Tall structures such as wind turbines cast shadows, which vary in length according to the sun’s altitude and position. Rotating wind turbine blades cast moving shadows which could under certain conditions cause flickering at nearby properties. This effect is similar to the flicker you may have experienced when driving, if the low winter sun is shining through trees and then your car window.
In order for a person in a property to experience flickering from a wind turbine the property would need to have a narrow window facing a wind turbine. The sun would need to be relatively low in the sky and be behind the tower. The turbine nacelle would need to be facing a certain direction so that the turbine blades were turning and casting the shadow in the direction of the property. Any flicker effect would only last while the sun is behind the tower and while the nacelle was facing in that one direction.
Shadow Flicker effects on properties are very rare as normally wind turbines are located too far from properties. However if nuisance occurs, a sensor can be installed which shuts down the wind turbine on the rare occasion the above sun and wind direction conditions occur.
As far as I am aware this has only been an issue at one wind turbine location in the UK. A wind turbine located 200m from a property was causing flicker and the above sensor mitigation is now utilised.
Photo – Paul Limahuli- Flickr