Temperature Humidity Sensors
Temperature sensors measure air temperature, while humidity sensors measure air humidity. Both sensors are often applied in combination to reduce cost.
The calculation of the air humidity does not directly influence a wind site assessment, but knowing this parameter helps assessing the potential danger of ice build-up at the measuring location.
Temperature humidity sensors should always be mounted at a height of at least 10 m to ensure sufficient distance from heat radiating of the earth.
Impact of Measurement Errors on AEP Calculation
Temperature and air pressure significantly affect the AEP (Annual Energy Production). Hence, according to IEC 61400-12-1 temperature and air pressure have to be measured in a wind measurement campaign.
Wind power is linear proportional to the invers of temperature 1/T (in Kelvin). At 15°C, 1°C error on temperature measurement induces 0.35% error on AEP. The standard IEC 61400-12-1 specifies the relation where the sensitivity factor for temperature is cT,i ≈ Pi / 288.15 K.
Therefore IEC 61400-12-1 requires measuring air pressure and temperature.
Impact of Humidity
The impact of humidity on AEP might be significant if air temperature is high.
- At sea level and at air temperature of 20°C, air density varies 1.2% between 0 … 100% humidity. It varies 2.0% at 30°C and 4% at 40°C.
- At high temperatures the IEC recommends to measure the humidity, as well.