Towers

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Another vital component of all wind systems is the tower, discussed in more detail in Chapter 6. Residential wind generator towers come in three varieties: (1) freestanding, (2) fixed guyed, and (3) tilt-up (Figure 3.2).

Freestanding towers may be either monopoles or lattice structures. Freestanding monopole towers consist of high-strength hollow tubular steel like that used for streetlight poles. Lattice towers consist of tubular steel pipe or flat-metal steel bolted or welded together to form a lattice structure like the Eiffel Tower or transmission towers used for high-voltage transmission lines.

Freestanding towers must be strong enough to support the weight of the wind turbine, but more importantly, they need to be strong enough to withstand the forces of the wind acting on the turbine and the tower itself. Towers must have a large foundation



Fig. 3.2: Tower Types. Three types of towers in use today: (a) freestanding, (b) fixed guyed, and (c) tilt-up.

to counteract the tremendous forces applied by the wind, forces that could easily topple a weak or poorly anchored tower. Large amounts of steel and concrete are required to accomplish this task. This makes freestanding towers the most expensive tower option.

The second tower type is the fixed guyed tower (Figure 3.2b). Guyed towers may be made of high-strength steel pipe or may be lattice structures supported by high-strength steel cables, known as guy cables or guy wires. Guy cables extend from anchors in the ground to tower attachment points. They stiffen towers so they don’t buckle and hold them in place so they don’t lean or fall over.

Because guy cables strengthen and stabilize the tower, less steel is required for them than in freestanding towers. Guy cables are attached to the tower every 20 to 30 feet, although wider spacing is also possible. A 120-foot-tall tower may require four sets of cables.

The third type of tower is the tilt-up tower, so named because it can be raised and lowered — tilted up and down. This makes it possible to lower a turbine so it can be inspected, maintained and repaired at ground level. Tilt-up towers typically consist of high-strength steel pipe or a lattice structure. Both are supported by guy cables.

Towers are as important as the wind turbine itself. Unfortunately, many wind turbines are mounted on towers that are much too short. This occurs out of ignorance and misguided frugality. Installing a turbine on a short tower is a common and costly mistake. Properly sized towers place wind turbines in the path of more powerful winds and raise turbines above turbulence created by ground clutter, which severely diminishes the quality and quantity of wind. Don’t let anyone talk you into a short tower!

Electricity produced by a wind turbine runs down wires attached to the tower. The wires typically run externally — for example, alongside a tower leg of a lattice tower — to a junction box at the base of the tower. From there, they typically run underground in conduit to the point of use.

As you shall soon see, wind-electric systems involve a number of additional components. We’ll describe them as we explore the three main types of wind energy system.