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If you believe that windfarms 'are not noisy', like the BWEA, we invite you to share the experience of these residents suffering from their local wind power station in Cumbria.
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Click here to read this important paper about wind farm noise.

Noise

A primary concern for residents living near to the site of the proposed Wadlow Wind Farm is noise. Just how noisy would this be? Would the noise affect you? How close to the turbines do you need to live for this to be a nuisance? Obviously this is a crucial issue for many residents. And perhaps not surprisingly, the opinions of the wind energy industry on this subject seems to differ markedly with the experiences of many people who already live near to operating wind farms.

The British Wind Energy Association website contains, on its FAQ Section the question "Are wind turbines noisy?" to which its answer begins: "Wind turbines are not noisy. The evolution of wind farm technology over the past decade has rendered mechanical noise from turbines almost undetectable with the main sound being the aerodynamic swoosh of the blades passing the tower."

Similarly, Renewable Energy Systems Ltd state "Aerodynamic noise from wind turbines is generally unobtrusive - it is broad-band in nature and in this respect is similar to, for example, the noise of wind in trees." (source: 'Wadlow Wind' Bulletin no. 2, February 2006, published by Renewable Energy Systems Ltd).

However, the wind industry has a history of dismissing the noise problem but those living close to wind farms sometimes find the noise levels completely unacceptable and some have been enraged that assurances about noise given in advance turn out to be worthless. The most intrusive noise comes from the blade moving through the air. The noise is a penetrating, low frequency "thump" each time the blade passes the turbine tower. For example, read this presentation by David Brierely a resident of South West Cumbria and a Wind Farm sufferer.

The 'Journal of Sound and Vibration', a respected scientific journal from Elsevier, published an extremely important and rigorously technical paper in 2003 by G.P. van den Berg, 'Effects of the wind profile at night on wind turbine sound'. You can read the whole paper here (PDF - external link).

The Abstract of this paper reads as follows:
"Since the start of the operation of a 30 MW, 17 turbine wind park, residents living 500m and more from the park have reacted strongly to the noise; residents up to 1900m distance expressed annoyance. To assess actual sound immission, long term measurements (a total of over 400 night hours in 4 months) have been performed at 400m and 1500m from the park. In the original sound assessment a fixed relation between wind speed at reference height (10m) and hub height (98m) had been used. However, measurements show that the wind speed at hub height at night is up to 2.6 times higher than expected, causing a higher rotational speed of the wind turbines and consequentially up to 15 dB higher sound levels, relative to the same reference wind speed in daytime. Moreover,especially at high rotational speeds the turbines produce a 'thumping', impulsive sound, increasing annoyance further. It is concluded that prediction of noise immission at night from (tall)wind turbines is underestimated when measurement data are used (implicitly) assuming a wind profile valid in daytime."

The turbines referred to in this paper are 1.8MW machines with a 98m hub height with 3-blade propellers of 35m wing length. The turbines proposed for Wadlow Wind Farm are similar in size (120m to the tip of the blade) though are more powerful - they will generate 27% more power (2.3MW each). The overall electricity generating capacity of the proposed 13 turbine Wadlow Wind Farm at 29.9MW is virtually identical to that in the above paper (30MW). Note also that parts of Balsham will be less than 1500m from the closest turbines, and parts of West Wratting and Six Mile Bottom are less than 2000m (see map).

The Journal of Sound and Vibration paper then goes on to say (p.3):
"There is a distinct audible difference between the night and daytime wind turbine sound at some distance from the turbines. On a summer's day in a moderate or even strong wind the turbines may only be heard within a few hundred metres and one might wonder why residents should complain of the sound produced by the wind park. However, on quiet nights the wind park can be heard at distances of up to several kilometres when the turbines rotate at high speed. On these nights, certainly at distances between 500 and 1000m from the wind park, one can hear a low pitched thumping sound with a repetition rate of about once a second (coinciding with the frequency of blades passing a turbine mast), not unlike distant pile driving, superimposed on a constant broadband 'noisy' sound. A resident living at 1.5 km from the wind park describes the sound as 'an endless train'. In daytime these pulses are not clearly audible and the sound is less intrusive or even inaudible (especially in strong winds because of the then high ambient sound level)." (parts in bold have been emphasized by us)

On p.14, in section 11 'Annoyance' it states:
...."1500m from the wind park, the immission level is for a considerable amount of time (at least 38% of night-time hours) higher than expected. ... at wind speeds of 2.4 m/s the actual sound level is up to 18 dB higher than expected, of which 3 dB are due to limitations of the calculation model, and 15 dB to the underestimate of wind speed at hub height. With these higher sound levels and the impulsive character of the sound more annoyance than predicted is to be expected.
Pedersen et al. have investigated the annoyance around wind turbines in the south of Sweden. Their paper gives preliminary results, and definitive results have yet to published [personal communication Pedersen]. They found highly annoyed residents at (calculated) sound levels as low as 32.5-35 dB(A). This study shows that tall wind turbines may in fact be up to 18 dB noisier than the calculated values suggest. A further increase in annoyance may be expected because of the pulse-like character of the wind turbine noise, especially at high rotational speeds."
[E.Pedersen, K.Persson Waye, Perception and annoyance of wind turbine noise in a flat landscape, Proceedings Internoise 2002 Detroit, 2002.] (parts in bold have been emphasized by us)

The concluding 2 sentences are as follows:
"The number and severity of noise complaints near the wind park are at least in part explained by the two main findings of this study; actual sound levels are considerably higher than predicted, and wind turbines can produce sound with an impulsive character. The relatively high wind speeds at turbine hub height at night also have a distinct advantage; the electric power output is higher than predicted and benefits the operator of the wind turbine." (parts in bold have been emphasized by us)

If you search online it is not too hard to find reports from residents living near wind farms detailing noise problems far worse than they were led to believe. You may find the following links useful:

G.P. van den Berg, 'Effects of the wind profile at night on wind turbine sound', Journal of Sound and Vibration. Extremely important and rigorously technical article in an industry standard journal on the underestimation of sound problems in developer reports. Click here (PDF) (external link)

Presentation by David Brierely a resident of South West Cumbria and a Wind Farm sufferer. This must be read by all, that includes both those in favour and those against the Wadlow Wind Farm. Click here (external link)

Casella report for DEFRA on Low Frequency noise. Click here (PDF)


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