Environmental Engineering Reference
In-Depth Information
other potentially damaging conditions, which may increase their cost. They may also
require special aviation permits or lighting.
3.4.2 Existing Multi-Use Tall Towers
At first glance, existing multi-use tall towers might appear to be a convenient and
cost-effective alternative to new, dedicated towers. No new structure is required and
often on-site power is already available for running existing equipment. However,
such towers of opportunity may also have significant drawbacks that make accurate
wind resource assessment more difficult. Points to consider when selecting an existing
tall tower for a monitoring campaign include the following.
If the tower is well outside the proposed turbine array, its value to the monitoring
campaign will likely be limited.
If the tower is unusually wide or it carries a lot of equipment such as commu-
nications dishes and radar repeaters, it may be difficult to obtain an accurate
reading of the free-stream wind speed.
The number of instruments that can be mounted and their heights and boom
lengths may be constrained by the tower owner or by structural considerations.
It may not be possible to access the tower whenever necessary to replace or
repair wind monitoring equipment.
The tower owner may install equipment at a later date that disrupts the continuity
of measurements; however, it should be possible to guard against this concern
in the tower lease agreement.
For these reasons, in practice, few wind projects are assessed solely or mainly on
the basis of data collected from existing multi-use towers.
3.5 PERMITTING FOR WIND MONITORING
Government-issued permits may be required before a wind monitoring tower can
be installed. Permitting requirements vary from country to country and even within
countries, and sometimes change over time, so it is recommended that the permit-
ting process and requirements be thoroughly researched early in the planning for the
monitoring campaign.
If the mast is to be installed on public or government-owned land, it will be neces-
sary to apply for permission from those agencies controlling access to and activities
on the land. Even on privately owned land, it is not unusual for a variety of regulating
agencies, from local to national, to establish permitting procedures for structures as
tall as wind monitoring towers can be. Civil aviation authorities, for example, may
establish a height above which a permit must be obtained; in the United States that
height is 61 m (200 ft). A permit may also be required if the structure will be under
an aircraft flight path or within a certain distance of an airport. Proximity to sites
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