Noise
Wind turbines emit two types of noise: aerodynamic noise produced by the movement of the rotating blades through the air; and mechanical noise, which may emanate from gearboxes or generators. During the last two decades there has been considerable progress in reducing both aerodynamic and mechanical noise from wind turbines. New designs are quieter and create significantly less noise relative to power output than older turbine designs. Mechanical noise in particular is negligible with modern turbine designs. In general terms government guidance (ESTU-R-97, The Assessment and Rating of Noise from Wind Farms) sets out that noise from wind turbines should be no more than 5dB above existing background noise levels during the day and night.
Careful attention to the number and layout of turbines, taking account of existing background noise levels that were measured at six representative properties, has established a turbine layout for the Rushy Mead site that complies with government guidelines in relation to predicted operational noise. In fact, at the majority of residential properties, noise levels generated by the wind turbines are expected to be below or the same as existing measured background noise levels. Only at Cocklebury Cottages, which is a property owned by the University to the east of the Research Centre, were predicted noise levels marginally above measured background noise levels but these levels are still, nevertheless, well within government guidelines.
To address construction noise that might at times be audible at properties close to construction activity, working hours would be restricted. However, in all cases, noise would be kept below the daytime significance criterion (This is defined within the government-endorsed guidance ETSU-R-97 (The Assessment and Rating of Noise from Wind Farms). In addition, for all activities, everything possible would be done to reduce noise levels albeit with due regard to practicality and cost as per the concept of ‘best practicable means’ as defined in Section 72 of the Control of Pollution Act 1974. Consequently the assessment predicts that no significant noise effects would occur as a result of construction activities.
A number of alternative turbine models are available that fit the dimensions proposed for the scheme. The assessment undertaken was carried out based on sound power levels of the Nordex N100 turbine which is considered to represent worst-case sound power levels. Any turbine selected for the site would need to comply with noise limits set by the Local Planning Authority.
It is therefore concluded that, taking into account the above and other issues, including low frequency noise, tonal penalties and aerodynamic modulation (explanations of which are provided in the Environmental Statement) and the proposed use of planning conditions to ensure compliance with noise limits, the proposed wind turbines would have no significant effects in relation to construction, operational and decommissioning noise.