I do not know how well the "Cheap Charlie" as rob so colourfully puts it installers consider their wiring layout for EMC but as the things become more prevalent, so will the problems, and there are already many reported issues....

So, if one is advising folk on how to layout tails I would also point out that  poor layout creates an accidental antenna that can greatly worsen the re-radiation of  inverter frequency related hash. In a perfect world there would be filtering on the DC side, but of course 'value engineering' means this is absent of minimal, but it costs nothing to point out things like it is very bad form to organise panels so they create an accidental loop of large area, and much better if the 'flow' and 'return' cables of any string are arranged so that cancelling currents are  run within a few cm of each other, (ideally as twisted pair but I cannot see that happening), and proper earthing of on-roof metalwork.

Mike

Hmm Mike, I havent heard of that concept - radiating Inverter frequencies thru panel cables - hasnt appeared on any forums particularly across the pond.  They are so far ahead of us (as are the Ozzies)

As for making tails, I suggest that a commercial professional crimped butt joint which can be filled with silicone grease before closure.  This needs to be done with a proprietary toolkit and its expensive ca £100.  I have seen Cheap Charlie crimping systems and these are nasty made even worse by fake thin sheet lugs that couldnt possibly make a "Cold Weld" joint.

I need to do some more research on this on other forums as I cant quote a suitable professional system just now

more work needed

Robin

I suggest you search for EMC problems from solar installations - there are certainly plenty of reported examples where a poor installation obliterates radio reception neighbours and in some cases for miles around.

Problems in the USA https://www.youtube.com/watch?v=SusTlmeEvqc

https://www.reddit.com/r/amateurradio/comments/3y3jef/neighbors_just_got_solar_yesterday_they_gifted_me/

In the UK we are less flightly and the RSGB is taking a measured look into it https://rsgb.org/main/technical/emc/solar-pv-panels/

In the mean time this is their advice

http://rsgb.org/main/files/2014/02/QST20Solar20April2020165b25d.pdf

The American Radio Relay League offer the following https://www.arrl.org/solar

And in Oz... https://qrm.guru/502-2/

I'm sure there are more.

Mike.

mapj1 said:

In the mean time this is their advice

http://rsgb.org/main/files/2014/02/QST20Solar20April2020165b25d.pdf

That's very interesting, thank you for posting and one for the "library".

(Granted some items in the baseline fail to meet what the IET CoP requires over here (albeit it might well be what is done in many domestic installs), and one might suggest module-level optimisers weren't perhaps the best choice for that customer... while the multiple windings around a core might raise questions of grouping vs cable rating)

I would be very interested to see how an installation that actually follows the CoP performs under this level of scrutiny as a mid-level comparison.

[Edited for formatting]

Hi Jam

I browsed the RSGB article as posted, its very well presented.  I f take a cursory look it seems one should avaoid creating a loop with the individual cables stringing around panels and should try to make parallel cable runs.  The interesting thing is the simple suggestion of twisting two cables +ve and -ve in as far as one can with a 6mm solar cable - quite stiff.  This should help reduce HF radiation.  The use of ferrite rings etc towards the inverter input is new to me as is twisting cables, but it seems some science is needed to formulate a practical guide for installers.

Indeed - in the electronics world such things have been known for years - those strange lumps on computer video cables and so on contain ferrite rings, for the same reason -well sort of - as much to keep interference out of the video or sound as well as to keep power supply interference inside the wire  as it were. Although on thicker wires the ferrite is quite often shaped as atight fitting tube longer than the hole up the middle  is wide, rather  than thin wire turns wrapped around a ring - and that may well be a better approach for solar panel wires too given your comment about inflexibility. Actually if you take a hacksaw and open an off the shelf filter 'brick' like the one I linked to above, a decent chunk of magnetic material in some shape or other is a large part of the weight of any reputable make. The rest is capacitors and sometimes a surge arrester or two. It is much cheaper to buy the ferrite cores separately, but you need to know  what you are doing to roll your own then.

But certainly the 'what to do if there are radio problems and how to avoid them by careful layout ' needs to be better advertised to the installation folk doing the job - I suspect many would be out of their depth.

Mike

PS

It is important that as far as possible the flow and return currents pass through the same magnetic path,  as then the filter core is only magnetized by  the unwanted out-of-balance component of the currents we want to dissipate and the core is not at risk of being saturated as it would if it only enclosed a single wire carrying a large current.

It also means that the inductance is not part of the wanted current loop, and does not affect normal operation in any way. 

In a fault the magnetic material saturates and the inductance 'switches off' at a low current (sub-amp for most suppression ferrites)  so any current required to blow a fuse flows essentially unhindered limited only by the wire resistance in the normal way.

Indeed - in the electronics world such things have been known for years - those strange lumps on computer video cables and so on contain ferrite rings, for the same reason -well sort of - as much to keep interference out of the video or sound as well as to keep power supply interference inside the wire  as it were. Although on thicker wires the ferrite is quite often shaped as atight fitting tube longer than the hole up the middle  is wide, rather  than thin wire turns wrapped around a ring - and that may well be a better approach for solar panel wires too given your comment about inflexibility. Actually if you take a hacksaw and open an off the shelf filter 'brick' like the one I linked to above, a decent chunk of magnetic material in some shape or other is a large part of the weight of any reputable make. The rest is capacitors and sometimes a surge arrester or two. It is much cheaper to buy the ferrite cores separately, but you need to know  what you are doing to roll your own then.

But certainly the 'what to do if there are radio problems and how to avoid them by careful layout ' needs to be better advertised to the installation folk doing the job - I suspect many would be out of their depth.

Mike

PS

It is important that as far as possible the flow and return currents pass through the same magnetic path,  as then the filter core is only magnetized by  the unwanted out-of-balance component of the currents we want to dissipate and the core is not at risk of being saturated as it would if it only enclosed a single wire carrying a large current.

It also means that the inductance is not part of the wanted current loop, and does not affect normal operation in any way. 

In a fault the magnetic material saturates and the inductance 'switches off' at a low current (sub-amp for most suppression ferrites)  so any current required to blow a fuse flows essentially unhindered limited only by the wire resistance in the normal way.