Background on Wave Energy

How it Works

Ocean waves, provided they’re captured at the right spot, can supply almost endless amounts of usable energy. Wave energy can be thought of as stored, concentrated wind energy, created as the wind blows over the surface of the water and transfers its energy to the waves. The waves create surface motion, as well as pressure fluctuations under the water’s surface, which can be captured by complicated devices called Wave Energy Converters (WECs).


These devices contain either a turbine or hydraulic motors, which convert the wave’s power into electricity. But their mechanisms are all very different. These devices are usually put together in “wave farms,” concentrated in sections of the ocean. Right now there are four major types of WECs, which can be used close to shore, offshore, and far offshore, depending on the needs of the device.


Terminators: One of the most complicated mechanisms, terminators are rooted on shore, and rely on breaking wave energy to move a column of air through a two-way turbine. As the water hits the air, it forces the air through a narrow column, the pressure of which turns the turbine as it enters and as it recedes. (See an example here.)


Point Absorbers: These mechanisms use buoy technology to float along with the waves. As they move up and down, water flows into a chamber through the bottom of the buoy and is forced into a narrow cylinder in the center. The force of the water then turns a turbine at the top of the buoy, creating electricity. (See an example here.)


Attenuators: Looking like a submarine about to emerge from the water, attenuators are long, cylindrical tubes that are positioned perpendicular to the incoming waves, usually close to shore. The tubes are connected by hinged joints, which move with the waves, causing pressure changes within an internal hydraulic system. As the hydraulic arms move they turn motors that in turn drive electrical generators to produce electricity. Many attenuators can be connected, in various layouts, to produce more energy. (See an example here.)


Overtopping devices: These structures act much like hydroelectric dams—except in the middle of the ocean. A semi-circular reservoir is constructed in deep water and moored to the seabed just like a ship. The sides of the reservoir are short and steep; as waves hit them they ride up the side and “overtop” into the reservoir, which is several feet above the ocean surface. Gravity pulls the water back into the ocean through common hydro-electric turbines which use nothing but the water’s energy to create electricity. (See an example here.)


Ocean currents: A developing technology
Another potential energy source uses the ocean’s natural currents to turn underwater turbines rooted to the ocean floor (much like wind turbines on land). Though water moves much more slowly than wind, its density—800 times that of air—can transfer much greater energy. According to the EIS, experts say that using just 1/100th of the available energy from the Gulf Stream would be enough to supply 35 percent of Florida’s energy needs. Though the technology is being investigated, currently no commercial current-fed turbines are connected to the grid.


Sources: The United States Department of the Interior, Minerals Management Service Environmental Impact Statement on Ocean Energy


Current and future potential
Since wave power is not consistent in all parts of the ocean, wave energy is not feasible in every part of the world. Currently the most viable wave-energy-rich locations are on the western coasts of Scotland, northern Canada, southern Africa, Australia, and the northwestern coasts of the United States.


Utilities and universities in Hawaii, Washington, Rhode Island, California and Oregon are testing various types of WECs. An exciting possibility would combine offshore wind turbines—already is use in the U.S.—with wave energy converters.


According the Department of Energy, the potential extractable wave energy around North America is some 2,100 TWh (terawatt, or a trillion watts, hours) per year, representing 75 percent of the US’s current demand. But the US lags behind many European countries that are already taking advantage of ocean power.


Disadvantages
Because of the invasive nature of wave energy converters, experts have isolated the following potential disadvantages to the technology:
-Possible disruption of shipping lanes and recreational boaters’ space
-Potential effects on marine habitats
-Toxic releases from hydraulic or other fluids necessary to work the devices
-Noise and sight disruptions, especially those close to shore. These vary according to the type of device, but can include underwater noise effects on marine life.


Local Information
Though you won’t see wave energy being added into the renewable portfolio in Colorado anytime soon, local scientists at NREL are part of the development technology.


The Obama Factor
Though wave energy is not a top priority within the Economic Recovery Package (according to this breakdown), the government has promised some $2.5 billion toward the study of new renewable energy technologies.


Additional Resources
The Department of Energy on wave power
A presentation by the Department of Energy on current research and developments in ocean energy
The Electric Power Research Institute
Watch a new generation wave energy mechanism in action

--Tiffany