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.
Links to our wind turbine pages
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