Residential Wind Power
At the Right Site, Wind Is Cheaper than Photovoltaic
Bird's eye view
Most generators need elbow room
Rural homeowners looking for a green electricityElectricity generated from renewable energy sources, such as photovoltaics (solar power), wind power, biomass, and small-scale hydropower. (Large, conventional hydropower sources usually are not included in definitions of green electricity.) source may be interested in a wind turbine. Like a photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. array, a residential wind generator is usually connected to a local utility so excess power is sold to the grid. When the generator isn’t producing, the house runs on utility power. Turbines also can power off-grid houses. In a windy area, wind-generated electricity may be cheaper than electricity from a photovoltaic array.
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The larger the diameter, the greater the output
Perched atop the tower, a small residential wind turbine is made up of a rotor, a generator or alternator, and a tail. Turbine systems are rated by the amount of electricity they produce at a particular wind speed. Just as the output of a PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. system depends on the size of the panels, the electrical output of a wind turbine depends on the diameter of the rotors — known as the swept area. The larger the diameter, the more wind power captured and turned into electricity. The tail helps control the yaw so the turbine is turned into the wind to maximize efficiency. The mechanical energy of the turning rotor spins a generator or alternator located directly behind the rotor to make electricity.
Wind and sun can work well together
Even if wind is plentiful in a particular location, it's still unpredictable.
Too little and power generation is reduced; too much can be dangerous. Properly sizing a turbine and the tower that carries it depends on several variables:
- average annual wind speed at the site
- consistency of windspeed
- terrain and nearby structures/trees
- local ordinances
- available budget vs. local utility rates
Get a taller tower. To avoid ground turbulence and reach steadier winds above ground level, residential wind turbines are typically mounted on towers between 80 ft. and 120 ft. tall. Wind speed generally increases with height. Doubling the tower height can increase power production by 34% to 45%.
Wind and solar can be complementary. If neither wind nor solar power can sustain a home alone, maybe try both. It's often windy when the sun's not shining and vice versa.
Tilt-up towers are easier to maintain
There are three types of wind towers:
Most wind towers require permanent guy wires for stability, although at least one manufacturer offers an unguyed 80-foot tilt-up monopole tower.
Code committee at work
A committee is currently working to develop a new article covering small wind generators for the National Electrical Code. For more information on code requirements for residential wind turbines, visit www.renewwisconsin.org/wind/Toolbox-Homeowners/Code%20compliance.pdf
You need at least 10 mph
As a rule of thumb, a building site should have an average wind speed of 10 mph to make the installation of a turbine worthwhile. At wind speeds much below this the turbine cuts out and no power is generated.
The U.S. Department of Energy has published a map showing average wind speeds that can be useful in calculating the potential of a site.
Wind conditions are highly localized. Especially hilly areas may require site-specific data collection to make sure it’s not in a wind shadow even if the general area looks promising.
The two most important variables determining a turbine's power production are the rotors' swept area and the wind speed. When it comes to wind power production, sites with low wind speeds are useless. Available wind power is proportional to the cube of wind speed. That’s why a site with an average wind speed of 18 mph can produce eight times more power than a site with an average wind speed of 9 mph.
Assuming a turbine's efficiency is constant, a turbine that produces 300 watts at 9 mph will produce 8 times more power — that is, 2,400 watts — when the wind speed is doubled to 18 mph.
Before you purchase a wind turbine, it would be great to know your site’s average wind speed. Unfortunately, wind site assessment is expensive. Most small wind turbines are installed without any prior wind monitoring; instead, installers look for clues to high wind speeds like flagging on trees. “To get an anemometer up high enough, you need to spend about $7,000 for a tower," says Anne Bijur, a customer communications representative for Earth Turbines in Hinesburg, Vermont. "So you might as well put the money into a turbine.”
One rule of thumb: a site isn’t windy enough to justify a turbine unless the wind is frequently irritating to residents.
Turbines need elbow room. Local restrictions may prohibit the installation of a wind tower in some neighborhoods. A conventional three-blade turbine usually sits on an 80- to 120-foot tower. The turbine needs to be 30 ft. above any object within 300 ft. and upwind of trees and buildings. Vertical-axis turbines take up less room but they also are less efficient than horizontally oriented turbines.
Because of the room that conventional turbines need, they are not an option in most urban and many suburban settings. The American Wind Energy Association recommends a residential installation requires at least an acre of land.
Wind potential is limited. The government estimates that about 6% of the land area in the contiguous U.S. has “good” wind potential.
Wind resources are ranked in seven classes, with Class 4 and above considered suitable for “advanced” wind turbine technology and Class 1 and 2 unsuitable. Class 3 zones may be suitable for future development.
Extensive research on wind potential is available. A number of states offer consumer guides tailored to local conditions.
Be wary of power production predictions. Many studies have shown that most performance predictions for small wind turbines are exaggerated. Inaccurate forecasts are due to a variety of factors, including optimistic estimates of average wind speeds, inaccurate performance data from turbine manufacturers, and in some cases deliberate deception by turbine dealers.
One recent study by Shawn Shaw of the CADMUS Group, “Progress Report on Small Wind Energy Development Projects Receiving Funds from the Massachusetts Technology Collaborative,” examined the performance of 19 small (under 10-kW) wind turbines. The study found that on average, the wind turbines produced only 27% of the annual electricity production estimated by the wind turbine installers.
The National Association of Home Builders Research Center says that a 10-kW wind generator costs between $40,000 and $50,000 and is capable of generating from 800 to 2,000 kW per month, depending on how much wind is available. (The average home uses 9,400 kilowatt-hours of electricity per year, or 766 per month.)
Cost estimates from the American Wind Energy Association are lower, between $6,000 and $22,000 for a residential wind turbine, although the size of the generator is not specified.
National Renewable Energy Lab: Guide to Small Wind Electric Systems
Wind Turbine Manufacturers
Green Ridge Energy
Wind Equipment Dealers
- Jim Westphalen
Aug 15, 2012 5:29 PM ET