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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
Marc Guyot EOLINK, France
Co-authors:
Marc Guyot (1) F
(1) EOLINK, Brest, France

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Presenter's biography

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

Marc Guyot has a Master’s of engineering from the Ecole Nationale Supérieure d’Electricité et de Mécanique. He started his career as automotive engineer for Renault. Then he joined France Energies Marines to lead R&D design topics. In 2014, he introduced technological issues at the First French Scientific Conference of Floating Wind Turbine in Marseille. His work is focused on LCOE opimization, aero-hydro-servo-structural modeling and fatigue analysis. He now works for EOLINK, a start-up which develops an innovative floating wind turbine concept.


Poster

Poster Download poster (22.63 MB)

Abstract

A low-cost innovative floating wind turbine : Suppressing the mast decreases LCOE by 20%

Introduction

Because of their mast, FWT are soft structures. Wind turbulence and waves lead to 80 million stress cycles during the FWT lifetime. Consequently, fatigue is an issue which leads to a high CAPEX (Capital Expenditure).
EOLINK solves these problems with a breakthrough concept using a semi-submersible floater with an innovative structure : Instead of the mast, the Rotor Nacelle Assembly (RNA) is supported by three thin, profiled arms. One arm is upwind while the two others are downwind. The above water part of the structure has therefore a pyramidal shape, with the RNA located at its top.


Approach

To demonstrate the benefits of this innovative concept, an aero-hydro-servo-structural code is deployed to determine stress time series everywhere in the structure. These computations are performed over wind and sea scatter diagrams. Then, damage is computed with rainflow countings.
In addition, a detailed cost analysis of each subsystem is performed in order to quantify LCOE (Levelized Cost Of Energy) benefits, using Myhr et al. (2014) data.


Main body of abstract

Regarding fatigue, one shall notice that a one-third reduction in stress range cycle multiplies by five the structure lifetime. Because the EOLINK design offers a better distribution of the forces, bending moments are drastically reduced. This permits a decrease in beam thickness and diameter and thus weight. EOLINK uses 40% less steel in comparison with the reference case using a mast. Because thicknesses are much lower, the process of cutting, assembling and welding requires less time and money. Assuming an axisymmetric semisubmersible floater, this reduces LCOE by 12 points.
The structure is stiff because the front and rear arms are linked together at the top of the pyramidal shape. This implies that the RNA uses a hollow shaft, as does the Alstom Haliade or Enercon. Here again, structural benefits are substantial because the shaft is no longer cantilevered. With EOLINK, the first Eigen frequency of the FWT is far higher than 3P rotor excitation.
EOLINK is a guided-leaning or weather-vaning FWT using a semi-submersible floater. The yaw motion needed to face the wind is provided by a turret, which is a proven technology in the Oil and Gas industry.
With a conventional RNA yaw system, the stability provided by the hull must be axisymmetric. With the EOLINK concept, wind thrust direction is always co-linear with the bow-stern axis. Therefore, the floater stability is higher along the bow-stern axis than along the beam axis. This reduces the floater size and thus CAPEX by 8 more points.
The resulting hull shape reduces the footprint of the floater and its ability to fit within dry-dock. The floater is also easier to tow because drag is reduced. Thanks to the turret, installation of the FWT, the moorings and power cables are decoupled. Therefore, only a tug is required to connect or disconnect the FWT. The RNA and floater are assembled together on the dock without any floating crane. Installation costs are reduced but not yet quantified.


Conclusion

EOLINK is a low-cost FWT using a semi-submersible floater. EOLINK innovates because it replaces the mast by three profiled arms. Thanks to a reduction of stress range cycles and a non-axisymmetric floater, EOLINK permits a stiffer and lighter structure.
This structural innovation reduces LCOE by 20% (+/-3%) which can be achieved with technologies available off the shelf.
EOLINK requires an RNA which uses a hollow shaft. Some wind turbine manufacturers already produce such RNAs which would perfectly suit EOLINK.



Learning objectives
A new FWT architecture is presented. It aims to reduce fatigue damage and also permits to sustain wind thrust with a smaller floater. Consequently, LCOE is reduced by 20% (+/-3%).