Introduction to Ocean Wave Energy
The wind acting on the ocean’s surface generates waves. They can travel for thousands of miles with little loss of energy until they near a shore where they begin to interact with the seafloor at depths of about 600 ft. Ocean waves consist of water particles that move in an orbiting pattern. Most (95%) of the wave energy occurs between the surface and a depth equal to one quarter of the wavelength. Wave energy system technology seeks to harness that energy as waves roll to shore, and convert it into useable power for communities.
Alaska has significant potential (estimated at about 60% of the total U.S. potential) for ocean wave energy development in offshore ocean basins near coastal communities. Wave energy systems can be used anywhere that has a regular wave pattern, but isn't inundated with ice or too protected to achieve true waves. Even small wave energy devices are capable of creating great amounts of energy regularly, but this technology is still in its infancy developmentally speaking.
There are obvious opportunities, but also significant environmental and technical challenges related to the deployment of ocean wave energy devices in Alaska’s ocean basins. Some of these are common to installations in any location, and other concerns are more specific to Alaskan waters.
National Renewable Energy Laboratory Ocean Wave Energy Data shows that even in high wave energy dense areas such as the Pacific Northwest, we can expect energy production rates of about 1.5 MW for every 100 feet of shoreline occupied by generators. By comparison, a large fossil fuel plant of 1,000 MW capacity would occupy about two hundred acres. Installing a similar capacity using on shore wave power would occupy over 12.5 miles of shoreline. That estimate is for places like the Pacific Northwest where the circumstances for this technology are most favorable.
Worldwide as of 2007, ocean wave energy devices are considered pre-commercial to early commercial. Design, performance, and economic assessments have been made by EPRI for sites in Hawaii, Oregon, California, Massachusetts, and Maine. To date there has been no examination of wave energy project design for Alaska, although the City of Yakutat contracted with EPRI in the fall of 2008 to perform a wave energy feasibility study. The only deployed wave energy project in the United States is a 40 kW buoy (PowerBuoyTM) for a Navy – Ocean Power Technology project in Hawaii. An initial, commercial wave energy wave farm with 2.25 MW capacity has been developed 5 km off the coastline of northern Portugal near Aguçadoura with plans to further expand the farm to 20 MW (www.pelamiswave.com).
Challenges in Wave Energy
Some challenges to Alaskan waters include:
- Environmental concerns – Not much is known about the impacts of wave and tidal technology on fish and other marine life. Such information would be vital for Alaskan tidal and wave energy development due to Alaska's heavy economic dependance on the ocean.
- Survivability and performance – Alaskan ocean basins have many potential hazards for ocean wave energy devices, including intense storms, strong ocean currents, debris, and seasonal ice (atmospheric, pack, and frazil). These issues also complicate the design of anchoring and cabling systems, as well as destroy installed systems.
- Resource assessment – there is a shortage of site-specific wave energy information.
- Effects on navigation – ship and barge delivery of bulk materials to both major and isolated coastal communities is common in Alaskan waters, so a major consideration is that these energy systems not impede marine traffic.
- Very little of Alaska is developed along the coastline, especially in areas where tidal or wave energy could be most efficiently harvested. Lack of transmission infrastructure in these areas would add to the cost of any potential projects and large electrical loads adjacent to the wave resources.
Wave Energy in Alaska
|TECHNOLOGY SNAPSHOT: WAVE POWER|
|Installed Capacity (Worldwide)||Over 3000 kW worldwide, most are demonstration projects. A commercial multi-unit 2.25 MW capacity commercial wave farm was commissioned offshore of Aguçadoura, Portugal in the summer of 2008|
|Installed Capacity (Alaska)||0 kW installed. Estimated recoverable resource of about 150 TWh/yr in southern Alaska (assuming 15% recovery at 80% generation efficiency)|
|Resource Distribution||Potentially available to communities in regions of Alaska located near an ice-free ocean and exposed to long fetches. The potential for wave energy development in protected waterways, such as those found in SE Alaska, or under winter ice is limited.|
|Number of communities impacted||Not assessed yet|
|Technology Readiness||Pre-commercial to early commercial with an early commercial site of over 2 MW installed with a follow-on second stage of about 20 MW in development|
|Environmental Impact||Impacts on local hydrology and aquatic species must be assessed on a case-by-case basis. EPRI anticipates that these impacts can be minimized by appropriate siting, design and operation.|
|Economic Status||A 2007 assessment of energy costs for conceptual wave power projects in North America ranges from about 10-39 ¢/kWh with the potential to decrease to about 4¢/kWh with installed capacities of 40 MW or more (consistent with price trends seen for wind energy) [Bedard et al., 2007]|
Wave Energy Systems
Wave and tidal energy works similar to the process of generating electricity from a dam. There are many kinds of ocean energy systems, but most work on the principle of air or water rotating a turbine. The turbine could be encased in an enclosure that sits on or below the ocean's surface and moves with the incoming and outgoing tides, or with incoming waves.
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 2008.1
Turbine technology, as it is used in wave and tidal energy systems, is made complicated by the unpredictable nature of the ocean. Whereas with a turbine in a dam, the supply and rate of flowing water is more or less constant, the ocean is subject to storms, large tide changes, and in Alaska, heavy moving ice in the winter months. All of these complications can damage ocean turbines, and can make the rate of turbine rotation and energy output very irregular. Despite the challenges, tidal energy is preferable to hydrokinetic from river currents or even wind because it can be reliably predicted centuries in advance by noting the cycles of the moon.
Alaska Specific Technology Challenges
Introduction: Wave and Tidal Projects In Alaska
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 two tidal projects in Southeast Alaska: Gastineau Channel near Juneau and Kootznahoo Inlet near Angoon. The Gastineau Channel project 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. Kootznahoo Inlet could generate up to 7.5 MW of power for sale to Angoon electrical facilities and other parts of the state. 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.
Yakutat – Yakutat Power, Inc has completed a feasibility study by the Electric Power Research Institute Inc., which yielded encouraging results. The project will focus on near-shore wave energy conversion and opening an Ocean Energy Research and Development center in Yakutat. As of 2011, the project remains under development.
Resources and Links
- Alaska Wave Power projects: A great resource to learn more about renewable energy projects in Alaska, including wave power projects and how they work.
- Wave Energy Systems: a link to the Renewable Energy Resource page where you can find more information about ocean based energy systems.
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