PRESENTATION ON WIND TURBINE AM by Geoffrey Weller I am a Chartered Engineer and a Fellow of the Institution of Engineering and Technology. Much of my career was devoted to developing electronic protection schemes for electrical power systems. This included analysis of noisy electrical signals using digital signal processing, for instance with fast Fourier transforms. I have experience of amplitude modulation of radio-frequency signals. Introduction My evidence shows that ETSU-R-97 is failing to protect windfarm neighbours from Amplitude Modulation, the most distressing characteristic of wind turbine noise. ETSU-R-97 is used throughout the UK to assess wind farm noise in planning applications. As it has been embedded into government policy, it is probably futile to insist that ETSU is wrong. However, I do assert that additional protection for AM is needed for windfarm neighbours where the AM exceeds the maximum level quoted in ETSU. This presentation will summarise some of my Proof of Evidence, mention some events that occurred since I submitted it, and amplify the conclusions I drew previously. What is AM? To demonstrate the character of AM, I would like to play two audio files located at the following web URLs i) https://dl.dropbox.com/u/51620331/Swish_to_Thump.mp3 Source: Dick Bowdler FIOA Noise Consultant http://www.dickbowdler.co.uk/content/publications/ ii) https://dl.dropbox.com/u/51620331/file0895_hi_lo_17dbeq_16b.mp3 Source: Recordings of Nature website. There are actually two separate recordings in this file. Proof of Evidence An important source of evidence is the DTI-commissioned 2006 Hayes McKenzie Partnership report The Measurement of Low Frequency Noise at Three UK Wind Farms which noted that Aerodynamic Modulation was occurring in ways not anticipated by ETSU-R-97 (ETSU). The authors of the report recommended as follows: […] the presence of aerodynamic modulation which is greater than that originally foreseen by the authors of ETSU-R-97, particularly during the night hours, can result in internal wind farm noise levels which are audible and which may provoke an adverse reaction from a listener. This may take the form of increased time in returning to sleep for an occupant although noise associated with the wind farms was not found to awaken the occupant. To take account of periods when aerodynamic modulation is a clearly audible feature within the incident zone, it is recommended that a means to assess and apply a correction to the incident noise is developed… The authors of this report found (page 64) that even when the overall noise level inside a bedroom was less than the sleep disturbance threshold proposed in the WHO guidelines, the acoustic nature of the AM sound attracted the attention of the listener and caused difficulty in returning to sleep.

