About Small Wind Turbines
Humans have used wind to grind corn, pump water or drive a ship for well over a thousand years. It was not until the end of the 19th century did we begin using wind energy to produce electricity.Today more than 50 companies around the world produce an estimated 50,000 wind generators per year.Small wind is now used to produce electricity for a variety of applications including utility-connected homes and businesses, remote homes, water pumping, telecommunication systems, off-shore platform lighting, and more.
Small Wind Basics
The use of wind energy has been around for well over a thousand years. Its uses are only limited by the mind. However, there are certain physics that guide us on what it can and cannot do. People have often dreamed of a small device that can be installed on the roof of a house which can provide all the needed energy. What is not understood by the non-technical are its limits. Like anything in nature, there are limits to what is possible. Below we have put together a number of interesting facts about wind.
What is a wind generator?
The proper name of a wind generator is actually “Wind Energy Converter” that being a device that converts the potential energy in the wind to another form of energy. This can either be mechanical or electrical.
How does the wind generator work?
When the wind blows, the rotor blade stops a percentage of the wind. That percentage is what is converted into energy. According to physics, the maximum amount of wind energy that can be converted is 59.3%. This is known as the Betz Limit.
I’ve seen lots of different looking designs, which is the best?
There are a number of types of wind generators. Research has been done on virtually every possible concept with the objective of producing the maximum amount of power for the lowest cost at the highest possible reliability. Conventional experimentation has found that the horizontal axis upwind or down wind design to be the best concept. The most common designs include:
- Horizontal upwind: The generator shaft is positioned horizontally and the wind hits the blade before the tower.
- Horizontal downwind: The generator shaft is positioned horizontally and the wind hits the tower first then the blade.
- Vertical Axis: The generator shaft is positioned vertically with the blades pointing up with the generator mounted on the ground or a short tower.
There are two basic types of airfoils (blades) a lifting and drag type.
- The drag style airfoil is typically what you see with an old Dutch wind mill or American water pumping wind mill. The blades are generally a flat plat which the wind hits and causes to rotate. This type of design is great for very low wind areas and will develop a lot of torque to perform an operation. However, in medium to higher winds, their capabilities to produce energy are limited.
- The lifting style airfoil is what you see in most modern wind turbines and on airplanes. A properly designed airfoil is capable of converting significantly more power in medium and higher winds. Actually, with this design, the fewer number of blades the more efficient this design can be. Two European companies actually produced one bladed machines however, dynamic balance issues prevented them from becoming a commercial success.
Is Wind Right for Me?
According to the U.S. Census, more than 17 million homes in America are located on land that is appropriate for a small wind system. Could your home be one?
IS WIND RIGHT FOR ME? – There are four important factors to consider using wind as an energy source for your house.
1. DO I HAVE A GOOD SITE? Siting a wind generator is extremely important to the performance of the machine. It is the difference between a machine that give you lots of energy and a garden sculpture. The ideal location for a wind turbine is 20 feet above any surrounding object within a 250 foot radius. This generally means your property should be at least one acre in size.
2. DO I HAVE THE RIGHT WIND RESOURCE? Wind is the “fuel” for your wind generator. You should have at least a 9 MPH average wind speed at your location. Wind maps are available for many countries and US states which will give you an idea of the wind resource at your house. Check out these maps and see if you have the right wind resource. You should live in a “Class One” or better site.If you cannot find your wind resource on the map, there are other ways.
- Contact your the closest weather station, TV or radio station. Wind patterns can change over short distances. We don’t recommend airports as they are generally located in places with the lowest potential wind.
- If you have trees in your area, use the Griggs-Putnam Energy Index This looks at a tree and how the wind changes its shape.
If you still don’t know the wind resource, locate a
Windpower Dealer in your area that can help you with a wind resource assessment.
3. WHAT ARE MY LOCAL LAWS: The next step is to determine if you have any local laws from a Home Owner’s Association or City or County that prohibit the use of towers.You should research:
- If you have a Home Owner’s Association read the guidelines relating to towers or tall structures.
- Contact your local County Planning and Zoning authority and ask about the use of towers and tall structures. Remember, the tower must be 20 feet above any surrounding object, if it is not, then performance will be lower.
4. WHAT INCENTIVES AND PROGRAMS DOES MY UTILITY OFFER? By law, the local utility (company you pay your electrical bill to) must purchase any excess electricity from you. There are both utilities that encourage the use of wind systems and discourage it. Locate your electrical bill and then find the number for customer service. Ask them for a copy of the policy relating to “connecting a renewable energy system to the electrical grid”.Finally – the best news of all. Many States in the union offer various types of
tax incentives and even rebates for your wind system.Congratulations! If you have made it this far then it is likely that a small wind system can save you a lot on your monthly electrical expense. Next is to contact your
local installer for an appointment.
Small Wind Facts
Small Wind Turbines are electric generators that use wind energy to produce clean, emissions-free power for individual homes, farms, and small businesses. With this simple and increasingly popular technology, individuals can generate their own power and cut their energy bills while helping to protect the environment. Unlike utility-scale turbines, small turbines can be suitable for use on properties encompassing as little as one acre of land in most areas of the country.
What size turbine is needed to power an entire home?
On average, a typical American home would require a small turbine with a 5 kilowatt (kW) generating capacity to meet all its electricity needs. A machine of this size has a diameter of approximately 18 feet. The exact size needed to power a home, however, can range from 2 kW to 10 kW (12-25 ft. diameter) based on a home’s energy use, average wind speeds, and the turbine’s height above ground (which affects its productivity).
