Vattenfall is a large European energy company with wind power activities in several countries. This document summarizes a conceptual design study for foundations for an offshore wind farm called Kriegers Flak in waters 15-45 meters deep. Five foundation concepts were developed - monopile, jacket, concrete tripod, gravity base cone foundation, and drilled concrete monopile. The study aimed to reduce costs and risks for the project planned to begin construction in 2013 through preliminary engineering of foundation options and establishing early contact with contractors.

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Conceptual Design Study
Kriegers Flak
Windforce 09, 18th june, 2009
Thomas Stalin, Vattenfall Wind Power AB

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Vattenfall Wind Power
• Activity in DK, FI, SE, UK, DE, PL
• Appr. 160 employee + x consultants
• VF Target in Europe, 49 TWh wind power
by 2030
• One offshore project will be built per
year in Europe
• Thanet, UK
• Electricity to 10 million households
• 1/3 Nordic 1/3 UK 1/3 Central Europe

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Targets for Sweden
• Vattenfall share 8 TWh of 16 TWh to 2016
– 4 TWh onshore
– 4 TWh offshore
• New political target 25 TWh to 2020
– Vattenfalls share even larger!!!!
• Focus in Sweden first be onshore in the forest
• Offshore has high technical risk and high investment cost
• Price for green certificates equal for onshore and offshore
• Vattenfall will first build offshore in the countries where we can
meet profitability, GB and DE
• When turbines have matured and total price for green electricity
has increased we will build offshore in Sweden
– Political process
• Kriegers flak is planned to be built in phases starting 2013

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SE 103 wtg
160 MW - 440 GWh
FI 10 wtg
4 MW - 8 GWh
DE 386 wtg
307 MW - 800 GWh
UK 30 wtg
90 MW - 270 GWh
Total: Appr. 560 wtg 600 MW 1.6 TWh
Nordic: Appr. 500 wtg 470 MW 1.3 TWh
1.6 TWh Annual Production
PL 15 wtg
30 MW - 60 GWh
DE 13 wtg
14 MW - 29 GWh

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Conceptual Design Study, Kriegers Flak
• Study during 2008
• Budget 700 000 Euro
• Four foundation concepts + ref. monopile
• Presentation 28th February 2008
• Proposals from Intrested parties
• Selected five experts
• Started work April/May
• Three meetings
• Draft report in January 2009
• Final Seminary March 2009
• EOW session KF + Final report

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Aim of Project
• Costefficient Foundations for 15 to 45 meter water deepths
– Calculations and drawings
– Installation method and specification of equipment
– Including estimate of fabrication and installation cost
• Reduce the cost = Reduce the risk
– Use the time to investigate the conditions
– Find areas that needs further investigations
• Conceptual design for the tender process
– Good base for estimate of volumes of material and labour
– Detailed drawings and worked through concepts
• Establish contacts to Contractors well in advance of tender
– Good knowledge of the project
• Transfer of knowledge to Vattenfall
– Ability to make conceptual design and estimate cost
• Support the generall knowledge
– Develop concepts for deeper waters

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Prehistory
• Year 2003 to 2005 Project development focused on permits and
not on implementations and long term ownership
– Millions on environmental investigation
– Before permit => 100% risk to loose money invested in technical
problem solving
– Long technical lead times when permit ready
=> Work in parallel
• Project development without knowing final cost
• No projects built on deep waters
• STEM Call for Offshore Pilot Studies
• Application in March April 2004
• In May 2005 project sold to Vattenfall
– Long term ownership
• Funds approved by STEM 2005

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Background
• Started Design Basis 2007
• Detailed geotechnical investigation 2007
– Geobore S, CPTs, Vibro core
– Analyse first half 2008
• How to utilize time to reduce risk
– While project starts 2013
• How to get lower prices for foundations
– Better information for tendering phase
– Several pre-engineered concepts
– Contractors see possibilities and understand risk
• Optimal time schedule for tendering process
– Adopt time to allow the best solution a chance to win
• Volunteer before tendering in order to get the things done in advance
that should be done but normally first is done after the contract is signed

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Consultants
• Ramböll and MTHojgaard
– Jacket
– Ref. Monopile
• ISC and Skanska
– Concrete Tripod
• COWI and Aahrsleff
– Cone Gravity foundation
• Ballast Nedam and MTPiling
– Drilled Concrete Monopile
• Pihl
– Automatic stone bed preparation robot

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Rambøll tasks
Two generic turbines of 3.6 MW and 5.0 MW
• Natural Frequency Range
• 3.6 MW 0.27 – 0.30 Hz
• 5.0 MW 0.23 – 0.26 Hz
• Life Time of Foundations 25 Years
Monopiles
• 3.6 MW and 5.0 MW Turbine
• 20-35 m Water Depth
Jacket
• 5.0 MW Turbine
• 35 m Water Depth
Two Concepts to be developed

