study about wind turbines

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WIND TURBINESSTUDY ABOUT RESIDENTIAL WIND TURBINES

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Prepared by 4th year Mechanical Engineering Students

Lebanese University Faculty of Engineering Roomieh

EliaTohme WadihKhater Jamil Chibany

INSTRUCTOR Elias Kinnab, PhD

Professor Professor Department of Mechanical Engineering

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Definition:

A wind turbine is a machine for converting the kinetic energy in wind into mechanical energy.

Types of wind turbines:

Windmills: Vertical Axis Wind Turbine Horizontal Axis Wind Turbine

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VERTICAL WIND TURBINES

 SAVONIUS WIND TURBINE

It is useful for grinding grain, pumping water, and many other tasks, but its slow rotational speeds make it unsuitable for generating electricity on a large-scale.

FLAPPING PANEL WIND TURBINE

This illustration shows the wind coming from one direction, but the wind can actually come from any direction and the wind turbine will work the same way.

DARRIEUS WIND TURBINEIt is characterized by its C-shaped rotor blades which give it its eggbeater appear ance. It is normally built with two or three blades.

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HORIZONTAL AXIS WIND TURBINES

UP-WIND TURBINES

Some wind turbines are designed to operate in an upwind mode (with the blades upwind of the tower). Smaller wind turbines use a tail vane to keep the blades facing into the wind.

DOWN-WIND TURBINES

Other wind turbines operate in a downwind mode so that the wind passes the tower before striking the blades. Without a tail vane, the machine rotor naturally tracks the wind in a downwind mode.

SHROUDED WIND TURBINES

Some turbines have an added structural design feature called an augmenter. The augmenter is intended to increase the amount of wind passing through the blades.

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CHARACTERISTICS

Cut-in Speed

Rated Speed

Cut-out SpeedTurbine size

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Betz’s Law

According to Betz's law, no turbine can capture more than 16/27 (59.3%) of the kinetic energy in wind

η= power12ρ A tU u

3=1

2 (1−U d

U u)(1+U d

U u)

2

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EQUATIONS

Available Wind Power: 3

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1VAP Ta

Wind Turbine Power and Efficiency 3

2

1VA

PC

Ta

Tp

Wind Turbine TorqueVAF Ta2

1

2

2

1VAT Ta

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Rotor Torque

Rotor Tip Relative Speed

V

NR

V

RVrw

2

V

RV

C

Crw

T

P

TVA

TC

Ta

rT

2

2

1

ρ = Density of air = 1.2 kg/m3 (.0745 lb/ft3), at sea level, 20 oC and dry air

A = swept area = (radius)2, m2

V = Wind Velocity, m/sec.

ρ = 1.16 kg/m3, at 1000 feet elevation

ρ = 1.00 kg/m3, at 5000 feet elevation

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ENERGY CONVERSION

Hot air goes up and creates low pressure region

Cooler air moves from high pressure region

• the wind is used to generate mechanical energy or electrical energy.

• Wind turbines converts the kinetic energy of the wind into mechanical energy first and then into electricity if needed.

• The energy in the wind turns propeller like blades around a rotor shaft.

• It is the design of the blades that is primarily responsible for converting the kinetic energy into mechanical energy.

• The rate of change of angular momentum of air at inlet and outlet of a blade gives rise to the mechanical torque.

Wind energy is created when the atmosphere is heated unevenly by the Sun, some patches of air become warmer than others. These warm patches of air rise, other air rushes in to replace them – thus, wind blows. A wind turbine extracts energy from moving air by slowing the wind down, and transferring this energy into a spinning shaft, which usually turns a generator to produce electricity. The power in the wind that’s available for harvest depends on both the wind speed and the area that’s swept by the turbine blades.

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Power Generated by Wind Turbine Wind turbines with rotors (turbine blades and hub) that are about 8 feet in diameter (50 square feet of swept area) may peak at about 1,000 watts (1 kilowatt; kW), and generate about 75 kilowatt-hours (kWh) per month with a 10 mph average wind speed.

Homes typically use 500-1,500 kilowatt-hours of electricity per month. Depending upon the average wind speed in the area this will require a wind turbine rated in the range 5-15 kilowatts, which translates into a rotor diameter of 14 to 26 feet.

Doubling the tower height increases the expected wind speeds by 10% and the expected power by 34%.

doubling the altitude may increase wind speed by 20% to 60%.

Tower heights approximately two to three times the blade length have been found to balance material costs of the tower against better utilization of the more expensive active components.

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THE INSIDE OF A WIND TURBINE:

Anemometer Blades

Brake Controller

Gear box

Generator

High-speed shaft

Low-speed shaft

Nacelle

Pitch Rotor

Tower Wind direction

Wind vane

Yaw drive

Yaw motor

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RESIDENTIAL WIND TURBINE

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BLADES DESIGN: NUMBER OF BLADES

NUMBER OF BLADES : ONE Blades easier to install because entire rotor can be assembled on ground.

Captures 10% less energy than two blade

design.

Ultimately provide no cost savings.

