Guy Wire Supported

FREE STANDiNG

FIGURE 5-45: Two types of towers.

towers to fail is a combination of wind turbine and tower drag. A pair of skinny windmill blades may not look like they could cause much drag, but when extracting full power at rated speed they create nearly the drag of a solid disk the diameter of the rotor.

The ways in which towers typically fail are:

1) Freestanding towers buckle due to higher-than-design wind drag load from the windwheel

2) A footing that anchors the tower to the ground becomes uprooted

3) A bolt somewhere along the tower fails due to improper tightening (or falls out because not tightened at all), resulting in a tower weak point that eventually fails t) Guy-wire-braced towers buckle from improper spacing of the wires up the tower. Here, a tower that requires, say, three sets of cables spaced evenly along the length of the tower, gets only two sets, resulting in intercable spans greater than design specifications

5) Guy wires fail from improper wire size, improper tension fasteners, or damage

6) Guy-wire anchors uproot from the ground or come away from the structure to which they are attached.

When selecting a tower, consider the difference between guy-wire braced and freestanding. Here, you must know something about the structure and about the soil supporting the tower. A wise decision would be to consult your county agent concerning the type of soil you have and its ability to act as a foundation.

Building codes for your area will detail the basis for foundation design, and the wind turbine dealer or manufacturer should have drag data for the product you select. A registered professional structural engineer can perform any calculations necessary to ensure that a particular tower installation will support your windmill. The cost of professional services in the area of tower selection and design should be considered cheap insurance for a sound installation. Vibratory loads induced by the wind or wind machine also should be considered and professional advice may be required.

One other point to consider is the potential hazard of guy wires, particularly to playing children.

OTHER EQUIPMENT Inverters

Inverters are devices which convert the dc voltage (power) to ac power. It is an age-old question whether dc or ac electricity is better. We do not propose an answer but suggest that many appliances are not designed to run on dc. Most motors, some stereos, TV sets, and certain other devices usually require 110 volts ac. Many wind turbine generators are rated at 12, 24, 32. or maybe 110 volts dc. To change dc to ac requires an inverter.

Some inverters use a dc electric motor to drive an ac generator. By driving the generator at constant rpm, a constant frequency, usually 60 hertz (cycles per second) is generated. The.** units are called rotary inverters. Other inverters, called static inverters, are solid state, using transistors to switch dc into ac. Some units, the lower-cost variety, generate a square wave output, while more expensive units and rotary inverters generate sine wave outputs. The most desirable output is sine wave, especially if a stereo or TV set is to be operated. Square waves powering a stereo sometimes distort the sound.

Inverters are rated by their maximum continuous capacity in watts. A small surge capability is possible for most models. Thus, a typical 500-watt continuous transistor inverter might be rated to 700 watts for ten seconds or even one minute, depending on the unit. Surge capability is needed, especially for inverterr> operating motorized appliances like refrigerators, because electric motors require considerable extra power for starting.

Selection of a suitable inverter involves another important factor, the efficiency of the inverter and, in more expensive models, automatic power adjustment. With a low-cost inverter, as would be available in most recreation vehicle supply stores, the inverter will draw (from the battery) almost the maximum rated power, regardless of the load the inverter is driving. Thus, a typical 500-watt inverter may draw 400 or more watts from the storage system, while only powering one 100-watt light bulb.. Higher-cost inverters offer the important option of a load monitor, which automatically adjusts the current draw by the inverter, according to the load.

A typical efficiency curve for a static inverter looks like Figure 5-48. From this, you can see that wherever possible it is best to select inverters that will operate near their maximum rated capacity. This could mean using several small inverters for various loads or one large automatic inverter for the entire system. In any case, cost of such inverters may dictate which inverter is selected. Ultimately, the cost of energy supplied is the primary consideration. Costs are discussed in Chapter 6.

Backup Equipment

We have already mentioned backup options during previous discussions. The concept of backup implies that wind is the primary energy source and that something else is the backup. That something else could be the utility lines (switched off until the wind dies down), solar heat, a gasoline- or diesel-

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

Get My Free Ebook


Post a comment