastline has the highest wave potential in the U.S.; in California, the greatest potential is along the northern coast.

California has more than 1,200 kilometers (745 miles) of coastline, and the combined average annual deep water wave power flux is over 37,000 megawatts (MW) of which an upper limit of about 20 percent could be converted into electricity.

This is sufficient for about 23 percent of California's current electricity consumption. However, economics, environmental impacts, land-use and grid interconnection constraints will likely impose further limits to how much of the resource can be extracted. Although technology is still at a relatively immature pilot project stage, economic projections indicate that ocean energy could become cost-competitive over the long-term.

Current Pilot Projects

In the spring of 2009, the Sonoma County Water District applied to the Federal Energy Regulatory Commission (FERC) for three wave project preliminary permits. The projects will be located in state waters offshore Del Mar Landing (the northwestern portion of the county) and off Fort Ross further to the south. Each of the three projects would begin as pilots in the two to five megawatt (MW) range, could potentially expand to commercial facilities in the 40-200 MW range, and would include substations, transmission lines, appurtenant facilities, and submersible electric cables.

With these applications, the total number of FERC permits and applications for wave and tidal projects in California waters totals twelve.

Wave Energy

Pelamis wave energy converter. Photo courtesy of Pelamis Wave Power Ltd.

Wave energy conversion takes advantage of the ocean waves caused primarily by interaction of winds with the ocean surface. Wave energy is an irregular and oscillating low-frequency energy source that must be converted to a 60-Hertz frequency before it can be added to the electric utility grid.

Although many wave energy devices have been invented, only a small proportion have been tested and evaluated. Furthermore, only a few have been tested at sea, in ocean waves, rather than in artificial wave tanks.

As of the mid-1990s, there were more than 12 generic types of wave energy systems. Some systems extract energy from surface waves. Others extract energy from pressure fluctuations below the water surface or from the full wave. Some systems are fixed in position and let waves pass by them, while others follow the waves and move with them. Some systems concentrate and focus waves, which increases their height and their potential for conversion to electrical energy.

A wave energy converter may be placed in the ocean in various possible situations and locations. It may be floating or submerged completely in the sea offshore or it may be located on the shore or on the sea bed in relatively shallow water. A converter on the sea bed may be completely submerged, it may extend above the sea surface, or it may be a converter system placed on an offshore platform. Apart from wave-powered navigation buoys, however, most of the prototypes have been placed at or near the shore

The visual impact of a wave energy conversion facility depends on the type of device as well as its distance from shore. In general, a floating buoy system or an offshore platform placed many kilometers from land is not likely to have much visual impact (nor will a submerged system). Onshore facilities and offshore platforms in shallow water could, however, change the visual landscape from one of natural scenery to industrial

The incidence of wave power at deep ocean sites is three to eight times the wave power at adjacent coastal sites. The cost, however, of electricity transmission from deep ocean sites is prohibitively high. Wave power densities in California's coastal waters are sufficient to produce between seven and 17 megawatts (MW) per mile of coastline

According to the European Union, "Among the different converters capable of exploiting wave power, the most advanced is unquestionably the Pelamis Wave Energy Converter, a kind of "undulating sea serpent" developed by Ocean Power Delivery. This technology is the object of a commercial contract for installation of a farm in Portugal. In 2007, three machines, with a total capacity of 2.25 megawatts (MW(, are in installation phase, and should be joined by 27 others in the years to come. Another 5 MW project is being studied for England this time."

None of these plants are located in California, although economic feasibility studies have been performed for a 30 MW wave converter to be located at Half Moon Bay. Additional smaller projects have been discussed at Fort Bragg, San Francisco and Avila Beach. There are currently no firm plans to deploy any of these projects

As of the mid-1990s, wave energy conversion was not commercially available in the United States. The technology was in the early stages of development and was not expected to be available within the near future due to limited research and lack of federal funding. Research and development efforts are being sponsored by government agencies in Europe and Scandinavia

Many research and development goals remain to be accomplished, including cost reduction, efficiency and reliability improvements, identification of suitable sites in California, interconnection with the utility grid, better understanding of the impacts of the technology on marine life and the shoreline. Also essential is a demonstration of the ability of the equipment to survive the salinity and pressure environments of the ocean as well as weather effects over the life of the facility

Permitting Issues. Some of the issues that may be associated with permitting an ocean wave energy conversion facility include:


Tidal Energy

La Rance Tidal Power plant. Photo credit: Popular Mechanics, December 1997

Another form of ocean energy is called tidal energy. When tides comes into the shore, they can be trapped in reservoirs behind dams. Then when the tide drops, the water behind the dam can be let out just like in a regular hydroelectric power plant.

Tidal energy has been used since about the 11th Century, when small dams were built along ocean estuaries and small streams. the tidal water behind these dams was used to turn water wheels to mill grains.

In order for tidal energy to work well, you need relateivel large increases in tides. An increase of at least 16 feet between low tide to high tide is generally needed. There are only a few places where this tide change occurs around the earth. Some power plants are already operating using this idea.

According to the European Union:

"Ninty percent of today's worldwide ocean energy production is represented by a single site: the La Rance Tidal Power Plant (240 MW) that was commissioned in 1966. This type of installation has remained unique in the world and has only been reproduced at much smaller capacities in Canada (20 MW), China (5 MW) and Russia (0.4 MW).

"This type of project was abandoned for many years because of very high initial investment costs as well as the strong local impact that results from it. However, the present economic situation has encouraged South Korea to build a 260 MW dam closing off Sihwa Lake, which is set to be commissioned in 2009. Lighter new techniques, like hydro turbines, are being developed today to harness ocean currents. The leader in this field, the British company, Marine Current Turbine (MCT), should install 1.2MW in Northern Ireland following its 300 kW pilot project in Bristol Bay."

Ocean Thermal Energy Conversion (OTEC)

Ocean Thermal energy plant in Hawaii. Photo courtesy of Pacific International Center for High Technology Research

The idea of using the temperature of water to make energy actually dates back to 1881 when a French Engineer by the name of Jacques D'Arsonval first thought of OTEC. The final ocean energy idea uses temperature differences in the ocean. If you ever went swimming in the ocean and dove deep below the surface, you would have noticed that the water gets colder the deeper you go. It's warmer on the surface because sunlight warms the water. But below the surface, the ocean gets very cold. That's why scuba divers wear wet suits when they dive down deep. Their wet suits trapped their body heat to keep them warm.

Power plants can be built that use this difference in temperature to make energy. A difference of at least 38 degrees Fahrenheit is needed between the warmer surface water and the colder deep ocean water. The cold ocean water can also be used to cooling buildings, and desalinated water is often a by-product.

Using this type of energy source is called Ocean Thermal Energy Conversion or OTEC. It was demonstrated in Hawaii at the Open Cycle Ocean Thermal Energy Conversion (OC-OTEC) system located at the Natural Energy Laboratory of Hawaii Authority (NELHA) at Keahole Point on the Big Island of Hawaii.

Commission Publications

References

Original source: Energy Awareness Planning Guide II: Energy Facilities

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