Wind Measurement Stations

 Measurement Stations for Wind Turbine Site Assessment  

Wind turbine

Wind measuring system: Shelter box

Wind measuring system: Mast installation, solar panel

During the promotion of wind energy projects it is required to obtain detailed information about the wind resource at the planned wind turbine site to guarantee a correct prognosis of the energy yield. Wind measurements provide the most accurate information. Wind speed, wind direction, and optionally other relevant data for wind turbine site assessment are recorded for at least one year in order to consider seasonal fluctuations.

A wind measurement station consists of the following components:
Anemometer
Cup anemometers measure the horizontal wind speed. In order to determine the vertical wind profile, wind speed is measured at a minimum of two or three different levels. The determined profile exponent is used to extrapolate the wind climate to hub height of the wind turbine.

The power of the wind flow increases proportional to the cube of the wind speed. An error in measurement of 5% for the wind speed results in an error of 15% for the energy yield. This underlines the importance of accurate wind speed measurements. The following aspects have to be considered when selecting the anemometers:

It is recommended to use high quality anemometers. The saving of money does not in the least justify the financial risk caused by a wrong prognosis of the energy yield due to cheap anemometers.
An individual wind tunnel calibration increases the accuracy of anemometers. DKD (Deutscher Kalibrierdienst) or MEASNET certified institutes guarantee a maximum of accuracy and comparability.
Wind vane
Information about the wind direction is usually required for the alignment of the wind turbines in a wind farm in order to minimize the wake losses. The wind direction is usually measured near the top of the mast. Potentiometric wind vanes are suitable for long-term measurements because of their high resolution and their low power consumption.
Temperature and barometric pressure sensor (optional)
The wind energy flow is proportional to the density of the air which is calculated from temperature and air pressure. The measurement of air temperature and barometric pressure improves the prognosis of the energy yield. IEC (International Electrotechnical Commission) recommends a cumulative accuracy of +/- 1%.
Data logger
All measured values are recorded by the wilog303/306 data logger. The preevaluated data are stored as time series. Additionally, recent measured data are indicated on the LCD.
Shelter box
A steel shelter box protects the data acquisition system against weather, theft, and vandalism.
GSM modem (optional)
The measured data stored in the wilog303/306 data logger are read out locally via notebook or pocket PC. Optionally, a GSM modem connected to the data logger allows remote data transmission to any PC with telephone modem.
Solar power supply (optional)
An external power supply for small wind measuring stations is not required. Data logger, anemometers, and wind vanes are supplied from the internal batteries of the wilog303/306 data logger. However, some sensors as well as GSM modems require a 12 Volt power supply. An autonomous power supply of the entire system is realized by means of a photovoltaic solar system.
Measuring mast
Sensors are placed at different heights on the measuring mast. The complexity of the terrain and the hub heights of the planned wind turbines determine the mast height. A complex terrain requires higher measuring levels in order to obtain reliable data. Measurements in hub height provide the most accurate results. However, a minimum mast height of 40m is recommended.

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