Wind Resource - Wind Energy: Renewable Energy and the Environment - page 62

Anemometer

FigUre 4.8 Meteorological station in Jujuy, Argentina.

a sine wave. The transducer counts zero crossings (sampling time is generally 1 Hz), so wind speed
is related to number of counts. The advantage is that signals can be transmitted 150 m without loss
of accuracy (none of the problems of attenuation and amplification needed with analog signals). An
estimate of the accuracy of cup anemometers in wind tunnels is reported to be ±2% [27].
Another type of cup anemometer has a disk containing up to 120 slots and a photocell. The peri-
odic passage of slots produces pulses in each revolution of the cup. This gives a better resolution, so
the sampling rate can be increased to 5 Hz.
The propeller anemometers ( Figure 4.11 ) have faster response and behave linearly in chang-
ing wind speeds. The wind speed is measured by measuring the voltage output of a DC generator.
The propeller is kept facing the wind by a tail vane, which also works as a direction indicator. The
accuracy normally is about 2% for wind speed and direction. The propeller is usually made of

Speed Power

6 250

5

200

4

150

3

100

2

50

1

0 0

72 74 76 78 80 82 84 86 88 90 92

FigUre 4.9 Wind speed data for Mexicali Airport, Mexico.