Overcoming the shadow flicker



Contrary to this lovely and peaceful scenery, spinning wind turbines in a late sunny afternoon can sometimes be visually uncomfortable. This disturbing optical effect called ‘shadow flicker’ is caused by the rotation of wind turbines blades casting shadow over the ground and surrounding buildings. This phenomenon typically occurs when the sun’s angle is very low and is often described by residents as a nuisance when lasting too long.

In order to preserve the well-being of inhabitants, different regional and national regulations have been put in place to assess and limit shadow flicker in residential and industrial zones. As a result, several authorities require to shut down wind turbines during the time period where shadow flicker effects are likely to occur.

In Flanders, for example, the legislation states that the maximum shadow flicker must be limited to 30 minutes per day and 8 hours per year for residential buildings, and to 30 minutes per day and 30 hours per year for industrial buildings. The Flanders region therefore requires that manufacturers equip their wind turbines with a shadow flicker control system if shadow receptors (i.e. dwellings, schools, offices, etc.) are expected to experience more than 4 hours per year of shadow flicker.

In practice, the parametrization of such a control system is prone to mistakes, which can either lead to shadow flicker exceeding the duration limit set by the regulation, or to unexpected wind turbine shutdown, meaning revenue losses for the owner. To overcome these issues, 3E developed a methodology for calculating the coordinates of the shadow receptors and for forecasting the exact shadow flicker duration at those locations. With this unique tool and methodology, 3E can review the shadow curtailment plan, suggesting shutting down specific wind turbines during longer or shorter period.

Such shadow curtailment compliance checks are key (1) to maximize wind energy production, (2) to meet the requirements set by the environmental permit, and (3) to ease public acceptance and maintain a good relationship with local residents.

If you are a wind developer willing to optimize your income or a bank representative looking for a technical due diligence service including shadow flicker study, you are at the right place! Send us your request through the contact form below and one of our wind experts will get back to you in a ‘flick’!