Wind Farm Developments

WTG Noise

What is the source of the wind turbine noise ?

Wind turbines emit low levels of noise. The main source of noise is the aerodynamic noise of the blades moving through the air. The character of the aerodynamic noise is broadband and similar to that of the surf. A secondary source of noise is the mechanical noise from the rotating machinery such as the generator and gearbox. Modern design techniques has resulted in turbines being largely free of mechanical noise.
The levels of noise produced by wind turbines are very low. A comparison between some every day noises and a wind farm is given in the adjacent chart. A wind farm at 500 m produces a noise level of lower than 40 dB(A) i.e. at the same level as a bedroom at night.
wind sound power table
The potential noise impact of a wind farm is assessed during the wind farm feasibility and design phases, and is achieved through the following steps:
Step 1. Noise measurement
Measurements of the existing background noise levels are undertaken at non stakeholder representative noise sensitive residences in accordance with recognized standards and guidelines. This allows an analysis to be completed to determine the existing baseline background noise level.
Step 2. Noise limits
A suitable limit is placed on the wind farm based on the existing background level and appropriate noise Standards and guidelines. These limits are set by relevant planning authorities and are often reviewed by agencies such as the Environment Protection Authority (EPA).
Step 3. Noise level predictions
Using the proposed wind farm layout, predictions of the noise levels at the noise sensitive residences are completed to ensure that the layout complies with the noise limits set by the relevant planning authority requirements.
graph turbine noise
These three steps result in an analysis which is best shown graphically as illustrated in the figure above. The black line represents the wind farm limit based on the existing background levels (purple line). The orange line shows the predicted wind farm noise level. Typically the limit is set at a level which is the higher of 40 dBA or background noise plus 5 dBA which is a standard set to avoid sleep disturbance at night. There are additional requirements if the turbine has a tonal noise element to its independently verified sound power curve.