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Towers
Wind Generators

When the wind blows, the rotor blade stops a percentage of the wind. That percentage is converted into energy.  The maximum amount of wind energy that can be converted is 59.3%. This limit is known as the Betz Limit.  In spite of this limit, the most efficiency that can be realistically be achieved is about 25%.

Effective use can be made of wind power generally starting at 10 mph. or about 16 kph. A wind energy system usually needs an average annual wind speed of at least 15 kph.

One of the first steps is to determine if a wind energy is feasibly by finding out how much wind energy is available. This is done with a measuring device called an anemometer. Anemometers come in all sizes and forms.  Before you purchase a device best suited for the handlebars of a child's bicycle consider the tens of thousands of dollars investment.  With data logged over time a wind speed distribution curve, a chart of the number of hours wind blows at various speeds can be produced.

Most Canadian locations in have occasional strong winds while prevailing winds are lighter  . In many Canadian locations, a wind turbine is an excellent supplement to a solar electric system. Small wind systems are often combined with photovoltaic because seasonal variations in wind and solar resources are complementary.  Most places in Canada do not have adequate wind to use it as a primary power source.

After installing an alternative energy system, most customers reduce their yearly electric bill substantially, both through the installation alternative energy technology and by learning how to use less electricity without making do with less amenities. Some customers have done away with their electric costs altogether! Check out our great links page and see which provincial and federal tax credits are available when buying an alternative  energy system are available to your home, cottage or business.  Our governments are getting into the swing of things as they help reduce dependence on existing infrastructure, reduce emissions and reduce your financial investment as an incentive for the use of alternative energy.

The common designs :

  • 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.

Two basic types of airfoils (blades) a lifting and drag type.

  • Like the blades on an old Dutch wind mill or American water pumping wind mill the drag style airfoil blades are flat. Wind pushes the blades causing rotation. Drag style blades work well in areas with light wind and develop considerable torque. In medium to higher winds, drag style airfoils are not as efficient.
     
  • The lifting style airfoil with a cross section like an airplane's wing are used on most modern wind turbines.  An 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..

Let's start with a simple commons sense statement. Wind generators or turbines may provide an economical source of power if you have the right location.   Like my economics teacher taught me about retail and restaurant businesses,  "Location! location! location!  Location is everything!"  The same is true for wind power generation.

What makes for a good location? There are many factors. The following is a list of especially good locations:

  • On the shore of large bodies of water, a western exposure is frequently best.
  • Within a wind tunnel that runs East/West, preferably with a clear Western exposure, an area where wind is funneled and concentrated.
  • High areas, especially high areas with an open view to the west clear of obstructions.

Locations are generally degraded by some of the following:

  • Tall and irregular forest canopy or other irregular obstructions surrounding the location.
  • Situation in a North/South running valley or behind a hill to your West.

Before investing in a wind generator and tower it is best to position an anemometer (wind measurement device) and monitor it's output for as long as a year. Commercial wind generating operations spend as much as $50,000 to $100,000 and more on a wind study before investing in a wind generating site. The wind in your location needs to be understood as this will determine whether a wind generator is practical and also the size and type of wind generator that will be most efficient in your location.

What does an anemometer cost? 

We've seen them for as little as $100.  Customers that have purchased these from big box and hardware stores tell us that they're only good for twirling a blade and probably best mounted on a child's bicycle handlebar as decorations.

Top-of the line models with their own logging devices and download to a computer can cost as much as $2,000.  ...then there's the tower you need to mount it upon.  There are good cost effective solutions in between these two extremes!

Towers

Because a wind generator needs "clean" or non turbulent air to work efficiently a wind generator must be mounted above the turbulence.  Normally this means that the wind generator must be mounted 30' higher than the surrounding trees and houses. 

We do not recommend towers attached to roofs or building structures.  Turbulence is caused by the shape of a pitched roof, the resulting vibration is transmitted to the structure.  Because of this and because a roof is designed for loads not torque and lift, we strongly recommend against mounting a wind generator on a roof our even against the gable of a structure.

Factors Affecting Wind Turbine Performance

Height - Wind speed increases by 12% as the distance between the turbine and ground is doubled. Canadian weather offices report wind speed at the standard height of 10 m above the ground.

Obstructions - Wind near is slowed by trees, buildings, hills and mountains which all create some form of friction which restrict free airflow. It is wise  to measure the wind speed at a proposed site for at least one year to determine project viability.

Clean Air - Turbulence, not high wind velocity is the main cause of wind generator failure during a storm.  Extreme wind velocity is more likely to harm a tower than to harm properly installed wind generators.  Buffeting and turbulence is to be avoided at all cost.

Air temperature - Colder air is denser and increases power output. The power from a wind turbine will increase almost 16% as the temperature drops from + 20 C to - 20 C for any given wind speed.

Distance / Resistance - Wind generators are usually mounted away from the point of use for the electricity they produce. Many or most wind turbines develop alternating current (AC) which is rectified to direct current (DC) for use in batteries. The higher the voltage (and the lower the current [amperage]) the less loss you will incur.  Keep voltage as high as possible while transmitting it.  The alternative is to use heavy (expensive) cabling to reduce line loss due to resistance.

Variable Resource

Because wind energy is a variable resource, wind generation systems usually require a larger battery storage bank to take advantage of the energy when it is available and to store it for extended calm periods.  An alternative if it is available in your area is to tie wind generated electricity to the grid and "sell" back your excess energy.

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Last modified: September 21, 2017