Offshore Wind Energy
In Europe, where vacant land is scarce and vast shallow water wind resources are available, more than 800 MW of offshore wind energy capacity has been installed in and around the North Sea and the Baltic Sea. Plans are underway for an additional 40 GW to be installed in the next decade. Although offshore wind turbines are not currently installed outside of Europe, interest is growing worldwide, because the global offshore wind resource is abundant, with the US potential ranked second only to China’s. For instance, the wind resource potential at 5 to 50 nautical miles off the US coast is estimated to be more than the total currently installed electrical generating capacity of the United States (more than 900 GW).
Most of the offshore wind resource potential in the United States, China, Japan, Norway, and many other countries is available in water deeper than 30 m. In contrast, most of the European offshore wind turbines installed to date are fixed-bottom and have been installed in water shallower than 20 m by driving monopiles into the seabed or by relying on conventional concrete gravity bases. These technologies are not economically feasible in deeper waters. Instead, space frame substructures, including tripods, quadpods, or lattice frames (jackets), will be required to maintain the strength and stiffness requirements at the lowest possible cost. (The above two paragraphs from Development and Verification of a Fully Coupled Simulator for Offshore Wind Turbines, Jason M. Jonkman and Marshall L. Buhl Jr., National Renewable Energy Laboratory (NREL)
Offshore wind-generated electricity in the United States has the potential to become a major contributor to the domestic energy supply, on a par with onshore wind, because it can compete in highly populated coastal energy markets where onshore wind energy is generally not available. Preliminary studies performed by the National Renewable Energy Laboratory (NREL) estimate the offshore resource to be greater than 1000 GW for the United States.
The wind blows faster and more uniformly at sea than on land. A faster, steadier wind means less wear on the turbine components and more electricity generated per turbine. Since winds increase rapidly with distance from the coast, excellent wind sites exist within reasonable distances from major urban load centers, reducing the onshore concern of long distance power transmission. In addition to proximity to the load, the offshore resource tends to be geographically located nearest the states that already pay the highest electric utility rates in the United States.
To be successful offshore, wind energy technologies must mature — using the combined experiences and expertise of the cost-conscious wind industry and the sea-savvy offshore oil and gas and marine industries.
Offshore wind energy began in shallow waters of the North Sea where the abundance of sites and higher wind resources are more favorable in comparison to Europe’s land-based alternatives. The first installation was in Sweden with a single 300-kW turbine in 1990, and the industry has grown slowly over the past 15 years. There are now 18 operating projects with an installed capacity of 804 MW. The majority of the capacity is now located in Denmark and the United Kingdom, using mostly Danish turbine technology.
Over 11 GW of new offshore wind projects are planned before the year 2010. Most development will take place in Germany and the UK, but at least 1,500 MW of offshore wind is in the permitting process in the United States. All installations have been in water depths of less than 18 m and distances from shore range from 1 km out to 14 km. The largest installations are operating off the coast of Denmark with two 160-MW power plants; Horns Rev in the North Sea, and Nysted in the Baltic.
(Updated from Energy from Offshore Wind, W. Musial and S. Butterfield, National Renewable Energy Laboratory; B. Ram, Energetics, Inc.,Offshore Technology Conference, Houston, Texas, 2006 NREL/CP-500-39450).