Post on 29-May-2018
Feasibility and
economics of floating
wind turbines in deep
water
Eystein Borgen, founder of Sway AS
1
II Offshore Energy
International Conference
2015 / 8th-9th October
8 Vigo / 9 Ferrol
Promédio velocidades del viento (10m altura). QuikScat.
Valores aproximados
The best wind resources are situated in deep water (> 50m)
100 véces más que
el potencial
hidroeléctrico?
100 véces más que
el potencial
hidroeléctrico?
Sway opera
entre 80 y 300m
de profundidad
Offshore wind in Galicia?
Technology Benchmarking of the most promising floating
foundation concepts for offshore wind farms
Multiple Tension leg platforms
• Stability during tow?
• Relatively high installation costs
• Small motions when installed• (bending moments taken by tension legs)
• Large anchor forces
(9 times larger anchor than Sway)
• Medium/high costs driven by
anchor system
Example: Blue-H
Tri-floaters
• Low installation costs
• Relatively large steel
weight
• Complicated nodes
• Active ballast system
• Relatively high anchoring
costs
• Relatively high total costs
Example: Wind Float
Elongated spar tower
(Sway Upwind)Upwind turbine with catenary mooring(licenses available from Sway to self-floating wind turbine
towers based on the spar concept)
• Good stability/small motions
• Fatigue in tower drives the
steel weight
• Medium steel weight
• Medium tow/installation costs
• Relatively high anchor costs
• Medium total cost
Example: Hywind
Elongated spar tower (Sway downwind)
10
Low cost single
point anchor system (patented by Sway)
Yawing by
individually pitching
the blades(motoring the rotor in no-wind
conditions)
Ballast
Single anchor leg
wind50% lower steel
weight for down
wind rotor with wire
suspension (patented by
Sway) Wire suspension (stays)
Passive yaw swivel
Elongated spar tower (Sway
downwind)With downwind turbine, wire stays and single
point mooring(licenses available from Sway)
• Good stability/small motions
• Fatigue in tower reduced by wire
stay supports
• Low steel weight
• Low to medium installation costs
• Low anchoring costs
• Low total costs
Example: Sway
Simplified dynamic analyses of all 4 systems to decide
dimensions and steel weights
• 10MW wind turbine on each floating foundation assumed
• Iterations of dimensions until acceptable stress levels achieved for both fatigue and extreme loads
3-TLP Main Dimensions
Hull Diameter 23 m
Tower Base Diameter 13 m
Arm Diameter 7 m
Operating Draft 31,1 m
Steel weight 3966 te
Multiple Tension Leg platform (3-TLP)
Semi-sub Main
Dimensions
Column Diameter Ca. 13 m
Column Height 40 m
Column Center to Center 65 m
Pontoon Diameter Ca. 2,4 m
Bracing Diameter Ca. 1,5 m
Operating Draft Ca. 29 m
Steel weight 3539 te
Tri-Floater/ Semi-sub
Elongated spar tower 1 (Sway upwind)
Main dimensions
Elongated spar tower (Sway 1)
Tower diameter above water 7-14 m
Tower diameter below water 21 m
Operating draft 80 m
Steel weight 3393 te
Main dimensions
Elongated spar tower (Sway 2)
Tower diameter above water 7 m
Tower diameter below water 14.5 m
Operating draft 80 m
Steel weight 1879 te
Elongated spar tower 2 (Sway downwind)
Summary comparison of steel weights (excl. anchor system)
10MW*Results from
dynamic analyses.
Rotor 474W/m2
10MWScaling of results.
Rotor 331W/m2
6MWScaling of results
Rotor 331W/m2
5MWScaling of results
Rotor 331W/m2
Multiple tension leg
platform (3-TLP)
3965 5335 2765 2200
Tri-floater / Semi-sub 3540 4760 2465 1965
Upwind spar (Sway and Hywind
type)
3390 4565 2365 1885
Downwind spar (Sway
type)
1880 2560 1295 1025
Total steel weight of tower + floating foundation, te (excl. anchor system)
*Turbine type in the dynamic analyses was based on Sway Turbine 10MW with 570te top head mass and 164m
rotor diameter. The rest of the above results is based on scaling of a conventional 5MW wind turbine with 368te
top head mass and a power to rotor area ratio of 331W/m2. For the below LCOE calculations a conventional wind
turbine is used.
