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 a 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.

Utility-Connected Homes

Enjoy the benefits of utility power while reducing your electric bill every time the wind blows! It's been a dream of many homeowners and now it is possible.

Remote Homes and Cabins

More than 50,000 Southwest Windpower wind turbines are used on remote homes and cabins around the world. Whether your remote home is for a weekend get-away or you live there full time, Southwest Windpower has a wind turbine to match your energy needs. Best of all, our products are designed to make it simple for the user to site and install.

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Is a Wind Turbine Right For Me?

Courtesy of Southwest Windpower

If you have a wind resource greater than 8mph (4 m/s) and your area is free from obstacles then a wind generator will likely be a good match. It is that easy! An important reason to have a wind turbine is because of the seasonal variations of your solar and wind resources. A hybrid system that uses both solar photovoltaic panels and a wind turbine will make the perfect compliment that provides minimal interruptions in power. Depending on your energy consumption and wind speed, the chart below will help you decide which turbine best fits your needs.

Southwest Windpower is the world's largest producer of small wind turbines. You can find them used on everything from remote cabins to sailboats and other applications including utility connected homes.

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?

There are four important factors to consider using wind as an energy source for your house.

Do I have a good site?
Siting your windmillSiting 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.
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 Southwest Windpower Dealer in your area that can help you with a wind resource assessment.
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.
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.

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Windmill Variety Guide

Battery Charging Windmills generate Power, converted to dc Voltage and store power on Batteries to be used during demand periods through an ac Inverter. In addition to the Windmill other parts are required including Batteries, dc source center, etc.

Grid-Tie Windmills generate power in ac Voltage form and an Inverter matches Utility Power. Excess power, not used by the home/building, is sent back to the Utility for credits or compensation back to the owner in a process called Net Metering. The Utility Grid acts as the battery for Grid-Tie systems.

Battery-Charging Windmill Guide

# Manfacturer Model Type Instant Power
Average Power
Cost (2007)
1 SWWP Air-Breeze 12/24v 265W 40 KWh/mo $725 +f
2 SWWP Air-X 12/24/48v 400W 50 KWh/mo $725 +f
3 SWWP Whisper 100 12/36/48v 500W 100 KWh/mo $2,575 +f
4 Bergey XL.1 12/24/48v 1000W 200 KWh/mo $2,790 +f
5 SWWP Whisper 200 12/24/48v 1000W 200 KWh/mo $3,115 +f
6 SWWP Whisper 500 24/48v 3000W 530 KWh/mo $8,059 +f

Grid-Tie Windmill Guide

# Manfacturer Model Type Instant Power
Average Power
Cost (2007)
7 SWWP Skystream 3.7 240v split 1,900W 380 KWh/mo $5,400 +f
8 Bergey Excel 10K 240v 3phase 10,000W 1200+ KWh/mo $29,400 +f

Tower Guide

# Tower Cost Items Required
(See below for details)
1 29' EZ tower tilt *** $535 +f a, b, c, d, e, f Contact us for a quote **
2 30' guyed, pole *** $450+ $450 pipe +f a, b, c, d, e, f
3 42' guyed, pole *** $975+ $879 pipe +f a, b, c, d, e, f
4 42' guyed, pole *** $450+ $450 pipe +f c, d, e
5 60' guyed, pole *** $1,600 +f a, b, c, d, e, f
6 60' guyed, pole *** $9,600 c, d, e

+f = plus freight, delivery & tax
** Depends on tower & site
*** variety available
Every windmill's power production is maximized with a taller tower.
Additional Requirements (depending on application): a. Batteries b. Battery string c. Wire to/up tower & building d. Disconnect e. Installation f. Inverter

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Southwest Windpower Windmills

Skystream 3.7 - $5,400.00 (J'08)

Skystream 3.7 Grid-Tie Windmill

Skystream is a wind generator designed to be installed on top of a tower to convert the kinetic energy in the wind into electricity to be used in a home's existing electrical system. Cut-in wind speed is about 8MPH and an average wind speed of 10MPH or greater is required for effective power production.