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Monopile Concept for Kriegers Flak
Total Steel Weights
• 3.6 MW 400-750 tons
• 5.0 MW 525-1050 tons
Pile Penetrations
• 3.6 MW 26-29 m
• 5.0 MW 25-29 m
Pile Diameters
• 3.6 MW 4750-6000 mm
• 5.0 MW 5750-6750 mm
Ice cone at
sea level
Grouted
connection
by mud line
Depending on soil profile

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Jacket Concept for Kriegers Flak - Results
Weights
– Jacket – 261 tons
• Piles – 248 tons
• Transition Piece – 700
tons
• Secondary Steel – 24
tons
Geometry
• Foot Print 12 x 12 m
• Interface 10.5 m
• Pile Penetration 42 m

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GRAVITY BASED FOUNDATION, COWI - AARSLEFF

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27/03/2015
Gravity Based Foundation - Conceptual design
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Concepts alternatives
"Traditional" cone,
Thornton type
Floating caisson,
KIS (Keep It Simple)
Semi floating cone,
Pontoon supported

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27/03/2015
Gravity Based Foundation - Conceptual design
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Cone foundation properties
Volume of concrete
 Base case solid ice cone:
1320 m³ (3300 t)
 Hollow ice cone:
1170 m³ (2925 t)
 0.2m reduced bottom slab height
1080 m³ (2700 t) (hollow ice cone)
Cost & time implications marginal due to
increased reinforcement
Volume of sand ballast
 1830 m³ (3550 t)
Gravel Bed
 1m thickness (575 m³)
Dredging
 2 m deep (~ 3,000 m³)
-32.0
FOUNDATION
LEVEL
+2.0
-2.0
+3.5
MSL

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Concept level Cost Estimate
1 Cone Foundation of 40 in total
EUR excl. VAT
Casting Yard (1 of 40) 175,000
Primary Structures: 1.125,000
Secondary Structures: 85,000
Ballast 40,000
Dredging and deposit: 135,000
Stone works: 470,000
Transport & Installation 350,000
SUM 2,380,000 ~ 480,000 EUR/MW
Assuming normal weather year,
Hs < 0.75 m 140 days Feb. - Nov.
Floating concept: ~ 4,000,000 EUR
Semi floating concept: ~ 3,000,000 EUR

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Construction/installation KIS - TOWING
Transport
 Towed to installation site by
tugs
Installation
 Lowered by ballasting , tug
aided positioning
 Stability to be assured during
lowering

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Construction/installation
SEMI FLOATING - Transport
Construction
 Completed on land, and immersed in shallow waters (dry dock,
skidding ramp, syncrolift)
Transport
 The GBF picked up by pontoon and transported to site
Installation
 Controlled lowering by hydraulic winches and released when in
place

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Concrete Tripod, ISC and Skanska

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DRILLED CONCRETE MONOPILE

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FABRICATION
Fabrication method conform project
Saudi Arabia Bahrain Causeway (1984):
• Prefab reinforcement cages;
• Casting ring elements;
• Storage and curing ring elements;
• Monopile assembly:
• Aligning ements;
• Grouting element joints;
• Installation post tensioning;
• Grouting post tensioning ducts.
• Finishing works:
• Installation cutting toe;
• Installation injection lines for drillmix;
• Installation pile plugs.

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Drilling inside and under monopile:
Inside monopile
• Start drilling process
• Soft upper layers
• Diameter 5300 mm
DESIGN DRILLING EQUIPMENT
Under monopile
• Deeper soil layers
• Extended cutter head
(6700/7100 mm)

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INSTALLATION

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INSTALLATION

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INSTALLATION

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INSTALLATION

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INSTALLATION

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INSTALLATION

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INSTALLATION

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COST
Total cost per MW as function of amount and turbine type:

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Purpose Built Vessel

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Catamaran

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Lowering

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Result
• Based on Geotechnical investigations and measurements on Wind and
Waves we have developed a Design Basis that was used in the project
– First test of design basis
• Individual experts developed the concepts with comments from the others
experts, team-work under competition, sharing of experience. Helge
Gravesen was the project manager
• Worked out five foundation concepts and one seabed preparation robot
• Managed to find some solutions in the range below 500 Euro/kW
• For the coming Tender process we have a good material in form of the five
worked out Conceptual designs
• Vattenfall gained knowledge on volumes, prices and time schedules
• The contractors knows about KF
– the conditions, the potential alternatives and the competition.
• Proved to be possible to create exchange between competitive parties
• Two complete new concepts have been developed
• All participants have enjoyed the process

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Thanks!