Exploring Wind Energy

Wind Occurrence

• The sun heats both land and water.
• Land heats up more quickly than water.
• Warm air over land rises.
• Cool air from over the water moves in to replace the warm air, creating wind.

Global Wind Patterns

• Warmer air rises, and cooler air descends, creating global wind patterns.
• Polar Easterlies
• Prevailing Westerlies
• NE Trade Winds
• Equator Doldrums
• SE Trade Winds
• Prevailing Westerlies

Wind Energy & Turbine

• Wind energy is created by the uneven heating of the atmosphere by the sun, causing warm air to rise and cooler air to rush in and replace it.
• A wind turbine extracts energy from the moving air by:
  • Slowing the wind down.
  • Transferring the energy into a spinning shaft.
  • The shaft usually turns a generator to produce electricity.
• The power available for harvest depends on both wind speed and the area swept by the turbine blades.

History of Wind Energy

• 5000 BC: Sailboats used on the Nile River showed the power of wind.
• 500-900 AD: First windmills developed in Persia.
• 1300 AD: First horizontal-axis windmills in Europe.
• 1850s: Daniel Halladay and John Burnham build Halladay Windmill, start US Wind Engine Company.
• Late 1880s: Thomas O. Perry conducted 5,000 wind experiments and started Aermotor Company.
• 1888: Charles F. Brush used a windmill to generate electricity in Cleveland, OH.
• Early 1900s: Windmills in CA pumped saltwater to evaporate ponds.
• 1941: In VT, Grandpa’s Knob turbine supplied power to the town during WWII.
• 1979: First wind turbine rated over 1 MW began operating.
• 1985: CA wind capacity exceeded 1,000 MW.
• 1993: US Wind Power developed first commercial variable-speed wind turbine.
• 2004: Electricity from wind generation costs 3 to 4.5 cents per kWh.
• 2013: Wind power provided over 17% of renewable energy used in the US.

Why Wind Energy?

• Clean, zero emissions:
  • No NOx, SO2, CO, CO2.
  • Better air and water quality.
  • Positive impact on climate change.
• Reduces fossil fuel dependence:
  • Promotes energy independence.
  • Supports domestic energy production.
• Renewable:
  • No fuel-price volatility.

U.S. Wind Resource Map

• Wind Power Classification:
  • Class 3 (Fair): 6.4-7.0 m/s, 300-400 W/m².
  • Class 4 (Good): 7.0-7.5 m/s, 400-500 W/m².
  • Class 5 (Excellent): 7.5-8.0 m/s, 500-600 W/m².
  • Class 6 (Outstanding): 8.0-8.8 m/s, 600-800 W/m².
  • Class 7 (Superb): 8.8-11.1 m/s, 800-1600 W/m².

Total Installed Wind Capacity

• Total Installed Wind Capacity: 136,650 MW (as of Q1 2024).
• Texas leads with 37,172 MW.
• Iowa follows with 10,014 MW.
• Oklahoma with 11,790 MW

Transmission Challenges

• The United States transmission grid map indicates voltage levels.

California Offshore Wind Speed

• Offshore wind resource data was originally estimated by AWS Truepower as part of an onshore wind mapping project.
• Data have been interpolated to 90 m and extrapolated to 50 nautical miles by NREL.

Levelized Cost of Energy (LCOE)

• Comparison of fossil, renewable, and alternative energy costs per kWh.
• Wind energy (onshore) is among the most competitive renewable energy sources.

Cost of Renewable Energy

• A graph illustrates the cost of renewable energy sources over time.
• Onshore wind is the most competitive.

Wind Energy: How It Works

• Wind turbines directly generate electricity.
• Efficiency depends on wind speed and blade area.
• Challenges include location, visual appearance, noise, and intermittent supply.

Wind Energy: Advantages

• High net energy yield.
• Clean source of energy (no pollution during operation).
• Long operating life with reasonable operating/maintenance costs.
• Almost competitive with hydro and fossil fuels.
• Land can be used for other purposes (e.g., wind and agricultural farms).

Wind Energy: Disadvantages

• Energy storage and grid availability issues.
• Only practical in windy areas.
• Potential danger to birds.
• Low energy density of wind, requiring large areas of land.
• Land use concerns.
• Property values, noise, and visual impact.

Modern Wind Turbines

• Categorized based on the orientation of the rotor.
• Two types: Horizontal axis and Vertical axis.

Wind Turbine Designs

• Horizontal Axis Turbine:
  • Can catch more wind, resulting in higher power output.
  • Requires a higher tower and more defined blade design parameters.
• Vertical Axis Turbine:
  • No yaw system required.
  • No cyclic load on the blade, making it easier to design.
  • Easier to maintain.
• Horizontal axis turbine offers better performance.

Wind Turbine Components

• Blades
• Rotor
• Low-Speed Shaft
• Pitch System
• Gear Box
• Anemometer
• Brake
• Wind Vane
• Yaw Drive
• Yaw Motor
• Nacelle
• High-Speed Shaft
• Generator
• Controller
• Power Transformer

Types of Wind Turbine

• Horizontal-Axis Turbines.
• Vertical-Axis Turbines.
• Darrieus.
• Savonius.

Vertical-Axis Turbine: Advantages

• Omni-directional (accepts wind from any direction).
• Components can be mounted at ground level for ease of service and lighter weight towers.
• Theoretically uses less material to capture the same amount of wind.

