Wind Farms & Small Wind Turbines
NoiseAssess has experience of noise assessments for major wind farms and smaller individual wind turbines.
Major wind farm schemes are normally assessed in accordance with ETSU-R-97. This involves the installation of noise monitoring equipment to record background noise levels at positions near to residential properties over an extended period (normally several weeks). The background noise levels are correlated with wind speed data from a meteorological mast installed on the wind farm site. Appropriate adjustments are made for site specific wind shear. The measured noise levels are separated into night time and quiet daytime periods and any data acquired during periods of rainfall is eliminated. Background noise levels for the night time and quiet daytime periods are plotted against wind speed. Then regression analysis is performed to obtain derived background noise levels at key integer wind speeds. A noise criterion is then set which is generally 5dB above the background noise curve except that where this criterion falls below a certain level a lower fixed limit applies. The noise from the proposed wind turbines is predicted using acoustic modelling software. NoiseAssess uses CadnaA noise modelling software. The predicted turbine noise levels are compared with derived criteria. Where the criteria are exceeded it is necessary to reduce noise levels by adjusting the turbine layout or the turbine design. Noise from wind turbines consists of two elements: aerodynamic noise from the blades and mechanical noise from the nacelle (hub) which houses the generator and gearing. There has been some reduction in source noise levels as designs have improved (e.g. better gearboxes, improved speed control mechanisms).
Smaller individual wind turbines do not always need to be assessed to ETSU-R-97. Some ‘small wind’ projects can be assessed in accordance with the Small Wind Turbine Performance and Safety Standard produced by the British Wind Energy Association (BWEA). Sometimes wind turbines have been assessed in accordance with BS4142. Normally full assessment to ETSU-R-97 is prohibitively expensive for ‘small wind’ projects. However, sometimes a shortened survey period can be agreed with the planning authority and in circumstances where there are large distances between the turbine and uninvolved residential properties it may be possible to use the ETSU-R-97 simplified noise condition thereby avoiding background noise survey work altogether.
Whether you are looking to develop a full scale wind farm or just a small individual wind turbine NoiseAssess would be happy to help with any noise assessment work you have been asked to carry out.