Wind-Generated Energy Brattleboro VT
South Burlington, VT
Taking energy from the wind is an old concept. Effective use of wind power dates back at least as far as the ancient Syrians, who used windmills to pump water. In the Middle Ages windmills provided the energy to mill grains, and in 17th-century Europe, the Dutch used wind power to drain water along the Rhine River delta and reclaim hundreds of thousands of acres of land.
Harnessing the power of the wind still pays off. Today, a wind system is a clean source of nondepleting energy. It does not burn fuel or pollute the air. Wind farms on land and offshore, consisting of large wind-driven turbines that turn generators or alternators, creating electricity, are an increasingly common sight in the United States. They complement traditional fossil, nuclear and hydroelectric fuel sources long used by energy companies to power everything electric in the country.
On this wind resource map from the National Renewable Energy Laboratory, areas designated excellent and good are suitable for utility-scale wind energy applications, while areas designated moderate are suitable for small wind turbine applications, including residential use.
The same technology that empowers wind farms is available on a much smaller scale for residential use. Small wind systems can help homeowners save on long-term energy costs, particularly where those costs are high and especially where encouraged by state, utility or other subsidy programs.
For homes that are connected to the grid, the supplemental energy produced by a residential wind-generation system can reduce utility bills by 50 to 90 percent. If you rely heavily on your local utility for heating and/or cooling, this could reflect substantial savings. The wind turbine works simultaneously with utility power, with the wind turbine acting as a negative electrical load, reducing utility power consumption by whatever the wind turbine is producing.
For homes that are off the grid by choice or necessity, a wind system can be the primary source of energy. Usually, however, it is part of a hybrid installation that includes solar power "which can provide energy during periods of low wind" as well as propane or gas generators for supplemental power, and wood or propane for heating.
According to one conservative estimate, only about 20,000 homes in the United States have small wind turbines, with about 10 percent of those interconnected with utilities. Another estimate puts that total much higher. Still, that may sound like a surprisingly small percentage of homes using wind power, especially when you consider that there are more than 100 million homes in the country. This is probably due in part to the upfront costs involved in installing a wind system. However, the number of homeowners using wind power is growing, driven by the high cost of electricity, increased environmental concerns, and rebate and subsidy programs that reduce the cost of wind systems.
Wind System Basics
Most residential wind systems consist of a single wind turbine rated in the 3- to 15-kilowatt (kw) range. However, to significantly reduce reliance on utility power, you'll need at least a 5-kw turbine. A typical home uses about 830 kwh (kilowatt-hours) of energy per month, or about 9,960 kwh per year. By comparison, a 10-kw wind turbine will produce between 10,000 to 18,000 kwh annually, according to the California Energy Commission. (The actual energy produced depends on wind speeds at the site.) There soon will be at least one wind system on the market with a rating of 1.8 kw, delivering in excess of 500 kwh per month.
A wind turbine (the complete unit atop the tower) performs best when it is surrounded by a lot of cleared land and is sitting on a tower that's between 45 and 120 feet high, so it can capture winds strong enough to make the installation worthwhile. The tower should be tall enough that the bottom tips of the rotors pass at least 30 feet higher than anything within 300 feet, says Heather Rhoads-Weaver of the Small Wind Advocate Team for the American Wind Energy Association, a national wind power trade association.
Studies have shown that the continual thumping of a wind turbine's propeller is similar to that of a distant helicopter or the sound of a washing machine. At 800 feet, the sound a wind turbine makes is considerably less than that produced by stereo music or heard inside a car or in a typical office. However, the noise factor also has to be considered when installing a wind system.
Given these issues, it is perhaps impractical, and most likely un-neighborly, to erect a wind system on less than about an acre of land. If you have land enough to mount a wind system, check with your local zoning board or homeowner's association about restrictions that could prevent you from erecting a tower of sufficient height.
In areas where zoning regulations limit structure heights on residential property, you or your installing dealer should be prepared to take on a bureaucratic challenge. Usually, the first permit within a community is a big challenge, and the second, a little less so, says Mike Bergey, president of Bergey Windpower Co., a manufacturer of small wind-energy systems. After that, the planning and zoning officials are generally more receptive. Bergey recommends locating the tower in a convenient spot that takes into consideration the length of the electrical wire that runs from the tower to the house.
The majority of on-grid homeowners with wind systems do not store the electrical energy being created. Energy generated by the wind turbine is either used immediately in the home or is sold directly to the utility company. Homeowners connected to the utility grid nationwide have the right under federal law to receive payment for any excess energy their home systems produce. In California, New Jersey, Ohio and 34 other states, excess energy (generated during times of adequate wind, moderate temperature and light load) sold to the utility will actually spin the meter backwards, which is called net metering.
Connecting to the utility requires an inverter to make the turbine power compatible with the utility company. Keep in mind that all electrical components have to be approved by the utility.
A 1-kw wind turbine and half a kilowatt of solar power are usually adequate to power an off-grid home of 1,500 to 2,500 square feet. Because wind and sunshine are intermittent sources of power, homeowners hoping to use a hybrid (wind and solar) system to provide electricity off the grid must include a way to store energy, using lead-acid storage batteries. The stored electricity is then called upon during periods when the energy generated by the wind and solar systems is not sufficient. The battery bank typically provides reserve power for a day or two. For longer periods of low wind and sun, off-the-grid homeowners need a backup generator, powered by gas, propane or diesel fuel.
