Fig. 6.1: Wind Tower Options. (a) Freestanding, (b) fixed guyed, and (c) tilt-up. Freestanding towers can be both lattice (shown here) and monopoles. Fixed guyed towers are typically lattice towers. Tilt-up towers can be either lattice or tubular.Freestanding Towers
Freestanding wind generator towers are self-supporting structures. They stand on their own, like flag poles or street lights or the Eiffel Tower. Freestanding towers are made of steel and are firmly anchored to the ground via well-reinforced concrete foundations. The combination of heavy-duty steel tower construction and a secure anchorage ensures that the tower can withstand powerful winds that could pry the foundation loose and topple the tower and your expensive turbine. They also ensure that the tower can support the turbine.
The most common type of freestanding tower is a lattice or truss tower, like those shown in Figure 6.2. The Eiffel Tower in Paris is a good example of a lattice structure.
Is Wind Right for You?
Periodic inspection and maintenance and occasional repair of wind turbines are essential to the long-term success of a wind energy system. The towers on which they stand present a formidable barrier to these activities. Many wind system owners fail to perform these tasks because they don’t want to lower or climb their towers once a year. If you are a “put it up and forget about it” kind of person and can’t afford to hire someone to perform an annual inspection and maintenance, we recommend that you consider installing a PV system instead. PV systems are as close to maintenance-free technology as you can get (provided there are no batteries in the system). If you install a wind system, you will either need to climb the tower or lower it to the ground once or, preferably, twice a year to inspect the turbine, wires, connections, and perform maintenance, as required.
Fig. 6.2a and 6.2b: Lattice Tower. Freestanding lattice towers are made of (a) heavy-duty angle iron, as in this tower erected at the Midwest Renewable Energy Association’s headquarters, or (b) tubular steel. Horizontal and vertical bracing made of steel angle iron that runs between the tubular steel legs.Lattice towers are made from tubular steel or angle iron with horizontal and diagonal cross bracing bolted to the vertical steel legs. Ladders or step bolts are incorporated so the towers can be climbed for inspection, maintenance and repair. Freestanding lattice towers are sometimes fitted with a small platform near the top, which provides a secure place to work.
Another, more expensive option for freestanding towers is the monopole (Figure 6.3). They consist of a single, sturdy pole made from round tubular steel. Rungs or foot pegs are attached for climbing.
Freestanding towers are secured to massive steel-reinforced concrete foundations, as shown in Figure 6.4. The taller the tower, the heftier (and more expensive) the foundation.
Fig. 6.3: Monopole Tower. Monopole towers are sturdy, well-anchored by a solid foundation, but extremely costly for reasons explained in the text. 
Fig. 6.4: Concrete Piers and Base of Tower. This massive, deep foundation supports a 120-foot freestanding lattice tower. Each leg of the tower will attach to a steel leg embedded in each of the vertical piers. The piers and base of the foundation are made of concrete reinforced with rebar.Assembling and Installing Freestanding Towers
Freestanding lattice towers are typically assembled on the ground in sections, 20 feet at a time. The legs and bracing are bolted together on the ground.
After a lattice tower is assembled, the turbine is often attached. The tower and turbine are lifted with a crane. The tower is bolted to steel anchors embedded in the concrete foundation. To facilitate tower construction, some lattice towers are hinged at the base. That way, the tower can be assembled on the ground, and then tilted up into position with a crane (Figure 6.5). In some instances, the tower is erected and raised without a turbine. The turbine is then hoisted onto the top of the tower. A reasonably level area is needed to assemble a freestanding tower and to lift it with the crane.
Although freestanding lattice towers are typically assembled on the ground and lifted with a crane, it is possible to construct towers vertically one section at a time using a vertical gin pole. This technique is time-consuming and requires extreme caution and is only used in crane-inaccessible sites.
Fig. 6.5: Crane Lifting Tower and Turbine. This 80-ton crane lifts a massive turbine and tower into place. The hinges at the base of the tower allow the crane to tilt the tower into position.
Like lattice towers, monopole towers come in sections. They are fitted together on the ground. When completed, the tower is hoisted into place with a crane and the tower is secured to the foundation.Freestanding monopole towers are typically the most expensive of all options, because they require the most steel and the most robust foundations (Table 6.2).
Pros and Cons of Freestanding Towers
Freestanding towers offer advantages over other types. One of the most important is that they require much less space (Figure 6.6). Their smaller footprint makes a freestanding wind generator tower ideal for locations with extensive tree cover.
