Hydrodynamic Analysis and Optimal Design of Floating Wind Turbine and Ocean Wave Energy Systems

Paul D. SclavounosProfessor of Mechanical Engineering and Naval Architecture

Department of Mechanical Engineering

LSPF Laboratory for Ships and Platform Flows

Advantages of Floating Offshore Wind Farms

Wind a Rapidly Growing, Free, Inexhaustible, Environmentally Friendly, Utility Scale and Cost Effective Energy Source

Vast Offshore Wind Resources with Higher and Steadier Wind Speeds in Deeper Waters

Over 75% of Worldwide Power Demand From Coastal Areas

Wind Power Output Increases with Cube of Wind Speed

Lower Offshore Wind Turbulence – Longer Farm Life ~ 25-30 Years

Connection to Electric Grid by Sub Sea AC or HVDC Cables

Experience of Oil Industry Essential for the Development of Safe and Cost Effective Spar and TLP Wind Turbine Floaters

Floating Wind Turbines Provide Infrastructure for Arrays of Wave Energy Converters in Waters Depths over ~ 40m with Significant Wave Power Density

Courtesy: NREL

Horns Rev Wind Farm (Denmark) - Rated Power 160 MW – Water Depth 10-15m

Expensive Installation Process for Seafloor Mounted Turbines

Floating Wind Turbine Attributes

Water Depths of 30 – 1000 m

5-MW Wind turbine: 1 GW Floating Wind Farm (200 Units)

Flexible Installation process:

Full Assembly at a Coastal Facility Ballasted TLP or Spar Buoy Tow Stable Floating Wind Turbine at Offshore Wind Farm Site Tow In of Floating Wind Turbine for Major Maintenance Gravity Anchors for TLP Tethers Conventional or Synthetic Catenaries for Spar Buoy

Attractive Economic and Financial Attributes

Coastal Zone of Visual Influence (ZVI)

L Distance from Shore for Turbine to be Invisible H Max Height of Turbine Blade Tip (90 + 65=155 m) R Earth Radius (~ 6,370,000 m)

L = 28 miles (45 Km) (H=155m - Blade Tip) L = 21 miles (34 Km) (H=90m - Hub)

2L H R

New Jersey Offshore Wind Farm

Courtesy: NY Times

Deep Water Offshore Platforms for Oil and Gas Exploration

Spar and TLP SML Simulation Modelsof MIT Laboratory for Ship and Platform Flows

5 MW Wind TurbineRotor Orientation UpwindControl Variable Speed, Collective PitchRotor Diameter/Hub Diameter 126 m/3 mHub Height 90 mMax Rotor/Generator Speed 12.1 rpm/1,173.7 rpmMaximum Tip Speed 80 m/sOverhang/Shaft Tilt/Precone 5 m/ 5°/ -2.5°Rotor Mass 110,000 kgNacelle Mass 240,000 kgTower Mass 347,460 kg

Overall c.g. location:

(x,y,z)t = (-.2,0,64)m

Coupled Dynamic Analysis

Wind Turbine Floater Analysis & Design

Design Studies Sea States Design Models

Tension Leg PlatformSpar Buoy in SLC (Single-Layer Catenary)Spar Buoy in DLC (Double-Layer Catenary)

Pareto Optimization Analysis

Sea Spectra

41

244.0

5

11

2

22

11.0)(

wT

s ewT

THwS

ITTC (International Towing Tank Conference) Standard

TLP; Water depth = 200 m; Seastate H=10m

TLP Water depth = 200 m; Seastate H=10mPareto Fronts

Design Models: Spar Buoy in SLC (Single-Layer Catenary)

Design Models: Spar Buoy in SLC

=

Fairlead Position

DraftPlatform

DepthFairlead

Design Models: Spar Buoy in SLC

Platform Diameter, 2R [m] 18

Draft, T [m] 40

Displacement [metric tons] 10453.586

Concrete Concrete Mass [metric tons] 9036.997

Concrete Height [m] 13.858

Center of Gravity [m] -25.522

Center of Buoyancy [m] -20

Seacondition

Water depth [m] 200

Mooring Catenary angle, [degree] 10 ~ 70

k [m/m] 0.995

Fairlead Location, [m/m] 1.0

* EA [N] 400E6

MBL [N] 20E6

Design Models: Spar Buoy in DLC (Double-Layered Catenary)

