Electromagnetic Interference from Wind Turbines - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 581

2008]. Radar interference assessments, the development of permitting processes, and tech-
niques and technology for mitigation of any radar interference by wind turbines are all on-
going activities involving the FAA, DOD, manufacturers of radar systems, and developers
of wind power stations.
A large-scale wind turbine tower has a radar cross section (RCS) equivalent to that of a
building, a hill, or the tower of a high-voltage transmission line. The major components of a
wind turbine contribute to its RCS approximately as follows [Seifert and Meyers 2008]:

- tower: 75 percent

- blades: 20 percent

- nacelle: 4 percent

- nose cone: 1 percent

There are two main types of potential interference with radar by wind turbines: Direct inter-
ference and Doppler interference . Direct interference can cause

- high reflectivity

- reduced sensitivity

- false images

- shadow areas

Doppler interference, caused by the rotating blades, alters signal frequencies and pro-
duces false targets. Doppler interference can impact both airborne and fixed radar. In gen-
eral, the effects of Doppler interference with radar signals can be studied using the techniques
described earlier for analyzing TV interference.
Seifert [2005] provides the following examples of potential impact and non-impact loca-
tions involving radar installations and wind turbines:

Potential Impact Locations

- airport approach and exit zones

- training routes used for testing radar systems

- routes used for training air crews

- low-altitude radar beam areas

- helicopter zones

- attack corridors

- specialized radar and telemetry areas

- test and evaluation ranges

- specialized military mission impact areas

Non-Impact Locations

- normal high altitude routes

- regions more than 15 miles from airports or transmitters

- wind power stations in areas served by radar systems with specialized filters

( e.g. Palm Springs, California, and Boston, Massachusetts) more than 95 per-
cent of wind power stations in the U.S.