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.
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