How Is Noise Generated By Windfarm?

The noise generated by windfarms is a very important parameter to be studied in the design phase. Sound propagation models like ISO 9613-2 is commonly used in noise prediction studies due to its simple input parameters required but it does not take into account some factors that have a significant effects on the results such as wind velocity, wind direction and some weather conditions like temperature gradient. Also it assumes the condition of downwind in all directions. So, the calculations can be affected by the absence of these important definitions which results in uncertainty percentage. This also leads to a project failure to be in a compliance with regulations.
Nord 2000 is one of the new standards used for noise propagation. The Nord
BS 5228: Part 1:1997 [10]
The BS 5228 standards doesn’t take the metrological conditions into account such as temperature change and wind direction. The standard of attenuation is 6 dB for doubling the distance if the ground effect is not taken into consideration. Wind direction should be taken into account when studying the sound propagation of windfarm as the noise is higher at receivers downwind of the farm and BS 5228 doesn’t predict this.
1.5.2. ISO 9613-2 [11]
The ISO 9613-2 is the most commonly used prediction method for noise propagation modelling due to its simple required inputs. It is also commonly used for wind turbines noise prediction. It assumes some simple assumptions and it doesn’t take into account the wind speed and direction, and weather conditions. It has an accuracy of +/- 3 dB for heights of sources up to 30 meters above ground and for 1000 meters from the sources. No other indication of accuracy is available for outside these conditions.
ISO 9613-2 states a prediction accuracy of ± 3 dB for sources of heights up to 30 meters above ground and for distances up to 1000 meters from the source. However, outside of these conditions, no indication of accuracy is provided.
1.5.3.
Conclusion
Nord2000 prediction method has been selected to perform the case study of windfarm noise prediction. The results of Nord2000 has a greater accuracy than ISO 9613-2 which is commonly used in windfarms noise propagation modeling.
Noise emission from wind turbines differs from noise emission from any other power generation facilities in terms of how it is produced, how it is measured and how it is received. Everything about wind turbines is unique and needs specialized techniques to assess its impacts and measure sound emission of the proposed projects.
In windfarms, the wind characteristics is a very important factor which has a significant effect on the produced noise levels. Nord2000 calculates the direct effect of the wind and can predict the noise levels when wind changes its speed and direction along the year and average the results to get the annual average.
Also Nord2000 is more accurate in evaluating the ground effect, as when the sources have a high elevation above terrain level, there are two paths from source to receiver, the direct path and the reflected path from ground. Nord2000 takes into account the signal phase of the two paths as waves reflected from ground have a phase shifting depending on the flow resistivity. ISO 9613 deals with ground reflection in an averaged way. So, Nord2000 is more successful than ISO 9613 in this