Page 1 of 7 Geoff Weller WINDFARM PLANNING PRESENTATION.doc 14 October 2013 Recent and Forthcoming Papers Wind turbine AM continues to dominate technical discussion for onshore wind turbines. From 5th International Conference on Wind Turbine Noise Denver 28-30 August 2013 Audible amplitude modulation - results of field measurements and investigations compared to psychoacoustical assessment and theoretical research Mike Stigwood, Sarah Large and Duncan Stigwood, MAS Environmental Ltd, UK http://www.masenv.co.uk/uploads/WTN13_Stigwood.pdf In the UK denial continues that AM is other than rare with reliance placed on a 2007 report prepared for Defra by the University of Salford which found low incidence of AM (Moorhouse et al, 2007). Re-analysis of the Salford data confirms many cases were missed (van den Berg, 2009). We and other independent researchers (Hoare, 2009) have also found that the Salford report understated incidence of AM. In the UK we have now identified at least seventy UK wind farms where it is known that AM is the cause of complaints. [...] as turbine hub heights have increased, incidence and complaints of AM have risen. Few regulators and decision makers visit wind farms under the conditions likely to give rise to enhanced AM, leading to a risk of ill-informed decisions. A table is appended reproducing a page of the MAS Environmental website. The table, updated in May 2013, lists 68 wind farms generating AM which MAS are aware of due to written evidence. Reference http://www.masenv.co.uk/Operational_Wind_Farms#item142. This adds to the body of evidence showing that AM is not rare. From the Renewable UK Annual Conference Birmingham 5-7 November 2013 http://www.renewableuk.com/en/events/conferences-and-exhibitions/renewableuk- 2013/programme/day-2.cfm#b9 Only 3 papers will be presented on technical issues (Session B8), all of them devoted to AM noise of Onshore Wind Turbines. Official abstracts follow: RenewableUK AM Research Project – Overview of Phase 1 Research Findings. The amplitude modulation (AM) of aerodynamic blade noise from wind turbines is always detected close to a rotating wind turbine. Such noise is commonly described as ‘blade swish’. However, on some wind farm sites AM has been reported that is subjectively different to ‘normal’ swish, with annoyance being reported in some cases due to the noise developing more of a ‘thump’ character. This presentation is [...] sponsored by RenewableUK specifically aimed at identifying the causes of this ‘other’ type of AM noise and the subjective consequences of such noise. Andrew Bullmore, Partner, Hoare Lea Acoustics. Affective Response to Amplitude Modulated Wind Turbine Sound The amplitude modulated sound character is frequently mentioned in the context of annoyance from wind turbines. While there are still questions about the source mechanisms and characterisation of amplitude modulation one of the most under-researched areas is the response of listeners to this type of sound. This paper will present results from listening tests conducted in a controlled environment during a comprehensive study on amplitude modulation. Funded by RenewableUK. Dr Sabine Von-Hunerbein, University of Salford. Mechanisms and Causes of Amplitude Modulation (AM) and Other Amplitude Modulation (OAM) of Aeroacoustic Wind Turbine Noise. The results of a work investigating the mechanisms and causes of amplitude modulation (AM) of aeroacoustic noise from wind turbine rotors and specially the occurrence of lower frequency amplitude modulation named (OAM) are presented. Helge Aagaard Madsen, Research Specialist, DTU Wind Energy

Page 2 of 7 Geoff Weller WINDFARM PLANNING PRESENTATION.doc 14 October 2013 ETSU-R-97 ETSU sets out the level of AM that was assumed in setting the noise limits: This modulation of blade noise may result in a variation of the overall A-weighted noise level by as much as 3dB(A) (peak to trough) when measured close to a wind turbine. As distance from the wind turbine/wind farm increases, this depth of modulation would be expected to decrease as atmospheric absorption attenuates the high frequency energy radiated by the blade. It is clear that ‘as much as’ indicates the maximum level of AM that was envisaged in the setting of overall noise limits, and cannot be interpreted as meaning a typical or indicative value. It is clear that lower levels were expected at increased distance from the turbine, such as at a neighbouring property. ETSU says: The noise levels recommended in this report take into account the character of noise described in Chapter 3 as blade swish. Given that all wind turbines exhibit blade swish to a certain extent we feel this is a more common-sense approach given the current level of knowledge. Statutory Nuisance In the absence of national standards regulating the maximum immissions of AM, it is often suggested that any neighbourhood noise problems can be dealt with using the Statutory Nuisance complaint procedure (Environmental Protection Act 1990), usually via the Local Authority. To this effect, a 127-page report detailing a complete Wind Farm Noise Statutory Nuisance Complaint Methodology has been produced for DEFRA. Reference https://www.gov.uk/government/publications/dealing-with-wind-farm-noise-complaints The document says this about AM: Amplitude Modulation of Aerodynamic Noise (AM) The sound level from turbine blades is often not completely steady, but is modulated (fluctuates) in a cycle of increased and then reduced level, sometimes called ―blade swish, typically occurring at a rate of around once or twice per second. In the majority of installations the modulation depth may be up to 2-3 dBA, which was regarded as being acceptable by the ETSU working group. In some situations, however, the modulation depth increases to the point where it can become more pronounced and potentially give rise to increased annoyance. This phenomenon is known as amplitude modulation of aerodynamic noise or more succinctly by the acronym AM. Experience in the UK has shown that obtaining redress from AM nuisance for local residents is extremely difficult and only possible following a lengthy, risky and expensive legal process. Solicitors say that in practice the Local Authority often does not act, or has its actions delayed by protracted appeals. The defence of ‘best practicable means’ is often available to the opponent. Reference http://www.richardbuxton.co.uk/v3.0/node/18. There is always a difficulty in proving that a noise nuisance exists – the noise may last many nights in succession, causing cumulative sleep deprivation, then disappear entirely for a while.

