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Wind Turbine Shadow Flicker Assessments

Why assess for Wind Turbine Shadow Flicker?

Wind turbine shadow flicker is a phenomenon that occurs when the rotating blades of a wind turbine cast shadows on the ground or nearby structures. This can cause a flickering effect, which can be annoying or even disturbing to people who live or work nearby.

The shadow flicker effect is most noticeable when the sun is low on the horizon and the blades are rotating at certain angles. It typically occurs for a few hours each day, but the exact timing and duration will depend on the location of the wind turbine and the time of year. In addition to being a nuisance, shadow flicker can also have health effects on some people, particularly those with certain neurological conditions such as epilepsy.

In the development phase of windfarm facilities, analysis can be carried out to determine of the location and characteristics of a wind turbine, in conjunction with the changing location of the sun, could cause the casting of shadows on nearby occupied buildings. Where an occurence is unavoidable, to mitigate the effects of shadow flicker, wind turbine operators may limit the turbines' operation during times of the day when shadow flicker is most likely to occur, or they may install screening devices or other mitigation measures. 

Shadow Flicker Analysis

Wind turbine shadow flicker analysis is typically performed using computer modeling software. The process involves collecting data about the location and design of the wind turbine, as well as the surrounding terrain and structures. This data is used to create a 3D model of the area using specialized software.

The 3D model is then used to simulate the movement of the sun and the wind turbine's blades throughout the day and over the course of the year. The software calculates the location and duration of shadow flicker for each location that may be impacted by the turbine.

The output of the analysis is typically presented as a map or chart that shows the areas that are most likely to experience shadow flicker and the times of day when it is likely to occur. This information can then be used by wind turbine operators to make decisions about turbine operation and to develop plans for mitigating the effects of shadow flicker on nearby communities.

It's worth noting that in some countries, regulations require wind turbine developers to perform shadow flicker analysis as part of the environmental impact assessment process prior to construction. This ensures that any potential negative impacts on nearby communities are identified and addressed before the turbines are installed.

Regulatory Frameworks

In Ireland, wind turbine shadow flicker is regulated by the Planning and Development Act 2000, as amended. The act requires that wind turbine developers carry out a shadow flicker assessment as part of the planning process, and that they take measures to ensure that shadow flicker does not have a significant impact on nearby homes, schools, or other sensitive locations. Guidelines were developed in 2006, revised in 2013 and draft revisions published in 2019, which can be found here

In addition to the planning regulations, there are noise and nuisance regulations that may apply to wind turbine shadow flicker in Ireland. For example, the Environmental Protection Agency Act 1992, as amended, sets out noise limits for wind turbines, and the Environmental Protection Agency may take enforcement action against wind turbine operators who do not comply with these limits.

Overall, the regulatory framework in Ireland is designed to ensure that wind turbine shadow flicker is carefully assessed and managed, in order to minimize its impact on nearby communities and the environment.

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