May 7, 2014
By Greg Matzat
With almost 80% of the U.S. electricity demand coming from cities and towns located in coastal states, offshore wind energy has vast potential to meet this demand and provide the nation with clean, renewable, and reliable electricity. The Energy Department today announced the selection of three projects that aim to advance the offshore wind industry with innovations which lower the cost of energy and address market barriers associated with deploying offshore wind technologies. Some of the technological innovations to be deployed by these projects led by Dominion Virginia Power, Fishermen’s Energy of New Jersey, and Principle Power of Washington are highlighted below:
All three of the selected projects will use direct-drive (DD) turbine technology from different turbine manufacturers. DD turbines don’t require as many moving parts compared with standard-geared turbines, leading to increased reliability and reduced operating costs. Each blade on these DD turbines is about the length of a football field. Dominion plans to install two Alstom 6-megawatt (MW) DD turbines off the coast of Virginia Beach; Principle Power plans to install five Siemens 6-MW DD turbines off the coast of Coos Bay, Oregon; and Fishermen’s Energy plans to install five XEMC 5 -MW DD turbines off the coast of Atlantic City, New Jersey. Watch this Energy 101 video to learn more about how wind turbines capture wind energy on land and offshore.
Offshore wind turbines are typically supported by a structure buried in the seafloor. One option is a traditional “jacket” foundation, which is a trussed structure that looks similar to a massive radio tower in the water. A recent innovation by a U.S. company has resulted in a twisted jacket foundation, where three “legs” are twisted around a central column. These structures are easier to manufacture and install than traditional foundations, helping drive down the cost of energy from offshore wind. Both Dominion Virginia Power and Fishermen’s Energy will use this type of foundation, which enables the companies to analyze and assess how the structural design performs at two separate locations with different turbine technology and site conditions. If the projects successfully demonstrate the twisted jacket foundations, engineers may use the design in future offshore wind projects in locations such as the Atlantic Wind Energy Areas established by the Bureau of Ocean Energy Management.
Floating technology represents the future of offshore wind. More than 60% of the offshore wind resources within 50 nautical miles of U.S. coasts are located in deep water, where traditional bottom-fixed foundations cannot be used. Semi-submersible foundations are somewhat similar to ships, where a portion of the structure sits below the water line, while the rest of the structure floats above. Unlike ships, offshore wind foundations need to stay in one place. In order to maintain their position, these foundations use a series of mooring lines and anchors attached to the sea floor. Principle Power’s semi-submersible WindFloat foundation is shaped like a triangle, with the turbine located on one of the three columns that form the structure. In the same way a ship uses extra weight, or ballast, to remain stable, the WindFloat uses both fixed ballast and an active ballast system, which keeps the platform stable by moving weight around to counterbalance the forces prevalent in the windy ocean environment. Additionally, semi-submersible foundations can be assembled on shore and then towed out to sea fully assembled – or taken back to shore for repairs – eliminating the need for expensive specialized vessels and reducing maintenance costs.
These innovations will help lower the cost of energy from offshore wind, spark industry advancement, and ensure that offshore wind becomes a viable renewable energy option for America’s future.