Spar Buoy OptimizationPareto Fronts

Offshore Wind Capacity Factor

Assessment of Offshore Wind Resource – Wind Velocity Probability Distribution

Ideal Efficiency of Wind Turbine in Steady Wind – Betz Limit : η=16/27=0.59

Reported Efficiencies of Large Scale Wind Turbines ~ 50%

Advanced Control Systems to Enhance Power Absorption from High Wind Gusts

Height of Tower, Size of Rotor and Electric Generator – Cost Benefit Analysis

Capacity Factor: Percentage of Time Wind Turbine Generates Power at its Rated Capacity

Offshore Wind Capacity Factors (CP) ~ 40-45%

Available Wind Power per 1 GW Offshore Wind Farm at 40% CP ~ 400 MW

Wave Energy Converters ~ 100 MW / Square Parcel

Hybrid Offshore Wind & Wave Energy Plant

Wave Energy Capacity Factor

Wave Power in Storm with 3m Height / 8 sec Period / 100 m Wavelength ~ 36 kW / meter

Wave Power in Storm with 10m Height / 12 sec Period / 200m Wavelength ~ 500 kW / meter

More Wave Power Encountered in Water Depths Over 40 m (Waves do not feel seafloor)

Maximum Wave Power Captured by Point Wave Energy Absorber ~ Wavelength/ 2π (m)

In 3m Seastate ~ 573 kW / Absorber; In 10m Seastate ~ 15 MW / Absorber

Spacing of Point Absorbers ½ a Wavelength – Wave Power Output Increases by 50%

Use of 100 Absorbers Rated at 1 MW Between 4 Wind Turbines – Power Output ~ 150 MW

Maximum Utilization of 1 GW “Offshore Wind Farm Real Estate” – 150x13x13 MW ~ 25 GW

Capacity Factor of Ocean Wave Energy ~ 30%

Available Wave Power per 1 GW Rated (400 MW Available) Offshore Wind Farm ~ 7.5 GW

Floating Wind Farm Financial Attributes

Annual Revenues of 1 GW Farm (200 5 MW Units) @ 40% Capacity Factor and @10 cents/KWh: ~ $400 Million

Breakeven Cost vs CCGT ~ $ 3 M/MW: Based on Natural Gas Price Projections $9-15/MMBtu from 2010-2027

Breakeven Cost per Floating 5 MW Unit: $15 M; 1GW Wind Farm: $3 B

Onshore 5 MW Unit Cost ~ $10 M; Breakeven Cost of Floater & Mooring System ~ $5 M

O&M: Unit Ballasted & Towed to Shore – On Site Routine Maintenance

Interconnection Costs ~ 15-20% of Capital Costs ~ $ 450-600 M for 1 GW Farm

AC Sub Sea Cables up to ~ 100-130 km. HVDC Light Technology over 100-130 km

Coal Plant Emits ~ 1 ton CO2/MWh; Combined Cycle Gas Turbine Emits ~ 300 Kg CO2/MWh

At $10/ton of CO2 – Emissions Credit ~ 1 cents/KWh; 10% Increase in Revenue

Floating Wind Farms vs. Oil & Gas Reservoirs

1 Barrel of Oil ~ 130 kg ~ 1.5 MWh of Energy (~ 12 kWh / kg)

1 MW of Rated Wind Turbine Power @ 40% Capacity Factor ~ 9.6 MWh / Day ~ 6.4 Barrels of Oil / Day

Conversion Efficiency of Oil & Gas Engines / Turbines, Wind Turbines ~ 40-50%

1 GW Wind Farm (30 year life) ~ 70 M Barrel Oil Field ~ 6,400 Barrels / Day

Breakeven Cost of Wind Turbines $3M / Rated MW = $3 B / Rated GW

Equivalent Cost per Barrel of Oil ~ $43 / Barrel

Investment Risk in Oil & Gas: Exploration Costs & Volatility of Oil & Gas Prices

Investment Risk in Wind: Volatility of Wind Speed & Electricity Prices

Summary

Optimized Spar Buoy and TLP Wind Turbine Floaters

Low Responses – Use of Onshore Wind Turbines

Hybrid Offshore Wind & Wave Farms

Optimal Control to Enhance Wind and Wave Power Output

Design of Offshore Electric Grids

Attractive Economic Attributes

Project Finance for Utility Scale Offshore Wind & Wave Farms