Wind Turbine Primer

1
Wind Turbine Primer
K. D. Visser Department of Mechanical and
Aeronautical Engineering Clarkson University
2
Contents

• Why Wind?
• A Bit of History
• Energy In the Wind
• Energy From the Wind

3
Why Wind?

• Renewable Energy Resource
• Embedded energy of construction is paidback in
  approximately 3 months
• 5 of World Population Consumes 43 of World
  Energy
• Reduce Emissions
• Interesting Problem

4
US Wind Distribution

• Annual Average Wind Resource Estimates in the
  Contiguous United States
  
• Battelle Wind Energy Resource Atlas

5
Wind Energy in the US

• U.S. Total Installed Wind Energy Capacity
  1883.01 MW (May 14, 1999)
• U.S. Planned New Generating Capacity 858.72 MW
  ( May 18, 1999)

6
U.S. Installed Capacity (Megawatts), 1981-1999
7
History Early Mills
The earliest-known design is the vertical axis
drag driven system developed in Persia (500-900
A.D) known as the Panemone . Believed that the
windmill was invented in China more than 2000
years ago , but earliest actual documentation of
a Chinese windmill was in 1219 A.D The first
windmills to appear in western Europe were of the
horizontal-axis configuration. As early as 1390,
the Dutch set out to refine the tower mill
design, which had appeared somewhat earlier along
the Mediterranean Sea

• See http//telosnet.com/wind/ for more history

8
History Advancements

• Perfecting the windmill took 500 years.
• Development of major features crucial to the
  performance of modern wind turbine blades
• camber along the leading edge,
• placement of the blade spar at the quarter chord
  position
• center of gravity at the same 1/4 chord position
• nonlinear twist of the blade from root to tip
  (Drees, 1977).

• Note leading edge airfoil

• 1850 - 1970 6,000,000 mostly small (1
  horsepower or less) mechanical output wind
  machines installed in U.S. primarily for
  water-pumping
• Most important refinement of the American
  fan-type windmill was the development of steel
  blades in 1870

9
Turbine Configurations

• Class 1 Drag Driven
• Class II Lift Driven

10
Turbine Aerodynamics

• Lift driven device has potential for 78 more
  power extraction than drag driven

11
Large Scale Projects
Green Mountain Powers 6.1 MW Searsburg Facility

• 11 Zond Z-40FS turbines
• 40-meter-tall tubular steel tower
• constant speed of 29 rpm
• 550 kW at 29
• Power for 1500 homes annually

12
Large Scale Projects
Vision Quest Windelectric Inc.

• Vestas Wind Systems A/S, Denmark
• Type Horizontal axis, upwind, pitch
• Regulated 600 kilowatt peak output, 1.75
  million kWh/yr per turbine to 300 homes use

13
Small Scale Turbines

• Bergey BWC 1500
• modern small 1500W wind turbine designed for high
  reliability, low maintenance, and automatic
  operation in adverse weather conditions.
• Type Horizontal axis, upwind, pitch
• 1.5 kilowatt peak output,

14
Power for Home

• What size turbine would I need for my home?
• Homes use approximately 9,400 kilowatt-hours
  (kWh) of electricity per year (about 780 kWh per
  month). Depending upon the average wind speed in
  the area, a wind turbine rated in the range of 5
  to 15 kilowatts would be required to make a
  significant contribution to meet this demand.

• Turbine Rating 900W
  3000W 4500W
• Output_at_12mph 109 kWh/month 507 kWh/month 543
  kWh/month
• Output_at_18mph 264 kWh/month 1091 kWh/month 1321
  kWh/month
• System Price 3090 9490
  11880

15
Power for Home

• Who should consider buying a wind turbine?
• The economics of a wind system are very sensitive
  to the average wind speed in the area, and to a
  lesser extent, the cost of purchasing
  electricity. As a general rule of thumb, if
  economics are a concern, a turbine owner should
  have at least a 10 mph average wind speed and be
  paying at least 10 cents/kWh for electricity.
• Residential wind turbines have been installed in
  at least 47 of the 50 states, but the majority of
  the units have been installed in the Northeast
  and the Midwest.

16
Small Turbine Power

• Rated Power
• PMG
• AC to DC to AC

17
Energy in the Wind

• Kinetic energy 0.5 mV2
• where
• m mass
• V velocity
• Power in the area swept by the wind turbine
  rotor
• P 0.5 r A V3
  
• where
• P power in watts
  (746 watts 1 hp)
• r air density
• A rotor swept area,
  exposed to the wind

18
Energy in the Wind

• Wind Turbine Power
• P 0.5 Cp r A V3 Ng Nb
• where
• Cp Coefficient of performance (.59 Betz limit
  is the maximum thoretically possible, .35
  currently for a good design)
• Ng generator efficiency (50 for car
  alternator, 80 or possibly more for a pmg or
  grid-connected induction generator)
• Nb gearbox/bearings efficiency (depends, could
  be as high as 95 if good)

19
Turbine Efficiency

• h Pout/Pin Cp Ng Nb

20
Energy from the Wind

• Betz Limit
• Simple Momentum Considerations
• Equate Power Extracted to ?KE per unit time
• Differentiate wrt velocity and set zero
• Result Vdownstream 1/3 Vupstream
• Speed at rotor 2/3 Vupstream

Cp max 16/27 of maximum power in windstream
21
Energy from the Wind

• Betz Limit(ations)
• Uniform velocity over swept area
• No mingling of slipstream
• No radial flow component, tip losses
• 8 number of frictionless thin blades - finite
  blades with friction reduces this optimum
• Better to use blade element theory, but this does
  give an upper bounds.

22
More Info

• http//www.clarkson.edu/visser/wind/windlinks.htm
  l
• http//www.windpower.org/core.htm