[TowerTalk] Large solar farm and RFI

[Lux, Jim]

On 4/22/23 12:12 PM, GEO Badger via TowerTalk wrote:
>   Suggest you contact the company and ask them. They are not allowed to radiate RF.

I'm sure they're allowed to radiate RF, just like any other electronic 
device.  The real question is "at what level can they radiate".  They'd 
be an unintended radiator - just like a motor controller, welding shop, 
etc.  Typically radiated emissions limits are imposed at the "box" 
level, not at a system or "boundary of the property" level, and for 
commercial equipment those limits are pretty liberal, and worse for this 
they end at the terminals of the device.  If you use a variable speed 
motor drive (which uses PWM internally), and you hook up 1000 ft wires 
to the motor, those wires make a fine and dandy antenna, as do the power 
supply wires.  You might look at CISPR11/55011 and IEC 61800-3.

The boxes would be Group 1 (basically anything other than an intentional 
radiator) class A (not residential)


https://www.electronic.se/en/2019/06/01/emc-challenges-and-solar-panel-systems/

gives some field measurements of 50-60 dBuV/m in 1 kHz BW, at some 
distance (probably 3 meters) in the HF band.

You'd need to convert that to "received signal power in a typical 
antenna".   Let's say 10 MHz, lambda = 30 meters, so effective aperture 
of a dipole is 1.5 * lambda^2/(4 pi) so: about 110 square meters.

0 dBuV/m is 1 uV/meter so 60 dBuV/m is 1 mV/meter.  Converting to power 
density-> S = E^2/377 -> 1E-6/377 -> 2.65E-9 watts/square meter

* 110 is 0.29 microwatts   = -35 dBm.  which is pretty healthy.

But hopefully it falls off at 1/r^2 and it's not being radiated by a 
power line.   Get 300 m away and you'd be down to -75 dBm. that's around S9.



https://www.nrel.gov/docs/fy17osti/67440.pdf  has some background info.

Things like Broadband over Power Line had specific radiated power limits 
vs frequency, measured at a particular distance, etc.


> Igancy NO9E sez:
>
> I have a ham radio property in a rural area. Fairly quiet. My
> neighbour informed me that a 1000 acre solar farm by Green Bolt is coming
> within a quarter mile. I am contemplating another tower but I am not sure
> now whether the site will still be ham friendly. Does anybody have any
> experience regarding RFI from large solar farms?
>
> ---
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> WA2LSI, KE6RJW, W6B, W7B, AAR9AG
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