Calculation and documentation of flickering effects in terms of hours per year during which a neighbor or an area would be exposed to flickering from nearby WTG rotors. Also maximum minutes per day are calculated. SHADOW can calculate the Worst Case results (sun always shining in daytime, WTG always rotating and wind direction “worst case”) or the “real expected values”, based on assumptions on solar statistics and operating hours divided by wind direction.

Calculation model

shadowCalculations can be made either for a set of shadow recipients (e.g. windows) or for a user defined area. The calculation engine then performs a complete simulation of the sun path throughout a whole year in user definable time steps. The size and orientation of shadow recipients as well as the raster size for an area calculation can be freely chosen. Results are presented in form of calendars, cumulated hours with flicker or – for the area calculation – as maps of flicker hour isolines. If a digital height contour map is available, the terrain levels can be taken into consideration. This includes a ZVI calculation that checks whether or not the recipients can see the individual turbines and whether the sun is behind the terrain or not.

Necessary Input Data (objects)

Please note that the objects are entered in the windPRO module BASIS.

Wind Turbines (WTGs):

One or more WTGs are entered (position and type). The WTG can normally be found in the WTG catalogue, which contains more than 900 different WTG types. The hub height, rotor diameter and blade width are used in the calculation.

Shadow recipients:

The shadow recipients are positioned where a calculation of the potential shadow impact is required. As many shadow recipients as needed can be included in the same calculation.

ZVI obstacles:

Obstacles to the visibility of the turbines or the visibility of the sun to the turbines are defined with the Line/grid object (for topography), as areas (e.g. forest) or as obstacles (e.g. buildings) .


The SHADOW module allows for the calculation and analysis of the shadow flickering impact caused by wind turbines. Which turbine is giving how much flicker at which location are the key questions answered by a SHADOW calculation. Different types of results are available: the annual number hours of shadow impact, the number of days with flicker impact and the maximum number of minutes of flicker within a day at a given area such as a window, terrace, etc… The results can also be presented as a calendar, a graphic or a map. A worst-case calculation based on the worst weather and operational conditions or a real/statistical case calculation based on entered solar statistics and operating hours per wind direction sector can be performed. The solar statistics can be obtained from a built-in database while the latter can be auto-calculated when an energy calculation is present. If the wind turbines are exceeding the allowed shadow flickering the calculated calendar can be used to plan the operation of the turbine to avoid flickering. The accumulated hours the turbine will be stopped due to flickering can be used as input in a loss & uncertainty calculation.

Calculation report

The calculation report includes the following four printout options:

Main printout: Prints the main assumptions including a map segment showing the positions of WTGs and the shadow recipients. For each shadow recipient, the potential amount of hours with shadow impact is printed.
Calendar (tabular and graphic) for recipients: Shows the exact days, the time of the day, the duration and origin of possible shadow impact. At the bottom line for each month, the deduction due to solar statistics and operating hours will appear. The graphic version shows the impact of the shadow clearly arranged for intuitive understanding.
Calendar (tabular and graphic) for the turbines: These are calendars giving the date, time and duration for the flickering caused by each turbine. This is useful for planning if and when to stop the turbines to protect against flickering.
Map: A map with isolines for potential shadow impact is plotted for areas with WTGs. This way, it is possible to reveal the extent of the possible shadow nuisance, e.g. for areas where future development is planned. The user can adjust the values of the isolines, the line colors and the line widths. Also map with raster graphic showing the values by color scheme is available.
Data to file: Export of Isolines in an Arc View GIS package format (Shape files) and to Google Earth (kmz).

View reports from the SHADOW module

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