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Small Wind

Selecting Turbine Model & Tower Height

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There are a number of buying guides to assist consumers in purchasing a wind system. You might consider using HomePower Magazine’s Annual Buying Guide. Until the Small Wind Certification Council data is more robust, this is one of the few sources that provide side-by-side comparisons of wind turbines.

Assessing Information Provided

Information will vary by manufacturer until testing standards become more common. It is a good policy to ask questions about the turbine information and power production estimates.

Questions to Ask About a Turbine

Here are a few questions to ask an installer or manufacturer:

Capacity Factors

The use of capacity factors in discussing small wind installation is not considered appropriate by some experts. (Gipe, 2006). However, many consumers find that their manufacturer or installer will quote capacity factors during the sales process. You should instead ask for Annual Energy Output calculations. Capacity factor is a ratio of the actual output of the turbine over the amount of output that it could have if it operated at full capacity 100 percent of the time. There are a variety of reasons that this measure is not helpful. However, if you are quoted a capacity factor, be aware that capacity factors in small wind range from nine to 22 percent. A higher number is better, but capacity factors above 22 percent are not realistic for small wind. Capacity factors of 30 to 45 percent and higher are typical for commercial machines of 1.5 to 2.5 megawatts, but are not possible for small wind turbines.

Site Visit

Visit with a current owner of the turbine model you are considering. Your manufacturer or dealer should be able to provide you with a list of current owners. Ask about their experience with the turbine. How much power is generated by the turbine and how did that compare with the estimates provided at the time of installation? Make time to visit an installed system. A site visit will help you create realistic expectations about wind turbine ownership. It will also give you a chance to hear the noise generated and to see the turbine footprint and visual impact to the property.

Selecting Tower Height

The tower should be tall enough for the bottom edge of the turbine blades to be at least 30 feet above the tallest obstacle within 500 feet. Many small wind manufacturers recommend a minimum tower height of 65 feet (20 meters). To better understand the importance of tower height in capturing the wind resource, refer to Step 3: Assessing Your Wind Resource.

Here are a few things to keep in mind on tower height:

What about…?

Here are common questions with regard to using short towers:

References

Association, A. W. (2008). Windletter. Retrieved December 2010, from www.awea.org: http://www.renewwisconsin.org/wind/Toolbox-Homeowners/Questions%20Any%20Manufacturers%20Should%20Answer.pdf

California Energy Comission Renewable Energy Program. (2002, February). Buying a Small Wind Electrical System. Retrieved April 2010, from Buying a Small Wind Electrical System Publication Download: http://www.consumerenergycenter.org/erprebate/documents/2002-05-01_WIND_GUIDE.PDF

Gipe, P. (2006, January 23). Wind-Works.org. Retrieved April 14, 2011, from Generator Ratings and Capacity Factors: Why You Should Avoid Them: http://www.wind-works.org/articles/generatorratingandcapacityfactors.html

NREL. (2005). US Small Wind Consumer’s Guide. Boulder: NREL.

NREL, Rebecca Meadows. (2009, December 7). Basics of Farm/Residential Small Wind Turbines. Presentation . Great Falls, MT: NREL.

Sagrillo, M. (2002, August & September). Apples and Oranges 2002: Choosing a Home-Sized Wind Generator. Home Power
Magazine, pp. 50-66.

Wind Works: Paul Gipe. (2000, Summer). Testing Power Curves of Small Wind Turbines.