Environmental Impact Statement for

Proposed Cluddaun Wind Farm Co. Mayo

VOLUME 2 MAIN EIS Chapter 11 Shadow Flicker

Table of contents 11 SHADOW FLICKER ...................................................................................................... 11-2 11.1

INTRODUCTION ................................................................................................................ 11-2

11.2

EXISTING ENVIRONMENT ................................................................................................. 11-5

11.3

LIKELY SIGNIFICANT IMPACTS .......................................................................................... 11-8

11.4

MITIGATION ................................................................................................................... 11-10

11.5

RESIDUAL IMPACTS ........................................................................................................ 11-10

11.6

CONCLUSION .................................................................................................................. 11-10

Table of Tables Table 11-1 Table 11-2

Average Hours of Sunshine and Average Hours of Day ........................................... 11-4 Existing Dwellings within zone of influence 1.2km. ................................................ 11-6

Table 11-3

Shadow Flicker Assessment Results ....................................................................... 11-9

Tables of Figures Figure 11-1

Shadow pone area as function of time of day........................................................ 11-2

Figure 11-2

Local Residences within 1.2km .............................................................................. 11-7

Environmental Impact Statement

Cluddaun Wind Farm Proposal

Volume 2

11 SHADOW FLICKER

11.1 INTRODUCTION Shadow flicker is defined as the alternating light intensity produced by a wind turbine as the rotating blade casts shadows on the ground and stationary objects, such as the window of a residence. No flicker will occur when the turbine is not rotating or when the sun is obscured by clouds or fog. A larger turbine rotor diameter will cast a larger shadow, meaning a larger area will be prone to incidences of shadow flicker. The three key factors related to shadow flicker occurrence (measured in number of hours per year) are i) the spatial relationships between a wind turbine and the receptor, ii) the wind direction and iii) the sunshine hours. These are discussed below.

11.1.1 Factors Influencing Shadow Flicker Occurrence 11.1.1.1 Spatial Relationships

At distances of greater than approximately 500 metres between a turbine and a receptor, shadow flicker generally occurs only at sunrise or sunset when the cast shadows are extremely long. It is generally considered the occurrence of shadow flicker is very low “at distances greater than 10 rotor diameters from a turbine”1. Figure 11-1 shows an approximation of the shadow cast by a turbine at various times during the day, where the red shading represents the area where shadow flicker may occur.

a. Near solar noon

b. Mid morning/mid-afternoon

c. Near sunrise/sunset

Figure 11-1. Shadow pone area as function of time of day

1

Extract from the DoEHLG 2006 Guidelines, on occurrence of shadow flicker

Chapter 11

Shadow Flicker

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Environmental Impact Statement

Cluddaun Wind Farm Proposal

Volume 2

11.1.1.2 Wind Direction

The angle between the sun and the rotor plane also plays a determining role for both shadow flicker occurrence and intensity. The rotor plane is determined by the direction of the wind: because the turbine rotor continuously yaws to face the wind, the rotor plane will always be perpendicular to the wind direction. Shadow flicker will be most pronounced when the rotor plane is perpendicular to the sun-receptor line of sight. 11.1.1.3 Sunshine Hours

The shadow flicker analysis assumes the sun is always shining. It is reasonable to factor any results by the percentage of time the sun is actually shining. Irish skies are completely covered by cloud for well over fifty percent of the time. Ireland normally gets between 1100 and 1600 hours of sunshine each year. Over the year as a whole, most areas get an average of between 3 1/4 and 3 3/4 hours of sunshine each day2. It was possible using the 30 year average sunshine data available from Met Eireann to determine the percentage of time shadow flicker could actually occur. These are presented in Table 11-1. Using the data in Table 11-1, this means that the conditions necessary for shadow flicker (clouds not present) are only predicted to be present at approximately 22% of the maximum theoretical hours predicted by the WindFarm software. Therefore, the theoretical maximum shadow flicker as predicted by WindFarm was multiplied by 0.22 (22 percent) to evaluate potential impacts at the Cluddaun Wind Farm. The above methodology is conservative in that it does not account for times when the turbine blades are not spinning, or when the flicker is blocked from view at a given receptor, or when the rotor is not perpendicular to the sun. Danish studies suggest that using these suppositions would result in a prediction of annual shadow flicker equal to approximately 18% of the worst case assumption.3

