page_title: Offshore wind power
section_title: Installation
hierarchical_section_title: Offshore wind power / Installation
context_page_description: Offshore wind power or offshore wind energy is the use of wind farms constructed in bodies of water, usually in the ocean, to harvest wind energy to generate electricity. Higher wind speeds are available offshore compared to on land, so offshore wind power’s electricity generation is higher per amount of capacity installed, and NIMBY opposition to construction is usually much weaker.
  Unlike the typical use of the term "offshore" in the marine industry, offshore wind power includes inshore water areas such as lakes, fjords and sheltered coastal areas as well as deeper-water areas. Most offshore wind farms employ fixed-foundation wind turbines in relatively shallow water. As of 2020, floating wind turbines for deeper waters are in the early phase of development and deployment.
  At the end of 2018, the total worldwide offshore wind power capacity was 23.1 gigawatt.
  All the largest offshore wind farms are currently in northern Europe, especially in the United Kingdom and Germany, which together account for over two-thirds of the total offshore wind power installed worldwide.
context_section_description: Specialized jackup rigs (Turbine Installation Vessels) are used to install foundation and turbine. As of 2019 the next generation of vessels are being built, capable of lifting 3-5,000 tons to 160 meters.
  A large number of monopile foundations have been used in recent years for economically constructing fixed-bottom offshore wind farms in shallow-water locations. 
  Each uses a single, generally large-diameter, foundation structural element to support all the loads (weight, wind, etc.) of a large above-surface structure.
  The typical construction process for a wind turbine sub-sea monopile foundation in sand includes using a pile driver to drive a large hollow steel pile 25 m deep into the seabed, through a 0.5 m layer of larger stone and gravel to minimize erosion around the pile. These piles can be 4 m in diameter with approximately 50mm thick walls. 
  A transition piece (complete with pre-installed features such as boat-landing arrangement, cathodic protection, cable ducts for sub-marine cables, turbine tower flange, etc.) is attached to the now deeply driven pile, the sand and water are removed from the centre of the pile and replaced with concrete. An additional layer of even larger stone, up to 0.5 m diameter, is applied to the surface of the seabed for longer-term erosion protection.
  For the ease of installing the towers and connecting them to the seabed, they are installed in two parts, the portion below the water surface and the portion above the water. The two portions of the tower are joined by a transition piece which is filled with a grouted connection. The grouted connected helps transfer the loads experienced by the turbine tower to the more stable monopile foundation of the turbine. One technique for strengthening the grout used in the connections is to include weld beads known as shear keys along the length of the grout connection to prevent any sliding between the monopile and the tower.
caption: Several foundation structures for offshore wind turbines in a port
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