Draft National Wind Farm Development Guidelines - July 2010

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Shape of the Sun The Sun can either be modelled as a point source or a disk. In some sources (Garrad Hassan, 2006) the disk is considered the more conservative and in others (Garrad Hassan, 2007), the point is considered more conservative. The basis on which the point source can be considered more conservative is that shadow intensity does not decrease with distance using this method (whereas it does with the disk). Since the shadow intensity is considered separately as a means to determine the region of influence in all approaches to modelling shadow flicker (including that proposed here), this argument is mute. The disk can be considered more conservative from the point of view that it leads to a slightly larger area of coverage, and is more realistic. On this basis, the Sun should be modelled as a disk. Time and duration of modelling It is common practice to produce a model for a single year (arbitrarily selected), to determine the shadow flicker that occurs in that year and assume this will apply to all years of the wind farm’s operation. This is slightly flawed, as the orbit and orientation of the Earth change marginally from year to year. Also, there could be some increase in the amount of shadow flicker during a leap year relative to any other year. The assumptions made here have little influence on the result; however, the annual limit is based on a non-leap year, so this should be used in the assessment. To account for variation in the Earth orbit, a year at approximately the middle of the lifespan of the wind farm should be chosen. Given a typical 25 year lifetime, calculation is recommended for a year between 12 and 15 years after the year in which the planning application is assessed. Orientation of the rotor The rotor can (typically) be modelled in one of the following ways: • As a disk lying in a plane whose normal points to the Sun (also referred to as a sphere). • As a disk lying in a plane whose normal is horizontal and points towards the azimuth of the Sun. • As a disk whose direction is determined probabilistically by the seasonal and time of day wind distribution. Of these models, the first is the most conservative as it generates the largest area of shade at any time. It is most inaccurate when the Sun is overhead and actually passes through a narrowed rotor plane (as opposed to the full rotor plane as assumed); however, this is when shadow flicker is of least concern and thus the assumption is of little consequence. Modelling the rotor as a disk whose normal is horizontal and points towards the Sun is also conservative. It is essentially the same as the sphere model but includes the effective narrowing of the rotor plane when the Sun is overhead. The third approach is theoretically most accurate but is difficult to implement in practice and is a statistical approach that is hard to test. It is non-conservative. Thus, the first or second approaches are recommended. Offset between tower and rotor Garrad Hassan (2007) notes that it is important to include the offset between the tower and rotor because the modelling is quite sensitive to the rotor position. While it is considered prudent to include this information in the model if available, such a high level of sensitivity is considered best addressed by other means, particularly given that micrositing of turbines during construction could result in far greater errors in the modelled position. Further consideration of sensitivity is included under Sensitivity (page 153). Time step for calculations When modelling shadow flicker, shadows are typically calculated at some time of day, the time of day is then incremented by a fixed amount and the process repeated. The increment in time can impact on the accuracy of the calculations. The increment used in Page 160 Draft National Wind Farm Development Guidelines – 2 July 2010
common practice varies between one (1) and ten (10) minutes (usually one or ten minutes). Ministry for Environment and Climate Change (2002) requires that one minute steps be used. The impact of the difference is relatively minor and the only difference in effort is additional computational time. Given that measures are recommended to reduce the sensitivity of the modelling (see Sensitivity, page 153), it is recommended that steps of ten minutes or less be used. Effects of topography The local topography will partially determine at what Sun angle a receptor is subject to shadow flicker. Commercial modelling software provides the capability to include the impact of topography. On this basis, it is recommended that effects of topography be included in shadow flicker models. Receptor height The receptor height is meant to allow for the typical height at which a person would experience shadow flicker (i.e. eye level). Values of 1.5 – 2 m are commonly used. The results are relatively insensitive within this range, and so it is recommended that the receptor height of 1.5 – 2 m be used. An exception exists in the case where dwellings are higher than single storey. In this case, shadow flicker may be experienced at other heights. Existing multi-storey buildings should include assessment at window height on all storeys. Receptor location The location of the receptor is important as in some areas, shadow flicker can change rapidly for small movements. With reference to Figure E-1, shadow duration may increase from zero to 50 hr/yr over a distance of 100 m. This is an important issue as shadow flicker is normally reported for a single point, which may represent a window, or the centre of a dwelling. Someone just outside the building may experience considerably different results. This is also a particular issue for public spaces and recreation areas, if they are to be included in the assessment. Shadow flicker maps can be calculated that show the variation with distance. These are produced in most current assessments but not actually used. It would be productive to use these maps to identify the highest value of shadow flicker within 50m (or some distance limit) of the receptor, and to use this as the reportable amount. The particular advantage of this approach is that it accounts for both the reasonable extent of use by residents (and others) at a site, and for the sensitivity in the modelling discussed in the Sensitivity section. Due to the effort required to interpret the output available from modelling packages, it is only considered feasible to use this approach in assessing the annual exposure. Daily exposure should be calculated for the dwelling centre only. Grid size for mapping Given the receptor location recommends using the maximum shadow flicker within 50m of a dwelling, it is necessary to define the grid size for which shadow flicker is calculated. A grid size of 25m x 25m is practical and should achieve sufficient resolution. This should be set as the upper limit on grid size. E.7.3 Basis for mitigation measures The wind is not always blowing – shadow flicker will not occur when the turbine is not rotating While the statement is true, many wind turbines will continue rotating slowly even below their cut-in wind speed to maintain lubrication to all parts. The alternative case where a turbine is stopped because the wind speed exceeds the turbine cut-out wind speed Draft National Wind Farm Development Guidelines – 2 July 2010 Page 161
