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Small Wind Electric Systems

Small wind electric systems are one of the most cost-effective, home-based renewable energy systems. These systems are also nonpolluting.

If a small wind electric system is right for you, it can do the following:

  • Lower your electricity bills by 50–90%
  • Help you avoid the high costs of having utility power lines extended to a remote location
  • Help uninterruptible power supplies ride through extended utility outages.

Small wind electric systems can also be used for a variety of other applications, including water pumping on farms and ranches.

 

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How a Small Wind Electric System Works

Wind is created by the unequal heating of the Earth's surface by the sun. Wind turbines convert the kinetic energy in wind into clean electricity.

When the wind spins the wind turbine's blades, a rotor captures the kinetic energy of the wind and converts it into rotary motion to drive the generator. The manufacturer can provide information on the maximum wind speed at which the turbine is designed to operate safely. Most turbines have automatic overspeed-governing systems to keep the rotor from spinning out of control in very high winds.

A small wind system can be connected to an electric distribution system (grid-connected) or it can stand alone (off-grid) .

This illustration shows the basic parts of a small wind electric system. It shows the wind turbine. The turbine features two, long, thin blades attached at one end. Next to the the blades is a rotor, which looks like a metal band next to the blades. The rotor's connected to a generator/alternator, a cylindrical-shaped device. A long, thin, triangular-shaped metal piece extends from the generator/alternator, with a tail at the end, which is shaped and placed much like the tail of one of those small wooden model planes. The turbine sits atop a tower, which is basically a long metal pole. The tower is connected beneath the generator/alternator.

 

Evaluating a Potential Small Wind Turbine Site

A small wind energy system can provide a practical and economical source of electricity if the following apply to you:

  • Your property has a good wind resource
  • Your home or business is located on at least one acre of land in a rural area
  • Your local zoning codes or covenants allow wind turbines
  • You can determine how much electricity you need or want to produce
  • It works for you economically , and you're comfortable with long-term investments
  • Your average electricity bills are $150 per month or more
  • Your property is in a remote location that does not have easy access to utility lines.

 

Small Wind Electric System Components

To capture and convert the wind's kinetic energy into electricity, a home wind energy system generally comprises the following:

  • A wind turbine (blades) attached to a rotor, generator/alternator mounted on a frame, and usually a tail
  • A tower
  • Balance-of-system components, such as controllers, inverters, and/or batteries.

 

Small Wind Electric System Turbines

Most small wind turbines manufactured today are horizontal-axis, upwind machines that have two or three blades. These blades are usually made of a composite material, such as fiberglass.  Some turbines use a downwind design, which has no tail to steer the turbine into the wind (upwind)

The turbine's frame is the structure onto which the rotor, generator, and tail are attached. The amount of energy a turbine will produce is determined primarily by the diameter of its rotor. The diameter of the rotor defines its "swept area," or the quantity of wind intercepted by the turbine. The tail keeps the turbine facing into the wind.

The wind turbine is mounted on a tower to provide better access to stronger winds. In addition to the turbine and tower, small wind electric systems also require balance-of-system components .

Sizing

Small wind turbines range in size from 400 watts to 20 kilowatts. What size wind turbine you'll need depends on your application. These are the most common applications for small wind turbines:

  • Residential electricity

  • Water pumping

Other applications include charging batteries for recreational vehicles and sailboats, which typically use "micro" turbines (20–500 watts).

Most U.S. manufacturers rate their small wind turbines by the amount of power they can safely produce at a particular wind speed, usually between 24 and 36 miles-per-hour.  Newer turbine designs provide peak power at much lower wind speeds, ranging from 8-12 mph. 

 

Small Wind Electric System Towers

Because wind speeds increase with height, a small wind turbine is mounted on a tower. In general, the higher the tower, the more power the wind system can produce. The tower also raises the turbine above the air turbulence that can exist close to the ground because of obstructions such as hills, buildings, and trees.

Tower Height

Relatively small investments in increased tower height can yield very high rates of return in power production. For instance, to raise a 10-kilowatt generator from a 60-foot tower height to a 100-foot tower involves a 10% increase in overall system cost, but it can produce 25% more power.

The estimated annual energy output and turbine size you'll need can help determine the best tower height.

Types of Towers

Most turbine manufacturers provide wind energy system packages that include towers. There are two basic types of towers: self-supporting (free-standing) and guyed. There are also tilt-down versions of guyed towers.

Most home wind power systems use a guyed tower, which are the least expensive. Guyed towers can consist of these components:

  • Lattice sections
  • Pipe
  • Tubing, depending on the design
  • Supporting guy wires.

Guyed towers are easier to install than self-supporting towers. However, because the guy radius must be one-half to three-quarters of the tower height, guyed towers require enough space to accommodate them.

While tilt-down towers are more expensive, they offer the consumer an easy way to perform maintenance on smaller light-weight turbines, usually 10 kilowatt or less. Tilt-down towers can also be lowered to the ground during hazardous weather such as hurricanes. Aluminum towers are prone to cracking and should be avoided.

Here are two illustrations of a tilt-down wind turbine tower. There are 4 wires extending from the tower, which looks like a pole. Two wires are attached near the top, and the other two are attached a little below the middle of the tower. The first illustration shows the tower tilted down, horizontally. The wind turbine is perpendicular to the ground, touching it, with its tail pointing to the sky. The wire closest to the ground is shown loose and slack. The caption reads: Tilt-down tower in the lowered position for maintenance or hurricanes. The second illustration shows a wind turbine tower in the upright position, vertical from the ground. All wires are shown taut. At the back of the turbine, a thin pole is shown extending from the tower to two of the wires. The caption reads: Tilt-up tower in the normal operating position.

