Navigant Research Blog

Floating Foundations in the Offshore Wind Market, Part 2

— December 21, 2015

This is the second blog of a two-part series discussing floating foundations in the offshore wind market.

Floating foundations face many challenges that must be overcome in order to become a major factor in the offshore wind industry. At the same time, there are many possible advantages these systems could have over traditional foundation types.

Obstacles to Overcome

Despite the tremendous opportunities floating foundations could provide the offshore wind industry, there are multiple obstacles and challenges that need to be addressed before this technology can be used in large-scale projects. The majority of these challenges can be attributed to the fact that this technology is still in its infancy. Numerical models that analyze and compute structural and aerodynamic behaviors of foundations are relatively advanced for grounded foundation types as a result of an increasing amount of empirical data to draw from. In contrast, there are only a handful of test sites with large turbines installed along with some small-scale experimental projects that can be used to model floating foundations on. More test projects need to be built and tested to improve the accuracy and reliability of these models. Additionally, the interface between these floating platforms and the wind turbines themselves needs to be better understood. These foundations need to be able to account for different tower types and sizes as well as varying rotor diameters and hub heights in order to be fully integrated into the market.

Around 20% of current offshore capital expenditure is in the production and installation of substructures. Thus, it’s important to developers that supply chains and port infrastructures are fully realized prior to the beginning of construction. Floating technology, being as immature as it is, will require time to catch up to the more seasoned foundation types. However, there is evidence to support the notion that construction and installation of floating substructures will be both cheaper and easier than their grounded counterparts.

Monopiles and jacket foundations need to be driven deep into the ocean floor, which requires extensive ocean floor surveys. GBS foundations require a large area on the ocean bottom to rest on, which demands extensive preparation. These grounded foundations also require large vessels and dock storage facilities to hold and transport these large structures. Floating foundations can be constructed and assembled almost entirely onshore prior to being loaded onto transport vessels. This reduces vessel usage fees, port storage fees, and potential lost time due to weather delays.

Outlook for Floating Foundations

Several projects are in the pipeline to test floating foundations in Europe, Asia, and in the United States, particularly on the west coast. Siemens has signed a contract with Statoil to install 5 6 MW turbines off the coast of Scotland that will use the Hywind floating spar foundation. A 30 MW floating project funded by Principle Power is also planned off the coast of Oregon. Additionally, France has launched a tender for floating offshore wind projects using three to five turbines of at least 5 MW. These projects and others will undoubtedly face substantial challenges, but their success could lead to a significant expansion of potential offshore wind sites across the globe.

 

Floating Foundations in the Offshore Wind Market, Part 1

— December 17, 2015

Traditional grounded foundation types have led the offshore wind market since its beginning in the early 1990s. Monopiles, jackets, gravity-based structures (GBSs), tripods, and tripiles combined account for over 98% of the market share in offshore wind as of 2015. As of this year, 11.6 GW of offshore wind has been installed globally, and floating foundations only account for 8.4 MW of this installed capacity. This capacity is all from only a handful of test projects in Europe and Asia. Floating technology is still very young, but there is significant research being dedicated toward it given the potential to unlock massive areas of wind resource over deep waters where grounded foundation types are not feasible.

Offshore Overview

Common offshore foundation types like monopiles, jackets, or GBSs are only suitable in water depths of 50m or less. Anything beyond that and construction, transportation, and installation of the massive foundations required for such water depths becomes almost impossible. In addition, the costs of such structures makes them unrealistic as an option in such environments. As a result, only shallow waters such as those found in the Baltic and North Seas in Europe are feasible locations for offshore wind plants, which is why European countries like the United Kingdom, Germany, and Denmark are currently leading in installed offshore wind capacity. This forces developers to avoid locations such as the Mediterranean Sea, Atlantic Ocean, and Pacific Ocean where the continental shelf extends only a short distance off the coast.  In the United States alone—where offshore wind is a growing area of exploration—60% of offshore wind resources within 50 nautical miles of the coast are located in deep waters. Floating foundations could be the linchpin technology in allowing the offshore wind industry to break through into these massive areas of untapped wind resource.

Offshore Wind Foundation Types

Adam Wilson Blog

 (Source: Principle Power)

Floating foundations involve a floating platform, buoys, and a series of mooring lines and anchors connected to the sea floor. There are three main types of floating foundations currently being explored.

  • Spar buoy: A large buoy below the surface stabilizes the platform above. A ballast within the buoy lowers the center of gravity below the center of buoyancy. A Norwegian project called Hywind uses this foundation.
  • Tension-leg platform (TLP): A floating platform is anchored to the ocean floor using tensioned mooring lines.
  • Semi-submersible: This combines the principles of the two previous designs with a semi-submerged structure added to optimize stability. Portuguese test project WindFloat uses a semi-submersible floating foundation.

The application of these different floating foundations is location-specific and dependent on a variety of factors such as ocean topography, tidal and weather forces, and specific ocean depth. In part two of this blog, I will examine the challenges and opportunities that lay ahead for floating foundations.

 

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