Radio interference ? with Solar Panels.

[clockmanFR]

Father in-law asked me if Solar Panels give of any DC magnetic interference, because he might object to them being installed next door, because he might not be able to receive his German LW Radio programs. He used to work as an German/English interperter.

I have not heard of this before, but then a Faraday Cage, DC plate shielding? my brain cells are struggling a bit with this! 

Can anyone shed any light on this shielding/interference ? 

[supremetwo]

Unlikely the dc from the panels, but possibly be an aerial effect from inverter RFI?

http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=41362
The problem is that the testing required for CE marking requires radiated emissions measurements to be made above 30MHz and below that conducted even though inverters emit large amounts of radiated energy below 30MHz.

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Where a member of the society has experience RFI issues with these types of inverters. Ofcom has investigated this problem and found that it was a PV array on a new housing estate, but they claim they are powerless to act.

The member has got hold of a copy of the instruction manual for one of the inverters and it does say in the manual "Warning, cannot use with HF SSB marine communications". But there is no reason stated for this warning.

There is also a member that has had a large array fitted to his roof right under his Antennas and has not had any problems with RFI at all.

If, and I do say if these types of inverters do cause broadband RFI issues, I would say it's more to do with noise radiation from the DC cable between the solar cell and the inverter. Good engineering practice such as installing a cable with 360 degree screening should stop any broadband RFI.

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The problem with inverters and things like switch mode power supplies are that they create broadband noise which can be generated over a very large frequency range.

As the cables running from the inverter to the PV array can be long, they can act as an antenna and radiate the broadband noise over a distance.

On some of these Inverters they have very good RFI filters on the outgoing AC side but very poor filtering or none at all on the incoming DC side.

AFAIK no installers use screened panel-connection cable.

[BruceB]

I concur with what is written above.  I had one customer who was paranoid about it as he is a radio ham.  There were a couple of articles I found in the GB radio hams magazine, but not much authoritative. I put the dc downleads in 4 core SWA to a Power One inverter beside his consumer unit, earthing the armour at the inverter end.  He has found no noticeable impact.  I think he works mainly at HF and VHF.  The aerials are remote in a field beside his house.

Regards
Bruce

[Pat_]

If I hold a radio tuned to Droitwich within a few feet of my Fronius inverter, the station gets interferred with and eventually drowned out by a . This is an observation I made a few weeks ago and I wasn't too concerned so didn't take closer observations. However I use that portable radio tuned to Radio 4 Droitwich while working in the shed, with the radio 3m from the inverter and don't get a problem.

Of course the german transmissions will be weaker than Droitwich, so more likely to be interfered with. As I understand it, Ofcom would only have to consider interference to domestic broadcasts.

[guydewdney]

being a non radio type - would such interference screw up wifi? Isnt CE compliance with this sort of thing (something I was involved vaguely with 15 years ago) supposed to make this interference impossible?

[eabadger]

Electrical; items shall not be susceptible to or cause interference to other items. I believe was the wording of some rule, I believe it went as far as stating even if item is faulty, which was a bit of a tall order.
I remember this because about 11 years ago I was working at an airport, all our external computers stopped communicating after dark, turned out faulty ballast in street lighting was issue, but which one? As far as I know they are still switching to generators after dark.

Normally interference is caused by the switching, so ac all the time (alternating, B,zzzzzzzz) or a single click on dc on/off may be heard, inverters switch at high frequency, or low, interference if any will be on these frequencies I expect, I guess low frequency inverters  would be better, but only a guess.

steve

[Pat_]

Rather disappointed that I'm not allowed to say 'whistle' without it being replaced by a silly 'smily'.

Anyway, I was going to add that it is mostly amplitude modulated radio signals which are likely to suffer. So FM and digital radio would typically not be affected unless the interferring signal becomes really large. Also wifi is working up at frequencies way above long wave so pretty immune to switching noise.

[eabadger]

Not sure I agree with comments about wif /fmi, I installed a "thing" which needed data connecting to it, could not get data cables under road so went for a wifi link, 20mtrs clear line of sight, used industrial wifi devices, blackbox if I recall, also with proper aerials.
Wouldn’t work, ended up sending data over the mains, briliant, when checking later we were told the west mids police am transmitter was across the road about 600mtrs away, no way of proving but pretty good idea.

Mended a remote operated gate at a very famous digger makers, remote wouldn’t work at certain times of day, loads of engineers visited but still fault persisted, I was tasked with fixing, I scoped the mains and found loads of ac noise on the neutral, temporarily earthed the neutral at that point and fixed problem, turned out the neutral connection was noisy and had been for sometime.
But remote was digital and fm, so should have been ok, not so.

Back to original question Clockman, why not buy an internet radio and get perfect radio reception???
I think the only chance of interference would be the inverters, but reading my Morningstar manual, it mentions clicking on radios an tv’s, I assume the fets switching.

steve

[Pat_]

Steve, no disagreement really. A digital service is immune to interference untill the strength of the interference gets big enough. Then it just stops working. For FM the capture effect maintains the original signal until the interfering signal is strong enough to pull the detector off the original signal, or strong enough to overload the input of the rf amplifier.

An analogue service like a.m. radio degrades gradually with the interferring signal.

I guess in the cases you refer to, the interferring signal was stronger than should be permitted by the EMC regulations, whereas having an a.m. radio in close proximity to a known switching source and expecting to pick up transmissions intended for reception in Germany is not covered by the EMC regulations.

[eabadger]

i trained as a tv/radio and video repair engineer. so used to have trace "noise" in the old days, central hetaing pumps were bad, also tv's caused noise on the radio's nearby.

steve

[GavinA]

don't know about radio frequencies, but we've installed several systems on roofs with TV aerials below them in the loft space pointing directly through the PV array, with no problems.

[clockmanFR]

Thanks Chaps.
supremetwo, Thanks for that, never thought about the DC cables acting as an aerial. So will tell father in law that if he has problems then get the neighbour to install shielded feed cables. Or i suppose he can make it a condition of install/approval?

When my Tristar controllers are on dump load and kicking out PWM, my LW radio, (radio 4) at approx 50 meters away is inaudible. Also at 20m mobile phones loose life.

LW is a good way of testing interference and Steve your right about ballast problems, if i drive into our nearest towns i have to turn the radio off, mostly shop front lighting is the problem.

Steve, father in law using internet radio, hang on, we phone him up to mention that we sent him an email.

Here, we only have 3 FM stations that we can get reasonably acceptable.

 

 

[GavinA]

tbf, in my experience there's rarely 3 acceptable radio stations anywhere...

[Ivan]

DC itself won't cause any interference. But conceivable AC radiating from the DC cables (where it SHOULDN'T be) could happen if something went wrong with the inverter. You may have interference in close proximity to the inverter (but put this into context by placing your mobile phone near a TV/radio/telephone/intercom etc to see how much worse the common mobile phone is! Or try a radio scanner in a room where a PC is operating).

Clockman, your father has absolutely no right to object or make any conditional argument on the installation of a PV system - PV is permitted development unless on a listed building - but radio interference wouldn't come into that. I'm not aware of any screened cable that complies with the electrical requirements of PV cable (they need to be 800V rated, whereas I've not come across screened cable rated to this voltage).

[eabadger]

twisted cable as in twisted pairs, are beter than screened cables at limiting interfearance.
early radio transmiters were dc, the arc between two electrodes was the rf source.

steve