2 3

http://www.met.ie/climate-ireland/sunshine.asp http://guidedtour.windpower.org/en/tour/env/shadow/shadowr.htm

Chapter 11

Shadow Flicker

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Environmental Impact Statement

Table 11-1

Cluddaun Wind Farm Proposal

Volume 2

Average Hours of Sunshine and Average Hours of Day

Month

Average hours of sunshine4

Average Length of day

Proportion of day with sunshine

Jan

1.3

8

16%

Feb

1.9

10

19%

Mar

2.6

12

22%

Apr

4.3

14

31%

May

5.0

16

31%

Jun

4.4

17

26%

Jul

3.7

16

23%

Aug

3.8

14

27%

Sept

3.2

13

20%

Oct

2.4

11

15%

Nov

1.7

9

18%

Dec

0.9

8

11%

Average

2.9

Yearly Average

22%

11.1.2 Assessment Criteria The Irish Windfarm Planning guidelines recommend a threshold of 30 hours of shadow flicker per year or 30 minutes per day, to evaluate potential shadow flicker impacts to residences within 500m of a turbine. There are no turbines within 500m of an occupied dwelling (see Figure 11-2 also). The current guidelines do not require an assessment of shadow flicker beyond 500m, however it is acknowledged that wind turbine technology has increased in size since these guidelines were drafted, and dwellings beyond this distance should be considered. It should also be noted that in general the occurrence of shadow flicker is very low at distances greater than 10 rotor diameters from a turbine. The study area has been limited to 1,200m around proposed turbine locations, which is 10 times the rotor diameter.

4

Claremorris 1971–2000 averages, http://www.met.ie/climate-ireland/1971-2000/claremorris.html

Chapter 11

Shadow Flicker

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Environmental Impact Statement

Cluddaun Wind Farm Proposal

Volume 2

11.2 EXISTING ENVIRONMENT Shadow flicker was calculated for the proposed Cluddaun wind farm using industry-standard simulation software WindFarm, a tool which has been successfully applied to a number of similar studies around the world. The model uses Ordnance Survey Ireland digital height data as its only topographical reference. Simulations are run on a ‘bare earth scenario’ without allowing for the obscuring effect of vegetation between the location of the residence and the position of the sun in the sky. Nor does the model consider any obscuring features around residences itself, which would minimise views of the site and hence reduce the potential for shadow flicker, thus the WindFarm model uses a worst case scenario when reporting shadow flicker results for the existing environment. The model assumes that: 1. The sun will always be shining during daylight hours, with no cloud cover or fog. 2. The wind will blow continuously throughout the day and always above cut-in speed, i.e. the turbine will always be rotating. 3. The wind will always be blowing from a direction such that the turbine rotor is aligned with the sun-receptor line. In other words, the rotor will yaw in parallel with the sun such that the rotor blades are always perpendicular to the sun-receptor view line. 4. There will be no screening by vegetation or trees, i.e. a bare earth scenario. A more realistic simulation would use the following assumptions: 1. The sun will not always be shining, therefore it is only necessary to calculate shadow flicker for the fraction of time when the sun would be shining. Average sunshine hours used in this assessment - are based on average monthly figures from the years 1971 to 2000, from the Claremorris National Meteorological Station. 2. The rotor will not be turning all the time. The wind turbine will not turn when there is not enough wind. 3. The rotor blades will not always be perpendicular to the sun-receptor view line. 4. Trees and vegetation in the vicinity of the receptor will reduce shadow or eliminate shadow flicker. An assumption is also made that the windows of the rooms, where the effects may occur, (i) directly face the development, (ii) that the rooms are occupied and (iii) that the curtains or blinds if present are open. Also worth noting is that the shadow flicker calculation does not consider any limit of human perception of shadow flicker. All dwellings located within 1.2km are illustrated in Figure 11-2 below. The distance to the nearest turbine is also displayed.

Chapter 11

Shadow Flicker

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Environmental Impact Statement

Cluddaun Wind Farm Proposal

Volume 2

11.2.1 Existing Residences In total there are 10 occupied properties within 1.2km of a proposed turbine. All of these properties are over 500m from a proposed turbine. Five are over 700m from the nearest turbine. Two are over 900m to the nearest turbine and the remainder are over 1,000m (1km) from the nearest proposed turbine. The 10 rotor diameter separation is illustrated on Figure 11-2. A description is presented in table 11-2. Table 11-2

Existing Dwellings within zone of influence 1.2km.

