Assessment of the gross U.S. offshore wind energy potential

Offshore wind energy development promises to be a significant domestic renewable energy source, especially for coastal energy loads with limited access to interstate grid transmission. The development of a reference and validated offshore wind resource database is one of the first steps necessary to understand the magnitude of the resource and to plan the distribution and development of future offshore wind power facilities. The U.S. Department of Energy and the National Renewable Energy Laboratory (NREL) are working to assess the full potential of the nation's indigenous wind energy resources by producing reports containing updated and validated offshore state wind resource maps and corresponding tables, and a national database developed using Geographic Information System techniques. The initial report published by NREL in June 2010 estimates the total gross offshore wind resource as 4150 gigawatts of potential installed nameplate capacity (the maximum output rating of a wind generator) for 25 contiguous states plus Hawaii. This estimate was based on assuming 5 megawatts of installed nameplate capacity per square km of windy water. Windy water was defined as areas with an annual average wind speed 7.0 m/s and higher at 90 meters above the water surface. Economic factors make development of areas with less than 7.0 m/s average wind speeds unlikely. Examinations of the offshore wind resource distribution show an abundant wind resource pool, with wind resources greater than 7.0 m/s, located in many offshore areas of the country including much of the Atlantic and Pacific coasts plus the western Gulf of Mexico. The total windy water area is based on the most current validated wind resource maps that extend 50 nautical miles from shore for the ocean areas and cover the United States portions of the Great Lakes. These maps were produced using mesoscale numerical modeling done by AWS Truepower of Albany, New York under subcontract to NREL. NREL validated the preliminary model estimates using data from a variety of sources including data from the National Data Buoy Center, and satellite-derived 10- m wind speeds from National Aeronautical and Space Administration archive. The offshore resource database breaks down the resource by wind speed, water depth, and distance from shore and combines these characteristics with state administrative areas to quantify the wind potential for several scenarios. Tables summarizing these scenarios are included in the June 2010 report. The resource estimates have not been reduced by any environmental or water-use considerations. Exclusions from offshore development, of which there will be many, must be done on a state or regional basis to assure that local issues are addressed properly. Incorporation of clearly defined environmental exclusions and ocean-use factors impacting offshore wind development will be included in future editions of the database. The offshore wind resource assessment is an evolving product with the potential estimates subject to modification and change as the offshore wind industry matures and new data become available. The mapping process is ongoing and the offshore wind resource estimates and the database will be updated as new resource maps are completed. The next mapping to be completed is the Mid-Atlantic States from Rhode Island to South Carolina in summer 2010. The database will eventually contain the wind resource for all coastal states.