22-12-2012, 03:13 PM
Offshore wind energy development
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INTRODUCTION
Offshore wind energy development has been an almost exclusively European phenomenon since the early 1990s. More than 35 wind projects totaling over 1500 MW of capacity are now operating off the shores of five countries, most within northwest Europe in the Baltic and North Seas. Another 2,500 MW of capacity are under construction in 16 projects. Overall, the European Union predicts there will be at least 40,000 MW of offshore wind energy in Europe by the year 2020. China has also begun construction on the Sea Bridge Wind Farm in the Bahia Sea, its first offshore wind project scheduled for completion in 2010. Although no offshore wind projects are under construction or in operation yet in North America, proposed projects or ones in the active development phase exist in several states and provinces. These include British Columbia, Delaware, Massachusetts, New York, Ohio, Ontario, Rhode Island, and Texas.
This large body of offshore experience provides an excellent basis to understand the wind turbine technologies and foundation designs likely to be applicable to the Long Island‐New York City Offshore Wind Collaborative project area for a wind facility built in the 2014‐2016 timeframe. The objective of this short report is to summarize applicable turbine technologies and foundation designs and to identify the primary design parameters for turbines and foundations.
Offshore wind power refers to the construction of wind farms in bodies of water to generate electricity from wind. Better wind speeds are available offshore compared to on land, so offshore wind power’s contribution in terms of electricity supplied is higher.[1] However, offshore wind farms are relatively expensive.[2]
Siemens, REpower, and Vestas are the leading turbine suppliers for offshore wind power. Dong Energy, Vattenfall and Eon are the leading offshore operators.[1] As of October 2010, 3.16 GW of offshore wind power capacity was operational, mainly in Northern Europe. According to BTM Consult, more than 16 GW of additional capacity will be installed before the end of 2014 and the United Kingdom and Germany will become the two leading markets. Offshore wind power capacity is expected to reach a total of 75 GW worldwide by 2020, with significant contributions from China and the United States.[1]
As of February 2012, the Walney Wind Farm in United Kingdom is the largest offshore wind farm in the world at 367 MW, followed by Thanet Offshore Wind Project (300 MW), also in the UK. The London Array (630 MW) is the largest project under construction. These projects will be dwarfed by subsequent wind farms that are in the pipeline, including Dogger Bank at 9,000 MW, Norfolk Bank (7,200 MW), and Irish Sea (4,200 MW).
Wind energy can be harnessed to produce electricity through two different types of facilities: onshore and offshore developments. Onshore wind projects typically include a group of wind turbines constructed on land – in coastal, forested or agricultural areas with strong winds. Very similar wind turbines can also be constructed offshore in lakes or the ocean. Currently, most offshore wind turbines are mounted on cement foundations or driven into the sea floor in areas where water depths do not exceed 100 feet (Figure 1).
While there are currently no offshore wind farms located in North America that may soon change. Offshore projects have been proposed for locations along North America’s Eastern Seaboard and in the American and Canadian waters of the Great Lakes. North American residents, including Michiganders, have many questions regarding offshore wind energy. This report examines social issues related to offshore wind, including public acceptance, visibility, noise and tourism. The final section reviews wind policy and regulatory issues in Michigan.
DEFINITION
Offshore wind power refers to the construction of wind farms in bodies of water to generate electricity from wind. Unlike the term typical usage of the term "offshore" in the marine industry, offshore wind power includes inshore water areas such as lakes, fjords and sheltered coastal areas, utilizing traditional fixed-bottom wind turbine technologies, as well as deep-water areas utilizing floating wind turbines.
DESIGN REQUIREMENTS
Site Conditions Affecting an Offshore Wind Farm
The design of an offshore wind project is based on the environmental conditions to be expected at a proposed site over the project’s lifetime (typically 20 or more years). These environmental conditions are primarily defined by the wind, wave, current, water depth and soil and seabed characteristics. Figure 1 illustrates the various dynamic factors impacting a wind turbine’s external environment.
Different project components are more sensitive to some of these characteristics than others. For example, a wind turbine’s rotor and nacelle assembly are most sensitive to wind and other atmospheric conditions while the support structure (tower and foundation) design is more dependent on hydrodynamic and seabed conditions. Wind turbine models tend to be designed for applicability for a specified range of wind conditions whereas turbine support structures are usually engineered for onsite conditions. This section provides additional insight into the design parameters relevant to the entire project.
OVERVIEW OF WIND PLANT COMPONENTS
An offshore wind plant’s principal components are the turbines, towers, foundations, electric collection and transmission system (including substations), and other balance of plant items. These components are described in detail in this section.