1 SHADOW FLICKER ACCIONA Energy has reassessed the extent of shadow flicker and blade glint impact for this revised development application. The revised layout considers up to 24 wind turbines of the following maximum dimensions: Maximum tower height – up to 120m. Maximum rotor diameter – up to 130m. Maximum blade tip height – up to 185m. Shadow flicker has been modelled and no dwellings are expected to exceed 30 hours per year. The property closest to the proposed wind farm is further than 2km from the nearest turbine. This reassessment employs the same shadow flicker assumptions adopted in the Shadow Flicker Report prepared by Acciona Energy (Sep 2006) , as part of the original planning permit application (71/06).
This current assessment
concludes that the modified turbine layout remains compliant with the Victorian Planning Guidelines.
Wind turbines are tall structures with rotating blades. As the blades rotate during operation, they may cast an intermittent shadow on the surrounding landscape. The extent of the shadow will depend mainly on the time of day and geographical position.
The Victorian Guidelines specify that shadow flicker at any dwelling must not exceed 30 hours per year. There are a number of factors influencing the effect and duration of shadow flicker, they include: Position of the sun in respect to the turbine (season/time of day). Position of the house/viewer in respect to the turbine and the sun. Rotor size and height of the wind turbines. Distance from the wind turbines. Terrain undulation. Vegetation. Presence of wind/direction of wind (turbines rotating/swept shadow area).
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Weather/cloud cover. Airborne particles/haze.
Flickering light or shadow may cause physiological and psychological reactions. Clarke (1991)1 recommends a threshold of 2.5Hz, that is, flickers per second at which an adverse reaction may occur. The predicted frequency of shadow flicker at the site of approximately 0.9Hz will be well below the recommended threshold of 2.5Hz (flickers per second).
Clarke further recommends that in order to avoid any negative influence of shadow flicker, the minimum distance between the turbine and a house should exceed 10 rotor
diameters. Assuming
a
maximum
rotor
diameter
of
130m
gives
a
recommended separation of 1300m.
SA Planning Bulletin2 “Wind Farms, Draft for consultation” suggests that the influence of shadow flicker is insignificant once a separation of 500m between the turbine and the house is exceeded.
1.1 Shadow Flicker Modelling Inputs Shadow flicker impact at Berrimal Wind Farm has been modelled using GL Garrad Hassan WindFarmer® software. The following information was used to generate the model: A Digital Terrain Model (DTM) for the area with 25m horizontal resolution. The twenty-four (24) wind turbine locations. The wind turbine physical characteristics (a generic turbine with a 120m hub-height and 130m rotor diameter). Location of houses surrounding the wind farm. No impact of shadow flicker beyond a distance of 3,000m from the turbine. 1
Clarke, A.D. 1991. A Case of Shadow Flicker/Flashing: Assessment and Solution, Open University, Milton Keynes. 2 Planning SA. August 2002. Planning Bulletin “Wind Farms, Draft for consultation”
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Use of terrain elevation to calculate turbine and sun visibility. Calculation time interval of 1 minute. Minimum sun height over the horizon for causing shadow flicker is 3º. The
minimum
elevation
angle
of
the
sun
of
3º is
based
on industry
accepted practice. When sun angles are lower than 3º, the light travels through more of the atmosphere and becomes too diffuse to form a coherent shadow. As a result, the difference of radiation intensity between the shadow maximum and minimum is low enough that people do not notice it. The results of the shadow flicker modelling are a theoretical maximum number of annual hours of shadow flicker that could be experienced under ideal conditions. The ideal conditions assumed are given and discussed below: There is always sun available to cast a shadow, that is, no reduction is made for cloud cover or other unfavourable weather conditions which will occur in practice. The turbine is always facing directly to or away from the sun, perpendicular to the sun path. In reality, the turbine blades will not always be perpendicular and may be parallel to the shadow path. The turbine is always rotating. In practice, the wind turbines do not operate at all times; there will be periods where the wind speed is too low to operate the wind turbines. The blades cast a shadow of the same intensity along their entire length. The sun is a point source and so casts strong shadows with no reduction due to interference from the wider light source. There is no vegetation or other obstructions to the path of the shadow; in practice, there may be obstructions to the shadow path that prevent the shadow reaching the point under consideration.
1.2 Shadow Flicker Modelling Results Shadow flicker has been modelled and no dwellings are expected to exceed 30 hours per year. The property closest to the proposed wind farm is further than 2km from the nearest turbine.
