Wind Turbines

- convert the wind's kinetic energy into electricity power through a mechanical means. Wind technology is adaptable and versatile and can be one of the most cost-competitive renewable energy technologies when produced on a large scale (wind farm). Smaller systems work very well when combined with a solar array, as cloudy days are often windy and a hot sunny day may not contain a steady breeze.

How much power can we get from the wind?

Warning: a little bit of math follows - not to hard, bear with us. We will give examples for 2 small turbines, one with 2 foot blades and one with 4 foot blades.

Power AVAILABLE in the wind = .5 x air density x swept area x (wind velocity cubed)

Air density = 1.23 kg per cubic meter at sea level. Swept area = pi x r squared. Our 2 foot blades = 0.609m, 4 ft = 1.219m. 10 mph = 4.4704 m/s, 20 mph = 8.9408 m/s.

How much power is in the wind: 2 ft blade, 10 mph winds = .5 x 1.23 x 3.14x0.609squared x4.4704 cubed

= .5 x 1.23 x 1.159 x 89.338 = 63.7 watts

With 4 foot blades and 10 mph winds = .5 x 1.23 x 4.666 x 89.338 = 256 watts

With 4 foot blades and 20 mph winds = .5 x 1.23 x 4.666 x 714.708 = 2051 watts

That's the MAXIMUM power in the wind. However, it's impossible to harvest ALL the power. The Betz Limit tells us that the maximum percentage of power we can harvest from the wind is 59.26%.

Thus our maximum power from these turbines would be:

2 ft blades, 10 mph wind = 37.7 watts

4 ft blades, 10 mph wind = 152 watts

4 ft blades, 20 mph wind = 1,215 watts

A very well built DIY horizontal axis wind turbine would not likely get more than 65% of the above numbers. Keep these numbers in mind when a sales person starts to tell you their small wind turbine will meet all your needs....

How Does a Wind Turbine Work?

Wind turbines operate on a simple principle. The energy in the wind turns two or three propeller-like blades around a rotor. The rotor is connected to the main shaft, which spins a generator to create electricity.

Wind turbines are mounted on a tower to capture the most energy. At 100 feet (30 meters) or more above ground, they can take advantage of faster and less turbulent wind.

Wind turbines can be used to produce electricity for a single home or building, or they can be connected to an electricity grid (shown here) for more widespread electricity distribution.

Types of Turbines

Modern wind turbines fall into two basic groups: the horizontal-axis variety, as shown in the photo, and the vertical-axis design, like the eggbeater-style Darrieus model, named after its French inventor.

Horizontal-axis wind turbines

- typically either have two or three blades. These three-bladed wind turbines are operated "upwind", with the blades facing into the wind.

Utility-scale turbines range in size from 100 kilowatts to as large as several megawatts. Larger turbines are grouped together into wind farms, which provide bulk power to the electrical grid.

Single small turbines, from 400 watts to 100 kilowatts, are used for homes, farms, telecommunications dishes, or water pumping. Small turbines are sometimes used in connection with diesel generators, batteries, and photovoltaic systems. These systems are called hybrid wind systems and are typically used in remote, off-grid locations, where a connection to the utility grid is not available.