Shadow flicker is the effect caused when an operating turbine is located between the sun and a receptor such as a dwelling. The effect occurs when the shadow of the turning blades falls over the dwelling, causing the light intensity within the rooms of the dwelling to brighten and darken. The significance of the effect is dependent on the:
- location of the relevant building relative to the path of the sun and the turbines
- distance of turbines from such buildings
- size of the window apertures and their location in the building relative to the turbines
- turbine height and rotor diameter
- presence of intervening topography, buildings or vegetation
- frequency of bright sun and cloudless skies
- time of the year
- prevailing wind direction and hence usual rotor orientation
Report to update government’s evidence base on shadow flicker
To ensure the guidance on shadow flicker contained in 'Planning for Renewable Energy: A Companion Guide to PPS22' was up-to-date, the Government commissioned consultants Parsons Brinckerhoff – following a competitive tender – to carry out a research project to update its evidence base on shadow flicker. The report was published in March 2011 and concluded there are not extensive issues with shadow flicker in the UK.
The report found the current government guidance on shadow flicker, which states impacts only occur within 130 degrees either side of north from a turbine, is acceptable. It also found it is widely accepted across Europe that potential shadow flicker is very low more than 10 rotor diameters from a turbine. We therefore have no plans to change current guidance on shadow flicker.