Homeowners should keep in mind, however, that storage-battery capability adds to the complexity of the installation and boosts the initial costs considerably, adding up to 25 percent to the cost of the system and lengthening the payback period. Therefore, most homeowners who have utility power opt not to add storage capability.
A typical home wind-system installation consists of a number of elements, including:
The wind turbine, which includes a rotor or propeller and a series of shafts and gears that turn a generator or alternator to create electrical power
The tower upon which the turbine is mounted
A concrete tower base, which can be up to 14 feet across for a 10-kw turbine without guy wires
Electric wires (usually underground) that run from the tower to the home
In addition, if you plan to attach the wind system to the grid, you'll need the appropriate utility-approved inverter.
Usually, the rotor used in an on-grid home energy system has two or three blades covering a diameter somewhere between 7 and 31 feet, a configuration that supports its ability to spin at high speed. The force of the wind spins the propeller that drives the electrical generator, converting the kinetic energy of the wind into electrical energy.
The Mightiest Wind
The best production from a wind-generation system is in areas of reliable high wind, typically found across the Great Plains or along coastal areas. In areas of low wind, homeowners can use wind turbines with longer rotor blades. When there is less wind energy available, you need to sweep a larger area, says Jim Green, senior project leader at the National Renewable Energy Laboratory.
However, in California, New York and Hawaii "states that have particularly high utility rates" wind systems may be justifiable in areas with lower average wind speeds, suggests Rhoads-Weaver of the AWEA.
While some energy experts recommend measuring the wind speed at your home over a long period of time (six months to a year) to determine what type of turbine best suits your site and payback requirements, most experts suggest relying on government maps or charts that detail the average wind speed for your area. (If your neighbor has a successful system already in place, take advantage of already-generated statistics.) The NREL and other wind-mapping companies have recently developed high-resolution maps that have an accuracy of +/-1 km.
About half of the states in the country can provide high-resolution geographic information system (GIS) maps of wind power that enable you to zoom in on your property. Other states are working to provide these types of maps, notes Rhoads-Weaver. You also can view detailed maps of average annual wind power in regions throughout the country by visiting the federal government™s Wind Energy Resource Information page online at http://rredc.nrel.gov/wind.
If you have a homesite that is sheltered from wind by hills, you will want to verify average wind power. You might want to invest in a formal wind analysis. Generally, wind-energy experts note that a wind system is suitable if you have an average wind speed of at least 11 mph. If your home is in a low area, you often can make up for that with a taller tower, Bergey suggests.
Wind speed increases with height above the ground. The taller the tower, the stronger the wind and the more energy you will derive from the system. The power in the wind improves with the cubic function of the velocity. In other words, power derivable from wind multiplies by eight as wind speed doubles. Wind speed is a variable affected by time of day and season, Rhoads-Weaver notes. On an annual basis, small wind turbines average 15 to 20 percent of their peak rated capacity in areas with good wind resources.
Choosing a Wind System
Most manufacturers offer a range of capacities in their wind systems and a choice of towers, which can include guyed, guyed lattice, tilt-up lattice (which is also guyed), self-supporting lattice and self-supporting monopole (tubular tower) designs.
It is very important to understand your building site, Rhoads-Weaver says. In addition to optimizing your system for height of the tower, you will also want to select a turbine well suited to your site. Various turbines are built to perform best under a specific range of wind conditions. Turbines designed for optimal operation on a gusty site with turbulence have shorter blades than those designed to operate at a site with more constant wind speed, she explains.
Today's multibladed wind turbines require very little maintenance. Once the return on investment is realized (usually in six to 15 years, although some studies show a significantly shorter payback period), they produce electricity at virtually no cost for the life of the system 20 to 30 years is common. Naturally, if you live in an area where there are financial incentives for alternative energy sources, that will help reduce the payback period. The Wind Energy Manual, available as a printable online document at www.energy .
iastate.edu/renewable/wind/wem-index.html, can help you determine payback periods.
Generally, manufacturers recommend an inspection of the system every year or two to check for loose hardware, corrosion or cracks. For the few models that have gearboxes, it's necessary to change the oil in the gearbox at manufacturer-suggested intervals. Also, every six to 10 years the high-tech tape that protects the rotor blades against erosion from grit or bugs may need replacement. Beyond 10 years, components such as blades and/or bearings may need to be replaced, Green notes.
If you've decided wind power is right for your home, you can purchase a complete turnkey installation, or you can buy the components and install the system yourself. A good rule of thumb when sizing a system for your home is to keep the potential annual production within the range of your annual electricity use. Broadly, cost generally falls within $3,000 to $5,000 per kilowatt of generating capacity.
For example, a 5-kw wind system connected to the grid, turnkey installed including hardware ranges from about $15,000 to $25,000, while a 10-kw system can cost anywhere between $30,000 and $50,000. Some systems with higher-end towers, without guy wires, could reach the $60,000 threshold. Those are substantial figures when you're considering the payback period. However, if you take advantage of rebates and tax credits offered by some states and some utilities, you can reasonably aim for payback within about 15 years. (According to Andy Kruse, vice president of Southwest Windpower, his company is introducing a 1-kw system that will cost less than $4,000. Look for it this year.)
As installation costs go down and energy prices continue to rise, it's apparent that more and more homeowners will be looking to the wind as a way to meet their residential energy needs.
William and Patti Feldman are frequent contributors to Smart HomeOwner. They're based in New York.