By helping our clients understand and manage shadow flicker impacts, we can help wind energy developers minimise the impact of their projects on local communities, while maximising renewable energy generation, supporting the transition to net zero.
We have compiled some of the most commonly asked questions in relation to shadow flicker effects. If you have a question that isn’t answered below, please don’t hesitate to get in contact.
What is Shadow Flicker?
Shadow flicker is the effect caused by shadows from wind turbine blades passing over a window. This effect causes the intensity of light within a room to vary, resulting in a flickering effect.
How is Shadow Flicker Assessed?
A Shadow Flicker assessment is typically required as part of the planning process for a new wind energy development (or changes to existing developments). An initial investigation would be undertaken to determine if impacts from shadow flicker are likely, typically based on the following criteria:
- In the UK, only properties within 130 degrees either side of north of the turbines can be affected. This angle is based upon the latitude at which the UK is situated, and therefore differs for other locations across the globe; and
- The potential for significant Shadow Flicker impacts is typically limited to a distance of ten rotor diameters from the wind turbine in question. For example, if the length of the turbine blades is 75 m, a study area of 750 m would be applied.
If properties are identified at locations which meet both the above criteria, then a more detailed consideration of Shadow Flicker impacts it likely to be required.
The key parameter in the assessment of shadow flicker is the duration of shadow flicker effects. In the UK, the assessment criteria detailed in The Best Practice Guidance to Northern Ireland Planning Policy Statement (PPS) 18: Renewable Energy is used, which indicates that shadow flicker effects should be limited to no more than 30 hours per year, and 30 minutes per day. These criteria are the same as those detailed in a number of international guidance and planning policies, including the World Bank Group Environmental, Health, And Safety Guidelines for Wind Energy and the Australian Department of State Development, Infrastructure, Local Government and Planning.
How is the Potential for Shadow Flicker Effects Calculated?
The calculation of shadow flicker effects is generally undertaken using specialist software which determines the position of the shadows based upon:
- The number, location and dimensions of the wind turbine(s);
- The position of receptors (typically residential dwellings), relative to each wind turbine;
- The position and size of windows on each assessed receptor;
- Local terrain; and
- The position (azimuth and elevation) of the sun in the sky at any given time of day, across the entire year.
How can Shadow Flicker Impacts be Mitigated?
Potential mitigation measures typical include one or more of the following:
- Optimising the wind turbine / wind farm layout:
- Provision of physical screening;
- Calculation and development of a ‘shut-down calendar’, which can be applied to a turbine’s control system to temporarily stop a particular turbine during periods where significant shadow flicker effects are predicted.
- This can be combined with the installation of sensors to determine when shadow flicker effects are occurring in practice.
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For further information, please get in touch with us at info@metricaconsulting.co.uk.
