Deep Water Foundation Concepts:
While deep water concepts have huge potential, current floating offshore wind foundation technology is not used on a commercial scale and has little operational track-record. Many of the proposed concepts utilize designs borrowed from the oil and gas industry. The advantages of deep water offshore wind is that winds are stronger further from shore and projects can be invisible from the shoreline lowering the chances of opposition. Cost may be one of the biggest challenges facing deep water offshore technology.
Several prototypes for offshore wind floating foundations exist including the ones seen below considered by MIT, NREL and DOE:
Overview-Floating Turbine Foundation Prototypes:
Depicts deep water concepts considered by MIT, NREL and DOE. Drawing based on image from NREL.
Note: Drawings not to scale, demonstrates simplified design concepts for the purposes of education only. Accuracy not warranted.
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 been deployed at the Beatrice offshore wind project in Scotland. The jacket foundations will allow Deepwater Wind to install its turbines 10-15 miles offshore.
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:
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
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.
PrinciplePower is also working on its WindFloat design, see below/
Blue H Prototype:
Source: Blue H
The SWAY concept consists of a floating spar buoy that is some 640 ft tall, designed to rise and fall with wave activity. The concept is unique in that the turbine will face downwind. A prototype of the SWAY concept will likely be installed by 2010.
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:
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 to
reduce 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).
Source: Principle Power