Wind Turbines are a popular and cost effective choice for producing electricity provided the location has sufficient land and good wind speed. The majority of suburban lots are not good wind sites due to structural wind blockages and most local zoning commissions won’t approve it. The perfect case scenario for utilizing a wind turbine is in an open field or on a hill top. Wind turbines are most often used on farms and areas where power lines are a considerable distance away.
Government wind charts can be a starting point, but unless you are positive you have sufficient wind, you should have a wind study done at the location. An anemometer will be placed at the expected turbine height for a period of time and it will accurately track the wind speeds. This information is critical since it tells the whole story; maximum, frequency of occurrence, and average wind speed over the seasons. This data is crucial to finding a wind turbine that fits your situation.
Turbines have a kilowatt rating but there is no standard that allows fair comparisons between manufactures. While a turbine may say it starts at a wind speed as low as 4 mph, substantial generation does not start until the wind speed is over 10 mph. A turbine rating gives a wind speed and kilowatt output. Only at the stated wind speed do you get the rated output (link to wind chart page). If the wind speed is less than the rating, the output drops exponentially. It is wise to carefully review the units wind graph and compare it to your average wind speeds.
Traditional wind turbines, often called windmills, have 3 long propeller type blades and are mounted 30+ feet in the air. The double helix design looks like vertical twisted ribbons. It has no arms. You can see it in action at www.Tangarie.com. Vertical turbines do not strobe, are quiet, and are “bird safe” since they are seen as solid objects by wildlife.
Especially with regular windmills, it is very important to install the unit in a clear open area. Putting a windmill between, or close to buildings or trees means the wind flow is blocked. “Clean wind” blows in one direction. When an object disrupts this pattern the turbulence impacts the wind turbine. Sometimes this can be used as an advantage. As seen in the link, the small Tangarie GALE 1 can be roof mounted and the wind blowing over the roof actually increases the turbines operation. A standard rule is the turbine motor should be 30ft above anything that is within a 500ft radius; more is better.
Tower height greatly impacts performance since usually the higher up, the greater the wind speed. Unfortunately towers are expensive and building codes may restrict the height. Unlike PV, you cannot “add on” to a wind turbine. Picking the right turbine and the correct tower size to start is critically important.
One note about roof mounted turbines; they can cause vibration noise and their output is normally quite low. One feasible use is if your turbine is just a supplement to PV and you have a garage or barn to mount a small unit.
Wind turbines are excellent complement to a photovoltaic (PV) electric system. Winds increase in stormy weather, and still blow at night, which are the times when a PV panels output drops.
According to Home Power magazine (June 2009, a great 9 page story on wind) some manufactures are “wildly optimistic in describing their product performance”. Purchasing a wind turbine, and making sure you have a good site, is a buyer beware proposition at times. We will be happy to consult with you as you “do your homework” on the benefits of Wind Energy.
The US government publishes wind charts base on location. Two good links are:
- NCDC Average Wind Speed Chart
- Wind Energy Resource Atlas of the United States
While they can be a good starting point, relying solely on their data could prove to be a very costly mistake. If the chart shows you are in a good wind area, and you consistently note, through all seasons, high average wind speeds then you may want to skip having a wind study done. Mountain top ridges and islands often have unquestionable winds. For most locations a 6-12 month wind study should be performed.
The output for wind turbines increases exponentially with wind speed. In simple terms this means if you get X kilowatts at 20mph, at 10mph you will not get half of X. The power available in the wind is related to the cube of wind speed/velocity (V3 ). Doubling the wind speed gives 8 times the energy. (20mph wind: 20x20x20=8,000 vs 10x10x10=1,000)
Some windmills do well at 20mph and then the output curve flattens out as the wind speed increases. Some perform best in the 25-30mph ranges but not at lower speeds. A wind study will help you analyze your site and determine the right turbine for the location.
Franklin, TN Wind Turbines