Freestanding towers are more aesthetically appealing to many people than guyed towers. A freestanding tower is also one of the safest towers to install. Almost all the work can be done on the ground, and a single crane lift can erect the tower, turbine, wiring, etc.
Embodied energy is the energy that it takes to make a product — from the extraction of the raw materials to the completion of the finished product, including shipping to retail outlets where it is sold. Because they require so much concrete and steel and because these materials require huge amounts of energy to produce, freestanding towers have a much higher embodied energy than other options. If your primary motivation is to decrease your environmental footprint by using renewable energy, a freestanding tower is not your best choice.
Fig. 6.6: Tower footprints: (a) Tilt-up, (b) Fixed Guyed, and (c) Freestanding.
Freestanding towers also require periodic ascent to perform routine inspection, maintenance, and repair, which can be a plus or minus, depending on your point of view. To prevent catastrophic falls, a safety harness or safety work belt must be worn while climbing and working on a tower (Figure 6.7). Safety harnesses are equipped with several D-rings (three-D-ring models should be used for tower work). The D rings are used to secure you to the tower via lanyards to prevent falls when working on a tower. A “positioning” or “restraint” lanyard holds a worker in place to allow him or her to work hands-free. A “shock absorbing” lanyard is used to
arrest a fall, that is, gradually slow a worker who has fallen to prevent a harmful jerk.
Towers should be equipped with a safety cable that runs the length of the tower along the climbing rungs or ladder (Figure 6.8). Workers attach their safety harness to the cable when climbing by an anti-fall device, such as a Lad-Saf. This sliding “climbing car” follows you as you ascend but locks onto the cable to arrest a fall if you lose your footing and fall.
Once you are atop the tower, belt in with lanyards and disconnect from the anti-fall cable. You must always be “attached” to the
Fig. 6.7: Safety Harness. Mick demonstrates proper use of a safety harness in one of his workshops.
Fig. 6.8a and 6.8b: Safety Cable and Lad-Saf. (a) Worker prepares to climb tower. Note safety harness and Lad-Saf attached to safety cable. This prevents the worker from falling. (b) Close up of connection to Lad-Saf and safety cable.tower. When climbing a tower without a safety cable, “Always climb using two lanyards in an alternating pattern so that one of them is clipped onto the tower at all times,” advises small wind expert Jim Green.
If you are not willing or able to climb a tower, you must be willing to hire someone to do it. If not, consider installing a tilt-up tower or a PV system.
Fixed Guyed Towers
The second type of tower is the fixed guyed tower (Figure 6.1b). Most are lattice towers. The legs of fixed guyed lattice towers are made of steel tube or pipe, or sometimes solid steel rods. The three legs of the lattice tower are usually 18 inches apart and are secured by horizontal and diagonal steel cross braces (Figure 6.9b).
Guyed towers are bolted to a concrete foundation and are supported by guy cables. Guy cables consist of high-strength stranded-steel cable or aircraft cable. They extend from attachments on the tower to steel-reinforced concrete anchors embedded in the
Fig. 6.9a and 6.9b: Fixed Guyed Lattice Tower. (a) This lattice tower is anchored by guy cables and is one of the most popular and least expensive tower options. (b) Close-up showing details.ground. Guy cables are strung out in three directions 120 degrees apart. The guy radius, that is, the distance from the base of the tower to the anchors, ranges from 50 to 80 percent of the tower height, depending on the construction of the tower. Usually it is about 75 percent. For a 100-foot tower, then, the anchors would be 120 degrees apart and 50 to 80 feet from the base.
Fixed guyed towers are also made from pipe or tubular steel that comes in 20-foot sections. Like guyed lattice towers, tubular towers are supported by guy cables.
Assembling and Installing Fixed Guyed Towers
Guyed towers are usually assembled on the ground. Lattice towers are bolted together, one section at a time. After the tower is assembled, the wind turbine and electrical wire are attached. The tower and turbine are then erected by a crane. If the tower is 80 feet or taller, it may be necessary to lift a lattice tower or tower made from steel tubing in sections. The wind turbine is lifted onto the tower after the last section is in place.
Fixed guyed towers can also be assembled vertically, one section at a time, using a vertical gin pole — an inexpensive, temporary vertical “crane” that’s bolted onto the tower. Installers use it to raise one section of a tower at a time. After a section is in place, the gin pole is moved up so the next section can be installed, and so on. Vertical gin pole assembly is time-consuming and tedious, and it can be a bit dangerous. Those who’ve tried it do not recommend it. If no crane
is available or the crane cannot access the site, however, a vertical gin pole may be your only option.
