Ocean (Wave and Tidal)
Overview
Photo by JJ Janee Watts
The ocean is a potential goldmine for renewable energy generation, as long as investment into ocean power technologies continues. A 2003 report by the European Thematic Network on Wave Energy estimates that there will be between 150 – 750 terawatt-hours (1 TWh = 1,000,000 MWh) of economically recoverable wave energy available worldwide once current technologies are refined and mature, and increases in efficiency could triple that amount in the future. An Electric Power Research Institute report estimates that there are 2,100 TW of total wave energy off the coast of the U.S., with over 50% of that potential off the coast of Alaska. Additionally, total energy from tidal friction is estimated at 2.5 TWs, or the equivalent of 2,500 one-thousand MW nuclear power plants. Development of ocean energy generation technologies are still in the demonstration stage, but have great potential to become a leading source of renewable energy in the near future.
Advanced ocean power technologies fall into three general categories: ocean thermal energy conversion (OTEC), tidal energy, and wave energy. OTEC technology requires warm waters and therefore is not suitable for development in Alaska. However, tidal and wave energy may prove useful in expanding Alaska’s energy diversity and providing stably priced power to Alaskan residents.
Tidal energy is a concentrated form of the gravitational energy exerted by the moon and, to a lesser extent, the sun. This energy is converted into electricity in two ways: by dams that force water through turbines at high and low tidal stages, and by underwater turbines activated by tidal flows. Most commercial tidal power facilities, including the 240 MW Rance tidal power plant in La Rance, France, use dams to channel tidal flows into narrow passages, thus extracting more energy. However, numerous “in-stream” tidal generators that work like underwater wind turbines are in the development or demonstration stages. The first commercial tidal facility using this technology opened off the coast of Ireland in 2008. The same underwater turbine technology was first applied to small (less than 100 kW) electricity generators in 2008 to test the usefulness of the turbines in river currents. The 5 kW prototype installed at the Yukon River town of Ruby, Alaska successfully generated enough electricity to power two homes for the summer. Similar projects are currently under consideration in Eagle and Nenana. Tidal energy is preferable to river currents or even wind because it can be reliably predicted centuries in advance.
Wave energy is harnessed from the rise and fall of ocean waves, which are driven by the wind. The world’s first commercial wave farm, the Aguçadora Wave Farm in Portugal, opened with 2.5 MW of capacity in September 2008. An additional 28 generators will be installed for 22.5 MW of electricity generation in the near future. Other wave power generation projects are under development off the coasts of Italy, Spain, South Africa, Scotland, and Oregon. Most use the same type of generator employed at the Aguçadora Wave Farm, the 750 kW Pelamis generators made by Ocean Power Delivery Systems. These work by using the energy of waves to move connected sections of the generator, which flex and bend as waves pass and pump hydraulic fluids through turbines, producing electricity.
Tidal and Wave Energy in Alaska
Photo by Kelly Findlay
With 44,000 miles of coastline and some of the largest tidal ranges in the world, Alaska has enormous potential to develop ocean energy as a viable renewable source of electricity. The total wave power flux on southern Alaska’s coast alone is estimated at 1,250 TWh per year, about 300 times the amount of electricity used by Alaskans annually, though only a small amount of that would be economically recoverable. Harnessing this power could be problematic, however, as much of Alaska’s wave energy is dissipated on remote, undeveloped shorelines. Additionally, Alaska’s western coast is often barraged by violent storms that could render upkeep and maintenance on ocean power generators too expensive. However, a few sites in Alaska have been targeted as economically feasible for the development of tidal or wave power.
Cook Inlet, with North America’s second largest tidal range, has attracted utility and government interest as an energy source for the Railbelt. Currently the State of Alaska is participating in an international tidal energy study led by the Electric Power Research Institute, a non-profit institute for electricity and environmental research. Knik Arm, adjacent to a proposed bridge near Anchorage, was chosen for study due to the substantial tidal flow. In 2008, Ocean Renewable Power Company, LLC obtained a FERC permit to begin development of a demonstration tidal project, with plans to begin the construction of a commercial power plant in 2012. The site could ultimately yield an estimated 17 MW of power, enough to power 17,000 homes.
Permitting has already begun for a tidal project in Gastineau Channel near Juneau, which would provide up to 24 MW of electricity generation that will supplement Juneau’s already existing hydropower sources and guard against sharp energy cost spikes resulting from disruption of the hydroelectric power as happened in winter of 2007 when avalanches destroyed transmission lines from the Snettisham hydro facilities. Cross Sound and Icy Strait near Gustavus also show enormous promise for tidal resource development; North Inian Pass alone has the potential to generate 1600 MW and all four sites together could produce up to 2650 MW for use in local communities, and potential export to Canada and the Pacific Northwest as a source of green power. According to an Electric Power Research Institute study, other sites for potential tidal power development include the Wrangell Narrows near Petersburg, Sergius Narrows near Sitka, and sites around Prince of Wales Island.
