The wind is the result of a difference in the air pressure. The air moves from regions of higher pressure to others with less pressure.
If you think about an inflated balloon, when the opening is not tied, the air flows out of the high pressure. When in the atmosphere, it will travel to a lower pressure zone, creating wind. The speed at which the wind moves can be calculated using an instrument called an anemometer.
An anemometer is similar to a weather vane, but it does not calculate in which direction the wind is moving using pointers. It consists of four cups so it can rotate in the wind, measuring its speed. Each cup is connected to a horizontal arm, which is mounted on a central axis. The axis rotates as the wind blows into the cups. The faster the wind pushes, the faster the central rod rotates.
To go even deeper into the subject, the air is made from very small molecules. When they are heated, the particles move faster. Therefore, when the air is heated, its particles move more quickly and stray further apart making the air less dense. This process means that the air has lower pressure.
The cold air, in contrast, consists of tightly packed molecules, making it denser, with higher overall pressure.
Since air pressures tend to balance out when there is a zone of lower air pressure, the enclosing air in higher pressure regions moves in. The movement of air from a high-pressure area to one with lower pressure is what produces the wind.
When the wind blows into the cups of an anemometer, they rotate the central axis. The speed of the axis spinning is measured in revolutions per minute or rpm. In other words, what is measured is how many times one cup returns to the original position in one minute.
As a consequence, a faster wind will produce a higher rpm than slower air movement. Depending on the geographical location, the wind speed is pronounced in miles per hour, kilometers per hour, or knots.
Collecting and analyzing data
The consistency and accuracy of measurements are critical in the design and optimization of the layout, as well as in the feasibility analysis. However, you will notice that you do not need any complex lab utility island, nor even a lab cabinet, as technology made things easier.
Some measuring solutions have been implemented by wind resource analysis, when it comes to collecting and analyzing wind data.
The met masts method includes running on-site meteorological measurements, utilizing a mast of variable size fitted with measuring and data-collection equipment.
Depending on the region size and terrain complexity, more masts can be installed on a given site.
The data produced by the sensors is stored at constant time intervals in a logger which is placed in a steel cabinet in the lower section of the mast. The power requirements of the electronic equipment are supplied utilizing photovoltaic boards.
Next, the logger is connected to a telephone line or uses a GSM connection to transmit data. After gathering the details, wind resource analysts carefully screen through the data and the gaps in the time series are filled in.
The information is then computed into a specific wind calculation software to produce the energy assessment of the site.
Remote sensing instruments
SODAR and LIDAR measurements provide the possibility to analyze the wind profile at various altitudes and over the rotor surface. The collected data is stored in the SODAR/LIDAR and can be obtained via email, internet or mobile connection.
A SODAR short from Sonic Detection and Ranging is a remote sensing instrument utilized for meteorological measurements.
The atmospheric data is calculated based on the speed of sound. Measurements are accomplished by sending out an acoustic signal. The return signal is then analyzed to assess wind speed, wind direction, and atmospheric turbulence.
A LIDAR, shot for Light Detection and Ranging, analyzes the wind profile through a laser signal in a similar way as the previous device. On the same principle as the SODAR, a light beam is sent out in the atmosphere in a 3-dimensional cone. The Doppler variation of laser radiation backscattered by air molecules is measured to establish wind properties.