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Meteorological (met) towers are structures used to mount atmospheric sensors to measure wind and other local conditions Met towers serve multiple purposes in the wind energy industry. Met towers
may be used for wind resource assessment,
for micro-siting, or for ongoing monitoring of an operating wind farm.
Towers for Wind Resource Assessment and Micro-siting
Met towers for wind resource assessment and micro-siting are typically temporary
installations, and their design is optimized for minimal permitting and
rapid deployment. Tower systems are sometimes referred to by developers
as anemometers, signifying the paramount importance of their wind
speed measurement function. Other sensors that may be mounted on towers include wind vanes, which measure wind direction; and temperature, humidity, and rainfall sensors. Tubular towers may be referred to as "masts",
although this is more of a British/European usage.
 Met tower designs fall into two principal types. Tilt-up towers are used for wind resource assessment studies and other shorter term applications. Tilt-up towers do not require a foundation, which allows them to meet definitions of a temporary structure. They are made of rolled steel or pipe segments that are erected using a gin
pole and secured with guy wires. The guys are wire ropes which extend from the tower to anchors in the ground, in the front, back, and left and right side positions. The larger tilt-up towers have double guys at each guy point for stability - an "inner" set and an "outer" set. The overall diameter of the guy footprint is wider than the tower is tall. For example, Second Wind's 60 meter tower has an 84 meter footprint. This is an important factor to consider when siting the tower, as uneven terrain creates challenges for raising tilt-up towers. Guys come in "sets," with each set connected to its own guy plate, typically every 10 meters. Guys are made fast in the ground with anchors, selected according to the soil type (refer them to our anchor selection guide).
Tilt-up towers in the United States are typically 60 meters high; 70 and 80 meter towers are common in Europe.
 Lattice towers get their name from their
structure of three or four vertical elements cross-braced with welded supports.
Lattice towers require a foundation for safe footing,
and thus are classified as a permanent structure requiring permitting.
The effects of tower shadow
on lattice booms may require longer booms for lattice towers
than for tubular towers. Lattice towers come in various widths ranging
from 12" in diameter to 72". The tallest lattice towers can reach nearly
400 meters in height.
Met Towers for Wind Farm Performance Monitoring
Often an intensive study is performed early
in the operating life of a wind project, but ongoing monitoring should always
be performed on a wind project to make sure that the turbines are operating
effectively.
Met towers on wind farm sites are viewed as permanent installations. Guyed lattice towers have a longer expected lifetime and are therefore preferred to tilt-up tubular towers. Lattice towers can also be equipped with climbing hardware, which allows a technician to climb the tower to maintain the sensors and wiring. Either type of guyed tower will need regular guy tightening in a permanent installation. Freestanding towers, or un-guyed towers, are very appealing, especially in agricultural settings, because they have a small footprint and no hassle of siting and anchoring guy wires. Un-guyed towers may be either lattice (in which case they will be much wider than a guyed lattice tower of the same height) or monopoles, like many cell towers. However, they are much more costly than lattice towers and thus are infrequently used.
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