Installation or Mounting

A general rule of thumb is to install a small wind turbine on a tower with the bottom of the rotor blades at least 30 feet (9 meters) above any obstacle that is within 300 feet (90 meters) of the tower.

Mounting small wind turbines on rooftops is not recommended. All wind turbines vibrate and transmit the vibration to the structure on which they are mounted. This vibration can lead to noise and structural problems with the building, and mounting on the rooftop can expose the turbine to excessive turbulence that can shorten its life.

 

Balance-of-System Components for Small Wind Electric Systems

The balance-of-system parts—those in addition to the wind turbine and the tower—you'll need for a small wind electric system depend on your application and the type of turbine that is selected. For example, the parts required for a water pumping system will be much different from what you need for a residential application.  In addition, while many turbines generate a DC voltage, some are designed to produce a regulated AC output, incorporating the inverter circuitry into the body of the turbine.

The balance-of-system parts required will also depend on the type of system:

Most manufacturers can provide you with a system package that includes all the parts you need for your particular application. For a residential grid-connected application, the balance-of-system parts may include the following:

  • Batteries
  • Charge controller
  • inverter 
  • Safety Equipment

These are the same components that are used in Solar Electric generation applications, which makes implementation of a hybrid PV-Wind system an obvious choice.

 

Grid-Connected Small Wind Electric Systems

Small wind energy systems can be connected to the electricity distribution system. These are called grid-connected systems.

A grid-connected wind turbine can reduce your consumption of utility-supplied electricity for lighting, appliances, and electric heat. If the turbine cannot deliver the amount of energy you need, the utility makes up the difference. When the wind system produces more electricity than the household requires, the excess is sent or sold to the utility.

With this type of grid-connection, note that the wind turbine will operate only when the utility grid is available. During power outages, the wind turbine is required to shut down due to safety concerns.

This illustration shows how a grid-connected small wind system works. It shows the wind blowing a three-bladed wind turbine sitting atop a tower, which looks like a pole. The electricity generated by the wind turbine is shown traveling to an inverter. The inverter is a gray-colored, square box with two gauges near the top of the inverter box. From the inverter box, electricity is shown traveling to both a meter (a white, square box) and a house, which is identified as the 'load.' From the meter, the electricity is shown traveling to an electricity transmission, which is drawn as vertical pole with two smaller poles drawn at the top. The pole nearest the top is slighting larger than the one beneath it.

Grid-connected systems can be practical if the following conditions exist:

  • You live in an area with average annual wind speed of at least 10 miles per hour (4.5 m/s).

  • Utility-supplied electricity is expensive in your area (about 10–15 cents per kilowatt-hour).

  • The utility's requirements for connecting your system to its grid are not prohibitively expensive.

  • There are good incentives for the sale of excess electricity or for the purchase of wind turbines.

 

Wind Power in Stand-Alone Systems

Wind Power can be used in off-grid systems, also called stand-alone systems, not connected to an electric distribution system or grid. In these applications, small wind electric systems can be used in combination with other components—including a small solar electric system —to create hybrid power systems . Hybrid power systems can provide reliable off-grid power for homes, farms, or even entire communities (a co-housing project, for example) that are far from the nearest utility lines.Off-grid systems, also called stand-alone systems, are not connected to an electric distribution system or grid.

Hybrid wind energy systems can provide reliable off-grid power for homes, farms, or even entire communities (a co-housing project, for example) that are far from the nearest utility lines.

An off-grid, hybrid electric system may be practical for you if the items below describe your situation:

  • You live in an area with average annual wind speed of at least 9 miles per hour (4.0 m/s).

  • A grid connection is not available or can only be made through an expensive extension. The cost of running a power line to a remote site to connect with the utility grid can be prohibitive, ranging from $15,000 to more than $50,000 per mile, depending on terrain.

  • You would like to gain energy independence from the utility.

  • You would like to generate clean power.

Small "Hybrid" Solar and Wind Electric Systems

                                                                             Photo of a wood building with a small wind turbine in front and photovoltaic panels on the roof.

According to many renewable energy experts, a small "hybrid" electric system that combines wind and solar (photovoltaic) technologies offers several advantages over either single system.

In much of the United States, wind speeds are low in the summer when the sun shines brightest and longest. The wind is strong in the winter when less sunlight is available. Because the peak operating times for wind and solar systems occur at different times of the day and year, hybrid systems are more likely to produce power when you need it.

Many hybrid systems are stand-alone systems , which operate "off-grid"—not connected to an electricity distribution system. For the times when neither the wind nor the solar system are producing, most hybrid systems provide power through batteries and/or an engine generator powered by conventional fuels, such as diesel. If the batteries run low, the engine generator can provide power and recharge the batteries.

Adding an engine generator makes the system more complex, but modern electronic controllers can operate these systems automatically. An engine generator can also reduce the size of the other components needed for the system. Keep in mind that the storage capacity must be large enough to supply electrical needs during non-charging periods.

Battery banks are typically sized to supply the electric load for one to three days.

 

                                                                Diagram of a hybrid power system that combines wind power and solar power to supply electricity to a home. At the left end, wind blows at a wind turbine, which turns and feeds energy into a box labeled Regulation and Conversion. Also connected to this box are a generator and PV modules that are heated by the sun. Connected below the Regulation and Conversion box are four small boxes labeled the Battery Bank. A line connecting the Regulation and Conversion box and a house is labeled AC or DC, and the house is labeled Load. The caption reads: Hybrid Power Systems. Combine multiple power sources to deliver non-intermittent electric power.

 

 

 

 

 

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