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Height Matters

heights matters     The problem facing a prospective wind turbine site should now be obvious: You need to minimize turbulence and take advantage of the power of incremental wind speed by getting the turbine higher into the wind. The solution is pretty obvious: Mount your turbine on a tall tower. If ground-dwellers afraid of heights don’t like to hear that message, they shouldn’t consider a wind turbine for their electricity.

How tall does the tower need to be? The first rule used in the small wind industry for determining minimum tower height is that the entire rotor of the wind turbine must be at least 30 feet higher than any obstacles within 500 feet of the tower. This rule is based on several facts:

.   Wind speed increases with height above the ground.

.   Turbulent winds have little extractable energy.

.   Increased vertical separation between ground clutter (trees and buildings) and the wind turbine rotor means that the rotor is moved out of chaotic turbulent winds and into clean laminar wind flow with more extractable energy.

Wind turbines are presumably installed for two to three decades of service, during which time the trees in the area will probably grow taller. As such, we also need to consider the mature tree height, not the current tree height, when determining tower height.

turbine usless

This wind turbine was installed in 1982 using the 30-foot rule for fixed obstacles—tree growth was not accounted for. In the last three decades, the trees have grown tall enough to render the wind turbine useless.

So, we need to modify the 30-foot rule to take into consideration tree growth over the life of the wind system. It now states: The entire rotor of the wind turbine must be at least 30 feet higher than any obstacles within 500 feet of the tower, or the mature tree height or tree line in the area, whichever is higher.

Keep in mind that the 30-foot rule with consideration for mature tree height dictates the minimum tower height for your site. Installing a taller tower reduces turbulence even further, while getting your turbine higher into the wind profile. All of this will result in more electricity production over the life of your wind        system. Don’t cut corners by scrimping and installing a short tower —you’ll be sacrificing long-term performance.

 

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