An Overview of the Technology and Economics of Offshore Wind Farms

transcript

Renewable Energy Research Laboratory

University of Massachusetts

An Overview of the Technology and Economics of

Offshore Wind Farms

James F. Manwell, Ph.D.

Typical Offshore Windfarm

Middelgrunden Wind Farm (off Copenhagen, Denmark)

20, 2 MW Turbines

Photo: J. Manwell

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

Typical Week of Wind in Nantucket Sound

Wind Speed, B&C, Nov 8-15, 2002

11/8 11/9 11/10 11/11 11/12 11/13 11/14 11/15 11/16Date

Primary Anemometer Redundant Anemometer Average

Water Depth• Moderate

depths (less than 100’) presently required

• Shallow water (less than 50’) preferred

< 120 ft< 90 ft

< 60 ft

Typical Wind Turbine• Converts energy in wind to electricity• Major components

– Rotor • Hub• Blades

– Gearbox– Generator – Tower

Constant Speed System

Rotor GearboxGenerator

Offshore Wind Farms

• Multiple wind turbines• Bottom mounted foundation• Electrical grid between turbines• Power cable to shore• Infrastructure for operation & maintenance

Conceptual Design of Typical Offshore Wind Plant

Wind Turbine

Maintenance VesselInstallation

Submarine Cable

Onshore Staging Area and

Control Room

Grid Connection

• Foundation –Bottom mounted up to ~ 60 ft.

depth –Floating structure in deep water

Wind Turbine

Submarine Cable

Control Room

Grid Connection

• Submarine cable to mainland for power and communication

Wind Turbine

Submarine Cable

Control Room

Grid Connection

• Barge with crane for installation

Support Options for Offshore Wind Turbines

Spar bouy

Gravity caissson

Steel piling Truss Artificial

island Pontoon

Electrical Cables

Typical cable layoutCable cross section

Cable laying shipCable trencher

Illustrations from www.hornsrev.dk

Installation

Photos: Courtesy GE Wind

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.)

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

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

Offshore Capital Cost Breakdown

• Turbine (w/out tower): 17-40%• Tower and foundation: 28-34%• Electrical grid: 9-36%• Other: 6-17%

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

2520151050Wind Speed, m/s

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

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

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)

Value of Energy

• Bulk energy sold at wholesale• Internalized social benefits

– Wind energy production tax credit (PTC)– Renewable energy portfolio standards (RPS)

certificates (RECS)

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

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)

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

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

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

Deep Water Possibilities

Delft University, 2001

UMass, 1974

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

An Overview of the Technology and Economics of Offshore Wind Farms

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