4 Tips for Buying a Home Wind Turbine

Jun 26, 2011
Angelika Ortlepp

1.5 kW Wind Turbine on 50 ft Tower - Angelika Ortlepp

It seems it's always windy in your yard! Wouldn't it be a great idea to buy a wind turbine and harness some of that energy? Let's look at what's involved.

Picture this. You wake up to the sound of wind and rain battering against the house - a lousy day for going to the lake. But - for you, there is something good about it. You look out the window and see your wind turbine blades disappear in a whirling disc. You are getting power - and lots of it! This is what people interested in setting up a wind turbine dream about - free power from the seemingly ever-present, and usually unwelcome, wind.

A home wind turbine can be a great investment for producing your own electricity. But is it a good investment for you? To be cost effective, a wind turbine needs the right conditions. Before buying a turbine, look at these 4 key factors that determine if a turbine will pay for itself at your site.

1. Energy Production: Understanding Power Output Charts

Wind turbines are listed by the power that they produce at a rated wind speed. For example, a 3.5 kW turbine will produce 3.5 kW at its rated wind speed of 25 mph. However, this number does not tell you how much energy, in kWh, the turbine will produce. Manufacturers provide this information in charts or graphs of Energy Production at various average wind speeds

Find the average wind speed for your area from the closest weather station and find the corresponding production number on the graph or chart. Notice that when the wind speed doubles, the output goes up 8 times. For example, if your output is 1000 kWh per year at 7 mph it will be 8000 kWh at 14 mph. This is important because it means that if you do not have a very high average wind speed in your area you will get very little production and a wind turbine may not be a good choice for you.

All wind turbines also have a cut-in wind speed below which they produce no energy. This cut-in speed is usually around 7 mph. You generally need at an average wind speed of at least 11 mph to make the cost of a turbine worthwhile.

2. Site Selection: The Effect of Terrain on Power Production

The production listed on the manufacturer's chart applies toideal conditions - a flat area (like an airport) with no obstructions and ideal weather conditions at sea level. But turbine production is strongly affected by features in the surrounding terrain - hills, trees, brush and buildings. These can drastically reduce the production of the wind turbine, as much as 20 - 50% or more, because of the turbulence that they create. Your farmyard shelterbelt, for example, also shelters the turbine from the wind.

Less obvious factors such as air density and tower height also have a significant impact on production. For any site, even one that looks close to ideal, you should assume a maximum of 85% of the rated production. For most sites 60 - 80% is a more realistic estimate. If your site is heavily treed, it probably will not be suitable for a wind turbine because you would need a prohibitively high tower to rise above the turbulence created by the trees.

3. Tower Height: Rising Above the Turbulence

A wind turbine should be mounted on a tower that rises at least 30 feet above any surrounding obstruction - this includes your house and any trees in your yard. Below that air turbulence seriously reduces the output of the turbine. Output also increases with height - the higher the tower, the more power the turbine will produce.

It is economical to install a taller tower since the basic costs, such as foundations and labour, would not rise significantly for a 70 foot tower over a 40 foot tower, for example. So it would seem that the higher the tower, the better. However, the biggest factor limiting the height is keeping it convenient to raise and lower for maintenance and repair.

4. Maintenance and Repair: Part of the Process

Wind turbines have moving parts that must often operate in very harsh conditions. Extreme temperatures, sleet, ice and snow, sandstorms - it is a challenge to design a machine to withstand such conditions. So it is not surprising that maintenance and repair are part of the reality facing a wind turbine owner. Worn bearings and brake malfunctions are some of the issues that you may encounter. These are repairs for which you would normally have to contact the supplier.

Statistics have shown that wind turbines tend to have down times of about 20%, so you should only count on your turbine producing about 80% of the time. This further reduces your expected annual power production. I have owned two different brands of turbines and have had to lower the tower for repairs on average at least once a year.

Is a wind turbine a good choice for you? If you have a high average wind speed in your area and few trees or other obstructions to create turbulence it can be a good economical choice. If you also have lots of sunshine, a solar power system - which requires no maintenance and has a longer lifetime - may be a better choice. A combined system, with both solar and wind power, takes advantage of both resources.