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Wind Power

Installation

Sites

Wind generators are installed at sites with frequently continuous high wind speed, such as the interior United States and Atlantic coast of Northern Africa:

Figure 1:  Proposed wind farm site on Northern African coast, to provide 5 to 10 GW of electricity to Europe. Trade winds provide suitable wind power sites on the coast of Northern Africa. Phosphate deposits indicate the trade winds have existed for millions of years. [NATO]
Figure 2:  Layout of the proposed wind power site. [World Bank]
Figure 3:  Suitable wind power sites in the United States are shown in purple, dark red, and blue. [DOE]

New Mexico

Portions of New Mexico are suitable for wind power, illustrated by purple areas on the preceding map. This section shows installation of a wind turbine in New Mexico in 2003. Newer wind turbines are even taller than this one.

Figure 4:  Large cranes are used to install a wind turbine tower in sections. The bottom section of tower is almost in place. Notice door/hatch in bottom section, to be used to enter the tower which has ladder built into the sections to climb to the top of the tower from within the tower. Section on the ground (right side of photo) shows ladder attached to the inside of tower. Vertical cables are later strung inside (to help hold sections together) in notches shown at far end of section on the ground.
Figure 5:  Generator (nacelle) is installed on top of the tower.
Figure 6:  Rotor with 3 blades is lifted (flown) to attach to the generator.

Wind Speed

To determine wind speed at heights above ground, a meteorological tower (“met tower”) may be installed at a wind farm.

Figure 7:  Installing a met tower in Texas in 2010. An anemometer sticking out near the top of the tower will measure wind speed at that height above the ground. The tower was assembled on the ground, and is being hoisted into vertical position with a truck winch. Newer met towers are taller with anemometers at different heights.

Taller met towers are more expensive to build. To measure wind speed at greater heights, Sound Detection and Ranging (SODAR) may be used. SODAR is like the doppler sonar on ship hulls that measure water currents underneath, but pointing upward instead of downward.

Figure 8:  SODAR levelling before operation.
Figure 9:  SODAR housing to reduce interference.
“interference occurs when side-lobe energy radiating from a SODAR antenna on transmit is reflected back to the antenna by nearby fixed objects such as buildings, trees, mountains, or towers.”
— 
Laura Bianco, “Introduction to SODAR and RASS-Wind Profiler Radar Systems” in Cimini et al., eds., Integrated Ground-Based Observing Systems, p. 104

The shapes of trees may be indicative of wind characteristics at a site:

Figure 10:  Flagging.

Land topography affects wind flow. Higher wind speeds may be found above ridges (slightly after), and in gaps between ridges.

Wake

A wind vane on the wind turbine determines the wind direction and controls a motor that changes the direction of the turbine rotor to make sure it points into the wind.

The wind passing generally perpendicular through the rotor area forms a tube that widens after the rotor plane because the rotor has converted some of the wind speed to electricity, causing that tube of wind to slow down (bunch up) thus widening the stream tube downwind.

That widened air tube after the rotor is called the wake and eventually disperses into the atmosphere downstream. After the wake disperses, another turbine can be positioned to extract kinetic energy from the wind again. It must be far enough away to not be in the wake of the turbine in front of it.

The wake starts disappearing from the outer part of the air tube first. Thus, positioning a downstream turbine between upstream turbines (instead of directly behind another turbine) allows it to be less far downstream. This is possible if the wind direction is usually in only one direction.

Figure 11:  Alternating wind turbine positioning.
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Wind Power

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