Page 115 - Fluid Power Engineering

W i nd Measurement 93

correlation of the measured data with concurrent long-term dataset.
If this correlation is low and the project economics is borderline, then
there is no option but to continue measurement for 2 –3 years. Even if
theprojecteconomicsisfavorable,butthedegreeofuncertaintyishigh
because of measurement for shorter duration, investors may perceive
the project as high risk and, therefore, demand a higher return. Longer
measurement period will reduce the degree of uncertainty associated
with wind speed and, thus reduce project risk. For large wind farms,
it is normal for financiers to demand 2–3 years of met-tower data.

Installation of Met-Towers
Detailed guidelines for installing met-towers are available in the doc-
umentation supplied by the vendor of the met-tower. Proper planning
and appropriate safety precautions can mitigate the risk of cost over-
runs and failures. Before installing a met-tower, the following should
be done:

Examine the wind rose at the location. This will describe the pre-

dominant direction of wind and, therefore, is the primary in-
put into orienting the instruments on the tower.
Understand the terrain. Ensure that there is sufficient lay down

area to assemble the tower. For example, a 60-m tower may
need a lay down area of at least 80 m × 6 m, if the wind
direction is consistent.
Procure gin pole and winch. The winch must have the right size

drum that can hold sufficient length of wire. For example, a
60-m tower will need about 100 m of wire on the winch drum.
A crew size of four or more personnel, or as specified by the

tower vendor, is required to erect the tower.
Obtain local permits for the type of met-tower that is being

installed. Check the soil conditions and procure the right type
of anchors for the guy wires. Some states require Rev-G tow-
ers, which means procuring the right kind of tower and base.
In some situations, a concrete foundation for the tower may
be needed.
Procure and install proper electrical grounding rods.

Check the weather conditions, specifically rain and wind, be-

fore scheduling an install. Met-towers cannot be installed in
moderate to high winds and during thunderstorms.
Plan the orientation of instruments based on “Placement of

Sensors” section. In addition, ensure that guy wires do not
disturb the airflow over the instruments.
Program the data logger and communication equipment and

prepare documentation and forms before going to site.