Fixed guyed towers rest on concrete pads, though the towers are generally not bolted to them. Guy cables are attached to the tower during assembly. After the tower is upright and plumbed,
workers tension the cables. If the turbine was not previously attached, it is then lifted by the crane and fastened to the top.
Pros and Cons of Fixed Guyed Towers
Fixed guyed towers cost much less than freestanding towers because they require much less steel and their foundations require a lot less concrete. Lattice towers used by installers are also mass produced for the telecommunications industry, making them less expensive and widely available. Fixed guyed towers require more space than freestanding towers, but less than tilt-up towers, discussed next.
Fixed guyed towers must also be climbed for routine maintenance and repair, like freestanding towers. Some people consider the guy cables to be an eyesore, although guy wires disappear into
the background from most vantage points, except up close. Guy wires may also present a hazard to birds, although we’ve never heard of a bird killed by them.
Tilt-Up Towers
The third type of tower option is a guyed tilt-up tower. Unlike freestanding and fixed guyed towers, a guyed tilt-up tower can be raised and lowered for inspection, maintenance and repair. Guyed tilt-up towers may be made from steel pipe or lattice sections.
Guyed tilt-up towers require four sets of guy cables at each level. Cables are located 90 degrees apart. The fourth cable is required for stability when raising or lowering a tower. That is, it allows workers to safely raise and lower the tower. Without them, the tower would topple during these operations.
As illustrated in Figure 6.10, a tilt-up tower is raised and lowered with the aid of a gin pole. Unlike the vertical gin pole discussed earlier, this pole is permanently attached to the base of the tower at a 90° angle to the mast. It is a lever arm that allows the tower to be tilted up and down.
Tilting a tower also requires a hinge between the mast and the concrete base (Figure 6.11). When the tower is down — that is, lying on the ground and ready to be raised — the gin pole sticks straight up. When the tower is vertical, the gin pole lies near and parallel to the ground. As illustrated in Figure 6.10, a steel cable connects the free end of the gin pole to a lifting device such as a tractor.
Fig. 6.10: Guyed Tilt-Up Tower. Guyed tilt-up towers are raised and lowered using a truck, tractor, electric winch or grip hoist.Guy cables hold a tilt-up tower upright and resist the force of the wind. The guy radius is 35 to 80 percent of tower height, depending on the type of tower. For a 100-foot tilt-up tower, the anchors should be located 35 to 80 feet from the base of the tower.
Assembling and Raising a Tilt-Up Guyed Tower
Steel pipe or tubing and lattice towers are both used for guyed tiltup towers. They come in 20-foot lengths. The individual lengths
Fig. 6.11: Hinged Base of a Guyed Tilt-Up Tower. The hinge at the base of this tilt-up tower allows it to be tilted up and down to maintain and service the wind turbine.
Fig. 6.12: Gin Pole. The gin pole is attached to the anchor. Notice the electric winch to the left of the attachment.of pipe are secured by bolts or joined by slip-fit couplings on the ground. While the tower is on the ground, guy cables are attached to the tower and the concrete anchors.
Once assembled, the tower is tilted into position (Figure 6.10). This is accomplished with the assistance of a tractor, a pickup truck, a heavy-duty electric winch or a manually operated device known as a grip hoist.
When installing a tall tower for the first time, some installers raise one or two sections of the tower at a time. After each section is raised, the tower is plumbed and the guy cables are tensioned. This tower is then lowered and an additional piece is added. It is then raised, plumbed, and cables tensioned. This continues until the entire tower is assembled, plumbed and properly tensioned.
Experienced installers also recommend lifting (and plumbing) the entire tower before attaching the wind turbine to be sure that everything is correct. Also, make sure to train workers so they all know what they are doing by the time the turbine and tower are lifted.
Pros and Cons of a Guyed Tilt-Up Tower
The main benefit of tilt-up towers is that they never have to be climbed. They can be raised and lowered fairly quickly and all inspections and work can be performed on terra firma.
Although they’re ideal for those who cringe at the idea of climbing a tall tower, tilt-up guyed towers have the largest footprint of all (Figure 6.6). You’ll need to ensure that there’s a clear path for the lifting vehicle and a lay-down zone as long as the tower.
Raising and lowering a tower requires a few helpers to ensure that everything runs smoothly — for example, that the cables don’t get tangled. And, of course, you’ll need a truck, tractor or some
other lifting device. Be careful when using a tow vehicle because they can slip. Accidents can also occur if the anchors are not correctly positioned or the guy cables get too tight while lowering or
raising the tower. A strong wind could come along and blow the tower over when it is being raised or lowered, ruining the turbine.
