Choosing a small wind turbine model

Wind turbines come in many different makes and models. Spending a little extra time while choosing a model will improve economics of your project as well as make it much more successful in the long run.

Before choosing a turbine you should figure out if the electricity produced will be consumed completely on site, if you want to sell excess energy back to the utility company or if you prefer to be off the grid. The turbine model you choose will be greatly affected by where the electricity will ultimately be used and what compensation you will receive from selling electricity back to the utility. If your facility will be net metered or off the grid a load analysis for your home should be done to determine your monthly electricity usage, for net-metering, or your peaking load and daily usage for off grid applications.

Turbine manufacturers have published power curves that estimate the monthly output for their turbines based on average wind speed at the site and the Rayleigh distribution of wind speeds around that average.

Home Power Magazine is a good resource for comparison of small wind turbines. See the following articles on their website: "Apples & Oranges: Choosing a Home-Sized Wind Generator" and "Wind Generator Buyer's Guide."

Vertical Axis Wind Turbines (VAWTs)

Vertical axis wind turbines (they look like egg beaters) have been around longer than horizontal axis wind turbines (the most common type of wind turbine). Some vertical axis turbines have been very effective at producing energy. The concern for consumers is that many manufacturers of vertical axis wind turbines make inflated or fraudulent claims about the technology.

No matter what anyone says, vertical axis wind turbines still need to be placed on tall towers for ground clearance. Wind turbines are placed on tall towers because the wind speeds are higher and there is less turbulence higher above the ground, producing greater energy yield.

Some claim that vertical axis wind turbines are more efficient and operate in lower wind speeds than horizontal axis wind turbines. Modern horizontal axis wind turbines are actually better at capturing the wind than vertical axis machines given the same amount of swept area (which is the size of the circle traced by the outside tip of the blades). This is because vertical axis machines always have at least one blade traveling into the wind creating additional drag on the machine as it spins. Additionally, neither horizontal nor vertical axis of machines will produce much energy in low wind speeds because there is little energy to capture from low-speed wind.

Vertical axis wind turbines should not be mounted on rooftops, even if that makes them easy to install. Buildings and other obstructions will create turbulence in the wind as well as decrease its speed, significantly reducing the wind turbine’s ability to produce energy, even for a vertical axis turbine.

For further information about Vertical Axis Wind Turbines:

• Robert Preus – Thoughts on VAWTs: Vertical Axis Wind Generator Perspectives from issue 104 of Home Power magazine
• Mick Sagrillo – The Myths & Mysticism of Vertical Axis Wind Turbines

Remanufactured Turbines

Buyers should beware of used, refurbished, or remanufactured machines. Even though these machines may initially be less expensive that comparable new machines, the initial savings can be negated very quickly by costly repairs from a machine that is nearing the end of its life time. Before purchasing a used machine read through this article by Mick Sagrillo from the November 2002 American Wind Energy Association newsletter about buying used wind equipment.

Choosing a Tower

Small wind system manufacturers often give you several different tower options to best match the economic, maintenance and space needs of your project.

There are four basic types of tower options for home and farm sized turbines: guyed monopole, guyed lattice, (self-supporting) lattice and (self-supporting) monopole.