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.
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).
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.
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.
Federal regulations (specifically, the Public Utility Regulatory Policies Act of 1978, or PURPA) require utilities to connect with and purchase power from small wind energy systems. However, you should contact your utility before connecting to its distribution lines to address any power quality and safety concerns.
Your utility can provide you with a list of requirements for connecting your system to the grid.
In off-grid (stand alone) 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.
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.
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.
Zoning Codes Or Covenants
Before you invest in a small wind energy system, you should research potential zoning and neighborhood covenant issues.
You can find out about the zoning restrictions in your area by contacting the local building inspector, board of supervisors, and/or planning board. They can tell you if you will need to obtain a building permit and provide you with a list of requirements.
In addition to zoning issues, your neighbors or homeowners' association might object to a wind machine that blocks their view. They also could be concerned about noise.
Most zoning and aesthetic concerns can be addressed by supplying objective data.
Some jurisdictions restrict the height of the structures permitted in residentially zoned areas, although variances are often obtainable. Most zoning ordinances have a height limit of 35 feet.
The sound level of most modern residential wind turbines is slightly above the ambient wind noise. This means that while the sound of the wind turbine may be picked out of surrounding noise if a conscious effort is made to hear it, a residential-sized wind turbine is not a significant source of noise under most wind conditions.
Estimating a Small Wind Turbine's Annual Energy Output
An estimate of the annual energy output from a wind turbine (in kilowatt-hours per year) is the best way to determine whether it and the tower will produce enough electricity to meet your needs.
A wind turbine manufacturer can help you estimate the energy production you can expect. The manufacturer will use a calculation based on these factors:
- Particular wind turbine power curve
- Average annual wind speed at your site
- Height of the tower that you plan to use
- Frequency distribution of the wind—an estimate of the number of hours that the wind will blow at each speed during an average year.
The manufacturer should also adjust this calculation for the elevation of your site.
To get a preliminary estimate of the performance of a particular wind turbine, you can use the following formula:
AEO= 0.01328 D2 V3
- AEO = Annual energy output (kilowatt-hours [kWh]/year)
- D = Rotor diameter, feet
- V = Annual average wind speed, miles-per hour (mph), at your site
Note: the difference between power and energy is that power (kilowatts [kW]) is the rate at which electricity is consumed, while energy (kilowatt-hours [kWh]) is the quantity consumed.
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
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.
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.
Small wind turbines range in size from 400 watts to 20 kilowatts. What size wind turbine you'll need depends on your application. The most common applications for small wind turbines are residential electricity and 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.
A typical home uses approximately 9400 kilowatt-hours of electricity per year (about 780 kWh per month). Depending on the average wind speed in the area, a wind turbine rated in the range of 5–15 kilowatts would be required to make a significant contribution to this demand. A 1.5-kilowatt wind turbine will meet the needs of a home requiring 300 kilowatt-hours per month in a location with a 14 mile-per-hour (6.26 meters-per-second) annual average wind speed.
To help you determine what size turbine you'll need, first establish an energy budget. Because energy efficiency is usually less expensive than energy production, reducing your home's electricity use will probably be more cost effective and will reduce the size of the wind turbine you need.
Wind turbine manufacturers can help you size your system based on your electricity needs and the specifics of local wind patterns. A manufacturer can provide you with the estimated annual energy output of a turbine as a function of annual average wind speed. The manufacturer can also 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.
The height of a wind turbine's tower also affects how much electricity the turbine will generate. A manufacturer should help you determine the tower height you will need.
To find the best site on your property for your small wind turbine, you have a lot to consider. A professional wind turbine dealer or installer should help you find the best location.
Wind Resource Considerations
You can have varied wind resources within the same property. In addition to measuring or finding out about the annual wind speeds, you need to know about the prevailing directions of the wind at your site.
If you live in complex terrain, take care in selecting the installation site. If you site your wind turbine on the top of or on the windy side of a hill, for example, you will have more access to prevailing winds than in a gully or on the leeward (sheltered) side of a hill on the same property.
In addition to geological formations, you need to consider existing obstacles, such as trees, houses, and sheds. You also need to plan for future obstructions, such as new buildings or trees that have not reached their full height. Your turbine needs to be sited upwind of any buildings and trees, and it needs to be 30 feet above anything within 300 feet.
Be sure to leave enough room to raise and lower the tower for maintenance. If your tower is guyed, you must allow room for the guy wires.
Whether the system is stand-alone or grid-connected, you also will need to take the length of the wire run between the turbine and the load (house, batteries, water pumps, etc.) into consideration. A substantial amount of electricity can be lost as a result of the wire resistance—the longer the wire run, the more electricity is lost. Using more or larger wire will also increase your installation cost.
Your wire run losses are greater when you have direct current (DC) instead of alternating current (AC). If you have a long wire run, it is advisable to invert DC to AC.
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.
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
- 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.
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.
Other system components
In addition to the wind turbine and the tower, the compnents you'll need for a small wind electric system depend on your application. For example, the parts required for a water pumping system will be much different from what you need for a residential application.
The balance-of-system parts required will also depend on whether system will be grid-connected, stand-alone, or a hybrid.
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:
- A controller
- Storage batteries
- An inverter (power conditioning unit)
- Electrical disconnect switch
- Grounding system
- Foundation for the tower.
Installing and Maintaining a Small Electric Wind System
With proper installation and maintenance, a small wind electric system should last up to 20 years or longer.
Before installing your system, you first need to do the following:
The manufacturer/dealer should be able to help you install your small wind electric system, but many people elect to install the systems themselves. Before attempting to install your wind turbine, ask yourself the following questions:
Can I pour a proper cement foundation?
Do I have access to a lift or a way of erecting the tower safely?
Do I know the difference between alternating current (AC) and direct current (DC) wiring?
Do I know enough about electricity to safely wire my turbine?
Do I know how to safely handle and install batteries?
If you answered no to any of the above questions, you should probably choose to have your system installed by a professional system integrator or installer.
Contact the manufacturer for help, or contact your state energy office and local utility for a list of local system installers. You can also check the yellow pages for wind energy system service providers.
A credible installer may provide additional services such as permitting. Find out if the installer is a licensed electrician, and ask for references and check them. You may also want to check with the Better Business Bureau.
Although small wind turbines typically are sturdy and reliable machines, they do require some annual maintenance.
- Check and tighten bolts and electrical connections as necessary.
- Check machines for corrosion and the guy wires for proper tension.
- Check for and replace any worn leading edge tape on the turbine blades, if appropriate.
- Replace the turbine blades and/or bearings after 10 years if needed.
If you do not have the expertise to maintain the system, your installer may provide a service and maintenance program.