Forthbank Wind Energy Development - Partnerships for Renewables

Forthbank Wind Energy Development
within ten rotor diameters of a turbine. Therefore if the turbine has 90m diameter
blades, the potential shadow flicker effect could be felt up to 900m from a turbine.
Around 0.5 % of the population is epileptic and of these around 5 % are photosensitive.
Of photo-sensitive epileptics less than 5 % are sensitive to lowest
frequencies of 2.5-3 Hz, the remainder are sensitive only to higher frequencies. The
flicker caused by wind turbines is equal to the blade passing frequency. A fastmoving
three-bladed machine will give rise to the highest levels of flicker frequency.
These levels are well below 2 Hz. The new generation of wind turbines is known to
operate at levels below 1 Hz.”
Baseline
14.2.4 A study area was initially defined based on a distance of 10 rotor diameters (900m) of the
proposed wind turbine locations, by mapping the site using GIS (Geographical Information
Systems) software. This was then further refined to include only areas within 130 degrees
either side of north of a proposed wind turbine location. Properties within this 900m/130
degrees area were identified from OS 1:25,000 scale digital map data. Figure 14.1 shows this
study area and the properties that lie within it. Only residential properties have been
considered as being potentially sensitive to shadow flicker effects.
14.2.5 A site visit was carried out to verify the location of sensitive receptors, to establish which
buildings identified were in residential use, and to determine which facades of the properties
contained windows. As access to the properties was not available, this was carried out from
public roads, and it was not always possible to view the full extent of all façades. Conservative
assumptions have therefore been made with regard to the presence of windows and their
dimensions (i.e. the entire wall is regarded as a window).
Assessment of Significance
14.2.6 The dates, times and durations of shadow flicker events have been predicted for each property
using ReSoft WindFarm software. This programme creates a mathematical model of the
proposed wind energy development, the surrounding area and the location of properties. The
following factors are taken into account in the calculation:
• turbine locations, rotor diameter and hub height;
• topography;
• locations of houses/buildings;
• position, size and orientation of the windows on the buildings; and
• latitude and longitude of the site (used in calculating the position of sun).
14.2.7 The software calculates the dates and times when the shadow of a wind turbine’s rotor will fall
onto a window. The following worst-case assumptions are made throughout the calculation:
November 2010 Chapter 14 Page 4
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