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Delegates are invited to meet and discuss with the poster presenters during the poster presentation sessions between 10:30-11:30 and 16:00-17:00 on Thursday, 19 November 2015.

Lead Session Chair:
Stephan Barth, ForWind - Center for Wind Energy Research, Germany
David Carrascosa Saitec S.A., Spain
Co-authors:
David Carrascosa (1) F Luis Gonzalez-Pinto (1) Alberto Galdos (1)
(1) Saitec S.A., Lejona, Spain

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2015 and are published here unedited

Mr. Carrascosa has been working in the offshore wind industry for almost 2 years . He is currently the Head of the Offshore Wind Department at Saitec. He has a great background in structural analysis due to his previous employment as Structural Engineer and his studies in Civil Engineering at the University of Cantabria in Spain.


Poster

Poster Download poster (24.62 MB)

Abstract

SATH, a competitive solution for Floating Offshore Wind Turbines

Introduction

Cost reduction in Floating Offshore Wind is required to be considered as a feasible way of generate electricity. In this regard, as stated in most of the specialized forums and publications, there is a need of reducing offshore operations and maintenance as well as undertake the whole construction process onshore.

To successfully meet this challenges SAITEC has developed a floating platform with the following main features: prestressed concrete as construction material to reduce cost and maintenance, cylindrical hulls since when they are subjected to hydrostatic pressure it produces compression stresses in concrete avoiding external cracking and finally a twin hull layout to achieve stability.


Approach

The SATH® floating platform consists of two cylindrical and horizontal floating elements with conical ends linked to each other through bar frames structures.

Furthermore, the tower support is fixed to the floating elements through another auxiliary structure.
In order to increase the natural periods in pitch and roll oscillations, the floating elements are attached to some flat and horizontal solid slabs lightened with a ribbed structure arranged submerged in the lower area of the platform.
Finally, the platform is moored by a single point mooring system that allows SATH to rotate around always facing wind.


Main body of abstract

After going through all the required design stages of pre-dimensioning, hydrodynamic analysis, scale test validation, software calibration, aero-hydrodynamic coupled analysis, structural and fatigue analysis as well as evaluating all the costs involved in the construction, transport, installation, transmission, O&M, decommissioning, we are now able to present a fully competitive solution which key features are listed below:

• The hydrodynamic behavior of SATH in both, operational and extreme conditions (North Sea worst conditions), has been demonstrated to be completely suitable to support the offshore wind turbines that are currently in the market.
• DNV stability requirements are easily fulfilled because of SATH’s hull geometry.
• Using concrete as material, construction costs are reduced as well as the maintenance ones become nearly zero
• SAITEC has planned an “onshorized” construction process for a serial production limiting offshore operations to cable and mooring lines installations and final connection.
• SATH is a “Plug & Play” solution.
• Its low draught, less than 10 m, allows not only to be installed in both shallow and deep waters but also to be launched in the majority of the main ports.
• After an intensive economic analysis of the solution found that the cost per MW taking in account cost of construction yard, auxiliary means, materials, turbine, construction, mooring, cable, transport, installation, transmission, etc. for a 500 MW wind farms of 100 of 5MW wind turbines is about 3 M€/MW what is a competitive cost even with offshore fixed-bottom wind turbines.
• SATH platform is a fully reliable for 5, 8 and 10 MW horizontal axis wind turbines (scalable solution). The greater the wind turbine is, the lower the foundation impact on cost per MW is.


Conclusion

SATH's development project has demonstrated the possibility of reducing offshore operations just to mooring installation and final plug and play connection as well as making Floating Offshore Wind competitive with fixed-bottom wind turbines at medium depth (30-40 m). It means that FOWT projects will not have to wait for deep waters wind farms to be feasible and may start tender for current ones.


Learning objectives
Initial concepts of floating solutions came from the Oil & Gas industry what might be caused by a misunderstanding of the clear differences with the Offshore Wind field, mainly in terms of revenues. That is why new concepts that better fit with the needs of this industry are required.