M€ 10MW upwind 10MW
downwind
Tower/foundation 9.0 5.0
Mooring system 5.0 1.5
Wind Turbine 14.5 14.5
Grid connection 4.0 4.0
Installation 1.5 1.5
Misc incl
contingency
2.0 2.0
Total wind farm
(per unit)
36.0 28.5
Cost benchmarking of total wind farm between upwind Sway spar with
catenary mooring (Sway upwind) versus downwind Sway spar with single
point mooring (Sway downwind)
The Sway downwind solution has the lowest capital costs and is therefore
used as the reference for the Levelized Cost of Energy calculations for
floating foundations below
Levelized Cost of Energy (LCOE)
The levelized cost of energy is equal to the necessary electricity price
needed to cover all annual costs of running the wind farm (operating costs
and capital costs)
In order to calculate the LCOE weighted average cost of capital (WACC)
must be given (the average interest rate for all the financing of the
project). The WACC vary depending on the required return on capital for
the banks and investors for each project.
Levelized Cost of Energy (LCOE) input assumptions
• 500MW wind farm 30km from shore (unless stated otherwise), 30m water
depth for fixed foundations and 120m water depth for floating foundations
• Weighted average cost of capital (WACC) of 9% assumed for all cases
• Generator to rotor area ratios; 331W/m2
• All wind velocities are referring to annual average wind velocities
• Assumed manufacturing costs: jacket=4.0€/kg, semi-sub4.0€/kg, piles 1.5€/kg,
tower 2.5€/kg, floating tower 3.1€/kg
• 40% less installation costs assumed for the Sway floating system compared to
fixed foundations
• 70% less installation costs assumed for the semi sub floating systems compared
to fixed foundations
The Cost of Energy calculations includes:
• Electrical grid connection to shore + a certain onshore grid reinforcement
• 33% additional costs of wind turbine is assumed due to offshore application
(additional corrosion protection, landing platforms, market factor, warranty risk
etc)
• 10% contingency on total wind farm Capex and 10% profit to the OEM.
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(€
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)
Turbine size (MW)
Levelized Cost of Energy (LCOE)
Typical LCOE curve for an offshore wind farm depending on size
of the wind turbines
Lowest cost of energy with 7-12MW turbines
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Turbine size (MW)
9m/s site, 9%WACC
Fixed foundation (jacket) versus Sway Floating foundation
Fixed jacket foundations, 30m water depth
Floating Sway foundations, 120m water depth
Levelized Cost of Energy (LCOE)
~4% lower LCOE for fixed foundations
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Turbine size (MW)
9%WACC
Fixed jacket foundation 10km from shore with 9m/s
versus Floating foundations 30km from shore with 10m/s
Floating Sway Upwind foundations, 120m water depth
Floating Semi-sub, 50m water depth
Fixed jacket foundations, 30m water depth
Floating Sway foundations, 120m water depth
Levelized Cost of Energy (LCOE)
~1,5% lower LCOE for Floating Sway compared to fixed foundations
~23% lower LCOE for Floating Sway compared to semi-sub floating foundations
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(€
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t/k
Wh
)
Turbine size (MW)
9%WACC
Fixed jacket foundation 20km from shore with 9m/s
versus Floating foundations 20km from shore with 10m/s
Floating Sway Upwind foundations, 120m water depth
Floating Semi-sub, 50m water depth
Fixed jacket foundations, 30m water depth
Floating Sway foundations, 120m water depth
Levelized Cost of Energy (LCOE)
~9% lower LCOE for Floating Sway compared to fixed foundations
~24% lower LCOE for Floating Sway compared to semi-sub floating foundations
Sway Prototype
Testing of Sway downwind
prototype at the norwegian west
coast 2011-2013
Operation of the system has been
successfully verified including
active yawing using individual blade
pitch
The system has also been
qualified in severe weather
during winter storms in 2012
and 2013 after modifications
carried out in Q2 2012.
Summary:
Levelized Cost of Energy (LCOE) is only
marginally higher for a floating wind
farm (Sway) in 120m water depth
compared to fixed foundations in 30m
water depth
Floaters can be positioned further
offshore where wind velocities are
generally higher
The LCOE for a floating wind farm
(Sway) in 10m/s average wind is lower
than a fixed wind farm in 9m/s wind.