|
Wind energy has been used
for centuries, for grinding grain, pumping water and generating
electricity. Small wind turbines were an important source of electricity
for rural families in North America in the 1920s and 1930s. Wind
energy faded into the background with the rural electrification
efforts of the 1940s and the development of reliable small engine
generators.
Today, we are seeing wind gaining tremendous popularity in generating
significant amounts of power both off-grid and as a source of energy
for large utilities. European countries are leading the way in wind
generation while Canada generally lags behind. Alberta has an established
base of large-scale wind generators. Downtown Toronto now has a
commercial-scale
turbine
How it works
Wind turns the blades of the turbine which spins a shaft within
the turbine structure. The shaft drives a generator to produce electricity.
The electricity is either used directly or stored in batteries.
Types of Wind Generators
There are many different types and styles of wind generators. Many
of the older, multi-blade units as seen on farms across the nation
generate mechanical energy, often used to pump water.
- Small-scale units (under 3 kW): used to charge batteries
or direct use (such as pumping water or grid intertie). Purchase
Online
- Medium sized units (up to 50 kW): used in a grid-intertie
environment to generate power and feed it to the utility grid.
Energy Alternatives designs and installs medium scale units. Due
to the nature of these projects, each system requires a detailed
assessment prior to quotation or ordering products. Investment
is typically $40,000+.
- Large-scale units (megawatts): large, towering units
that cost millions of dollars and generate power to run hundreds
or thousands of homes or businesses. Generally suited to large
utilities and power co-operatives.
Wind and PV
In many Canadian locations, a wind turbine is an excellent supplement
to a solar electric system. Small wind systems are often combined
with photovoltaics because seasonal variations in wind and solar
resources are complementary. Most places in Canada do not have adequate
wind to use as a primary power source. Locations such as the prairies
that have constant prevailing winds are most suited to wind power.
Contrary to popular belief, coastal areas do not always provide
the best source of wind power - the winds are not as constant and
predictable as those on the prairies.
Battery Size
Wind is a variable resource. The winds may be calm for a week or
more, but when it does become windy it often blows very hard, most
notably in the winter. For this reason wind energy systems usually
require a larger battery to take advantage of the energy when it
is available and to store it for extended calm periods.
Maintenance
Unlike photovoltaic modules, wind turbines have moving parts. Periodic
maintenance of bearings, brushes and shafts is required. It is important
when installing a wind generator to consider how easy it will be
to access the generator and conduct maintenance.
Towers are a critical component of wind power systems. Proper location
and height of your tower is necessary to get maximum energy from
a wind turbine. Improper tower design or installation may result
in personal injury, property damage or a damaged generator. It will
also likely result in less-than-satisfactory performance from your
wind turbine.
You should be completely familiar with the installation procedures
before you begin. Safety equipment should be used at all times.
Check your local building department for bylaw or zoning restrictions
for towers.
Tower Height
Wind generator operation is dependent on the quantity and quality
of the wind hitting the blades. Turbulent wind will reduce the power
output as the turbine swings back and forth hunting for the wind.
The unequal stresses caused by turbulence and the variation in wind
speed between the upper and lower blades of a wind turbine installed
too close to the ground will reduce power output and wind turbine
life.
Wind speed increases rapidly with tower height. Doubling tower
height increases the available wind power by about 40%. It is often
more economical to install a higher tower rather than purchasing
a larger generator. A wind generator should be installed a minimum
of 33 feet (10 meters) above any obstruction within 330 feet (100
meters).
Tower Construction
Guyed towers are economical and are able to withstand very high
winds if properly installed. They require a fairly large area of
cleared land around the tower to facilitate the installation of
the guy lines. To supply the desired amount of support and keep
the stresses on the tower to a minimum, the guy lines should extend
as far as possible around the tower to a maximum radius of 80% of
the tower height. Guyed towers may be either lattice towers or tubular
towers. The tubular towers are frequently designed for tilt up installation.
They have the advantage of easy installation and turbine maintenance.
Self-supporting towers are the least visibly intrusive wind turbine
towers. They can be installed in rough terrain with a minimum of
cleared area. Very small wind turbines may be installed on a short
self-supporting tubular tower, but larger turbines require a lattice
tower.
Grounding
Tower grounding rods and wire provide lightning protection and assure
a low resistance path to ground. The grounding wire should be straight,
without sharp angles.
What you need for a wind system
Wind
• Wind generation is dependent on the quality and quantity
of the wind hitting the blades. The better the wind you have, the
more power you will generate.
• The power available in wind increases by the cube of the
wind speed - if wind speed doubles, power output increases by eight.
• Turbulent wind (from obstructions, geographical features,
etc.) will reduce the power output as the turbine swings back and
forth hunting for the wind.
A Good Site
• The higher a turbine, the more power is generated, the better
quality the wind.
• A wind turbine should be at least 40 ft above any object
within a 400 ft radius. Note there are often exceptions to this
rule depending on your site.
• It is often more economical to install a higher tower than
purchasing a larger turbine.
• Space. Generally locations with an acre or more will be suitable.
Most urban locations will not permit you to install a wind generator
in your yard. A guyed tower requires 1/2 the height of the tower
as a radius at a minimum for location of anchor points. Space is
also required for ground assembly and erection of the tower. Lattice
towers require less surface area, but are more complex and expensive
to install.
Get the data
Measuring Wind
There are three primary ways of determining how much wind is available
on your site:
1. Installing an anemometer:
• The most accurate way to determine wind speed.
• Can take several years of readings and some expensive equipment
to compile accurate data - unless you plan on spending $15 000 or
more on a wind energy system, this is usually not a necessary step.
• Inexpensive anemometers can be read manually on a daily or
weekly basis - a minimum of 3 months of data should be recorded
and correlated with another source of wind data for a small wind
generator.
• Some people install a small wind generator and use it as
an anemometer if they are planning for a much larger installation.
• Home weather stations will often have a facility to measure
wind speed - this may or may not be completely accurate, but will
allow you to notice trends in speed and direction.
2. Using existing data:
• Local airport or meteorological stations.
• Universities, colleges and radio stations.
• There may be some data from government sources, but unless
a weather station is nearby the data may not be accurate for your
site.
• Wind speeds can vary a great deal within a small area, so
this information should be correlated with another method such as
visual observations.
3. Visual observations (the Griggs-Putnam Index):
• The simplest and quickest method of determining average wind
speed is to observe the effects on vegetation at the site.
• If the trees or shrubs are growing with a definite slant
to one direction, or only branches on one side of the tree, you
will have a very good wind site. It takes constant, prevailing winds
to affect vegetation in this way.
• If you have a flag at your site and the flag is stiff in
the wind for a few hours a day then the site is a good candidate
for wind power. Keep a log book of flagpole observations to help
give you some idea.
• Flying a kite is a lot of fun and lets you get to know the
wind at your site and offers you some predictions as to what height
of tower will be best for your site.
• If there is another wind turbine in your area, track down
the owner or person responsible and they will more than likely be
willing to share their observations of wind patterns
|
