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Back to Basics: wind-site assessments
by MICK SAGrILLO
mick sagrillo (msagrillo
@ wizunwired.net) of
sagrillo Power & Light is
a small-wind consultant
and educator.
In the September/October issue, I described the best ools for estimating the wind resource for a small wind turbine and discussed the need to have a trained wind-site assessor evaluate your potential wind site. This column
will lay out the items that should be covered in a thorough
wind-site assessment.
What to
expect from
a wind-site-assessment
report.
Initial contact
On first contact, determine the site assessor’s qualifications and any ties he or she might have to small-turbine manufacturers, however loose those ties may be. For example,
many practitioners (but certainly not all) were trained at
a workshop sponsored by a manufacturer. Such trainings
vary considerably in quality. Some adequately cover the all-important topics of wind turbine towers and siting, while
others focus far more on simply closing the sale. Training
from or association with a manufacturer is not a fatal flaw,
but it is good to know if there will be any potential bias. For
instance, if the assessor represents a company that offers one
tower size for all sites and applications, look elsewhere, as all
you are likely to come away with is an intense sales pitch.
The first piece of information that the assessor will
require is your annual electricity usage. She will likely
ask you about your major appliances and try to identify
energy-efficiency strategies that make sense in your situation. Keep in mind that it is always cheaper to use energy
more efficiently (with compact fluorescent lighting and
high-efficiency appliances) than it is to install renewable
energy equipment to offset electricity consumed by wasteful appliances. The rule of thumb is that every dollar spent
on efficiency saves three dollars in generating capacity.
Make sure that you settle on a price for the site-assess-ment service, which should include a written report to be
delivered on some reasonable date.
the site Visit
When the assessor visits, he will want to walk around
your premises. He is simply getting a lay of the land and
looking for current and potential future obstacles that will
affect the performance of the wind turbine by restricting
wind flow. The assessor will also want to know your preferred location for the turbine and tower, as well as the
location of the building where the controls and inverter for
the system will be housed. The assessor will determine the
heights of tallest obstacles on the property, usually trees,
and their distance from the proposed tower site. These
numbers will be used to determine the minimum acceptable tower height for the location and help in estimating
the average annual wind speed for the site.
A good assessor will take pictures of the site in eight
or more directions, for two reasons. The first is simply to
refresh his or her memory when reviewing your site infor-
mation. The second reason is to include these pictures in the
wind-site-assessment report. It is not unusual for a wind- site-assessment report to be reviewed by the permitting or zoning
authority, the local utility, financing or granting institutions
including banks, the state public benefits program or the U.S.
Department of Agriculture (USDA). Photographs will help
them understand what you plan to do.
the final report
The assessor’s formal report should include —
•;The;minimum;acceptable;tower;height;for;the;site
based on terrain and ground clutter. This should take into
account the height that the surrounding trees will attain in
the 20- to 30-year life of the wind system.
•;The;wind;rose;for;the;site,;detailing;the;seasonal;pre-vailing wind directions and any patterns. This is useful for
siting the tower upwind of obstacles to minimize ground
drag and turbulence.
•;Aerial;photographs;of;the;property;showing;all;struc-tures, infrastructure and trees within a 500-foot radius of
the tower location.
•;Topographic;maps;of;the;area;with;a;1;to;3;mile;radius
that conveys a sense of the lay of the land.
•;The;conservatively;estimated;wind;resource;at;the
site at the minimum tower height specified, as well as an
explanation about how the average annual wind speed for
the site was arrived at.
•;A;list;of;several;wind;turbine;models;that;will,;ideally,
offset the electrical consumption of the owners. The suggested turbines may include systems that are larger than
required to account for future growth in consumption, or
smaller than currently required if there are opportunities
for efficiency savings.
•;The;estimated;annual;energy;output;of;the;suggested
turbines, at this location, at the specified tower height and
estimated wind speed. In the end, this is really the purpose
of a wind-site assessment — to estimate how much electricity this investment will generate that offsets utility-supplied
energy. An explanation of how the annual energy outputs
were arrived at should also be included.
In addition, some public benefits programs, as well as
the USDA, may require additional information for their
grants — specifically, any historical disruptions or environmental ramifications of the project.
Based on the above, the assessor will make recommendations to the customer to optimize the wind resource at
the site with a small wind system.
Finally, the assessment will need to specify how the customer should proceed. The customer’s first tasks should be
contacting the local utility for the interconnection requirements and an application and the local zoning authority for
the building permit. ST
