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Windfarms are now popping up and selling electricity to the grid at around 4 cents per KWH and costs are projected to lower. Modern turbines, such as those pictured below, can achieve efficiencies of up to 40%.
Windfarms containing up to 5,000 individual wind turbines have now been created such as this facility in California (near Stockton).
Of course, the idea of a windmill as a device
to turn a wheel has been around for centuries
which proliferated in Holland (a flat, windy place where Don Quixote hung out).
In the 1920's and 1930's the rotary style windmill, shown belown, became a common mixture on farms in the Midwest as a means of running a water pump
Recently, aviation technology has advanced windmill design quite a bit to produce todays's modern wind turbines:
The concept of the windfarm is now being put into practice:
Power per square meter goes as (wind velocity)3 requires good energy storage for later use.
What makes the wind blow?
Air pressure represents the amount of atmosphere that is pressing down on the surface of the earth at some point, as shown here:
Pressure differences yield wind (bulk motion of the air)
Local topography (mountains) can enhance
or restrict the natural wind flow
downslope winds off of mountain ranges represent ideal
locations for wind turbines as do narrow mountain passes
and river canyons such as
Hood River
Large scale patterns are thus setup by the interplay of the locations of high and low pressure systems and the topology of the land leading to places in the US which are on average significantly windier than other locations. The overall capacity, in MegaWatts, in the US is large:
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:
In essence, as shown in the above animation, the power on the windmill is proportional to the kinetic energy transfer per unit time as well as the density of the air (which is represent by the mass of the air above).
For average atmospheric conditions of density and moisture contant:
(Don't memorize .0006 V3; you will never need to know the 0.0006 part!)
How much energy is there in a 20 mph wind?
20 mph wind =10 m/s
.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 at our latitude.
The above calculation is known as a scaling calculation; you simply need to scale the original conditions to the final conditions. You only need to know the v3 to do this.
Windmill Efficiency
Windmills can not operate at 100% efficiency because the structure itself
impedes the flow of the wind. The structure also exerts back pressure
on the turbine blades as they act like an air foil (a wing on an airplane).
In most all cases, the efficiency of the wind turbine depends on the
actual wind speed. For the three blade design the efficiency curve
looks like this:
Because the power goes as v3, there is no real need to optimize design for highest efficiency at highest windspeed because the power capacity in the wind will greatly exceed that which can be obtained by the generator.
Rotary type windmills have high torque and are useful for pumping water. High torque means efficient operation at low wind speeds.
High speed propeller types have low torque and are most efficient at high
rotational velocities useful for generation of electricity
To Generate 10,000 KWH annual then from a 20 mph wind that blows 10% of the time
Wind Energy can be competitively priced:
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: