There has been a lot of research into the impact of wind farms on television reception, much of it originating from Australia. We have brought together some of the more useful documents for your information.
This is a select bibliography of articles on wind farm electromagnetic compatibility that we have found useful. Where the paper is believed to be available for general distribution we have made it available here for free download. For other papers we have provided an abstract and a link to the source.
D F Bacon
Wind Engineering, Vol. 16, No 6 1992. 8.
A proposed method for establishing an exclusion zone around a terrestrial fixed radio link outside of which a wind turbine will cause negligible degradation of the radio link performance.
Obstruction or reflection of radio waves by a wind turbine can degrade the performance of a fixed radio link due to the effect of large blades rotating at approximately 32 rpm. Typically there are 2 or 3 blades. Thus any significant interfering signal, such as a delayed multipath component, will fluctuate in signal level around 1.0 to 1.5 Hz. This is particularly problematic to a digital link where the performance is assessed on a second-by-second basis.
Thus a special criterion for the proximity of wind turbines to radio links is considered necessary. This document proposed a practical method for establishing an exclusion zone around the path of a fixed radio link within which it would be inadvisable to install a wind turbine.
Carlos Salema, Carlos Fernandes, Luca Fauro
Wind turbines may be a source of disturbance in the radiation fields of TV broadcast transmitters. The situation is particularly serious when the direct path from the transmitter to the receiver antenna is obstructed while both transmitter and receiver antennas have a unblocked path to the wind turbine. Starting from an analysis of the diffracted field by the pylon we proceed to implement a simple rule derived from ITU Recommendation 805 to define a minimum clearance distance from an isolated wind tur- bine and a TV transmitter antenna. Measurements using a scaled model confirm the existence of the floor level in the scatter model used in ITU Recommendation BT.805.
The paper deals exclusively with impairment of analogue signals. ITU-Rec BT.805 is discussed in Report ITU-R BT.2142-1 (10/2010), where a draft replacement recommendation is described.
NB The publishing source of this paper has not been identified.
A. Calo, M. Calvo, L. de Haro y Ariet, Pedro Blanco-Gonzalez
International Renewable Energy Congress November 5-7, 2010 - Sousse, Tunisia
One of the environmental effects of wind farms is the electromagnetic interference due to the scattering produced by the wind turbines on the electromagnetic waves of different radio communication services propagating through them. A previous work is updated here and the scattering models for the nacelle and the wind turbine are shown and validated. Radio wave propagation losses are estimated more precisely through a parabolic equation approach. Finally, a comparison between theoretical and measured values for the Power Delay Profile (PDP) of the multipath channel through a wind farm is showed.
Emmanuel Van Lil, Dave Trappeniers, Antoine Van de Capelle
Previous studies have been focusing on the influence of moving objects like wind turbines on aeronautical and maritime radars, working usually respectively in the L/S band and in the X-band. Here, those results will be summarized for a special kind of radars, usually working in the C band, namely meteorological radars. We have used both UTD methods as well as simplified methods to quantize the effects. Indeed, not many moment method solvers have the possibility to deal with moving objects (creating Doppler shifts), but with UTD it is within easy reach of the modern computers. However, for some particular applications, the procedures can be simplified to quantize efficiently the near-fields around moving objects. After a description of the general phenomena, two simplified methods will be compared. The first consists in a Physical Optics based method, and the second does make use of the flat wedge approximation.
Sustainable Energy Australia Pty Ltd
This document is briefing paper discussing the electromagnetic compatibility (EMC) and electromagnetic fields (EMF) implications of wind farming in Australia. This paper was prepared as background information for the preparation of a fact sheet for dissemination to the general public.
Prepared May 2004.
Gavin J Poupart
UK DTI Report Number: W/14/00614/00/REP
This study has focused on the development and validation of a computer model that can be used to predict the radar reflection characteristics (Radar Cross Section, which is measured in square metres and is normally presented on a logarithmic scale) of wind turbines and understand the complex interaction between radar energy and turbines. The scope of the model includes:
- The affects of the radar propagation over the terrain between the radar and the wind farm;
- The dynamic radar scattering from the wind turbines;
- The signal processing in the radar;
- Display of results via a simulated radar display.
The model was validated through a full–scale trial, using a QinetiQ mobile radar system to collect data for a single operational wind turbine at Swaffham in Norfolk. The model was then used to perform a detailed sensitivity analysis and to compile a list of the key factors influencing the radar signature of wind turbines.
The following are some of the results generated by the project:
- The design of the tower and nacelle should have the smallest Radar Cross Section (RCS) as possible. The RCS of these components can be effectively reduced though careful shaping and choice of construction materials;
- Large turbines do not necessarily lead to large RCS (i.e. tower height does not greatly affect RCS);
- Blade RCS returns can only be effectively controlled though the use of absorbing materials;
- Spacing of wind turbines within a wind farm needs to be considered in the context of the radar cross range/down range resolutions.
- Spacing the turbines such that only one turbine can appear in any range cell has advantages in identifying the wind farm, filtering out the turbines and in tracking aircraft over the farm area;
- Single wind turbines do not create a significant ‘radar shadow’. Any shadow region is only dark to a distance of a few hundred metres behind the turbine. Beyond this there is some reduction of the radar power, and a time-variation, but these will not prevent detection except possibly for very small targets.