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Renewable Energy Research Laboratory University of Massachusetts An Overview of the Technology and Economics of Offshore Wind Farms James F. Manwell, Ph.D.
Renewable Energy Research Laboratory
University of Massachusetts
An Overview of the Technology and Economics of
Offshore Wind Farms
James F. Manwell, Ph.D.
Renewable Energy Research Laboratory
University of Massachusetts
Typical Offshore Windfarm
Middelgrunden Wind Farm (off Copenhagen, Denmark)
20, 2 MW Turbines
Photo: J. Manwell
Renewable Energy Research Laboratory
University of Massachusetts
Winds off Massachusetts
• Excellent wind resource off the coast
• Wind speeds highest furthest from shore
Map: True Wind Solutions, with support from Mass. Tech. Collaborative, Northeast Utilities, CT Innovations
Renewable Energy Research Laboratory
University of Massachusetts
Typical Week of Wind in Nantucket Sound
Wind Speed, B&C, Nov 8-15, 2002
0
5
10
15
20
25
30
35
40
11/8 11/9 11/10 11/11 11/12 11/13 11/14 11/15 11/16Date
Spee
d, M
ph
Primary Anemometer Redundant Anemometer Average
Renewable Energy Research Laboratory
University of Massachusetts
Water Depth• Moderate
depths (less than 100’) presently required
• Shallow water (less than 50’) preferred
< 120 ft< 90 ft
< 60 ft
Renewable Energy Research Laboratory
University of Massachusetts
Typical Wind Turbine• Converts energy in wind to electricity• Major components
– Rotor • Hub• Blades
– Gearbox– Generator – Tower
Constant Speed System
Rotor GearboxGenerator
Renewable Energy Research Laboratory
University of Massachusetts
Offshore Wind Farms
• Multiple wind turbines• Bottom mounted foundation• Electrical grid between turbines• Power cable to shore• Infrastructure for operation & maintenance
Renewable Energy Research Laboratory
University of Massachusetts
Conceptual Design of Typical Offshore Wind Plant
Wind Turbine
Maintenance VesselInstallation
Crane
Submarine Cable
Onshore Staging Area and
Control Room
Grid Connection
• Foundation –Bottom mounted up to ~ 60 ft.
depth –Floating structure in deep water
Renewable Energy Research Laboratory
University of Massachusetts
Conceptual Design of Typical Offshore Wind Plant
Wind Turbine
Maintenance VesselInstallation
Crane
Submarine Cable
Onshore Staging Area and
Control Room
Grid Connection
• Submarine cable to mainland for power and communication
Renewable Energy Research Laboratory
University of Massachusetts
Wind Turbine
Maintenance VesselInstallation
Crane
Submarine Cable
Onshore Staging Area and
Control Room
Grid Connection
• Barge with crane for installation
Conceptual Design of Typical Offshore Wind Plant
Renewable Energy Research Laboratory
University of Massachusetts
Support Options for Offshore Wind Turbines
Spar bouy
Gravity caissson
Steel piling Truss Artificial
island Pontoon
Renewable Energy Research Laboratory
University of Massachusetts
Electrical Cables
Typical cable layoutCable cross section
Cable laying shipCable trencher
Illustrations from www.hornsrev.dk
Renewable Energy Research Laboratory
University of Massachusetts
Installation
Photos: Courtesy GE Wind
Renewable Energy Research Laboratory
University of Massachusetts
Determinants of Cost of Energy• Total installed costs
– Turbines, Foundations, Electrical System– Installation
• Energy produced– Wind resource– Turbine operating characteristics– Turbine spacing
• Operation and Maintenance (O & M)– Scheduled maintenance and repairs
• Financial considerations (interest rates, etc.)
