Rooftop wind turbines offer a relatively inexpensive way to
participate in the rush to renewable energy. The principle allure is low
installation cost. Typically, tower installations for larger turbines add
50-80% to the cost of the system. With a rooftop turbine, an $800 tower is
replaced by a $39 roof mounted tripod, or a length of pipe attached to the side
of the house.
According to Ron Stimmel of the American Wind Energy
Association, "…rooftop turbines still account for only 1 percent or so of
the 10,000 small wind turbines that are sold each year in the country."
For this reason, few performance statistics are available from actual owners.
It's possible, however, to get an idea of the estimated
power output of a rooftop turbine from the manufacturer's website. For example,
the Energy Performance chart for Southwest Wind power's 200W Air Breeze predicts 20-30 kWh (kilowatt hours) per month
from 10-12 mph winds occurring 6 hours per day.
To put this in perspective, 30 kWh is less than 5% of the
power consumed each month by the average household. Overall, the payback from a
single, roof mounted turbine in tangible financial terms leaves a lot to be
desired; especially in light of the fact that unlike solar, there is no Federal
tax credit for residential wind power.
But anyone thinking about installing a rooftop turbine(s) is
probably aware of this already. The rooftop wind enthusiast is not motivated by
financial relief, but rather the intangible rewards of pride of ownership,
walking the walk, or simple satisfaction as a hobbyist.
Motivation aside, it doesn't make sense on any level to
proceed with a wind powered project unless the three following requirements are
met:
1. Higher than average cost per kWh. The more you pay per
kWh for electricity, the more economical wind power becomes. A rule of thumb in
the wind turbine industry states a residential wind powered system shouldn't be
considered unless you pay $0.10 or more per kWh for electricity.
The easiest way to determine your cost per kWh is divide the
current monthly balance on your electric bill by kWh usage (also plainly stated
on your bill).
2. Building codes. Visit your building department to find
out if there are any zoning restrictions for roof top turbines. Don't build
your rooftop system first and ask questions later - only to be told it violates
zoning laws and must come down.
3. Minimum wind speed. Wind speed of 7 mph, or 3 m/s (meters
per second) is the start up speed for just about every wind turbine. However,
in order to get any "juice" out of the turbine, minimum wind speeds
of 10-12 mph for 6 hours per day are necessary.
Although wind speed charts for the United
States and
are available to help site larger turbines, they're of little use for rooftop
systems because the data is collected at a minimum altitude of 30 meters (98.4
feet).
However, you can get a good idea of the wind speed at
proposed turbine locations by purchasing an anemometer (wind speed meter) for
around $150. The kit comes with a rooftop sensor, 60' of cable and mounting
hardware for the read out display. These are not data logging meters, so you'll
have to keep notes on your observations.
If you're really serious about wind speed data collection,
you can purchase a data logging anemometer kit with tracking software for $400.
Depending on where you live, wind speeds generally fluctuate
with the seasons. taken
during the hot summer months of July and August, when you're begging for a
breeze, are not usually a reliable indicator of average yearly wind speed.
Also, rooftop turbines located at the edge of a long flat
roof experience much more wind than those located on roof peaks.
If, after a month or two of collecting data you determine
there just isn't enough wind for a rooftop wind turbine, you can always resell
the anemometer and turn your attention towards solar.
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