Page 3 of 7 Geoff Weller WINDFARM PLANNING PRESENTATION.doc 14 October 2013 Control to avoid Statutory Nuisance Claims In view of the evidence I have produced, there is an unacceptable risk of foreseeable harm in allowing the level of AM to be uncontrolled. A precautionary approach requiring a planning condition controlling the level of AM would be an advantage for both the developer and the neighbour. For the developer, it would be a defence against noise complaints made by persons who are ‘unduly sensitive’ to noise. For the neighbour, it would provide a means of proving excessive noise if such exist. The conditions imposed at Den Brook would provide an excellent basis for a planning condition, and there is no evidence that this would inhibit the development of properly-designed onshore windfarms. Conditions The Den Brook planning conditions 20 and 21 regarding AM need not be reproduced here as they are quoted in many documents, for example http://www.bailii.org/ew/cases/EWCA/Civ/2011/638.html The Den Brook Planning Condition 20 sets a 3 dB limit for Amplitude Modulation, the maximum value for AM quoted in ETSU. Although this value has no regard for any dose-response studies, it should be noted that no dose-response studies were deemed necessary in setting the acceptable level of windfarm noise, including AM, of 5 dB above background level in ETSU. ETSU just says: On balance it is considered that a margin of 5dB(A) will offer a reasonable degree of protection to both the internal and external environment without unduly restricting the development of wind energy. The Den Brook planning condition was reviewed by Moroney and Constable. Reference http://www.ref.org.uk/publications/242-the-den-brook-amplitude-modulation-noise-condition This work included tests of the planning condition with real-world data collected by the Hayes McKenzie Partnership as part of their Government contract in 2005 to investigate low frequency noise at wind farms. Moroney and Constable concluded: The Den Brook condition is straightforward and that it is possible for this condition to be employed in a transparent and objective manner to demonstrate the existence of excess AM in wind turbine noise. Moroney and Constable’s report goes on to state: These findings should be welcomed by both wind farm neighbours, developers, and decision makers in the planning process. AM noise provokes complaints and heated debates, and an enforceable, objective, condition to cap such noise gives all parties clarity, as well as sparing neighbours and developers the trouble, expense, and uncertainty of private nuisance actions. The Den Brook condition appears to be a readily workable solution to this very real problem. The Den Brook wind farm developer, RES, challenged the AM planning condition. Their acoustic consultant Dr Jeremy Bass reported that background noise alone, that is, without turbines present, creates significant false positive indications of AM, so effectively making the condition unworkable. The Moroney and Constable report has this to say about false positives: It is also relevant to this discussion to consider if the amplitude modulation displayed here is attributable to wind farm noise or perhaps arises from some other noise in the environment. There are a number of ways of ensuring that the noise measured is wind farm noise, the obvious one being a simultaneous audio recording. However, we can also inspect the noise levels displayed in the various graphs for any characteristic signature or structure, and in this case we observe that there are periods of clearly regular beats. If the wind farm is the source of the noise then the frequency of the

Page 4 of 7 Geoff Weller WINDFARM PLANNING PRESENTATION.doc 14 October 2013 beats will agree with the blade passing frequency of the turbines. [...] This conclusion could be verified against the SCADA (Supervisory Control and Data Acquisition) data automatically accumulated at each turbine... MAS Environmental (Reference http://www.masenv.co.uk/Den_Brook_AM_Condition) also analysed the data used by Dr Bass, and concluded: When MAS correctly applied the condition to the RES data it was found that during the hours when AM typically occurs (after sunset and before sunrise) no false positives were found. If false positives were identified, mainly during daytime, the trigger was clearly identifiable in the data; these were typically common noise sources that would be noted and disregarded when applying any noise condition, such as bird calls, aircraft and car alarms. Conclusions Each of the five windfarms involved in this Conjoined Public Inquiry has more turbines than Den Brook All the turbines are of similar height or taller than Den Brook. More numerous and taller turbines lead to an increased risk of AM. The experience of AM is likely to be worse in areas of low background noise such as Mid Wales. A precautionary approach is needed to granting Planning Permission. In the absence of nationally specified controls for AM, I submit that if one or more of the windfarms is granted planning permission, the Den Brook AM test, or another test for AM agreed by the parties involved, should be a condition of development and operation.

