Shadow Flicker

Shadow Flicker happens when rotating turbine blades pass between an observer and the sun. To experience Shadow Flicker at a particular location, a number of factors must coincide: sun location, wind direction and clear skies, among other things.

Shadow Flicker predictions involve estimating the probability of these factors coinciding at potential receivers. In general, Shadow Flicker becomes insignificant beyond about 10 rotor diameters, or 824m at Killhill (DoEHLG Guidelines, 2006).

Shadow Flicker predictions have been carried out for Killhill Windfarm. The key results are shown below, as contours of predicted Shadow Flicker per year. The results clearly show that the expected Shadow Flicker at surrounding dwellings will be well below the DoEHLG Guideline figures of 30 hours per year.

For details view the contour map

In terms of shadow flicker per day, mitigation measures will be adopted to ensure that no dwelling within 10 rotor diameters of the windfarm will experience more than 30 minutes per day of shadow flicker. The DoEHLG Guidelines state that beyond this distance the potential for shadow flicker is very low.

Rotors have three blades and rotate at about 22 revolutions per minute. This implies a frequency of Shadow Flicker of about 1.1 per second or 1.1Hz. This is well below the levels at which observers experience flicker as a particular nuisance (5-10Hz).