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Green Collar Careers - Wind
Turbine Design
Over the last 5 years Wind Turbines has seen a phenomenal growth in
commercial AC production. Several European countries have taken
a strong leadership role including Germany, Great Britain and Spain.
From a commercial standpoint wind energy makes a strong economic case;
it has a higher production cost then natural gas or coal although it
is less expensive then nuclear when all operational costs are
considered. Commercial AC systems are quite different from the
systems you'll see on farms and private homes due to the scale of
production. Two reasons account for the differences:
| First, commercial AC
generation uses a much larger scale system measured in megawatts
rather then kilowatts. The towers are very tall, typically
300' high. Wind flow closer to the ground below about 100'
tend to be interrupted by objects and a condition known as laminar
flow - the lower boundary layer of air between the ground and the
undisturbed natural layer of flowing air.
The image at right depicts the difference in wind speed for a 75
and 300 foot tall tower. Different terrain has different
effects on the lower boundary layer but you get the idea.
Wind turbine production is not a linear
relationship to wind speed; most wind turbines need at least
8MPH wind to turn at all, and generally the power produced at 20
mph wind speed is 3-4 times that at 10 MPH wind speed. |
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Second, the mechanical nature of a wind turbine tends to make the
system significantly more maintenance intensive then a solar PV cell
system. For someone with only one or two wind turbines the
occasional service required may not be a problem. Full scale
commercial AC wind farms hire a staff to climb the towers and perform
maintenance.
Wind speed is the crucial factor in design. No
matter how tall the tower is, if you don't have a sufficient average
sustained wind speed a wind turbine will be nothing more then an
expensive yard ornament. Wind speeds are generally very
unpredictable from one location to another mostly due to surface
features of the earth. For example locations with hills,
mountains, and passes may offer a spectacular application site while
sites less the a mile away won't produce enough juice to run a light
bulb. San Gorgonio Pass near Palm Springs California is an
example of the perfect location for wind turbines; wind speeds in San
Gorgonio Pass average about 18 MPH year round while the Palm Springs
airport has an annual average wind speed of 7.3 MPH - less then 10
miles away.
With over half the population living in a coastal community, and as
wind tends to be more powerful along the coast there are some good an
bad points to consider. The good point is there will almost
always be a enough wind to produce power. The bad points are
that occasional storms and very high winds are likely to pose a risk
to a long term installation and salt spray carried inland 1-2 miles
may tend to accelerate maintenance requirements.
If you find a site that has a steady supply of wind that exceeds an
annual average wind speed of 8 MPH it may be an excellent candidate
for a wind turbine. The
Solar Site
Survey Regional Wind Speed worksheet has the average annual wind
speeds reported for 275 locations across America. The site
specific may vary for local terrain reasons.
The design technology varies among the dozens of manufacturers, but
there are the key system design elements to look for:
- Brushless Alternator design
- Gearless technology - newer rare earth magnets allow the
alternator to produce sufficient power at shaft speeds equal to the
turbine speed.
- Low wind start up speed
- Output Graph performance - kWh/Wind Speed - compare systems
- Survivable wind speed
- Manufacturer Warrantee
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