Page 5 of 7 Geoff Weller WINDFARM PLANNING PRESENTATION.doc 14 October 2013 MAS Environmental Health Consultancy

We have compiled a list of over 30 wind farms across the UK that we are aware of as generating Amplitude Modulation (AM). See below

At MAS Environmental we have currently measured unreasonable wind farm noise or been asked to investigate complaints of noise from wind farms at 13 developments including Bicker Fen, Blaen Bowi, Coldham, Darracott, Delabole, Fullabrook, Deeping St Nicholas, North Pickenham, Red Tileand Swaffham. The occurrence of AM is often noted by the industry as rare; the table below contains only wind farms generating AM of which MAS are aware due to written evidence. We understand there are many other cases. As can be seen from the table below, the occurrence of AM is not specific to turbine make, model, size, rated power or number of turbines.

Table updated May 2013

1 Wind Farm Location MW per turbine No. of turbines Hub Height (m) Reference

2 Aggregate Ind Cornwall 0.5MW 1 59 Audio examined Newquay

3 Alltwalis Carmarthenshire 2.3MW 10 65 Statement from complainant - clear case

4 Askham Cumbria 660kW 7 40 Salford - clear case added

5 Site B Banff and Buchan ANON Confirmed AM by resident - anonymous at moment

6 Bears Down Cornwall 600kW 16 30 Salford - clear case added

7 Bicker Fen Lincolnshire 2MW 13 59 Statement from complainant - clear case

8 Black Law, Forth South Lanarkshire 2.3MW 42 82 Reported by others

9 Blaen Bowi Carmarthenshire 1.3MW 3 46 Salford - clear case but not added

10 Carland Cross Cornwall 400kw 15 30 In ETSU-R-97 and Salford - now repowering

11 Cairnmore Aberdeenshire 850kW 3 55 Information on complaints is second hand

12 Causeymire Highland 2.3MW 21 60 In Salford but not added by Salford

13 Coal Clough Lancashire 400kw 24 30 In ETSU-R-97 missed in Salford

14 Cold Northcott Cornwall 300kw 22 25 In ETSU-R-97 - in Salford but not added by them

15 Coldham Cambridgeshire 1.75MW 8 60 Statements from complainant matches AM

16 Conisholme East Midlands 800kW 20 65 Evidence from others

17 Cotton Farm East Anglia 2MW 8 80 MAS have measured EAM

18 Cruach Mhor Argyll & Bute 850kw 35 45 Salford - but not added

19 Crystal Rig Scottish Borders 2.3MW 51 + 9 60 + 80 Evidence from others

20 Dalswinton Dumfries 2MW 15 80 Confirmed by the LA and affected resident

21 Darracott Devon 850kW 3 50 Complaints by residents of AM clearly ID AM

22 Deeping St Nicholas Lincolnshire 2MW 8 59 In Salford and added, MAS confirmed

23 Delabole Cornwall 2.3MW 4 99 (tip) Direct complaints and advice of acoustician

24 Forestmoor, Devon 1MW 3 48 Evidence of others Bradworthy

25 Four Burrows Cornwall 300kW 15 30 In Salford - 'another' noise complained of

26 Fullabrook Devon 3MW 22 65 Complaints by many residents of AM, post Salford

27 Gedney Marsh (Red Lincolnshire 2MW 6 59 Indirect evidence House)

28 Glens of Foundland Aberdeenshire 1.3MW 20 46 In Salford but not added

29 Glyndebourne Lewes District 850kW 1 44 Independent source - see also article in Private Eye No.1334

30 Hadyard Hill South Ayrshire 2.5MW 52 60-70 In Salford, possible case, but no direct evidence

31 Hafoty Ucha Gwynedd 850kW 1 39-44 In Salford, questionable case, but no direct evidence

32 Harlock Hill Cumbria 500kW 5 35 In Salford, but no direct evidence

33 Hazlehead Yorkshire 2MW 3 60 Indirect complaints from residents - monitoring by developer being undertaken

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34 High Volts County Durham 2750kW 3 60 Indirect evidence

