Assessing Your Wind Resource

In this article, I am going to discuss the method to determine the amount of wind available to you and when it is available.  From this information, you can select a wind turbine that will produce enough electricity to meet your needs. 

An assessment of available wind resources can be made using one or a combination of techniques. Professional small wind site assessors, however, rely principally on state wind maps and online sources.   

State Wind Maps   

One of the best and easiest ways to assess the wind resources in a region is to  consult a state wind map. State wind maps list average annual wind speed in meters per second and miles per hour. Unfortunately, wind speed estimates on the  map are reported at 165 and 195 feet (50 or 60 meters) above the surface of the  ground.   

Most states have good wind maps. You can locate your state’s wind map at the  Wind Powering America website. Another  great source AWS Truewind prepared most of the Wind  Powering America maps.

While wind maps are an excellent source of information for your area, they do  have some limitations. One of them is resolution. In some areas, like the plains of  western Kansas, wind maps show uniform wind speeds over large areas. If you live  in one of those areas, the map will give you a pretty accurate idea of average wind  speed.

However, wind speeds over more complex topography can vary considerably over short distances. The resolution of the maps isn’t good enough to pinpoint an exact location.

The state wind map shows three different classes of winds in his  area. Which one applies depends on the specific location. A neighbor a tenth of a  mile away in a valley may have very little wind, while a neighbor perched on top of a  mountain will have a great deal of wind. In general, the more complex the terrain,  the less accurate the wind maps are.   

When assessing wind resources, remember that hills, cliffs, forests and buildings can reduce wind speed. However, some types of hills and cliffs can magnify  winds. It depends on where you’re located. In most cases,  though, wind maps are adequate for siting a small wind turbine.

That said, it’s always a good idea to assess the topography, vegetative cover, and ground clutter  when estimating average annual wind speed. If you live in an open field on top of a  knoll, your wind resource may be significantly higher than a neighbor who lives a  mile away in a tree-covered valley.   

Online Databanks   

While state wind maps are an excellent source of information, a few states have not  invested in the best mapping technology. Because of this, some professional small  wind site assessors perform small wind site analyses using a very extensive online  database developed by NASA on the website, Surface Meteorology and Solar Energy. 

This site provides a wealth of data on wind energy, including tables that show  both the monthly and annual average wind direction and average wind speed at  sites throughout the world. The site is pretty user friendly, but you will need to start  by setting up a free account. 

Like wind maps, NASA data provides good information, but you should still assess your site very carefully, especially in complex topography. If your site is in a  valley or surrounded by trees or buildings, the wind speed at the hub height may  be significantly lower than the satellite data suggests.   

When in doubt, hire a professional wind site assessor to analyze your site and  make recommendations for tower/turbine placement and minimum acceptable  tower height.

How Much Electricity Will a Wind Turbine Produce? 

Once you’ve determined the average wind speed at a site, it is time to determine  how much electricity a wind generator could produce at the proposed tower height  — and therefore whether it can meet all your needs or what percentage of your  needs it will satisfy. This step is fairly easy. 

Let’s assume that the average wind speed at a site (at hub height) is 12 miles per  hour. Let’s also assume that your load analysis, after efficiency measures have  been implemented, indicates you’ll need, on average, 900 kilowatt-hours per  month, or 10,800 per year.

In the 12 mile-per-hour column, you’ll discover two  wind turbines that match your electrical requirements, the WT6000 (by Proven)  and BWC (Bergey Wind Power’s) XL-S. If the wind speed at your site is 13 miles per  hour, an Endurance wind turbine would meet your needs. The Proven WT 6000  and the Bergey XL-S would produce more than you need.   

You can also obtain annual energy output data directly from wind turbine manufacturers. While this data is useful, manufacturers tend to overstate the electric  production of their turbines. As a result, we recommend derating their estimated  outputs by 20 percent — just to be conservative.

Once you’ve found the wind turbine that meets your needs, you need to be sure  it is the appropriate type of turbine. That is, you need to be sure you select a grid-  tied turbine or battery-based turbine, depending on the type of system you are  planning on installing.