Rooftop Wind Turbines: Do You Have What It Takes?
Rooftop wind turbines, also called rooftop wind generators,
offer a relatively inexpensive way to participate in the rush to
renewable energy systems.
The same technology used in large residential turbines has
been incorporated into smaller, rooftop versions costing as
little as $600.
But the limitations of a rooftop installation require your specific
location to "have what it takes," or meet certain requirements
before a rooftop turbine begins to make economic sense.
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
shown below for Southwest Windpower'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
Overall, the payback from a single, roof
mounted turbine in tangible financial terms
leaves a lot to be desired; even in light of the
new 30% Federal tax credit for residential
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
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
Although wind speed charts for the United States and Canada 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.
Readings 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.