Foundations for offshore wind turbines

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, utilizing traditional fixed-bottom wind turbine technologies, as well as deeper-water areas utilizing floating wind turbines.

Types of underwater structures include:

  • Monopile (single column) base, six meters in diameter, is used in waters up to 30 meters deep.
  • Gravity base structures, for use at exposed sites in water 20–80 m deep.
  • Tripod piled structures, in water 20–80 m deep.
  • Tripod suction caisson structures, in water 20–80 m deep.
  • Conventional steel jacket structures, as used in the oil and gas industry, in water 20–80 m deep.

Monopiles up to 11 m diameter at 2,000 tonnes can be made, but the largest so far are 1,300 tons which is below the 1,500 tonnes limit of some crane vessels. The other turbine components are much smaller.

For locations with depths over about 60–80 m, fixed foundations are uneconomical or technically unfeasible, therefore floating wind turbine anchored to the ocean floor are needed.

Floating Wind Turbines: An Overview

  • 2007: Since 2007 single wind turbine prototypes have been installed off the coasts of Norway, Italy, Portugal, Sweden, Japan and the United States.
  • 2009: The first turbines for Hywind’ s floating farm project became operational in the North Sea. At maximum capacity, Hywind’s turbines can produce energy for 20,000 homes.
  • 2017: The first and only fully-operational floating wind farm, Hywind Scotland was commissioned in, situated 25 km off the coast of Aberdeen. Developed by Norwegian oil and gas company, Equinor (ex Statoil), Hywind has six floating turbines with a total capacity of 30 MW.

 Hywind park will further increase the global market potential for offshore wind energy, contributing to realising our ambition of profitable growth in renewable energy and other low-carbon solutions

-Irene Rummelhoff, Executive Vice President, Marketing, Midstream & Processing (MMP), Equinor

5 major challenges with placing wind turbines in deep sea

  1. Development of floating turbine technology requires time.
  2. Floating wind turbines usually operate in harsh climates.
  3. Maintenance of turbines is expensive and difficult
  4. When waves cause the turbines to move too much, efficiency goes down.
  5. Effects of offshore wind farms on marine animals and birds are not fully understood.

 Floating wind turbines: 5 reasons why

  1. The space necessary to install windfarms is more easily available.
  2. The windspeed is turning stronger and more uniform as it is not affected by buildings or trees.
  3. Wind turbines are steadier in deep sea than on land.
  4. Offshore, floating wind farms can help to meet those energy needs from nearby sources.
  5. Floating wind farms do not consume water; they provide a domestic energy source;  create jobs; and do not emit environmental pollutants or GHG.

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Experts expect offshore wind to grow by more than 20% each year over the next several years, and floating wind farms will open up completely new growth opportunities.