MONITORING STATION INSTRUMENTATION AND MEASUREMENTS - Wind Resource Assessment: A Practical Guide to Developing a Wind Project - page 38

Figure 4-2. A propeller anemometer and wind vane. Source: R.M. Young Company.
• Durability. A wind resource monitoring campaign generally involves collecting
wind data for at least a year or two. To avoid the need for frequent and costly
replacements, the use of at least some anemometers capable of surviving and
holding their calibration in the field for the period required is recommended. In
some environments, a mixture of sensor types may be called for to achieve a
balance between survivability, data recovery, and accuracy. In an extended wind
monitoring program, provision should be made for the regular inspection and
replacement of anemometers.
• Operating Environment. Not every anemometer is suited to every environment.
Conditions that may cause problems include icing, heavy rain, lightning, sand and
dust, extreme temperatures, and saltwater intrusion. Extreme conditions can cause
anemometers and direction vanes to read incorrectly or stop working altogether.
Heated anemometers are available from most manufacturers to cope with icing,
and it is recommended that at least one or two be installed on every mast where
significant icing is expected. This will reduce data loss. Heated anemometers are
discussed further in Section 4.2.
• Starting Threshold. This is the minimum wind speed at which the anemometer
starts and maintains rotation. Since low wind speeds are of no interest in wind
energy generation, the starting threshold for most anemometers on the market is
adequate for wind resource assessment. The exception is anemometers designed
to measure vertical wind speeds, which must be sensitive to small departures
(both positive and negative) from zero.
• Distance Constant. This is a measure of how long an anemometer takes to
respond to an abrupt change in wind speed. It is defined as the distance that must