Energy from the Wind:

Wind is the response of the atmosphere to uneven heating conditions. Local topography (mountains) can enhance or restrict the natural wind flow.

While wind is certainly a renewable energy source, it is also an erratic one. Energy storage is probably more critical for wind power than for any other form of alternative energy.

Basics of Wind Energy:

• Kinetic Energy of wind is: 1/2 * mass * velocity * velocity
• momentum in the wind = mass x velocity
• Power per unit area = KE * momentum --> MV² *MV
• So Power that can be extracted from the wind goes as velocity cubed (V³)
• 27 times more power is in a wind blowing at 60 mph than one blowing at 20 mph

For average atmospheric conditions of density and moisture contant:

Power per sq. meter = .0006 V³

• velocity measured in meters per second
• Power then measured in KILOwatts
• 1 meter per second is approximately 2 mph
• 20 mph wind =10 m/s --> Power generated equals

  .0006 * 10³ = .0006 * 1000 = .6 KILO watts per square meter
  which is 600 watts per square meter
  this is identical to average solar power per square meter

Windmills can not operate at 100% efficiency because the structure itself impedes the flow of the wind

• Theoretical maximum efficiency is 59%
• Picaresque Dutch Windmill (4=arms) = 16%
• Rotary, multiblade = 30%
• High speed propeller (vertical) = 42%

Clearly, wind power is a highly variable source and hence energy storage is crucial.

Rotary type windmills have high torque and are useful for pumping water

High speed propeller types have low torque and are most efficient at high rotational velocities --> useful for generation of electricity

Example calculation:

• Windmill efficiency = 42%
• average wind speed = 10 m/s (20 mph)
• Power = 0.0006 x 0.42 x 1000 = 250 Watts per square meter
• Electricity generated is then .25 KWH per sq. meter
• If wind blows 24 hours per day then annual electricity generated would be about 2200 KWH per sq. meter

• But, on average, the wind velocity is only this high about 10% of the time
• typical annual yield is therefore 200-250 KWH per sq. meter

To Generate 10,000 KWH annual then from a 20 mph wind that blows 10% of the time

• windmill area = 10,000 KWH/220 KHW per sq. meter = 45 sq meters
• This is a circular disk of diameter about 8 meters
• This is not completely out of the question for some homes
• Even a small windmill (2 meters) can be effective:
  • 20 mph 10% of the time --> 2500 KWH annually
  • 40 mph 10% of the time --> 20000 KWH annually
  • 20 mph 50% of the time --> 12500 KWH annually
  • 4 small windmills at 20 mph 10% of the time --> 10000 KWH annually

Wind Energy can be competitively priced:

• Wind turbine technology has steadily improved
• Typical capacity for a single unit is now 250-500 KW
• Relatively low capital costs; very low operating costs
  Price Comparison from a recent study . Levelized Costs: (includes start-up costs)
  • Wind: 4.8 cents per KWH
  • Coal: 6.2
  • Photovoltaics: 16.0
  • Advanced Gas Turbine: 4.6

Current Grid Connected Wind Power:

    Country/region          MW Installed
        ------------------------------------
        United States   -       1700
        Denmark         -       520
        Germany         -       330
        United Kingdom  -       145
        Netherlands     -       132
        Spain           -       55
        Greece          -       35
        Italy           -       10
        Other OECD      -       70
        India           -       50
        China           -       25

Some aggressive goals for wind power:

• to install 10,000 MW of capacity in the U.S.;
• to build a $4 billion domestic wind industry capable of delivering 3,000 MW annually;
• to create tens of thousands of new, long-term, skilled jobs;
• to achieve levelized costs below four cents per kilowatt-hour;
• to make wind power a major option in achieving the nations global climate change objectives; and
• to make the U.S. wind energy industry the worlds technology leader and lowest cost supplier.

Capacity in the US is Large

• Contour Map

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The Electronic Universe Project

e-mail: nuts@moo.uoregon.edu