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EPHC National Wind Farm Development
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Acknowledgements These Guidelines h
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A.6.1 Site selection 28 A.6.2 Proje
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E.7 Technical discussion of key con
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The 20/20 target is challenging; ho
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Table 1-1 Elements of a ‘wind far
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2 Principles for responsible wind f
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3 Wind Farm Specific Issues The spe
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Specific noise limits are not provi
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3.5 Shadow flicker The issue Shadow
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Guidance notes Heritage issues are
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Table 4-1 Typical decision process
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The studies and community consultat
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A Community and Stakeholder Consult
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• Responsive There is a comm
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Figure A-1 IAP2 Public Participatio
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Specific components which should be
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Figure A-2 Example of Good Practice
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Recording the occurrence and outcom
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A.6.6 Decommissioning Planning & Co
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Potential Stakeholders Consultation
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B Noise B.1 Introduction This Appen
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the converse. These Guidelines reco
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The Standard should form the basis
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Stage and methodology Construction
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Other noise-sensitive uses such as
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Table B-2 Existing state and territ
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Establish background noise monitori
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As noted in Section 6.3.1 of AS4959
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predicted levels are significantly
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Prepare expert evidence (as require
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Undertake unattended monitoring to
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assessment of wind farm noise emiss
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B.4.5 Decommissioning Noise-related
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If a significant amount of time has
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B.7 Technical discussion of key con
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The HGC Engineering report 10 also
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C Landscape C.1 Introduction This A
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• Cumulative impacts “Cumulativ
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C.2 Overview of Methodologies Figur
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C.3 Task Methodologies C.3.1 Projec
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• State Relevant State herita
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The preliminary landscape character
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• Identifying and describing (in
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Advanced photomontages should also
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C.4.2 Visual Impact Assessment The
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C.4.2.4 Assessment of cumulative im
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the implementation of agreed change
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Figure C-2 IBRA mapping of Australi
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Table C-4 Mapping of landscape char
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C.7.2 Levels of significance What a
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Consider ‘Supporting Evidence’
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information available for other sit
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Figure C-4 Example of viewshed mapp
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Figure C-6 Example of photomontages
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communicate broad-scale ideas and p
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Table C-5 Mapping other wind farms
Page 119 and 120: C.7.9 Glossary & acronyms Australia
Page 121: Viewpoint The point from which a vi
Page 124 and 125: D.1.2 Underlying approach The under
Page 126 and 127: All of the above is generally appli
Page 128 and 129: the operational wind farm is aimed
Page 130 and 131: D.4 Task methodologies D.4.1 Site S
Page 132 and 133: area as it was not collected accord
Page 134 and 135: used throughout these Guidelines as
Page 136 and 137: wind farms. Such data from existing
Page 138 and 139: considered acceptable, undesirable,
Page 140 and 141: construction phase are identified d
Page 142 and 143: Searches for dead birds and bats ar
Page 144 and 145: D.5 Cumulative impacts D.5.1 Defini
Page 146 and 147: in the absence of any turbine colli
Page 148 and 149: that it was first observed. Where m
Page 150 and 151: e the case that assessment for bats
Page 152 and 153: Department of Primary Industries, W
Page 154 and 155: Percival, S.M. 2003, Birds and wind
Page 157 and 158: E Shadow Flicker E.1 Introduction T
Page 159 and 160: • The use of recreational facilit
Page 161 and 162: • The method is inherently linked
Page 163 and 164: Table E-1 Recommended exposure limi
Page 165 and 166: E.4.4 Construction Assessment of th
Page 167 and 168: E.7 Technical discussion of key con
Page 169: Figure E-4 Variation in shading wit
Page 173: as the actual limit, rather than th
Page 176 and 177: likely to be obstructed. Radiocommu
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Page 180 and 181: Figure F-1 EMI mitigation methodolo
Page 182 and 183: F.4 Task methodologies F.4.1 Projec
Page 184 and 185: Expected timeframe for evaluation r
Page 186 and 187: The near field zone can be calculat
Page 188 and 189: Develop mitigation strategy As a st
Page 190 and 191: aseline RF survey which involves th
Page 193 and 194: G Wind Farm Development Process G.1
Page 195 and 196: Project Sub-stages Activities to be
Page 197 and 198: Preliminary Technical Studies Issue
Page 199 and 200: Planning application (PA2) The plan
Page 201 and 202: Develop mitigation strategy Finalis
Page 203 and 204: Environmental Management Plans Issu
Page 205 and 206: Monitoring: confirmation (O3) Confi
Page 207 and 208: Decommissioning (D2) Once a decisio
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Draft National Wind Farm Development Guidelines - July 2010

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