In a typical residential application, a home is served simultaneously by the Skystream and a local utility. If the wind speeds are below "cut-in speed" (8 mph) there will be no output from the generator and all of the needed power is purchased from the utility. As wind speeds increase, the Skystream's output increases and the amount of power purchased from the utility is proportionately decreased. When the Skystream produces more power than the house needs, the meter spins backwards creating a "credit" that can be used later. All of this is done automatically without any interaction by the homeowner. Batteries are not required with Skystream. This wind generator model is not for 'off-grid' systems but is designed to produce power that is combined with your utility power only.

In some areas a premium is paid for excess power produced and not used in the building. Check for incentives in your area inside the USA

Rated Capacity: 1.8 KW
Rotor: 12 feet / 3.72 meters; 50-325 RPM
Alternator: Gearless, permanent magnet brushless
Voltage Output: 240 VAC (Optional 277 VAC)
Estimated Energy Production: 400 KWh per month at 12 MPH (5.4 m/s)
Weight: 154 pounds
Tower: Towers from 35-110 feet are available; height is dependent by site
Technical Specifications: Skystream 3.7 Spec Sheet [PDF]
Availability: Beginning August 2006 4-6 week lead time

WHISPER 100 w/controller - $2,085.00

Formerly the Whisper H40, the Whisper 100 has been updated with new features. The factory setting of 24v is now adjustable to 12/36/48. The Whisper 100 is designed to operate in a site with medium to high wind speed averages of 12mph, 5.4m/s and greater.

Provides 100+ kWh / month, 3.4kWh/day, in a 12 mph average wind.

Whisper 100 features:

  • Four bearing spindle for a smoother operation and longer life
  • Upgraded Yaw shaft delivers current more efficiently to batteries
  • Larger diameter furling pin and bronze bushing for smoother furling action
  • New castings allow easy access to stator for changing voltage

Includes Whisper Controller which has diversion load to ensure safe quiet operation when the batteries are charged.

Rotor diameter: 7 feet (2.1 meters) Weight: 47 lbs (21 kg)
Mount: 2.5 inch Schedule 40
Start-Up wind speed: 7.5 mph (3.4 m/s)
Voltage: 12, 24, 36, 48 VDC
Peak Power: 900 Watts @ 28 mph (12.5 m/s)

AIR-X and AIR-X Marine

AIR-X Windmill

The new AIR X improves on the revolutionary features of the 403. New Electronics: The AIR-X incorporates an entirely new rectifier and controller. The new microprocessor based controller provides voltage regulation, peak power tracking and quiet, stall control in high winds.

New Alternator: The alternator was designed to complement the Peak Power Tracking ability of the new control electronics. MPPT and dynamic braking mean no blade flutter, making the AIR-X significantly quieter. Braking and regulation shorts all three stator windings, instead of two in the 403, so the AIR-X operates 100°C cooler than the 403.

AIR-X Windmill Controller

Improved Battery Charging: Previous AIR designs required 300-400 amp hour battery banks so the trickle charge of the wind turbine could be adequately absorbed. The AIR-X's charge controller periodically stops charging, reads the battery voltage, compares it to the voltage setting and if the battery is charged, it completely shuts off all current going to the battery. This function is performed within a few milliseconds. The closer the battery is to reaching its full state of charge, the more often the AIR-X's circuit repeats this action. This means any size battery bank from 25 to 25,000 amp hours or higher can be charged safely. When the battery has reached its charged state, the AIR-X will slow to an almost complete stop. Only when the battery has dropped below its voltage set point will it startup and resume charging. The Benefit: Extended battery life, no overcharging.

Available in 12 and 24 volts.

New Blades: The rotor blades use a highly efficient, true airfoil. The result is quieter performance and minimal vibration. The control electronics will slow the blades before the turbine reaches the point of flutter.

