Shadow Flicker

Contact:

M.Eng. C. Hoffmann
M.SC R. Gradewald

When planning and operating a wind turbine (WT), the shadows that are casted on neigboring estates, fields and windows of buildings (point of immission) during sunshine have to be taken into consideration besides the noise emission, too.  The decisive feature is the fast change between light and shadow caused by the moving rotor blades.

For the calculation of the all-year shadow course of the wind turbine WIND-consult developed the application program SHADOW which is used within the scope of the planning services. The procedure is based on:

• the generally known spheric-trigonometrical relations to the sun’s position
• the laws of plane trigonometry for the calculation of the duration of shadowing caused by the WT rotor on the point respectively at the site of immission
• a formulation by BEHR [Licht und Schatten; WIND-KRAFT JOURNAL 3/92] for the determination of the probable duration of shadowing
• long-term regional climate data on the duration of sunshine and wind direction distribution

Regarding the point of immission a standard area with a size of 1 m x 1 m respectively a point of immission forms the basis. The procedure also allows shadow calculations for partial areas of any size. Furthermore the climate statistical probable (real) duration of shadowing to be expected is determined besides the astronomical one.

Input quantities for the calculation are the geographical location of the WT site, the coordinates of the WT and of the point of immission (height: 2 m a.g.l.) respectively the corners of the respective partial area to be evaluated as well as the WT parameters (hub height, rotor diameter).

The results of the calculations that are shown as graphics and tables are:

• Representation of the annual shadow field shown graphically (see illustration)
• Tabulated representation of the astronomic possible (annual and daily) shadowing, the probable annual shadowing as well as the season and the mean daytime of shadowing
• Single overview of the sites of immission during the astronomic possible period of time of the shadowing
• Tabulated summary of the possibly required disable times

Based on the calculation program for the shadow course of WT a service, which makes the evaluation and optimization of WT sites possible, is offered to e.g. operators, planning offices and approving authorities.