Shadow flickering occurs when rotating wind turbine blades cast moving shadows on nearby buildings. To comply with its strict regulations, energy supplier ENGIE needs to assess and mitigate the effects. They teamed up with GIM to prepare the necessary input data and simplify the analysis.

Wind in the sails
In 2023, Belgium witnessed a remarkable 43% increase in onshore wind generation, equaling 6,268 gigawatt hours (GWh). With more wind turbines planned, Belgium is making significant strides toward a greener future.
However, building new windmills is only part of the journey. It’s also important to make sure that the existing turbines are fully compliant with the strict Belgian regulations. Some of those regulations pertain to shadow flickering.
What is shadow flickering?
Shadow flickering occurs when rotating turbine blades cast moving shadows on nearby buildings. If these shadows fall on homes or workplaces, they can create a bothersome flickering light-and-shadow effect. The extent depends on various factors, such as the turbine’s location, the season, and the sun’s position. Since people living or working near wind turbines often experience shadow flickering, strict environmental regulations have been introduced to minimize its impact.
“In Flanders, legislation limits shadow flickering on adjacent houses to a maximum of 8 hours per year and 30 minutes per day. For industrial buildings in industrial areas this is maximum 30 hours per year and 30 minutes per day. In Wallonia, the maximum is 30 hours per year and 30 minutes per day for all buildings” explains Lena Brondeel, Project Manager at GIM. “If these limits are exceeded, wind turbines must temporarily stop operating. So, managing shadow flickering is important for many reasons. It reduces discomfort for nearby residents and professionals, ensures compliance with the law, and avoids unnecessary shutdowns.”
Making data collection and preparation easier
Calculating and managing shadow flickering involves a multifaceted approach, including feasibility studies before construction and careful monitoring during the operational phase. One primary challenge is identifying which building façades need to be analyzed. For example, ENGIE needs to exclude non-relevant buildings and consider existing areas of shade, etc.
This calls for a variety of data: addresses, coordinates, terrain topology, façade properties that affect the shadow projection, the buildings’ shape and usage… “Gathering and analyzing these data is no small task,” confirms Lena. “The results have to be aligned with various parameters, such as seasonal variation and sun positioning, to properly predict the shadow flickering effect.”
ENGIE partnered up with GIM to streamline the collection and preparation of those input data. GIM’s Belmap solution has provided great value in that process, for it offers a comprehensive 3D digital model of the built environment and location-specific information for buildings and addresses. Combined with the use of the FME data integration platform, it gives ENGIE all the necessary data to determine the thresholds and upload this input to the shadow management system of the wind turbine.
Image: mapped representation of a wind turbine shadow flicker and its impact on the buildings.
Collaboration for a more sustainable sector
The collaboration between ENGIE and GIM doesn’t just simplify the analysis of shadow flickering effects. It ultimately helps ENGIE to ensure compliance with environmental regulations, decrease discomfort for the surrounding community, and contribute to a more sustainable and efficient wind energy landscape in Belgium.
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