House

Distance to

Location

Nearest Turbine

Reference

(m)

H7

H8

1066

1013

Comments At over a kilometre away from the nearest turbine the potential for any significant intensity of shadow flicker is greatly reduced. Also there are no turbines due north, south or east of this dwelling significantly restricting the times of any occurrence. At over a kilometre away from the nearest turbine the potential for any significant intensity of shadow flicker is greatly reduced. Also there are no turbines due north, south or east of this dwelling significantly restricting the times of any occurrence.

H12

755

H13

730

H14

921

H15

1015

H28

537

H29

n/a

H40

969

H53

1193

H74

794

H79

740

H94

733

Chapter 11

There is significant potential for natural screening at this location due to forestry and out buildings. There is significant potential for natural screening at this location due to forestry and out buildings. Nearest turbine which could possibly impact is over 2km west. Located due south of closest wind turbine (921m). Shadow flicker cannot occur due to orientation of sun. In reality this location is outside any zone of influence. Nearest turbine which could possibly impact is over 2km west. Located due south of closest wind turbine (1015m). Shadow flicker cannot occur due to orientation of sun. In reality this location is outside any zone of influence. Involved landowner and nearest turbine is located on their property Derelict building owned by involved landowner and excluded from assessment. Located due south of wind farm. Shadow flicker cannot occur due to orientation of sun. No turbines ever between dwelling and sun. Located due south of wind farm. Shadow flicker cannot occur due to orientation of sun. No turbines ever between dwelling and sun. Unoccupied old school building. There are no windows located on the house gables which are orientated east and west. As the potential for shadow flicker is greatest in the early morning and late evening the potential for occurrence is significantly reduced at this location. No building here.

Shadow Flicker

Page | 11-6

Project Title: 14112 Cluddaun Wind Farm Drawing Title: Figure 11-2. Local residences within zone of influence (10 rotor diameters) Client: Coillte Drawn by: JK Checked by: PB Drawing Date: 11/09/2013 Drawing Size: A4

! A

Legend

! A

! A

" ) ! A

Turbine Layout

" ) Houses within 1.2km Buffer Houses Site Boundary

" )

0

1.25

2.5 km

Map Reproduced From Ordnance Survey Ireland By Permission Of The Government. Licence Number EN 0015713

´

" )

H13

! ! A A ! A ! A ! AA ! ! ! A A ! A ! H29 A H28 " ) ! A ! A " ) H79 H74

Turbine Layout 1.2km Buffer

" )

H12

" )" )" ) " )" ) ) " ) " " ) " ) " ) " ) " )" ) " ) " ) " ) H7 " ) H8 " )

! A

! ! A A A ! " )" ) ! A ! ! ! A A A ! ! A ! A A ! ! A A ! A ! A ! A ! ! A A

! A ! A

! ! A A A! ! AA ! A ! A ! ! A A ! ! A A ! A H94 ! A " H15 ) !

" )) " "" ) ) "" ) ) " ) " )" )

) H14 " ) "

" )

H40

" )

H53

" )

" ) " ) ) " )"

Environmental Impact Statement

Proposed Cluddaun Wind Farm

Volume 2

11.3 LIKELY SIGNIFICANT IMPACTS WindFarm software was used to run the shadow flicker model for all properties located within 1.2km of the proposed wind farm. The turbine envelope for which planning is being sought is 150m tip height. The rotor diameter could be either 100m or 120m depending on the final turbine procurement. For the purpose of this assessment both scenarios were considered, i.e. 90 hub height and 60m blade length and 100m hub height and 50m blade length. There will be some smaller turbines located on Shenettra hill, to minimise visual impact and these have been input into the model accordingly. The majority of the turbines will be up a max tip height of 150m. The most onerous scenario of 90m hub height and 60m blade length was used to incorporate conservatism into the results. To present a more likely but still conservative estimate of the actual shadow flicker that could be experienced at the dwellings identified in Table 11-3, the Theoretical values have been multiplied by 0.22 to allow for the annual average sunshine hours in the area, i.e. on average a 22% chance of occurrence of sunshine daily. The results of the prediction modelling are presented in Table 11-3 and illustrated in Figure 11-2 below. The results are compared against the 30 minute per day and 30 hour per year limit as set out in the DoEHLG wind farm planning guidelines. The prediction modelling found that several of the residential properties within a 1.2km radius of the site have the potential to be affected by shadow flicker. The results are presented in -Table 11-2. The value calculated by the model is a theoretical worst case scenario and assumes the suns shines every day, the wind blows every day, the wind blows above cut in speed every day, the rotor is always perpendicular to the sun, there is no screening by vegetation, that windows of dwellings directly face the development, there is somebody to see the shadow flicker and that it is perceived to be an annoyance.

11.3.1

Cumulative Impact

The nearest third party wind farm is the Permitted/ Proposed Oweninny wind farm. The nearest Oweninny turbine is over 2.5 km to any property which could potentially be impacted at Cluddaun. At this distance Cumulative impact will not be an issue and is not considered further.

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Shadow Flicker

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Environmental Impact Statement Table 11-3 House/ Window 7/ 3 7/ 4 8/ 3 8/ 4 12/ 1 12/ 2 12/ 3 12/ 4 13/ 1 13/ 2 13/ 3 13/ 4 14/ 1 14/ 2 15/ 1 15/ 2 15/ 4 28/ 1 28/ 2 28/ 3 28/ 4 40/ 1 40/ 2 40/ 3 40/ 4 53/ 1 53/ 2 53/ 3 53/ 4 74/ 1 74/ 2 74/ 3 74/ 4 79/ 1 79/ 2 79/ 3 79/ 4 / 94 1 94/ 2 94/ 4

Chapter 11

Degrees from North 180 270 180 270 0 90 180 270 0 90 180 270 0 90 0 90 270 0 90 180 270 0 90 180 270 0 90 180 270 0 90 180 270 0 90 180 270 0 90 270

Mean hours per day

Proposed Cluddaun Wind Farm

Volume 2

Shadow Flicker Assessment Results Corrected to

DOEHLG Daytime

allow for

Limit

cloud cover

(30 minutes)

0.4 0.4 0.4 0.4 0.4 0.6 0.5 0.4 0.2 0.1 0.6 0.5 0.3 0.3 0.2 0.2 0.2 0.7

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2

0.5

0.1

0 0 0 0 0 0 0 0 0.5 0.3 0.5 0.4 0.5

0 0 0 0 0 0 0 0 0.1 0.1 0.1 0.1 0.1

0.6

0.1

0.3 0.2 0.2

0.1 0.1 0.1

Total hours

0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 No Gable Windows 0.5 No Gable Windows 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 No Gable Windows 0.5 No Gable Windows 0.5 0.5 0.5

Shadow Flicker

Corrected to allow for cloud cover

DOEHLG Annual Limit (30 hours)

59 59 52 53 24 52 75 47 6 2 71 76 30 30 19 10 8 97

13 13 12 12 5 12 16 10 1 0.3 16 17 7 7 4 2 2 21

30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30

72

16

30

0 0 0 0 0 0 0 0 62 57 65 71 83

0 0 0 0 0 0 0 0 14 12 14 16 18

30 30 30 30 30 30 30 30 30 30 30 30 30

67

15

30

33 25 8

7 6 2

30 30 30

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Environmental Impact Statement

Proposed Cluddaun Wind Farm

Volume 2

11.3.2 Discussion of Results Thirteen locations have been identified within the potential shadow flicker zone of influence. Given the large separation distances, dwelling locations relative to wind turbines and the presence of local screening the potential for any significant intensity of shadow flicker is greatly reduced at all the locations. Regardless a simulation model was run using worst case scenario assumptions and corrected to allow for actual sunshine hours in the area. The results show that when adjusted to factor in actual sunshine hours, the DoEHLG Wind Farm Planning Limits for Shadow Flicker will not be exceeded at any location. 11.4 MITIGATION As the DoEHLG Wind Farm Planning Guideline limits will not be exceeded, mitigation measures are not required. 11.5 RESIDUAL IMPACTS There will be some occurrence of shadow flicker under certain meteorological conditions, however these events will be considerably lower than the guideline limits as identified in the Irish Wind Farm Planning Guidelines and no dwellings will significantly impacted. 11.6 CONCLUSION In conclusion shadow flicker that may be experienced by local residents within 1.2km of the proposed wind farm will be significantly below the DoEHLG Wind Farm Planning Guidelines.

Chapter 11

Shadow Flicker

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