An Overview of the Technology and Economics of Offshore Wind Farms James F. Manwell, Ph.D.

Typical Offshore Windfarm 20, 2 MW Turbines Middelgrunden Wind Farm (off Copenhagen, Denmark) 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

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

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 Foundation Bottom mounted up to ~ 60 ft. depth Floating structure in deep water

Conceptual Design of Typical Offshore Wind Plant Submarine cable to mainland for power and communication

Conceptual Design of Typical Offshore Wind Plant Barge with crane for installation

Support Options for Offshore Wind Turbines

Electrical Cables Typical cable layout Cable cross section Cable trencher Cable laying ship 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

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