The aim of this proposal is to support the commercial exploitation of wind energy by increasing the reliability of wind farm planning in terms of acoustic noise radiation, thereby improving public acceptance of such developments in future. The concerted action is proposed by the members of the CENELEC BTFF 83-2 WG4, which has been mandated to develop a unified method to declare a wind turbine's noise emission.
Much knowledge about noise reduction has been gained during the rapid development of wind energy in Europe in recent years. New measurement standards have been developed to improve the determination of the noise emission values for a single turbine under test. This has, however, occasionally led to problems. Wind farm planning within Europe has generally been based on the results of such measurements, i.e. those made on a single example of the type of wind turbine under consideration. As the standard deviation of reproducibility and the standard deviation of production will generally be unknown, this is clearly not a reliable basis for such planning. This has, on occasion, led to noise problems during subsequent operation, so that a certain number of wind turbines have to be parked or de-rated during 'noise sensitive' times of the day (e.g. night-time, certain wind conditions) in order to comply with agreed noise limits at nearby dwellings. The resultant losses in energy production are unacceptable for operators of wind farms.
To avoid such losses manufacturers, planners and authorities urgently need to improve the reliability of their planning by considering 'declared' values for a wind turbine's sound power levels and tonality. This would be a measure of the noise emission values of a particular model of wind turbine, rather than just a single example of it, and would take into account the scatter of noise emission value expected within a batch of such machines. Such an approach would translate directly into improved technical confidence and in better economic risk assessment (e.g. warranty purpose) - this latter aspect is a major factor in promoting wind energy in the financial marketplace.
The objective is to provide manufacturers, developers and operators of wind turbines and authorities with a reliable basis on which to perform wind farm planning taking into account national noise criteria and limits. The declaration (based on ISO 4871 and ISO 7574) shall facilitate the comparison of noise emission of different types of wind turbines and will be used by planners, manufacturers, customers and authorities as a reliable base for planning issues.
For the declaration of sound power level and tonality, results from measurements and inputs from research projects will be brought together with the requirements of planning authorities (taking into account the protection of people living in the neighbourhood of wind farms) and the developer's objectives. The declared values will be used for the prediction of noise immission levels at nearby dwellings.