New Yaw Shaft: The AIR-X features a new yaw shaft that allows for stronger clamping forces to the tower.

Rotor Diameter: 46" (1.14 meters)
Weight: 13 lbs. (6kg)
Start up wind speed: 7 mph (3m/s)
Voltage: 12, 24Vdc (36/48 addn'l)
Output:400 watts at 28 mph (12.5 m/s)
12 mph average = 45KWh per month
15 mph average = 80KWh per month

Three year standard warranty or five year extended warranty

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Bergey ™ Residential Windmills

The Bergey line of residential Windmills offers advanced-technology products that let homeowners and businesses generate their own clean power and even spin their utility meter backwards.  The Bergey turbines are also used for off-grid homes, for rural electrification.

  • Bergey residential Windmill systems connect to your household wiring, just like a large appliance.
  • Bergey Windmills work fully and cooperatively with your utility power.  Often you will be getting a mix of power, from both the wind turbine and the utility company.
  • As the Bergey wind turbines begin to produce power the power you draw from the power company is reduced. This causes our power meter to slow down thereby reduce your utility bills.
  • If there is no wind, the power company supplies all the power needed, or, hybrid customers may be using Solar when the wind is down.
  • When your wind turbine is producing exactly the amount of power your home demands, the power company's meter (on your house) will stop turning. At this point you are not buying any power from the power company, you are producing your own power and saving money.

BWC XL.1 Wind Turbine

Bergey XL.1 Windmill

Bergey Windpower's newest product is the 1,000 Watt BWC XL.1. The BWC XL.1 is currently available only as a 24 VDC battery-charging system.

With a rotor diameter of 2.5 meters (8.2 ft) and a peak output of approximately 1,300 watts the XL.1 is intended for the off-grid home market in the U.S. and for rural electrification programs in developing countries. It is also a perfect upgrade system for current owners of micro-turbines, such as the Air 303

The XL.1 combines a number of advanced technical features, including a completely new airfoil, to provide the highest efficiency yet achieved in a small wind turbine at a cost of energy ~ 10% lower than the current price leader. And, the XL.1 carries the industry-leading Bergey 5-year warranty. "We are very excited about the XL.1. We think customers are really going to like this machine" notes Mike Bergey, BWC's president.

The XL.1 is an up-wind, horizontal-axis, three- bladed turbine. The blades are pultruded fiberglass, a material that is over ten times stronger than the injection- molded plastic used on most small wind turbines. In fact, pultrusions have a breaking strength exceeding 100,000 psi, which is twice as strong as normal steel. "Just about any blade material will hold up in light to moderate winds. But, when the storms come, weak blades can put the whole system at risk." And the new BWC SH3045 airfoil makes the XL.1's blade probably the most efficient ever on a small wind turbine.

The photo to the right shows an XL.1 installed by Brooks Solar (Chelan, WA) at a renewable energy trade fair in Oregon.

The blades attach directly to a specially designed very-low-speed permanent magnet alternator which uses state-of-the-art neodymium super- magnets. "We have designed an oversized alternator that slows the rotor down and makes the turbine very quiet." Overspeed protection is provided by the proven BWC AutoFurl passive sideways furling system. "In spite of the claims otherwise, no other overspeed protection system has proven to be more reliable or effective than AutoFurl."

Bergey Windmill PowerCenter

The XL.1 includes the BWC PowerCenter controller which controls battery charging, has a low-end boost for superior low wind speed performance, "slow-mode" rotor idling when the batteries are full, an electrical braking system, and even includes a 30 A controller for the solar modules that are often a part of a complete hybrid system. The PowerCenter allows an auxiliary or "dump" load to be connected to utilize excess wind (and/or solar) power after the batteries are fully charged.

Low wind speed performance is greatly enhanced by a low-end-boost circuit that optimally loads the wind turbine down to wind speeds as low as 5.6 mph (2.5 m/s). Combined with the new blade system, this circuitry allows the XL.1 to produce useful power more than 6,000 hours a year at a typical site. For reference, a typical solar system produces power 3,500 hours a year at a typical site.