Higher speed means more noise, visual, and wildlife impacts.

NUMBER OF BLADES : TWO Advantages & disadvantages similar to one blade.

Need teetering hub and or shock absorbers because of gyroscopic imbalances.

Capture 5% less energy than three blade designs.

NUMBER OF BLADES : THREE Balance of gyroscopic forces.

Slower rotation.

Increases gearbox & transmission costs.

More aesthetic, less noise, fewer bird strikes.

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BLADES DESIGN: BLADE COMPOSITION

WOOD

Strong, light weight, cheap,

abundant, flexible.

Solid plank.

Laminates.

Veneers.

Composites.

METAL Steel: Heavy & expensive.

Aluminum: Lighter-weight and easy to work with.

Expensive.

Subject to metal fatigue.

FIBERGLASS Lightweight, strong, inexpensive, good fatigue characteristics

Variety of manufacturing processes:

Cloth over frame.

Pultrusion .

Filament winding to produce spars.

Most modern large turbines use fiberglass.

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Airfoil Shape

Lift/Drag Forces Experienced by Turbine Blades

Twist & Taper

Fast

Faster

Fastest

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Tip-Speed Ratio

There is an optimum angle of attack which creates the highest lift to drag ratio. Because angle of attack is dependent on wind speed, there is an optimum tip-speed ratio TSR=Ω𝑅/𝑉

Performance over Range of Tip Speed Ratios

• Power Coefficient Varies with Tip Speed Ratio.• Characterized by Cp vs Tip Speed Ratio Curve.

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Rotor Solidity

Solidity is the ratio of total rotor platform area to total swept area.

1-Low solidity (0.10) = high speed, low torque 2-High solidity (>0.80) = low speed, high torque

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Location for a small or micro-scale wind turbine

Ideally, the turbine should be 10m above any obstacle within 100m. As a rule of thumb, a wind generator should be installed no closer to an obstacle than at least ten times the object's height, and on the downwind side. The preferred distance is twenty times the height of the object.

Many residential areas are not suitable for wind turbines as buildings and trees shade the wind and create turbulence which can reduce the efficiency and lifespan of a turbine considerably. Generally speaking, the ideal location is on top of a high mast on a south westerly facing hill with gently sloping sides surrounded by clear countryside which is free from obstructions such as trees, houses or other buildings. Here the wind flows relatively smoothly and steadily enabling it to drive wind turbines with greater efficiency.

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Calculation of the energy produced over a year:

Here is a chart that estimates annual energy production for different sized turbines in different annual mean wind speeds.

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The figure below shows the data from which the power curve (the green line) was obtained as an average of the binned power and wind speed readings. The peak power is obviously electronically regulated so that there is a sharp cut-off at 5.2 kilowatts.

The table below shows the equivalent annual energy production in kilowatt-hours obtained by multiplying the mean power results by 8,760 - the number of hours in a year.

Annual energy production in kilowatt-hours Mean wind speed (m/s) = 5 6 7 8 9 10 Power calculation 8,669 13,101 17,378 21,222 24,544 27,341

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Economical Approach: Leading Manufacturers of Wind Turbine: 1. Vestas (Denmark) - 35,000 MW 2. Enercon (Germany) - 19,000 MW 3. Gamesa (Spain) – 16,000 MW 4. General Electric (USA, Germany) – 15,000 MW 5. Siemens (Denmark, Germany) – 8,800 MW 6. Suzlon (India) – 6,000 MW 7. Nordex (Germany) – 5,400 MW 8. Acciona (spain) – 4,300 MW 9. Repower (Germany) – 3,000 MW 10. Goldwind (china) – 2,889

1.0 – 2.5 million per MW for large scale - Most commercial wind turbine are in the range of 2 MW $3,000 – 5000 per kW in range less than 10kW - $15,000 - $25,000 for residential home application

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References: American Wind Energy Association (AWEA). 2013a. AWEA U.S. Wind Industry Annual Market Report: Year Ending 2012. Washington, D.C.: American Wind Energy Association. Anderson, D. A., Tannehill, J. C., Pletcher, R. H., 1984: Computational Fluid Mechanics and Heat Transfer. New York: Hemisphere Publishing Corporation, pp. 599. Wind Turbines Theory - The Betz, Equation and Optimal Rotor Tip Speed Ratio, Magdi Ragheb1 and Adam M. Ragheb2, 1Department of Nuclear, Plasma and Radiological Engineering, 2Department of Aerospace Engineering en.wikipedia.org IEEE PES Wind Plant Collector System Design Working Group National Energy Education Development Project (public domain) University of Tennessee, October 28, 2009 at 11:26 from IEEE Xplore University of Illinois at Urbana-Champaign, 216 Talbot Laboratory, USA www.telosnet.com www.whirlopedia.com www.windenergy.gov Xcel Energy and EnerNex Corp. 2011. Public Service Company of Colorado 2 GW and 3 GW Wind Integration Cost Study. Denver, Colorado: Xcel Energy.

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THANKS FOR YOUR ATTENTION