Wind Power and Radio Astronomy

A. Jessner, MPIfR Effelsberg

April 2010

1. Introduction

2. Possible Impact Mechanisms

3. Compatibility Estimates

4. A Case Study

• Because of the grave environmental and energy problems facing humanity on a global scale, all efforts to utilize sustainable energy sources ought to be supported.

• Wind power for electricity generation is one of the few sustainable ways of power generation with minimal CO2 emissions.

• Farms of wind turbines are planned to be installed next to radio astronomy facilities. Planning procedures have started in Sweden, Belgium, Italy (Sardinia) and Germany

• Compatibility of wind parks has been studied w.r.t. TV reception, fixed links and radar

• But not yet for radio astronomy

IMPACT MECHANISMS

The interference to radio astronomy can be produced by:

1.Primary emissions: generator and associated circuitry used by variable speed wind turbines or HVDC systems generate harmonics These can be radiated and also received by RA station as interference.

Electrical power 3 MW (65 dBW) RA sensitivity 10-20 W (-200 dBW) 2. Secondary emissions: multipath propagation effects (reflections, diffractions, etc) produced by tower and rotating blades of the wind turbine. They act as a passive repeaters for other transmitters.

Reflective areas of ca. 5000m2

3.Thermal Emission: At distance of 3km a 100m disk subtends an angle of 1.9° HPBW of a 100m dish at 600 MHz = 0.34° => ‘Artificial Moon’

Generic Case: Impact assessment procedure

1. Calculate the effective path loss Lb(p,f) from the telescope to the site for each frequency band using the methods (8a) of ITU-R P.452-12.

For cases where there is no direct line of sight because of elevated terrain between the observatory and the proposed structure, a path profile analysis according to Appendix 2 to Annex 1 of ITU-R P.452-12 has to be undertaken to include the sub-path diffraction losses.

2. If the antenna cannot point at the structure, then calculate the maximum side-lobe gain Gmax(f) = 32 - 25log(fmin) If the antenna can point at the structure, then use the full main beam gain of the antenna.

3. ITU-R RA. 769 gives a table of emission limits of continuum input power PH (table 1, column 7) for each radio astronomical frequency. Any emission from the site of the planned structure must be kept below the site limit of

Psite= PH+ Lb(0.05,f) - Gmax(f)

4. Repeat for all relevant frequencies to estimate site emission limits

The operator has to prove beyond all reasonable doubt that his equipment will not exceed these emission limits through the sum of all emissions from

a.direct emission Pd(f) from the plant and its control and power electronics including transmissions from power lines. It is the burden of the operator to prove that the equipment will stay within the operating constraints, by providing proper emission measurements of his equipment in the required bands.

b.radiation Pscat(f) from other sources scattered by the turbine and support structures.

Assessment of scattered radiation :

Measurements of the power flux densities Ssite(f,h) (= pfd given in dB(W/m2) on all bands and at heights h up to the top of the structure should to be made so that a statistically meaningful survey of the ambient maximum signal levels Sambient(f) and the band occupancy at the proposed planning location is available.

 For a proper assessment, these measurements should be performed at different heights h and then an integration over the effective surface contributions with varying heights should be made, yielding the effective scattered power of

Pscat(f)= Sambient(f)+10·log((f))+10·log(Ar/m2)

Compatibility

means, that for all frequencies f, the sum of direct and scattered emissions stays below the interference limit on all considered frequencies in at least 98% of the time

a. Pd(f) + Pscat(f) < Psite(f) (in band limit)b. Pd(f) + Pscat(f) < Psite(f)+ Gout (out of band limit)c. Pd(f) + Pscat(f) < PIM+ Lb(0.05,f) - Gmax(f) (out of band IM limit)

If there is to be more than one Wind turbine, the cumulated effect of all structures will have to be considered.

The administration should list the wind turbine site as a coordination location, where the limits derived above may not be exceeded when new transmitters are brought on-line elsewhere (i.e. The new 2.6 GHz mobile internet band).

