Health impacts of wind turbines

This report presents the results of a rapid, desk based analysis of peer reviewed UK and international literature from the last four years on the effects of wind turbines on human health. The review covers literature specified by the Scottish government, peer-reviewed original studies and recent peer-reviewed literature reviews. Recent original studies consist mostly of cross-sectional studies and case studies on the effects of wind turbines on local residents. All studies present evidence for annoyance due to wind turbine noise and most concur that there is evidence for sleep disturbance in the presence of wind farms but not necessarily from noise. Both results are in agreement with the effects of noise from other environmental sources. Other health effects are increasingly reported in the presence of wind turbines but the reviewed literature does not provide firm scientific evidence of a causal relationship with wind turbines or even more specifically wind turbine noise. The most widely quoted cross-sectional studies show correlations between annoyance and visual impact, economic benefit and attitude related to wind turbines. Wind turbine sound is reported to be comparatively weakly related to annoyance and inseparable from the other contributing factors. Literature on low frequency noise and infrasound (LFIS) can be categorised as reviews, sound level measurements around windfarms and discussion of mechanisms of perception and response. A Swedish review finds no evidence to support ‘wind turbine syndrome’ while another concludes that further research is required. Regarding noise measurements, there are concerns that a new generation of wind turbines will produce a sound with a spectrum shifted down in frequency. However, a study in Australia concluded that infrasound levels near windfarms were no higher than elsewhere and that higher levels in urban areas were probably due to traffic and other human activity rather than wind turbines. Some other studies found measured sound levels near wind farms to conform with a range of criteria for LFIS. Papers by Salt et al. propose that LFIS may differentially stimulate structures in the human inner ear, and may instigate health effects even when inaudible. The authors seek to build a speculative case utilising experimental data gleaned from guinea pigs and some observations on human experiences with specific pathological conditions. Based upon the documents submitted, the proposal is unproven, and would need clear data from hypothesis driven independent research in humans in order to be credible. A proposal by US consultants that motion sickness-like symptoms reported at one wind farm might be caused by acoustic excitation of the balance organs is not new and has previously been discounted as an explanation for similar reported effects not involving wind turbines. Other evidence on acoustic stimulation of the balance organs has been noted but not reviewed. Health effects from other wind turbine related sources such as shadow flicker have been reported in several studies and guidelines to be less of a problem. Careful wind farm design and operational restrictions are suggested to be sufficient to minimise the impact. The mitigation strategies have been found to vary widely internationally with some countries and federal states using fixed noise limits, others using noise limits relative to existing background levels and many like the UK using a combination of both. Set-back distances are also used internationally but have a number of disadvantages. The relevant UK guideline document ETSU-R-97 aims to provide a reasonable degree of protection to noise sensitive listeners; without unduly restricting the development of wind turbine renewable energy resources. In the international comparison the ETSU-R-97 guidelines tends to result in comparatively low noise limits although direct comparisons between fixed and relative noise limits are difficult. ETSU-R-97 has been criticised for its inconsistent implementation and relative complexity. Good practice guidelines by the Institute of Acoustics which aim to address the implementation issues are due to be published in May

Fixed echo rejection in sodar using non-coherent matched filter detection and Gaussian mixture model based post-processing

Doppler sodar (SOund Detection and Ranging) is a technology used for acoustic based remote sensing of the lower planetary boundary layer. Sodars are often used to measure wind profiles however, they suffer from problems due to noise (both acoustic and electrical) and echoes from fixed objects, which can bias radial velocity estimates. An experimental bi-static sodar was developed with 64 independent channels. The device enables flexible beam forming; beams can be tilted at the same angle irrelevant of frequency, a limitation in most commercial devices. This paper presents an alternative sodar signal processing algorithm for wind profiling using a multi-frequency stepped-chirp pulse. A non-coherent matched filter was used to analyse returned signals. The non-coherent matched filter combines radial velocity estimates from multiple frequencies into a single optimisation. To identify and separate sources of backscatter, noise and fixed echoes, a stochastic pattern recognition technique, Gaussian Mixture Modelling, was used to post-process the non-coherent matched filter data. This allowed the identification and separation of different stochastic processes. After identification, noise and fixed echo components were removed a clean wind profile produced. This technique was compared with traditional spectrum-based radial velocity estimation methods and demonstrated an improvement in the rejection of fixed echo components; this is one of the major limitations of sodar performance when located in complex terrain and urban environments

UpWind: integrated wind turbine design - Salford final summary on WP 6.1, WP.6.2, WP 6.3 And WP 6.4

Within the Upwind project the University of Salford provided development work for SODAR instruments in relation to the next generation of wind turbines. The main focus of the work was on the identification and proposal of design improvements, the development of a calibration device and the novel design of a bi-static SODAR to overcome limitations in the use of remote sensing in complex terrain. Data accuracy and availability of SODARs suffers during rain. Therefore an algorithm to detect data affected by rain and to extract the wind information has been developed and successfully tested to determine the scope of the technique. In mountainous terrain another source of inaccurate wind estimates is the separation of measurement volumes which results in inaccuracy of up to 5%. A simple flow model has been proposed and evaluated for a case study showing that the applied corrections can improve accuracy. A calibration transponder and a new bi-static Sodar design with vertical transmission and three scanning receivers have been designed and successfully tested