overview of offshore wind energy...

Renewable Energy Research Laboratory

University of Massachusetts

Overview of Offshore Wind Energy Technology

EBC Seminar Series on Offshore Wind Energy

September 28, 2007

J. F. Manwell, Professor and Director


Department of Mechanical and Industrial Engineering

Univ. of Mass./Amherst, MA

www.middelgrunden.dk



Overview

• History of offshore wind energy

• Offshore wind overview

• Design of offshore wind turbines

• Economics/policy

• Environmental issues

• The future: deep water



Early Offshore Wind Energy

(for transportation)

Mural from Akrotiri, Santorini (Greece), c. 1,500 BC



First Idea for Offshore Wind Turbines

• Hermann Honnef

• Germany, 1930’s

• Multiple rotors



Wm Heronemus, UMass

First detailed offshore wind concepts, ~1972

•Floating

•Spar buoy

•For hydrogen



First Offshore Wind Turbines Built

• Vindeby, Denmark,1991

• Eleven wind turbines

• Shallow water, close to shore

• Protected waters: low waves



Typical Land Based Wind Turbine

Hub Drive train

Main frame/yaw system

Roto

r

Tow

er

Generator

Nacelle cover

Foundation

Balance of electrical system

Control

Hull, MA 2003



Impetus for Offshore Wind Energy

• Land use constraints

• Distance of large land based resource areas

from load centers

• High winds offshore

• Limit to size of land based turbines



Conceptual Design of Typical

Conventional Offshore Wind Plant

Wind Turbine

Maintenance

VesselInstallation

Crane

Submarine Cable

Onshore Staging Area

and

Control Room

Grid

Connection



State-of-Art Offshore Wind Turbines

• GE Wind

– 3.6 MW

– 104 m rotor diameter

– Shown in Ireland

• Copenhagen Windfarm

• Hornsrev Windfarm

(Denmark)



Offshore Wind Turbine Design

Considerations



Wind Turbine Support Structure

• Typical offshore

wind turbine

support structure

options

• Type used will

depend on seabed

properties

s u b - s t r u c t u r e

p i l e

f o u n d a t i o n

p i l e

p l a t f o r m

t o w e r t o w e r

s u b - s t r u c t u r e

sea floor

s u p p o r t s t r u c t u r e

rotor-nacelle assembly

seabed

water level



Design Drivers

• Wind Speed/Extremes

• Waves/Extremes

• Distance from Shore

• Depth

• Standards

– International Electrotechnical

Commission: IEC 61400-3

– Det Norske Veritas (DNV)

– Germanischer Lloyd (GL)



Typical Hourly Average Windspeed, 1 year

0

20

40

60

80

1001

499

997

1495

1993

2491

2989

3487

3985

4483

4981

5479

5977

6475

6973

7471

7969

8467

Time. Hrs

Win

dsp

ee

d,

mp

h

Illustrations of Wind Variability



Illustration of Wave Motions

Data: Shoaling Waves Experiment, ONR



Wave Forces• Considerations

– Water depth, sea-bed slope, wave period, etc.

– Linear/non-linear waves

– Breaking/spilling/plunging waves

Photo: D. Quarton



Extreme Events

• High Winds/High Waves

• Sources:

– Hurricanes

– Northeast Storms



Sources of Extreme Events

• Hurricanes

– “Extended fetch” ⇒ large wind-waves



Sources of Extreme Events

• Northeast Storms

– Extratropical cyclones

– Winter, cold core

– Larger diameter (> 1000 km) ⇒ large wind-

waves

Jan90 Jan91 Jan92 Jan93 Jan94 Jan95 Jan96 Jan97

0

2

4

6

8

10

12

14

Date

Sig

nific

ant

Wave H

eig

ht

[m]

Dec. 1992

Mar. 1993

Jan. 1996

Oct. 1992

Hurricane Bob

Perfect Storm



Economics: Cost of Energy

• Total installed costs– Turbines, Foundations, electrical system

– Distance from shore, depth, Installation

• Energy produced– Wind resource

– Turbine operating characteristics

– Turbine spacing

• Operation and Maintenance (O & M)– Scheduled maintenance and repairs

• Financial considerations (interest rates, etc.)



Offshore Wind Cost Elements

• There is much more to the cost than the turbine

itself

Electrical

Infrastructure

15%

Operation and

Maintenance

25%

Support

Structure

24%

Engineering

and

Management

3%

Turbine

33%



Cost of Energy

• On the order of $0.10/kWh today

• Overall, cost of energy still high compared to

conventional energy or onshore wind

• Policy required to overcome barriers

– Financial incentives

– Research & development

– Facilitate initial siting



Environmental Issues

• Visual impact concern close to shore

– Less so farther from shore

• No noise issues

• Avian (bird) impacts appear to be minimal

• Minimal impact on fisheries

– Beneficial to some

• No information on marine mammals in deep

water



Radar Images of Migrating Birds at

Nysted Wind Power Plant - DenmarkOperation (2003):

Response distance:

day = c. 3000m

night = c. 1000m

Bird perceive the

presence of wind

turbines even in bad

visibility

Source: W. Musial, NREL



Future for Offshore Wind Farms

• Deeper water– 100’ and deeper

• Further from shore

• Larger turbines

• High voltage DC cables

• Floating?

• Offshore fuel production?

– Using hydrogen from electrolysis of sea water



Impetus for Deep Water Wind

• Far larger resource area

• Higher winds

• Out of sight

• However:

– Much more difficult environment

– Higher costs

– Technology not commercially available



Deep Water Considerations

• Extensive support structures

• Moorings; stability; motion for floating

supports

• Access/operation/maintenance

• Distance from Shore

• Higher waves

• Costs may be high



Other Deep Water Issues

• Environmental Impact

– Marine mammals

– Fisheries

• Ocean Use Policy

– Jurisdiction

– Competing uses

– Ocean sanctuaries



Multiple

Floater,

Tension Leg

D. Hannevig,

Ocean Synergy

Recent Deep Water Wind Concepts

Multiple Turbines, Moored

Floater (A. Henderson)



Relevant Experience from

Oil & Gas Industry

• Platform, mooring and foundation system concepts

• Design procedures & codes

• Analytical & experimental modeling tools

• Installation strategies

• Cost reduction & system optimization techniques



Technology from Offshore Drilling

Industry

Tension leg

platform

Semi-submersible

PlatformFloating Production

SystemR. Mercier



Relevant Example: Deepwater Tripod

Graphic: R. Mercier

Graphic: R. Mercier



Current Deep Water R&D Efforts



Beatrice Offshore Wind

• Off the coast of Scotland

• Largest offshore turbine yet

(~420 ft rotor diameter)

– REpower 5 MW turbines

• Deepest water (~150 ft)



Interior of Beatrice Turbine



Beatrice Offshore Wind

• Installation



Spar Buoy R&D

• Norsk Hydro (Norway)

Model being testedArtist’s concept



Tension Leg Platform (TLP) R&D

• Dynamics of TLP supported wind turbine

investigated at MIT

• Prototype TLP supported wind turbine being

built in Italy



Conclusion

• Offshore wind energy has enormous potential

• Economic feasibility close in shallow water, more difficult in deeper water

• Offshore wind energy has advanced, but new concepts needed for deeper water

• Offshore oil/gas experience is relevant but not sufficient

• Development of requisite, cost-effective technology will be challenging

overview of offshore wind energy...

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