Renewable Energy Research Laboratory
University of Massachusetts
Factors Affecting Cost of Energy
• Number of turbines • Size of turbines • Distance from shore• Water depth• Mean wind speed• Turbine reliability and maintainability• Site accessibility
Renewable Energy Research Laboratory
University of Massachusetts
Typical Offshore Capital Costs
• Turbine costs (inc. tower): $800-1000/kW• Cable costs: $500k-$1,000,000/mile• Foundation costs:
– Costs depend on soil and depth– North Sea: $300-350/kW– Price increases ~15%-100% when depth
doubles (from 25 ft to 50 ft)• Total installed costs: $1200-$2000/kW
Renewable Energy Research Laboratory
University of Massachusetts
Offshore Capital Cost Breakdown
• Turbine (w/out tower): 17-40%• Tower and foundation: 28-34%• Electrical grid: 9-36%• Other: 6-17%
Renewable Energy Research Laboratory
University of Massachusetts
Energy Production
• Wind resource• Turbine power curve• Capacity factor
– Actual energy/maximum energy– Typical values offshore: 35-45%
• Availability– Fraction of time turbine can run
1600
1200
800
400
0
Pow
er, k
W
2520151050Wind Speed, m/s
Renewable Energy Research Laboratory
University of Massachusetts
Typical O & M Costs
• 1.0 – 2.0 US cents/kWh• O & M increases with
– Increased distance from shore– Increased occurrence of bad weather
• O & M decreases with– More reliable turbine design– Greater number of turbines
Renewable Energy Research Laboratory
University of Massachusetts
Cost of Energy
• Cost of energy (COE), $/kWh, depends on:– Installed costs, C– Fixed charge rate, FCR – fraction of installed
costs paid each year for financing– O & M– Annual energy production, E
• COE = (C*FCR+O&M)/E
Renewable Energy Research Laboratory
University of Massachusetts
Simple Payback
• Simple alternative economic measure• Simple payback period (SP), years, depends
on:– Installed costs, C– Annual energy production, E– Net price obtained for electricity, P
• SP = C/(E*P)
Renewable Energy Research Laboratory
University of Massachusetts
Value of Energy
• Bulk energy sold at wholesale• Internalized social benefits
– Wind energy production tax credit (PTC)– Renewable energy portfolio standards (RPS)
certificates (RECS)
Renewable Energy Research Laboratory
University of Massachusetts
Social (External) Costs of Electricity Production
• Costs not accounted for directly in fuel price or production costs
• Examples:– Air pollution health affects– Damage due to global warming
• Typical estimates:– Coal: 2-15 cents/kWh– Gas: 1-4 cents/kWh
Renewable Energy Research Laboratory
University of Massachusetts
Actual Costs of Energy, Existing European Projects - 2001• Turbine size: 450 kW-2000 kW• Number of turbines: 2-28• Wind speeds: ~7.5 m/s• Water depth: 2-10 m• Distance from shore: 250 m-3 km• Cost of Energy: 5.3- 11.2 cent (EC) /kWh
( ≈ 5.3 – 11.2 US cent/kWh)
Renewable Energy Research Laboratory
University of Massachusetts
Costs as a Function of Distance and Total Size
• 1997 European study:• 7.5 MW wind farm, 1.5 MW turbines,
– 5 km from coast – 4.9 US cent/kWh– 30 km from coast – 6.9 US cent/kWh
• 200 MW wind farm, 1.5 MW turbines, – 5 km from coast – 4.1 US cent/kWh– 30 km from coast – 4.4 US cent/kWh
Renewable Energy Research Laboratory
University of Massachusetts
Sample Economic Assessment• Assume
– Installed cost: $1500/kW– Capacity factor: 40%– Availability: 95%– Value of Energy: 8.3 cents/kWh, based on:
• Wholesale: 4 cents/kWh• PTC: 1.8 cents/kWh• RPS: 2.5 cents/kWh
– Operation & Maintenance: 1.5 cents/kWh– Fixed charge rate: 14%
• Simple payback = 6.6 years• COE= 7.8 cents/kWh
Renewable Energy Research Laboratory
University of Massachusetts
Technical Considerations with Sites Further from Shore
• Greater energy production• More extreme environment• Greater cable length• Deeper water, larger foundation costs
– Technology development useful to reduce costs– Floating supports for deep water
Renewable Energy Research Laboratory
University of Massachusetts
Deep Water Possibilities
Delft University, 2001
UMass, 1974
Renewable Energy Research Laboratory
University of Massachusetts
Summary• Offshore wind energy is a reality in shallow
water, close to shore• Cost of energy higher than from
conventional sources, ignoring externalities• COE competitive, including RECS and PTC• Technology for moderately deep water still
expensive• Technology for deep water, far from shore
remains to be developed
