Small wind turbines and basic components

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Wind turbines used to generate electricity come in a wide variety of sizes. Large wind turbines, which are usually installed in clusters called wind farms, can generate large amounts of electricity. Large wind turbines may even produce hundreds of megawatts (MW) of electricity - enough to power hundreds of homes. Small wind turbines which are generally defined as producing no more than 100 kW of electricity, are designed to be installed at homes, farms and small businesses either as a source of backup electricity, or to offset use of utility power and reduce electricity bills. Very small wind turbines (20-500 watt units) are used to charge batteries for sail boats and other recreational uses.

Wind turbine.

A small wind energy system could prove to be a practical and economical source of electricity for your home or farm if some or all of the following are true:

• Your property has a good wind resource.
• Your property is at least one acre in size.
• Your local zoning ordinances allow wind turbines.
• Your electricity bills tend to be high.
• Your property does not have easy access to utility lines, i.e. off electrical power grid.
• You are comfortable with making long-term investments.
• Turbine is 250-300 m away from your neighbour's house (closer for small turbines i.e. 1 kW).

Types of Wind Turbines

There are two basic types of wind turbines: horizontal axis wind turbines and vertical axis wind turbines. Horizontal axis turbines (more common) need to be aimed directly at the wind. Because of this, they come with a tail vane that will continuously point them in the direction of the wind. Vertical axis turbines work whatever direction the wind is blowing, but require a lot more ground space to support their guy wires than horizontal axis wind turbines.

 Two basic wind turbines, horizontal axis and vertical axis.

Components of Wind Energy Systems

The basic components of a typical wind energy system are shown on following figure.

Components of a wind energy system.

 These basic components include:

• A rotor, consisting of blades with aerodynamic surfaces. When the wind blows over the blades, the rotor turns, causing the generator or alternator in the turbine to rotate and produce electricity.
• A gearbox, which matches the rotor speed to that of the generator/alternator. The smallest turbines (under 10 kW) usually do not require a gearbox.
• An enclosure, or nacelle, which protects the gearbox, generator and other components of the turbine from the elements.
• A tail vane or yaw system, which aligns the turbine with the wind.

If you plan on building a horizontal axis wind turbine, you will need a tower on which to mount the turbine (vertical axis turbines are usually built on the ground).

Several types of towers are available:

• Guyed lattice towers, where the tower is permanently supported by guy wires. These towers tend to be the least expensive, but take up a lot of space on a yard. A radio broadcast tower is a good example of a guyed lattice tower.
• Guyed tilt-up towers, which can be raised and lowered for easy maintenance and repair.
• Self-supporting towers, which do not have guy wires. These towers tend to be the heaviest and most expensive, but because they do not require guy wires, they do not take up as much space on a yard.

An important factor in how much power your wind turbine will produce is the height of its tower. The power available in the wind is proportional to the cube of its speed. This means that if wind speed doubles, the power available to the wind generator increases by a factor of 8 (2 x 2 x 2 = 8). Since wind speed increases with height increases to the tower height can mean enormous increases in the amount of electricity generated by a wind turbine.

 Relationship between wind speed and wind power.

It has been recommended that towers be 24-37 m (80- 120 ft) high. Installing a wind turbine on a tower that is too short is like installing a solar panel in a shady area. At a minimum, mount a wind turbine high enough on a tower that the tips of the rotor blades remain at least 9 m (30 ft) above any obstacle within 90 m (300 ft).

Make sure to check local laws about height restrictions for wind turbine towers. Use a tower approved by the wind turbine manufacturer otherwise the warranty on the turbine may become invalid. Also ensure the tower is connected to an underground metal object to ground the tower in case of a lightning strike.

You need a disconnect switch that can electrically isolate the wind turbine from the rest of the wind energy system. An automatic disconnect switch is necessary to prevent damage to the rest of the system in case of an electrical malfunction or a lightning strike. It also allows maintenance and system modifications to be safely made to the turbine. There are other system components you may choose or need to purchase. You may need batteries to store excess energy generated by the wind turbine. Because energy is stored in batteries as DC power, you may need an inverter to convert power from the batteries to the AC power required to run electrical appliances in your home.

 Diagram of a grid-tied wind electric system.

If your home or farm is connected to the power grid on windier days you may be able to "sell" excess power generated by your wind turbine to your utility. Then, at other times when your turbine cannot generate all the power you need, you would buy power from the grid. This concept is called "net metering", or "net billing". Net metering is currently unavailable in most parts of Ontario, but may be available fall 2003. Contact your local utility or Hydro One.

Even if net metering is unavailable, you might be able to reduce your power bills by using the electricity you generate using a grid-connected wind turbine. If you do this, then you would not have to buy as much electricity from your utility.

If you do connect your wind turbine to the grid, your utility will require a transfer switch between the wind turbine and the utility line as a well as a two-way meter to keep track of the energy you have stored in and taken from the power grid. It is very important that your wind generator meets certain standards and that it does not pose a risk to your utility's personnel or equipment. It is also important that the quality of power coming from your turbine adequately matches the electrical characteristics in your utility's power grid.