feasibility and economics of floating wind turbines … and economics of floating wind turbines in...

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


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


Main dimensions

Elongated spar tower (Sway 2)

Tower diameter above water 7 m

Tower diameter below water 14.5 m

Operating draft 80 m


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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Turbine size (MW)


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


~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




~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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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




~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.

feasibility and economics of floating wind turbines … and economics of floating wind turbines in...

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