Wind turbines and radars, the wind of discord will not blow
The objectives of the legislation covering the energy transition imply the development of renewable energy, including wind. Now, wind turbines, which are large moving structures overlooking the horizon, can interfere with radars. The ANFR is well aware of this issue and has attempted to make them coexist for 20 years.
Military radars, weather monitoring equipment or air navigation systems must be able to detect everything that arrives on the horizon, whether aircraft or thunder storms: our safety depends on it. But, for several years now, wind turbines have been wreaking havoc on the control screens! Indeed, when their metal turbines start moving, they reflect or diffract the radio pulses sent by the radars. Compared to a metal hangar which also creates an echo, their effects are much more disruptive:
- wind turbines are always installed in clear areas, on high pylons and their blades represent an increasingly high surface area with the increased power of the generators; today it is not possible to build strong blades without at least part of them being metal;
- wind turbine blades rotate at variable speeds producing variable echoes. In addition to this modulated amplitude, the blade speed also creates a signal phase modulation via the Doppler effect.
In 1998 the National frequency agency was consulted for the first time for a request concerning the installation of wind turbines in Brittany. The ANFR then set up an information procedure so that all spectrum users could identify the risks before the projects were completed.
The first report on the interference caused by wind turbines was drawn up by the ANFR in 2002. The purpose was to assess their effect on television reception.
In 2004, Méteo France, Civil aviation and the Ministry of Defence consulted the ANFR for the first time about the issues of interaction between radars and wind turbines. In response, within its Electromagnetic Compatibility Commission, the ANFR created a specific group on this subject. Three successive technical reports examined the subject in more depth:
- Report CCE5 n° 1 (September 2005) studied the interference on weather radars; in particular it showed the sensitivity of Doppler weather radars to the presence of wind turbines;
- Report CCE5 n° 2 (April 2006) covered the question of static Civil aviation and Defence radars (static air monitoring radars).
- Finally, report CCE5 n° 3 (February 2008) looked at static sea, river and port radars.
The recommendations contained in these reports made it possible to draw up regulations to govern this cohabitation:
- 3 March 2008: circular signed between the Ministry for Ecology and sustainable development and the Ministry of Defence, recommending protection zones (5 km) and coordination zones (from 5 to 30 km) to limit the effect of wind turbines on radars;
- 26 August 2011: an order defining the distances for weather radars in the C and S bands, primary civil aviation radars and port radars. Other systems such as X band weather radars or secondary civil aviation radars or VORs were then added to the order. For military radars, the wind farm operator must have permission from the defence air zone in question. [link]
- 6 November 2014: an order allowing that the models forecasting the interference caused by wind turbines can be validated by the minister in charge of installations classified for the protection of the environment. [link]
In parallel, the ANFR contributed to studies conducted by different countries and European institutions as part of the European Post and Telecommunications Conference (CEPT). Despite the diverse methodologies used in the different countries, it was possible to identify the institutions with extensive experience in this field. Therefore, the ANFR put the ministry for Ecology in contact with Bilbao Basque University (Spain), which has a simulator covering a wide spectrum of radio services in order to identify a new methodology for weather radars.
This same methodology developed in an ECC 260 report on the landline service is currently being analysed by Bouygues Télécom to assess the impact of wind turbines on microwave radio links. The ANFR has also launched a study subject for the current school year with ENSTA Bretagne 2nd year students with the objective of assessing certain wind turbine simulation models.
The evolution of technology is a permanent challenge, by making bigger and more powerful wind turbines but also more sensitive radars over longer distances possible. The same applies to changes in uses, which imposes using renewable energy on the one hand, but also detecting more stealthy aircraft, or even drones, or warning populations of unexpected weather phenomena sufficiently early. The delicate balance between radars and wind turbines is therefore permanently put into question, and the work of the ANFR and assignees makes it possible to avoid discord between these two sectors of activity which are both essential to our country!