### Electromagnetic Interference from Wind Turbines on Onsala Space

```Electromagnetic Interference
from Wind Turbines on Onsala
Space Observatory
Eskil Bendz
Johan Malmström
ÅF-INFRASTRUKTUR AB
Outline
 Introduction
 The Saab report
 Methods to calculate interference levels
 Main results
 The ÅF report
 Assessment of Saab report
 Other important considerations
2
Introduction
34 Wind Turbines
focus is the 10 encircled
Purpose:
Estimate and compare
interference levels from
direct signals and
scattered signals
[dBW/m2/Hz]
3
18 km
Space Observatory
The Saab report
Approach:
 Calculate direct signals from UMTS radio base
stations
 Calculate scattered signals from wind turbines
 Compare the two levels of interference at Onsala
4
Direct Signals
Method:
 Contribution from nearby radio base
stations
 Free space path loss at 2 GHz
 Extra attenuation due to terrain
profile (heights and vegetation)
 Summarize all signals
 Spectral power density:
-132 dBW/m2/Hz
5
Scattered Signals
Method:
 Divide wind turbine into two parts:
1. Tower - conical cylinder
2. Blades – elliptical cross section
 Material – perfect electric conductor
6
Scattered Signals
Method:
 Spherical wave
 Scattering cross section
from each segment
7
Scattered Signals
Method:
 Calculate contribution from base stations close to
the 10 wind turbines
 10 towers - spectral power density:
-164 dBW/m2/Hz
 One blade - spectral power density (maximum):
-164 dBW/m2/Hz
8
Main results
 Both signals above recommended -250 dBW/m2/Hz @ 2 GHz
 Direct signal is 32 dB higher than scattered signals (~1500 times)
 or Scattered signals increase interference level <0.1%
9
The ÅF report
 Assessment of the Saab report found no severe errors
 Simplifications overestimated the direct signals
E.g. down-tilt reduce direct signals in the Saab report 6-8 dB
10
 New values:
 Direct signal: -142 dBW/m2/Hz
(Saab: -132 dBW/m2/Hz)
 Scattered signals: -159 dBW/m2/Hz (Saab: -164 dBW/m2/Hz)
 Direct signal still 17 dB higher than scattered signals (~50 times)
11
Other important considerations
Direct emission from radio base stations
contributes largely to the interference level
 E.g. UMTS, GSM, LTE
 Direction of antennas
 Usually three antennas at a site, covering 120
each
 Suggestions to decrease interference level:
1. Turn off sectors
2. Rearrange antenna directions to obtain a ”zero”
3. Rearrange antenna away from telescopes
4. Increase down-tilt (10 might be obtained)
 In accordance with mobile telephone service
providers
12
Other important considerations
Some other sources that might contribute to the
interference level are:
 Neighboring radar stations (high power sources)