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Zoning for Small Wind Turbines
A reasonable setback for a wind turbine tower
is equivalent to the height of the structure itself.
By MICK SAGRILLO
Mick Sagrillo, a small-wind consultant, owns
Sagrillo Power & Light
and is wind energy
specialist for Focus on
program. Research for
this article was funded
in part through
Wisconsin’s Focus on
Energy Program. Contact him at msagrillo@
Wind tower setbacks don’t
have to be onerous, but
consider the possibility
that a power line could fall
against the tower.
The past two columns have examined zoning considerations for small wind turbines. In the first, we
explained why wind turbine towers need to be so
tall, while the second laid out the best practice rules for
determining a wind turbine’s minimum tower height. In
this column, we’ll look at the issue of setbacks for towers.
Let us assume that zoning regulations on small wind
turbines exist to protect public health and safety. We will
not address the third leg of many zoning ordinances, general welfare, a catch-all category for noise, visual impact
and other annoyances. Health and safety are objective categories that can be backed up with facts and experience.
General welfare is far more subjective, often based on
emotion, whim, what’s in vogue, “community standards”
or pressure from a disgruntled neighbor. As a result, regulating on subjective criteria is categorized as “arbitrary and
capricious” in legal terms.
On the other hand, health and safety threats are more
or less easily documented and verified. I say more or less,
because some groups opposed to wind farms have imagined a variety of health threats. Over the 30-year history
of wind in the United States, we have a complete lack of
evidence that wind turbines pose any kind of health threat.
So we will address only the safety concerns of small wind
turbines, with the goal of meeting the concerns of the applicant, the neighbors and the local zoning authority.
People have erroneously referred to the need to protect the “fall zone” around a wind turbine. The “fall zone”
thus became a circle of land around the base of the tower
where the tower might land should a catastrophic failure
occur. The term “fall zone” conjures up a vivid image of the
consequences of what might happen in that area. The only
problem with the term is that few wind turbine towers have
ever fallen over.
There are several reasons why few towers have fallen
completely. The first is the engineering involved. Conventional engineering calls for a safety factor of twice the failure mode. Conventional engineering for towers, however,
often exceeds this margin of safety, frequently going as high
as five times the failure mode. Towers, based on the number of failures seen in the field relative to other structures,
are pretty safe structures. This includes their foundations.
In addition, when we analyze the failure modes for
towers of all sorts (communication, utility, observation
and wind turbine towers), we find that towers, when they
do fail, tend to buckle, not fall over. It is actually quite a rare
tower failure where the tower falls completely over, pivoting at its base.
Zoning regulations frequently include setbacks (from
the property line) for various types of construction, so it is
common to delineate a setback for a wind turbine.
A distance that is reasonable to protect safety is a setback
from the tower base equal to the “total structure height”
of the tower with one blade raised in the upright position.
This is the tallest that a wind turbine and tower could ever
be. For example, a wind turbine with a 10-foot blade on a
120-foot (36-meter) tower would dictate a setback of 130
feet ( 39 meters).
This setback can be required from adjacent property
lines or from neighboring inhabited structures, but also
from overhead utility lines and roads. In theory, a setback can be shortened with the permission of the affected
party, usually an adjacent landowner or the local department of transportation.
It is my experience that, for liability reasons, utilities
will not grant permission to do anything. Utilities typically have far shorter setback requirements. Just look at
the proximity of trees to utility lines, and the power outages that occur when limbs and whole trees fall over. It is
still good practice to adopt a total structure setback from
overhead utility lines. I know of no wind installers who are
interested in getting close to a utility line while climbing a
tower. For that matter, you don’t want the utility line falling
against the tower, either.
Finally, the tower setback does not apply to the homeowner’s residence or other structures on the property.
Are Greater Setbacks Needed?
While some neighbors may call for greater setbacks for
any number of subjective reasons, there is really no rational
justification based on safety for a setback greater than the
total structure height.
On the other hand, there are many instances of shorter
setbacks for wind turbine towers. I know of one tower only
four feet from the property line. This distance accommodates the foundation that extends four feet from the base
of the tower. The adjoining neighbor made no objection to
Next time, we’ll look at other items to consider in a zoning ordinance for small wind turbines. ST