One of the concerns often faced in wind turbine installations is a shadow flicker or sun flicker. This occurs when the blades spinning on a turbine installed between a residential location and the rising or setting sun causes shade patterns to move across windows creating what would undeniably be a distracting light pattern.
There are no associated health risks with this phenomenon, as it is highly unlikely that even an epileptic would have a seizure from the low frequency of the shadows from spinning blades (typically less than 1.75Hz for a 3-blade wind turbine).
To reduce the likelihood, or eliminate shadow flicker entirely, the use of a shadow flicker map can help to determine the areas most likely to be affected by the flicker of wind turbine blades. Calculations can also be made to determine the worst times of the year, and even days, for the shadow flicker to occur.
Shown on the left: A Shadow Flicker Map
With a little site investigation and the smaller blade size of small wind turbine systems, shadow flicker can be completely eliminated with careful planning and spacing. Even in situations where proper planning and site evaluations did not occur, wind turbines can be stopped at specific times of the day or year to reduce the annoyances of shadow flicker.