35 Hill of Easterton Aberdeenshire 850kW 3 45 Indirect evidence / information

36 Kessingland Suffolk 2.05MW 2 80 Complaints and MAS measured, post Salford

37 Knabs Ridge North Yorkshire 2MW 8 58 Complaints and MAS measured - post Salford

38 Lissett Yorkshire 2.5MW 12 80 Controls introduced to reduce noise

39 Llandinam P&L Wales 0.3MW 103 31 In ETSU-R-97

40 Llangwryfon Ceredigion 0.85MW 11 40 Indirect information - complaints from residents

41 Llyn Alaw Anglesey 600kW 34 31 In Salford and WAS added

42 Lynch Knoll Gloucestershire 500kW 1 42 In Salford but not added

43 Lynemouth Northumberland 2MW 13 78 Indirect evidence / information

44 Mablethorpe Lincolnshire 600kW 2 65 Indirect evidence

45 Michelin Tyre Dundee City 2MW 2 85 In Salford but not added Factory

46 Moel Maelogen North Wales 1.3MW 9 50 Indirect information, in Salford but not added

47 Mynydd Clogau Powys 850kW 17 34 In Salford, possible case, but no direct evidence

48 Mynydd Gorddu Ceredigion 0.5-0.6MW 19 34-35m Indirect information

49 Newstead Cuminstown 0.8MW 1 49 Multiple sources of evidence from residents

50 North Pickenham Norfolk 1.8MW 8 80 MAS measured - residents not complaining officially

51 North Rhins Dumfries 2MW 11 60 Indirect information

52 Parc Cynog Carmarthenshire 720-850kW 5+6 60 When extended in size

53 Penrhyddlan & Powys 300kW 103 45 Noise problems noted in ETSU-R-97 Llidiatywaun

54 Red Tile / Warboys Cambridgeshire 2MW 12 59 MAS measured and complaints - missed by Salford

55 Rhyd y Groes Ceredigion 300kW 24 31 Noise problems noted in ETSU-R-97

56 Royd Moor South Yorkshire 500kW 13 35 In Salford but not added, MAS heard

57 Site P - single Pembrokeshire ANON Confirmed by EHO turbine

58 Skelmonae Ellon, Aberdeenshire 0.8MW 4 64 Controls in place to reduce noise

59 South Sharpley Easington District 1.3MW 2 65 Evidence from affected residents

60 St Breock Cornwall 450kW 11 35 In Salford but not added

61 Swaffham Norfolk 1.8MW 1 67 Complaints and MAS measured, missed by Salford

62 Taff Ely South Wales 0.45MW 20 35 Indirect information

63 Tir Mostyn & Foel Denbighshire 850kW 25 49 In Salford but not added Goch

64 Trysglwyn Gwynedd 400kW 14 25 In Salford but not added

65 Wadlow Cambridgeshire 2MW 13 80 MAS have measured and confirmed with direct observations

66 Walkway Wind Sedgefield District 2MW 7 69 Evidence from affected resident clearly identifies AM Farm

67 Wharrels Hill, Bothel Cumbria 1.3MW 8 76 Complaints by residents of AM, post Salford

68 Whittlesey Cambridgeshire 1.8MW 1 80 Turned off at night

Many references derive from a study by Salford University in 2007. Reference to "not added" or "added" means that there was evidence of AM but Salford did or did not include it as AM related in their study. "MAS have no direct evidence" means we have not been able to verify the likelihood that complaints relate to AM.

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