Doing Your Research: Comparing Wind Turbines

There is an active effort underway to set standards and certify small wind turbines, but unfortunately right now there is no standard for rating power. Until this system is in place (around 2010), power ratings provided by small wind manufacturers should be viewed with caution. Without standards, manufacturers are free to rate their turbines at different wind speeds, so it is very difficult to compare one with another. Some manufacturers choose unusually high wind speeds to get a high power rating - however the rating is meaningless, since the wind rarely reaches such high speeds in most locations. Rated wind speeds should typically be in the range of 21-26 mph (10-12 m/s). Although in most locations the wind only gusts up to these speeds from time to time, this defined wind speed creates a simple means of comparing turbines.

The tested power output of some wind turbines can be substantially lower than the rated power output. The best way to evaluate different wind turbines is to look for published independent field test data. The testing should provide the turbine power curve (power output versus wind speed) for the complete system, not just for one component. There are several credible testing facilities for small wind turbines. The Windspire has been extensively tested by Windward Engineering, with future tests planned at Appalachian State's North Carolina Wind Energy Test Site, so you can be assured that the power curves and ratings we publish are from real-world testing.
 
In the end, what really matters is the amount of energy that a wind turbine, or other renewable energy source, can provide to your home or business over the course of a year. Rated power can provide a general idea, but it does not tell about the shape of the power curve over the wind speeds that are most relevant to your area. Most reputable turbine manufacturers publish independently tested power curves, and they should also be able to tell you how much energy you can reasonably expect to produce for your average wind speed.