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small wind turbine tower Foundations
Inspectors should make sure the groundwork is well-laid.
by MICK SAGRILLO
mick sagrillo (msagrillo@
sagrillo Power & Light is
a small-wind consultant
Ifrequently get calls from permitting authorities con- cerned about wind turbine and tower engineering, and how best to assure a good small wind installation. They
often want to require an independent engineering review of
the project. That engineering review is not only extremely
expensive, but also unnecessary.
turbine and tower engineering
The building inspector
should affirm that the foundation will meet the specifications of the drawings
— this is one of the most
critical, yet overlooked,
A local engineer is forced to make many assumptions. The
local firm has its own expensive insurance policy in case
those assumptions prove wrong. The cost of this second
level of insurance is built into the review fee.
Copyright © 2011 by the American Solar Energy Society Inc. All rights reserved.
so, what’s the Problem?
Most permitting officials find this explanation acceptable. That doesn’t mean they should just sign off on the
system. There are a couple of requirements that can help
assure a successful project.
First, local permitting authorities should require that
turbine specifications and tower drawings from the manufacturers be submitted along with the building permit
application. These need not be wet-stamped engineering
drawings — photocopied documents from the manufacturers are sufficient. After all, submitting falsified documents is
fraud, and no responsible party wants to go there.
The drawings should include foundation plans and
specifications. This turns out to be one of the most critical, yet overlooked, requirements for a building permit.
For whatever foolish reason, several disreputable installers
have cut corners under-sizing their foundations. I’ve seen
several corner-cutting installations pull a concrete pier
right out of the ground, destroying the whole system as
the tower crumpled.
The simple solution is a quick inspection of the
excavation, forms and rebar before the concrete pour.
The building inspector should affirm that the foundation
will meet the specifications of the drawings. “Pre-pour”
inspections would have prevented the foundation failures
mentioned above. Those turbines would still be flying, and
the lawsuits avoided.
Interestingly, the original requirement for an independent engineering review would not have prevented these
failures. In fact, requiring a wet stamp can actually induce a
false sense of safety since the drawings themselves have no
bearing on the quality or safety of the installation, except
to verify the manufacturer’s specifications for what should
be done. After that, the assurance of a safe installation can
only come by carrying out the instructions to the specifications of the drawings, with follow-up by an inspector who
actually reviews the drawings and measures the forms in
the ground for compliance.
This simple process saves the applicant unnecessary
wet-stamp engineering costs, yet provides the permitting
agency with the assurance that the installation is completed to industry standards. This, along with the National Electric Code requirements for wiring, indicates that
the system was installed using small wind industry best
practices and due diligence — the most that a permitting
authority can ask for. ST