The XL.1 is offered with a tubular Tilt-up tower in heights from 18 m (60 ft) to 29 m (100 ft). These kits will be be easy to install and will offer customers a complete "ready to install" kit. "There's been a need for more complete integration between turbine and tower packages for small wind turbines and we think our new line will fill that gap."

The Owners Manual and the Installation Manual for the XL.1 are available on-line as PDF files.

Bergey XL.1 Windmill

Type: 3 Blade Upwind
Rotor Diameter: 2.5 m (8.2 ft.)
Start-up Wind Speed: 3 m/s (6.7 mph)
Cut-in Wind Speed: 2.5 m/s (5.6 mph)
Rated Wind Speed: 11 m/s (24.6 mph)
Rated Power: 1000 Watts
Maximum Power: ~ 1,300 Watts
Cut-Out Wind Speed: None
Furling Wind Speed: 13 m/s (29 mph)
Max. Design Wind Speed: 54 m/s (120 mph)
Blade Pitch Control: None, Fixed Pitch
Overspeed Protection: AutoFurl
Gearbox: None, Direct Drive
Temperature Range: -40 to +60 Deg. C (-40 to +140 Deg. F)
Generator: Permanent Magnet Alternator
Output Form: 24 VDC Nominal
Functional Features: Low-End Boost, Slow-Mode, Electric Brake, 30A Solar Regulator, 60A Dump Load, Timed Battery Equalization, Watt Meter Display Mode, Polarity Checker

BWC Excel

Bergey Windmill

The BWC EXCEL is a modern 6.7 meter (22 ft) diameter, 10,000W wind turbine designed for high reliability, low maintenance, and automatic operation in adverse weather conditions. It is available in two configurations: battery charging and grid-connected (the pumping version is not currently available). The BWC Excel is a ruggedly built turbine that comes with the longest warranty (5 years) in the industry.

Battery charging BWC EXCEL's can be supplied with outputs of 48, 120 or 240 VDC. They are well suited for large rural homes, remote villages and facilities, eco-tourism resorts, and larger telecommunications sites.

Connected to the grid, the BWC EXCEL can provide most of the electricity for an average total electric home at moderate wind sites. The all new GridTek 10 power processor (inverter) is the most advanced in the industry and it carries a full UL certification to the latest utility standards.

The BWC EXCEL is most often installed on a guyed lattice tower, which is available in heights of 18 m (60 ft.) to 43 m (140 ft.). Prices range from (please call). Tilt-up versions of these towers are available for sites without crane access. Non-guyed lattice type towers and monopoles (tapered tubular) towers are also available to heights of 37 m (120 ft). Customers may also supply their own towers if they follow BWC's technical requirements for Excel towers (see Requirements).

The BWC EXCEL was introduced in 1983 and it has been installed at over 900 sites around the world.

Start-up Wind Speed: 3.4 m/s (7.5 mph)
Cut-in Wind Speed: 3.1 m/s (7 mph)
Rated Wind Speed: 13.8 m/s (31 mph)
Rated Power: 10 kW for grid intertie, 7.5 kW for battery-charging
Cut-Out Wind Speed: None
Furling Wind Speed: 15.6 m/s (35 mph)
Max. Design Wind Speed: 54 m/s (120 mph)
Type: 3 Blade Upwind
Rotor Diameter: 6.7 m (22 ft.)
Blade Pitch Control: None, Fixed Pitch
Overspeed Protection: AUTOFURL
Gearbox: None, Direct Drive
Temperature Range: -40 to +60 Deg. C (-40 to +140 Deg. F)
Generator: Permanent Magnet Alternator
Output Form: 3 Phase AC, Variable Frequency (Regulated 48 - 240 VDC after VCS-10 or 240 VAC, 1ř, 60 Hz or 220 VAC, 1ř, 50 Hz with GridTek® inverter).

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