Page 111 - Fluid Power Engineering

W i nd Measurement 89

8%
40-m tower 50-m tower 60-m tower
7%
Wind speed error at hub height 5% 1 4
6%

4%

3%

2%

1% 2 3 Upper anemometer
at mast height
0%
10 20 30 40 50 60
Lower anemometer height [m]

FIGURE 6-11 Error in wind speed at 80 m that is computed using wind shear
based on wind speed measurements at two heights. The measurements were
with anemometer of Class 1.5. (From Taylor, M., Mackiewicz, P., Brower, M. C.,
Markus, M., An Analysis of Wind Resource Uncertainty in Energy Production
Estimates, EWEC, London, 2004.)
an uncertainty of 4% in the computation of shear and wind
speed at 80 m height will be assumed.
Total uncertainty because of the three independent sources is:

2
2
2
2
ε = 0.039 + (0.015 + 0.005 ) + 0.04 = 5.8%
Other Sensors
A temperature sensor, barometric pressure sensor, and solar radia-
tion sensor may be added to the met-tower. The temperature and
pressure sensors help to compute air density accurately. The temper-
ature sensor is also used to detect icing conditions that can cause the
sensors to stop or produce errors in measurement.

Data Logger and Communication Device
Data logger is a device to which all the sensors are connected. Typical
data loggers have 12–15 channels to which, for example, six anemome-
ters, two wind vanes, a temperature sensor, a solar radiation sensor,
a barometric pressure sensor, and others are connected. Data loggers
also have: