Linfairn Wind Farm Addendum Chapter A13: Shadow Flicker

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1 A13. SHADOW FLICKER 13.1 Introduction The purpose of this chapter is to review amendments to the Project design and to advise of any consequent alterations to potential shadow flicker impacts as previously reported in ES Chapter 13. The assessment has been carried out by SgurrEnergy Ltd Scope of the Assessment Study Area and Assessment Criteria There have been no updates to guidance, of relevance to the shadow flicker assessment, since the ES was submitted. Therefore the assessment criteria remain as detailed in Section of ES Chapter 13. Using the ReSoft WindFarm software, a potential shadow flicker impact map was produced for the revised layout of 17 WTGs (see Figure A13.1) which highlights proties potentially affected by the Project Consultation Responses The Section 36 application was submitted to the Scottish Government ECDU on 27 September 2013 with responses received in November and December No consultation responses were received in relation to shadow flicker Assessment Methodology Analysis Software Parameters The shadow flicker analysis was conducted using the Shadow Flicker module of the ReSoft WindFarm software. Please refer to Section of ES Chapter 13 which provides further detail Parameters used in the Analysis WTG dimensions and layout The modelling was undertaken based on the proposed 17 WTG layout and a WTG with a 101m rotor diameter and 76m hub height, which is a larger rotor diameter and lower hub height than originally modelled. 14/7048/001/GLA/O/R/001 Revision B1 Page 1 of 7

2 Shadow flicker potential impact area and receptor locations As identified in section of the ES, the shadow flicker impact is likely to be negligible beyond a distance of 10 rotor diameters. This is equal to 1,010m for a WTG with a 101m rotor diameter. Using the WindFarm software, a potential shadow flicker impact area map has been produced (Figure A13.1). As shown on the figure, only certain houses are predicted to be within this potential impact area. Consequently, only these proties would be expected to exience shadow flicker effects and therefore have been included in the modelling analysis. It should be noted that the amended Project design, with 17 WTGs, has a reduced impact area compared with the layout in the ES. Consequently, proty numbers 1, 2 and 3 which were considered in the ES Chapter 13, are no longer relevant to the shadow flicker assessment. Proty number 5 consists of non-residential outbuildings and has therefore been removed from the assessment. The numbering of proties remains consistent with the original ES. Window distribution, orientation and size The same approach was adopted as described in section of the ES Assessment Results WindFarm Shadow Flicker Analysis Results For each of the potential shadow flicker receptors, a total number of shadow flicker hours in a year was modelled. The results of this modelling are shown in Table A13-1. It should be noted that these results represent theoretical hours for which the individual receptor could potentially be affected by shadow flicker based on worse case scenario modelling. Again it should be noted that the results do not take into account factors that would reduce shadow flicker such as iods when there is insufficient sunshine due to cloud-cover, iods when the WTG is not rotating or screening from any existing vegetation and buildings. The sensitivity is considered to be High at the proties which are residential receptors. The results have been provided and then examined in relation to the guidance limits, as section of the ES, of 30 hours year or 30 minutes day on the worst affected day, based on an astronomical worst case scenario. 14/7048/001/GLA/O/R/001 Revision B1 Page 2 of 7

3 Table A13-1: Potential Shadow Flicker Occurrence at Identified Proties (WTG with 76 m Hub Height and 101 m Rotor Diameter) No. Name Co-ordinates Window Orientation (degrees from north) Days year* Max hrs day* Mean hrs day* Total hrs year* 4 Knockskae Linfairn Genoch Cottage *Theoretical modelled values As can be seen in Table A13-1, only one proty (proty number 6: Linfairn) is predicted to exience more than 30 hours of shadow flicker year, using worst case modelling. It is understood that the owner and occupier of proty 6 (Linfairn) has a financial interest in the project. Proties 4 (Knockskae) and 7 (Genoch Cottage) do not exceed 30 hours year. Proty 4 (Knockskae) is predicted to exience slightly over 30 minutes in the maximum hours day assessment. A summary of when shadow flicker is expected to occur at Proties 4, 6 and 7 is given in Table A13-2 below. Table A13-2: Timing of Shadow Flicker Occurrence at Key Proties (WTG with 76 m Hub Height and 101 m Rotor Diameter) Proty Distance to WTG (m) Potential Shadow Flicker Occurrence Time of the Year Time of the Day 4: Knockskae 695 Winter Late morning 6: Linfairn 837 Autumn, Winter Afternoon 7: Genoch Cottage 992 Autumn, Winter Afternoon Based on this worst case modelling exercise, proties 4 (Knockskae) and 6 (Linfairn) are both predicted to exience a maximum daily duration above 30 minutes day, specifically 0.6 hours (36 minutes) and 0.9 hours (54 minutes) respectively Potential Factors Reducing Shadow Flicker Impact There are a number of factors that are likely to reduce the incidence of shadow flicker. Details of these and annual average sunshine for the study area can be found in Section of the ES. The annual average sunshine, as the ES, was 25.1%. This was applied to the annual shadow flicker results for proties 4, 6 and 7. 14/7048/001/GLA/O/R/001 Revision B1 Page 3 of 7

4 The adjusted shadow flicker hours for individual proties are given in Table A13-3. Table A13-3: Adjusted Shadow Flicker Results based on Sunshine Hours (WTG with 76m Hub Height and 101m Rotor Diameter) Proty Total Shadow Flicker Hours Year (as modelled) Adjusted Shadow Flicker Hours 4: Knockskae : Linfairn : Genoch Cottage As can be seen, proty 6: Linfairn is predicted to exience 18.1 hours of shadow flicker year following the adjustment to account for sunshine hours. This equates to approximately 0.4% of the available daylight hours year, which is not considered to represent a significant impact. The adjusted shadow flicker hours for proties 4 and 7 are lower still and are likewise deemed insignificant impacts. This adjustment for sunshine hours results in a more realistic prediction of shadow flicker effect and duration. However, the adjusted results are still considered to be conservative because the modelling assumes a worst case scenario with regard to wind direction / WTG alignments and screening effects. In addition, the results are still based on a conservative window size, window orientation and minimum sun height. Accounting for sunshine hours and the other considerations discussed in the ES would also be expected to reduce the maximum daily duration of shadow flicker exienced at nearby proties 4 (Knockskae), 6 (Linfairn) and 7 (Genoch Cottage) Assessment of Effects Following assessment of the revised Project layout design and WTG dimensions, the potential magnitude of change in relation to shadow flicker is considered to be Negligible at the oational phase. Mitigation has however been provided to address the potential shadow flicker effects on the three proties identified above Mitigation Measures Mitigation includes software control on relevant WTGs during iods when conditions exist that could result in shadow flicker effects. The potential impact from shadow flicker will be monitored for 12 months after commissioning has been completed and a shadow flicker mitigation scheme will be submitted and approved as part of a suitable condition. This will address any potential significant effects on affected proties. 14/7048/001/GLA/O/R/001 Revision B1 Page 4 of 7

5 13.6 Summary of Effects Table A13-4 provides a summary of the potential effects associated with the revised Project. 14/7048/001/GLA/O/R/001 Revision B1 Page 5 of 7

6 Table A13-4: Summary of Effects Receptor Development Stage Sensitivity Magnitude of Change Predicted Effect Prior to Mitigation Mitigation Residual Effect Proty No. 4: Knockskae Proty No. 6: Linfairn. Proty No. 7: Genoch Cottage Oational Oational High High Software control on relevant WTGs during iods when conditions exist which could result in shadow flicker effects. Oational High 12 month monitoring scheme following commissioning of the Project. Shadow flicker mitigation scheme produced as part of any relevant condition. 14/7048/001/GLA/O/R/001 Revision B1 Page 6 of 7

7 13.7 Statement of Significance The assessment has concluded that there will be no significant impacts on proties in the vicinity of the Project as a result of shadow flicker. 14/7048/001/GLA/O/R/001 Revision B1 Page 7 of 7