Vertical-Axis Turbine: Disadvantages

• Rotors generally near ground where wind is poorer.
• Centrifugal force stresses blades.
• Poor self-starting capabilities.
• Requires support at the top of the turbine rotor.
• Requires entire rotor to be removed to replace bearings.
• Overall poor performance and reliability.

Horizontal-Axis Wind Turbines

• Small (<10 kW):
  • Homes
  • Farms
  • Remote Applications (e.g., water pumping, Telecom sites, ice making).
• Intermediate (10 - 250 kW):
  • Village Power
  • Hybrid Systems
  • Distributed Power.
• Large (250 kW - 2+ MW):
  • Central Station Wind Farms
  • Distributed Power
  • Schools

Large Wind Turbines

• Common Utility-Scale Turbines:
  • 328’ base to blade.
  • Each blade is 112’.
  • 200 tons total.
  • Foundation 20’ deep.
  • Rated at 1.5-2 megawatts.
  • Supply about 500 homes.

Wind Turbine Components (Detailed)

• Anemometer: Measures wind speed and transmits data to the controller.
• Blades: Lifts and rotates when wind is blown over them.
• Brake: Stops the rotor mechanically, electrically, or hydraulically in emergencies.
• Controller: Starts the machine at wind speeds of about 8-16 mph and shuts it off at about 55 mph to prevent damage.
• Gear box: Connects the low-speed shaft to the high-speed shaft, increasing rotational speeds from 30-60 rpm to 1,000-1,800 rpm.
• Generator: Produces 60-cycle AC electricity.
• High-speed shaft: Drives the generator.
• Low-speed shaft: Turns at about 30-60 rpm.
• Nacelle: Sits atop the tower and contains the gear box, shafts, generator, controller, and brake.
• Pitch: Turns blades out of the wind to control rotor speed.
• Rotor: Blades and hub together form the rotor.
• Tower: Supports the structure; taller towers capture more energy.
• Wind vane: Measures wind direction and communicates with the yaw drive.
• Yaw drive: Orients upwind turbines to face the wind.
• Yaw motor: Powers the yaw drive.

Offshore Wind Platforms

• Important considerations include:
  • Wind resource assessment
  • Cable landing point
  • Submarine cable
  • Corrosion-resistant materials
  • Extreme wave forecasting
  • Marine structural engineering
  • Anchoring and retention
  • Seabed Engineering
  • Offshore substation
  • Riser cable

Wind Turbine Anchoring Mechanisms

• Monopile: 0-30m water depth, 1-2 MW capacity.
• Jacket/Tripod: 25-50m water depth, 2-5 MW capacity.
• Floating Structures (Spar, TLP, Semi-Sub): >50m water depth, 5-10MW capacity.

Blade Designs

• Drag Design: Wind pushes the blades out of the way. Slower rotational speeds and high torque.
• Lift Design: Airfoil principle. Air flows past the blade, creating a pressure differential.

Blade Design: Angle of Attack

• The angle between the chord line of the airfoil and the flight direction. Typically ranges from 1.0 to 15.0 degrees.

Blade Design: Increasing Number of Blades

• Increasing the number of blades from one to two yields a 6% increase in efficiency, whereas increasing the blade count from two to three yields only an additional 3% in efficiency.

Typical Wind Turbine Operation

• 0 ~ 10 mph: Turbine is not operational; rotor is locked.
• 10 ~ 25 mph: Minimum operational speed (Cut-in speed); generated power increases with wind speed.
• 25 ~ 50 mph: Rated power is reached (Rated wind speed); further increase in wind speed will not result in substantially higher generated power.
• > 50 mph: Turbine is shut down (Cut-out speed) to prevent structure failure.

Key Wind Turbine Speeds

• Cut-in speed: Minimum wind speed to generate usable power.
• Rated Speed: Minimum wind speed to generate rated power.
• Cut-out Speed: Wind speed at which the turbine shuts down to prevent damage.

Theoretical Power Generated by Wind Turbine

• Power = {1 ewline 2} (ρ)(A)(V)^3
  • A = Swept area = $π(radius)^2$, $m^2$
  • V = Wind Velocity, m/sec.
  • ρ = Density of air = 1.2 kg/m3 (.0745 lb/ft3), at sea level, 20 oC and dry air
  • ρ = 1.16 kg/m3, at 1000 ft elevation
  • ρ = 1.00 kg/m3, at 5000 ft

Example Calculation

• For a wind turbine with a 50-meter blade at 1000 feet above sea level and a wind speed of 12 m/s, the power generated with 40% efficiency is:
  • $Power = 0.5(1.16 kg/m^3)(π * 50^2 m^2)(12 m/s)^3(0.4) = 3.15 x 10^6 Watt = 3.15 MW$

Betz Limit

• The theoretical maximum efficiency for a wind turbine is 59.3%.
• In reality, turbines operate at 35-45% efficiency.

RPM Speed

• RPM for 3 blade turbine is dependent on 3 parameters:
  • Rotor Diameter
  • Wind Speed
  • Tip Speed Ratio (TSR)
• Formula is: $RPM = 60 * V * TSR / ( Pi * D )$
• TSR = (Blade tip speed)/(wind speed mph) = (for 3 blade 5-6) = 6
• Example values for a V= 9 m/s ; TSR~6:
  • 9m Rotor : 114.595 RPM
  • 10m Rotor: 103.135 RPM
  • 12m Rotor: 85.946 RPM