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Small Wind Turbines
Q & A
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.
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What is wind power?
Wind energy is a form of solar energy. Sunlight falling on oceans and continents
causes air to warm and rise. Cooler air rushes into the space left by the risen
air, which in turn generates surface winds. Wind systems capture the energy in
wind using large blades mounted on tall towers called turbines. The wind turns
the blades and the blades rotate a generator, which produces electricity.
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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.
Wind turbines consist of large blades mounted on tall towers attached to a
horizontal shaft. As the wind blows, these blades cause the shaft to turn. The
shaft is attached to a generator located inside the head, or “nacelle” of the
turbine, which creates electricity.
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How do residential wind turbines work?
A wind turbine, which is installed on top of a tall tower, collects kinetic
energy from the wind and converts it to electricity that is compatible with a
home's electrical system.
In a normal residential application, a home is served simultaneously by the wind
turbine and a local utility. If the wind speeds are below cut-in speed (7-10
mph) there will be no output from the turbine and all of the needed power is
purchased from the utility. As wind speeds increase, turbine output increases
and the amount of power purchased from the utility is proportionately decreased.
When the turbine produces more power than the house needs, the extra electricity
is sold to the utility. All of this is done automatically. There are no
batteries in a modern residential wind system.
Small wind systems for remote applications operate somewhat differently.
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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.
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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.
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Will a small wind turbine save me money?
The wind turbine typically lowers your electricity bill by 50 to 90 percent. It
is not uncommon for wind turbine owners with total-electric homes to have
monthly utility bills of only $8 to $15 for nine months of the year. In northern
parts of the country where less air conditioning is used the bills can be very
low year-round. The amount of money a small wind turbine saves you in the long
run will depend upon its cost, the amount of electricity you use, the average
wind speed at your site, and other factors.
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What size turbine would I need for my home?
Homes use approximately 9,400 kilowatt-hours (kWh) of electricity per year
(about 780 kWh per month). Depending upon the average wind speed in the area, a
wind turbine rated in the range of 5 to 15 kilowatts would be required to make a
significant contribution to meet this demand.
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Who should consider buying a wind turbine?
A residential wind turbine can be a relatively large device and is not suitable
for urban or small-lot suburban homes. Except for very small wind turbines
(i.e., with rotors one meter or less in diameter) on very small towers, a
property size of one acre or more is desirable.
The economics of a wind system are very sensitive to the average wind speed in
the area, and to a lesser extent, the cost of purchasing electricity. As a
general rule of thumb, if economics are a concern, a turbine owner should have
at least a 10 mph average wind speed and be paying at least 10 cents/kWh for
electricity.
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Will it help the environment if I install a wind turbine at my home?
Yes. Wind turbines produce no pollution and by using wind power you will be
offsetting pollution that would have been generated by your utility company.
Over its life, a small residential wind turbine can offset approximately 1.2
tons of air pollutants and 200 tons of greenhouse gases (carbon dioxide and
other gases which cause climate change).
What are the environmental benefits of wind energy?
Wind energy is a very clean source of energy. It does not produce air emissions
or hazardous waste.
Wind energy offsets the emissions of other energy sources, thus reducing our
contribution to global climate change.
Using wind to produce enough power for over 200 homes (2,000,000 kWh) of
electricity instead of burning coal will leave 900,000 kilograms of coal in the
ground and reduce annual greenhouse gas emissions by 2,000 tonnes. This has the
same positive impact as taking 417 cars off the road or planting 10,000 trees.
Wind energy generation avoids the production of greenhouse gases, sulphur
dioxide, carbon dioxide, nitrogen oxide, heavy metals and particulate matter.
Using wind energy in place of conventional energy reduces the generation of smog
and acid rain.
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Do wind turbines make noise or interfere with TV reception?
Small wind turbines do make some noise, but not enough to be found objectionable
by most people. A typical residential wind system makes less noise than the
average washing machine. Wind turbines do not interfere with TV reception.
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Will I have to change any of the wiring in my house?
No. A wind turbine is easily retrofitted to virtually any home without the need
to change any wiring or appliances. In most cases, the utility will install a
second utility meter to measure how much surplus electricity it is purchasing
from the turbine owner.
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What about towers?
An 80- to 120-foot tower is usually supplied along with the wind turbine. Towers
this tall are necessary to raise the wind turbine above turbulence generated by
obstacles on the ground and trees. Wind velocity and, therefore wind turbine
performance, increases with altitude. Several different types of towers are
available, depending upon which manufacturer you select. Each type has its
advantages; the most economical type of tower is the guyed lattice tower, but a
hinged tower can be easier for you to install yourself and provides easier
access for maintenance.
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How reliable are wind turbines? Will I have to perform much maintenance?
Most small turbines have very few moving parts and do not require any regular
maintenance. They are designed for a long life (up to 20 years) and operate
completely automatically.
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How do wind turbines perform as an investment?
The wind system will usually recoup its investment through utility savings
within six to 15 years and after that the electricity it produces will be
virtually free. Over the long term, a wind turbine is a good investment because
a well-sited wind system increases property value, similar to any other home
improvement. Many people buy wind systems in preparation for their retirement
because they don't want to be subject to unpredictable increases in utility
rates.
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Do the wind turbines operate at low wind speeds? Can the winds be too hard?
Today's 1 to 3 megawatt utility-scale wind turbines need winds of about 7mph to
"cut in" and can operate in winds up to 55 mph, at which point safety measures
activate to prevent damage. They are rated to survive gusts in excess of 130 mph
winds. Machines with advanced electronic control systems continually adjust to
get the most power out of different wind speeds. This "variable speed" operation
enables the extra energy in wind gusts to be converted into electrical power
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