Permitted Emissions from Equipment complying with CISPR-22 (in Germany: EN 55022)

For industrial plant the radio disturbance characteristics and emission limits are given by CISPR-22 for a measurement distance of 3 m (10m for frequencies below 230 MHz):

40 dBV/m for f < 230 MHz47 dBV/m for 230 MHz < f < 1 GHz56 dBV/m for 1 GHz < f < 3 GHz•dBV/m for f > 3 GHz

In the US, the standards according to FCC Rules and Regulations, Title 47, Part 15 B apply.

10 100 1 103 1 104 1 105250

200

150

100

50

0Permissible Radio Emission

MHz

Pow

er d

B(W

)

Diamonds indicate the permitted signal level receivable on the telescope site DPH(f) according to ITU-R RA 769-2 and the blue line shows the emission EEN(f) permitted by the CISPR-22 standard. The difference is the minimum path loss L(f) required to shield the telescope from the permitted equipment emissions.

10 100 1 103 1 104 1 105110

120

130

140

150Required Path Loss for Protection

MHz

dBPathloss required for Compatibility of Industrial Plant with Radio Astronomy

100 1 103 1 1040

200

400Separation Distances

frequency (MHz)

min

. sep

arat

ion

(km

)The graph below shows the required separation distance for various frequencies (red) and the line of sight horizon for a 50 m telescope and a 150 high structure with electrical equipment that is in compliance with CISPR-22.

Horizon for free space propagation in flat terrain

Case Study:  Proposed Placement of Windpower Generators close to the Radio Observatory in Effelsberg (Germany). Twenty-one sites have been marked for development as locations of 150m high windturbines in a district about 24 km south-east of Effelsberg.

Map of the district where wind parks are planned (TOP50) Proposed sites are not marked, as they would be easily lost in the detail.

The lake shown is 2.0 km long and 1.2 km wide.

The path loss between the telescope at a height of 50m and the centre of a wind turbine at the same height has been calculated for four different frequency bands (0.61 GHz, 1.41 GHz, 5 GHz, 10 GHz).

Four digital maps, one for each frequency, showing the expected path loss in a 60km by 60 km area centred on Effelsberg were provided by ANFR.

longtude (deg)

latit

ud

e (d

eg)

path loss

+ Gebiete 27.62 18.67

* WKA Kempenich

* WKA Weibern

+ 19.10

+ 12.53

+ 21.57+ Gebiete 0.16 1.29

+ 8.57+ 5.42

+ 6.51

+ 6.29 + 0.68

+ 10.44+ 0.28

+ 3.55

+ 1.41

+ 85.74 Sued

+ 17.78+ 1.16

+ 5.73

7.05 7.1 7.15 7.2 7.25 7.3

-50.5

-50.48

-50.46

-50.44

-50.42

-50.4

-50.38110

120

130

140

150

160

170

180

190

200

Characteristics of Proposed Sites for Wind Turbines 24 km SW of Effelsberg

Minimum Path Loss in dB for Compatibility between CISPR-22 and ITU-R 769-2

610 MHz 1400 MHz 5000 MHz 10 GHz

134 135 141 136

=> Site specific ambient radiation levels are still unknown, the planning procedure continues

Summary:

1. The use of wind power is necessary to minimize CO2 emissions and to provide energy sources that are indepented of fossil fuels.

2.The compatibility of wind power plant and radio astronomy stations has not been studied before, but there is the potential of very strong interference over a great distance.

3.Primary and secondary emissions from wind power generators vary from site to site and depend on construction details. Their levels need to be established prior to any compatibility assesment.

4.Propagation of radio waves between wind power site and radio telescope is strongly frequency and location dependend.

5.Direct line of sight placement of wind parks near radio telescopes should be avoided .

6.Good modelling procedures are available to establish protection criteria

7.Compatibility and co-existence of wind power and RAS can be achieved in the small areas around a telescope that do require coodination.