Your Wind

The most important factor in producing energy from a wind turbine, any wind turbine, is the availability of wind. There are many perceptions of what "windy" means. Before you assume that your conditions are windy enough, you should find out what they actually are in terms of approximate average wind speeds (mph or m/s).

How much wind do you need?

In general, you want average wind speeds of around 12 mph (miles per hour), although in some places Windspire makes sense with lesser wind resources. For example, if you have high electricity rates, or substantial rebates or incentives available to you, it may make sense to place a Windspire in a zone with an average wind speed of only 10 mph. Note that "average wind speed" means the average 24 hours a day, 365 days a year, for an average year (and year-to-year averages can vary by a good deal).

How much wind do you have?

Great question. Here are some suggestions for how to find out:

1. Use visual references. This is cheap, but not very precise. On the other hand, people have a very good inherent ability to estimate many things. A couple of more common scales allow you to estimate wind speeds based on open water and land indicators (Beaufort Scale), and tree deformation (Griggs-Putnam Index). We have put together a useful guide to both scales for you to use.
   
   You should also take note of wind patterns - for example, is it generally windy at one time of day or another? Do the patterns change between seasons? In most places, the answers will be yes.
   
   
2. Use nearby data. Check out data from nearby weather stations. This can be used to determine wind conditions on a given day - a reality check. Some stations may provide average data too.
   
   One BIG caution is, don't rely on any data unless you have checked out the circumstances. Old or poorly calibrated anemometers (wind-measuring devices), poor siting, variable anemometer heights, damage, etc. can cause very erroneous measurements. Also, your local site may have anomolies of its own, so nearby data can only give you a general idea. Some sources for nearby data include:
   
   1. National Climatic Data Center. Search for local stations, and check for wind data. Not all stations have wind data.
   2. Weather Underground: A great source for information from people's personal weather stations across the country. Many include wind data.
   
   
3. Check wind maps. Short of collecting a year's worth of wind data using a sophisticated anemometer, wind maps can give you a good ballpark estimate of your average wind speed. The limitation is that wind maps have a broad resolution, whereas wind can vary greatly from one spot to another on the very same plot of land or within the broad radius of wind zones from maps. Wind varies based on the local geography (hill or valley) and obstructions (forest or open plains). It is important to find a location for your Windspire with unobstructed access to good wind.
   
   
4. Install an anemometer at your proposed site. An anemometer measures wind speeds, and higher end anemometers have a data logging capability. While simple handheld anemometers can be useful, you will get the most accuracy by installing a sophisticated anemometer on a pole to monitor wind over an extended periods of time. However, this is generally more costly than it is worth for a small wind installation (it can cost upwards of $3000 to just test your wind in this way). Some retailers and installation contractors can also offer more detailed wind site testing, and some states offer anemometer loan programs to help with wind power siting.

What about Wind Quality?

Other factors to consider are the direction of wind. If there is a prevailing direction, make sure you choose a location that is not block access to this wind with a building, tree or hill. Other considerations are the quality of the wind, including turbulence and gustiness. The Windspire handles gustiness well, since it does not have to re-align to changing wind directions and it can immediately capture the energy from changing wind speeds. It also handles turbulence relatively well, but extreme turbulence can be harsh on the equipment. Close to the ground winds are generally turbulent, but in some settings turbulence is amplified. If the wind needs to navigate an obstacle course before it reaches your turbine, the turbulence will be much higher than average. 

Another frequent question is about wind tunnel effects in urban settings, or wind amplification over the edges of tall buildings. These conditions do exist, but they have very narrow ranges. For sites in densely built environments or for commercial roof-top installations, we recommend conducting wind modeling to ensure optimal placement of the Windspire.

How far should Windspires be from buildings, trees, or each other?

The following are recommended minimum distances between a Windspire and an object. For the purpose of this table, position references are relative to the prevailing wind direction. For example, "in front" means that the object is blocking the prevailing wind; "behind" means the Windspire gets the benefit of the prevailing wind before it reaches the object. The reason there is still a minimal distance is because objects cause turbulence, even if behind the Windspire. Regardless of the distance recommendations, you should check that the wind speeds are still adequate in the exact spot where you plan to site the Windspire.

Obstacle	Position	Min. Distance
Buildings, trees, etc.	in front of Windspire beside Windspire behind Windspire	100 feet 50 feet 30 feet
Other Windspires	beside each other diagonally from each other 60 degrees behind 75 degrees behind directly behind each other	8 feet 11.2 feet 15.4 feet 26.5 feet 50 feet

For more information, see this guide

What are Wind Classes?

The US Department of Energy has divided winds into classes, as follows:

Classes of Wind Power Density at 10 m (33 ft) Above Ground

Wind Class	Mean Wind Speed (mph)	Mean Wind Speed (m/s)	Power Density (Watts/m2)
1	9.8 or less	4.4 or less	100 or less
2	11.5	5.1	100-150
3	12.5	5.6	150-200
4	13.4	6.0	200-250
5	14.3	6.4	250-300
6	15.7	7.0	300-400
7	21.1 or more	9.4 or more	400-1000
Notes: These calculations are based on standard temperature and pressure, and mean wind speeds are the long-term average (the average taken over a full year, from data from many years). Mean wind speed is based on Rayleigh speed distribution of equivalent mean wind power density.