How tall are they?
The average height of a small wind turbine (of any capacity) is about 80ft. (about twice the height of a neighborhood telephone pole), with a range of 30-140 ft. Generator size and tower height are not generally related; a 5 kW turbine could be on a tower anywhere from 30-140 ft., for example.
What is the average payback period?
The length of the payback period depends on the turbine, the quality of wind at the installation site, prevailing electricity rates, and available financing and incentives. Depending on these and other factors, the time it takes to fully recover the cost of a small wind turbine can take anywhere from 6 to 30 years.
How much do they cost?
The purchase and installation of a system large enough to power an entire home costs, on average, $30,000. But, the price can range from $10,000 to $70,000 depending on system size, height, and installation expenses. The purchase and installation of very small (<1kW) off-grid turbines generally costs $4,000 to $9,000, and a 100kW turbine can cost $350,000. The federal government and many states have rebate or tax credit programs in place to encourage investment in small wind (see http://dsireusa.org).
What happens when the wind does not blow?
For grid-connected systems, the user will not notice a difference when the wind is not blowing. The utility provides electricity when the wind does not blow, and any extra electricity the turbine generates is sent back to the utility system to be used by a neighbor. Off-grid turbines store power in batteries for on-demand use and are often complemented by solar electric panels to provide more consistent generation.
Do I need to take wind measurements?
Taking detailed measurements to gauge your wind resource is usually unnecessary. Individual installers/dealers or manufacturers are able to determine whether your property is suitable for a system by inspecting the surrounding area.
How much land is required? Will my town let me install a turbine?
Land requirements vary from place to place. Zoning codes sometimes impose a minimum requirement on lot size or distance a turbine can be placed from a property line, and may vary depending on the height of the proposed turbine. Also, it is essential to have a site with unobstructed access to winds, which most often requires higher towers, larger land lots, and non-urban locations. Currently, less than 1% of all small wind turbines are used in urban applications partly due to zoning restrictions, but mostly because wind quality is much poorer in densely built environments. Contact your turbine factory dealer or see AWEA’s small-wind permitting guide at www.awea.org/smallwind to for help navigating the permitting process.
How does the rated capacity of a small wind system compare to its actual performance?
Rated capacity indicates the rate of energy production at a given wind speed, so the answer depends on wind speed - and the turbine. A more accurate indicator of energy production however is blade length. A 5kW turbine (average residential size, 18ft. rotor diameter) produces around 10,000 kWh per year in 12mph average winds, which is about 100% of what an average U.S. home requires. At the larger end of the spectrum, a 100kW turbine (60ft. diameter) in these conditions will generate around 250,000 kWh per year.
Are batteries or other storage needed?
For very small systems, yes, but not for residential-scale turbines or larger. There are two types of systems: those connected to the electricity grid (“on-grid”) and those used off-grid for battery charging or backup power. Most systems sold today are off-grid, but demand is rising for on-grid systems which essentially use the grid as a "battery": when the wind blows, the owner uses electricity from the turbine; when winds are low and consumption is high, the owner uses electricity from the grid. A small wind turbine is more commonly used in conjunction with solar photovoltaic technology than it is with a battery storage system.
How are small wind systems maintained?
Routine inspections are performed once every few years of a turbine’s 20+ year lifespan. A professional installer or trained technician (usually the manufacturer or dealer that sold the turbine) maintains the turbine and tower through physical inspections, though some turbines can be monitored remotely from a home computer.
Download The Economics of Small Wind
Residential Wind and Birds
Sizing Up Your Situation
Small wind systems pay off most consistently for rural homes and businesses with at least an acre of property, Class 2 winds, and utility bills averaging at least $150 monthly.
Under these circumstances, a 10-kilowatt wind turbine mounted on an 80-foot tower should generate an average of 1,000 kilowatt-hours (kWh) monthly. With a net metering arrangement, each kWh generated can be valued at the retail electric rate charged by the utility, since that's power you don't have to buy and may even be feeding back into utility lines. Residents with reasonable electric rates will note that the payoff period can be lengthy. But the situation may look better when you factor in state incentives. In California, which offers a full range of rebates, state tax credits, and net metering, turbine owners can recoup their investments in less than 10 years, enjoying free electricity for the next 20. That's a healthy, tax-free return between 15 and 20 percent, depending on your electricity use and wind strength.
The Numbers on Smaller Systems
Smaller wind generators with a 1-3 kilowatt capacity don't usually produce excess generation and are often used to power specific applications such as water pumps or recreational vehicle lights and appliances.
But the smaller turbines can still cut down energy bills. A 3-kW turbine mounted on a 60 to 80-foot tower costs about $15,000, including accessory components and batteries (if needed). A homeowner spending $60-100 per month for electricity could knock 30-60 percent off their bill, depending on the wind speed, tower height, and price of electricity.
Systems smaller than 1 kW are often used in stand-alone applications, or as part of a hybrid system with solar PV cells. A 400-watt system can be installed for $1,500.
Wind Turbines Far Cheaper than Utility Lines
The cost of extending utility lines to a new home can cost as much as $20,000-30,000 per quarter mile. The same money could buy a renewable energy system that will meet the electricity needs of an energy-efficient home. Such a system typically combines a wind turbine with photovoltaic panels, batteries, and a back-up generator. These systems avoid a much large expense right off the bat -- the absence of utility bills is an added benefit.
The Electric Power Research Institute suggests that in some areas of the United States utilities would save money by removing under-used transmission lines that are costly to maintain and serving loads with hybrid stand-alone power systems instead.
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