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Wednesday, 12 March 2014
11:15 - 12:45 On- and off-shore installation technologies
Hardware Technology  


Room: Tramuntana
Session description

Installation of wind turbines is an area that has attracted significant attention, in an attempt to increase efficiency and reduce costs. Bigger, better, cheaper ways of transporting and installing turbines are vital in the drive to reach grid parity. Onshore, increasing tower heights lead to alternative materials and assembly procedures. Offshore, costs can be reduced by optimising design, transportation and installation of foundations.

Learning objectives

  • Discover the design concepts and assembly procedures that ensure steady installation rates of concrete towers
  • Identify the current challenges and solutions in the installation of new onshore technologies
  • Summarise the calculation, design and manufacturing criteria for optimised offshore monopile foundations
  • Examine the savings in materials and cranes derived from an innovative transportation and installation structure for a floating foundation
Lead Session Chair:
Jose Luis Sevillano Izarra, GES, Spain

Co-chair(s):
Thorsten Kramer, GES
Eyal Taub Mecal Wind Turbine Design, The Netherlands
Co-authors:
Eyal Taub (1) F P
(1) Mecal Wind Turbine Design, Enschede, The Netherlands

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Eyal Taub has been a Project engineer in MECAL Wind Turbine Design for the past 5 years. During that time he has done FEM based strength and stability calculations for different wind turbine components. He has previously worked for 3 years for the offshore oil&gas industry (KCI BV).
During that time he has done FEM and hand calculations for different offshore structures (jackets, stingers, crane pedestals, top sides, accommodation modules, lifting appliances). Before that he was a career officer in the army for 5 years.

Abstract

MECAL ITS system – installation and transportation of a TLP supported floating wind turbine

Introduction

The majority of offshore wind turbines are built on bottom mounted foundations (mono-pile, jacket, tripod, Gravity base).
These foundations represent a big part of the CAPEX of an offshore wind park and require long and expensive installations with offshore cranes.
Floating foundations, which are common in the oil&gas offshore industry, can be an alternative for bottom mounted foundations and might help reduce the cost of offshore wind.

Approach

One floating foundation concept is the TLP (tension leg platform).
This concept has big potential to reduce the weight of offshore foundations, but needs complicated transportation and installation procedures that add to the final LCOE (levelled cost of energy) of the wind turbine.
A structure for a TLP support is developed in order to solve the described problem of installation and transportation of a floating TLP foundation and reduce the LCOE of offshore wind turbines.

Main body of abstract

An optimise TLP support structure for a 5MW wind turbine can weigh as little as 900ton, compared with around 5000ton for a semisubmersible structure supporting the same turbine.
The saving in material and manufacturing costs make this solution very suitable for large scale offshore wind farms requiring a large amount of wind turbine units.
Furthermore, this amount of material is in the same range as jacket and tripod foundations for shallow water wind turbine foundation.
However, an optimize TLP support structure will not have sufficient stability to be floated into location.
Thus, an offshore crane will be needed.
The presentation will bring the concept study for a structure that solves the problems related to the transportation and installation of a TLP floating foundation for offshore wind turbines.

The following guiding principles were used in the design:

• Assembly in harbour and towing to location by tug boats (25000 €/day).
• Avoiding using offshore cranes (40000 – 600000 €/day).
• Using drag embedded or gravity based anchors (avoid using expensive pile driving ships).
• Speed of installation – reducing down time (25%-30% in previous offshore wind projects).
• Using the offshore environment to your advantage - using the principles of buoyancy, ballast and mooring lines (high strength to weight ratio).
• Copying existing solutions for floating offshore structures from the oil&gas industry, whilst taking into account fundamental differences with the wind industry.
• Floating wind turbines are not meant only for deep waters: also shallow water locations (25-50 [m]) can benefit from the same advantages of floating turbines in deep waters.


Conclusion

There have been several attempts in the past to design a TLP structure with sufficient stability during transport and installation.
The resulting structures are very heavy (usually weighing around 5000 ton) and thus the cost savings of avoiding an offshore crane are eliminated by the extra cost for construction material.
The presented solution for a transportation and installation structure enables that initial cost savings by avoiding of an offshore crane are not eliminated by extra cost for additional construction material.


Learning objectives
• Disadvantages of bottom mounted offshore foundations.
• Advantages and disadvantages of TLP (tension leg platform) floating foundations.
• Solution for the installation and transportation of TLP (tension leg platform) floating foundations.