Environmental Engineering Reference
In-Depth Information
enough to a source of AC power to make connecting to it worthwhile. Nevertheless,
where AC power is conveniently at hand, the instrumentation loads are unusually large,
or solar panels are not practical, then AC power can be the right choice. It should
be used only to trickle-charge a storage battery, not to power the logger directly. A
surge/spike suppression device should be installed to protect the system from electrical
transients. In addition, all systems must be properly tied to a common earth ground
(Chapter 5).
4.7.4 Other Power Options
Other power sources that may be used in some circumstances include small wind
systems, wind/solar hybrid systems, and diesel generators. Small wind and wind/solar
hybrid systems can be a good choice where there is plenty of wind and limited solar
radiation (e.g., in arctic environments) or where solar panels are likely to be blocked
by trees or other obstacles most of the time. Diesel generators require refueling, but
there are sites where they are practical.
4.8 TOWERS AND SENSOR SUPPORT HARDWARE
4.8.1 Towers
Towers for wind resource monitoring come in several varieties. There are two basic
structural types: tubular and lattice. Tubular towers consist of a single hollow pole or
several segmented hollow poles connected end to end, whereas lattice towers consist
of either three or four segmented corner poles attached by interconnecting struts. For
both types, three versions are available: tilt-up, telescoping, and fixed. Tilt-up towers
are mounted on a hinged base, and the unhinged end is raised into place using a
winch and cable. Telescoping towers are jacked up from a vertical position. Fixed
towers are generally lifted into place. In addition, towers can be either self-supporting
or stabilized by guy wires anchored in the ground. Self-supporting towers require
sufficient structural strength to resist lateral wind loads on their own. Guyed towers
can be less massive since they derive their lateral stability from the wires.
For most sites, tubular, tilt-up towers are preferred for wind resource assessment
because they are relatively easy to raise and lower (i.e., the tower can be assembled
and sensors mounted and serviced at ground level), they require minimal ground
preparation, and they are relatively inexpensive. However, tilt-up tubular towers are
currently limited in height to 80 m, and so fixed towers (usually lattice type) must be
used if a greater height is desired. In some regions, lattice towers are widely used for
all heights because they can be cheaply manufactured locally.
Towers should be strong enough to withstand the extremes of wind and ice loading
expected at the location and should be stable enough to resist wind-induced vibration.
Tower manufacturers should be able to provide guidance on allowable environmental
conditions. Note that some jurisdictions have their own design requirements for wind
and ice loading, which can have implications for the permitting process. In coastal
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