This page contains information on the following types of offshore wind turbine foundations:
- Current Foundation Types– includes foundations currently available to offshore wind developers
- Future Prototypes– includes floating and deepwater concepts
Foundations Used On Utility-Scale Offshore Wind Projects Today:
The common foundations used for current offshore wind projects are shown in the diagram below:
- Mono pile– Consists of a steel pile which is driven approximately 32-64 ft into the seabed.
- Gravity foundation– Currently used on most offshore wind projects, the gravity foundation consists of a large base constructed from either concrete or steel which rests on the seabed. The turbine is dependent on gravity to remain erect.
- Tripod foundation– Designs tend to rely on technology used by the oil and gas industry. The piles on each end are typically driven 32-64 ft into the seabed, depending on soil conditions. This technology is generally used at deeper depths and has not been used on many projects to date.
Overview- Basic Offshore Wind Turbine Foundation Types:
Note: Drawings not to scale, demonstrates simplified design concepts for the purposes of education only. Accuracy not warranted.
(sources used in this section include the Danish Wind Industry Association)
Grounded Deep Water Concepts:
Deepwater Wind has proposed using a jacket foundation, similar to a lattice tower, for both of its semi-deepwater projects in New Jersey and Rhode Island. The jacket foundation technology has been licensed from OWEC Tower AS and has previously been deployed at the Beatrice offshore wind project in Scotland. A link to the OWEC Jacket Foundation brochure.
The jacket foundations allow Deepwater Wind to install its turbines 10-15 miles offshore. In December 2015, Deepwater Wind finished installing all five jacket foundations at its Block Island offshore wind project off of the coast of Rhode Island. Once completed in 2016, the Block Island project will become the first operational offshore wind project in the United States.
Video of DeepWater Wind Foundation Manufacturing:
Jacket Foundation Concept:
Source: Deepwater Wind
OWEC Jacket Foundation at Beatrice Offshore Wind Project:
Offshore Wind Power Systems of Texas has designed the Mobile Self-Installing Platform (MSIP), a three legged platform able to be towed out to sea and lowered into place.
Source: Offshore Wind Power Systems of Texas
While several floating offshore wind concepts exist, two designs are the best known:
In June 2009, Siemens and StatoilHydro installed the first megawatt-scale floating turbine in 700 feet of water approximately 12 km south east of Karmøy in Norway, see Hywind below. In January 2015, Statoil announced a 30 MW commercial project using the hywind foundation off of Scotland.
PrinciplePower is also working on its WindFloat design and in 2011 installed a full scale 2 MW prototype off the coast of Portugal.
There are also two spar buoy offshore wind projects in Japan, Kabashima Island, Kyushu installed in 2013 and Hakata Bay Wind Lens, Kyushu.
HyWind- Spar buoy:
In June 2009, Siemens and StatoilHydro installed the first megawatt-scale floating turbine in 700 feet of water. Following assembly in the Åmøy Fjord near Stavanger, the Hywind pilot was towed in to a location 10 kilometres south-west of Karmøy island for a two-year test period. The turbine is a modification of Siemens’ SWT-2.3 MW offshore machine with a rotor diameter of 82 meters and an a 65 meter hub height.
The Hywind technology is designed for installation in water depths between 120-700 m deep. StatoilHydro was responsible for the floating structure, which consists of a steel floater filled with ballast of water and rocks. This floating element extends 100 m beneath the surface of the water and is fastened to the seabed by three anchor wires. StatoilHydro and Siemens have jointly developed a special control system for the Hywind turbine to address the special operating conditions of a floating structure. In particular, the advanced control system takes advantage of the turbine’s ability to dampen out part of the wave-induced motions of the floating system. StatoilHydro is invested about NOK 340 million in the project, with Enova providing an additional NOK 59 million. The project was offically inaugurated on September 8, 2009.
Turbine size: 2.3 MW
Turbine weight: 138 tons
Turbine height: 65 m
Rotor diameter: 82.4 m
Draft hull: 100 m
Displacement: 5300 m3
Diameter at water line: 6m
Diameter submerged body: 8.3 m
Water depths: 120-700 m
Mooring: 3 lines
Hywind Prototype Installation:
In January 2016, Statoil announced that it would build a full-scale offshore wind project using the Hywind foundation. The 30 MW Hywind pilot project will be installed at Buchan Deep, 25 km offshore Peterhead in Aberdeenshire, Scotland. The project is expected to begin construction in 2017.
HyWind Pilot Project Map:
According to Statoil, Hywinds pitch motion controller is integrated with the turbine’s control system and mitigates the excessive motions of the structure. This also eliminates the loss of energy due to aerodynamic or hydrodynamic movements and maximizes the power output. The structure is ballast-stabilized and anchored to the seabed using three mooring lines attached to anchors suited to the site-specific seabed conditions.
HyWind Pilot Project Simulated View:
WindFloat (PrinciplePower)- Semi – submersible :
Conceived by Marine Innovation & Technology and owned by Principle Power, the WindFloat is a semi-submersible,
three-column structure, with a turbine tower, truss and “water entrapment heave plates” at each column’s base, designed toreduce pitch and yaw, and make the entire structure more compact. It aims to support deployment of large capacity wind turbines (3.6 MW to 10MW) in deep water (50 metres or greater) (Source: RECharge Americas).
In October 2011, Principle Power installed a full-scale 2 MW WindFloat prototype (WF1) 5km off the coast of Aguçadoura, Portugal. The structure was fully assembled onshore before being towed approx. 400km along the Portuguese coast from it’s point of assembly near Setubal, Portugal. Principle Power used a Vestas 2 MW turbine for this project. The following is Principle Power’s WindFloat Brochure.
In October 2015, Trident Winds proposed a 1 GW offshore wind project off the coast of California using Principle Power’s WindFloat foundation.
Video of Principle Power Windfloat Onshore Assembly:
Blue H Technologies, a Dutch company proposing an offshore project off of Massachusetts, has launched a test an 80 Kw Submerged Deepwater Platform (SDP) off the coat of Puglia, Italy. The company uses a tension-leg platform design which relies on a platform that floats below the surface of the water (similar to the ballast stabilized concept below) moored to the bottom with chains. The design is unique in that it uses a two bladed turbine. The company has proposed an offshore wind project using this technology off the coast of Massachusetts but the company has not made any progress recently.
Additional Resources: (more to come)
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