RFI from Enphase micro-inverters...

M

Mat Nieuwenhoven

Guest
Hi,

I am considering having solar panels installed. The main non
serial-string-of-panels systems seem to be SolarEdge and Enphase.
Solaredge apparently causes RFI; that system uses switching DC-DC
converters on the panels and a DC-AC converter inside. Enphase has
micro-inverters that produce the mains voltage straight on the solar
panel.
As these must be switchers, has anyone experience with these with
regards to RFI? I am mostly concerned for noise in the range 0-30 Mhz
genaral, and 77 kHz specifically (clocks).
Can any RFI be prevented by used ferrite clamps like those on mains
leads?

Mat Nieuwenhoven
 
On Wednesday, October 28, 2020 at 8:47:19 PM UTC+11, Mat Nieuwenhoven wrote:
Hi,

I am considering having solar panels installed. The main non
serial-string-of-panels systems seem to be SolarEdge and Enphase.
Solaredge apparently causes RFI; that system uses switching DC-DC
converters on the panels and a DC-AC converter inside. Enphase has
micro-inverters that produce the mains voltage straight on the solar
panel.
As these must be switchers, has anyone experience with these with
regards to RFI? I am mostly concerned for noise in the range 0-30 Mhz
general, and 77 kHz specifically (clocks).
Click to expand...

Everybody has run into switching power supplies that generate radio-frequency interference. Quite a few of us have worked out how to design them and lay them out so that they don\'t generate much. If you are stuck with other peoples designs, there are ways of confining most of the interference to the immediate vicinity of the power supply itself.

> Can any RFI be prevented by used ferrite clamps like those on mains leads?

Ferrite clamps can can reduce the amount of high frequency current travelling down mains leads, but nothing prevents that reduced current from radiating. It\'s not the only way the radio-frequency interference gets out of inverters. I\'ve run into an inverter that had to be wrapped in a grounded flywire enclosure (Faraday cage) to stop it from interfering with everything else electronic in the same rack.

There\'s one excellent book on the subject - Ralph Morrison\'s \"Grounding and Shielding Techniques in Instrumentation\"

https://www.amazon.com/Grounding-Shielding-Techniques-Instrumentation-3rd/dp/0471838055

I\'ve got a copy of the fourth edition. You could buy the sixth edition.

You\'d be much better off finding exactly how much interference the switching inverters that you are thinking of buying spew out, and how they spew it out, but that isn\'t easy to find out.

--
Bill Sloman, Sydney
 
On 28/10/20 8:47 pm, Mat Nieuwenhoven wrote:
I am considering having solar panels installed. The main non
serial-string-of-panels systems seem to be SolarEdge and Enphase.
Solaredge apparently causes RFI; that system uses switching DC-DC
converters on the panels and a DC-AC converter inside.
Click to expand...

I said \"no thanks\" to SolarEdge and installed passive panels with a
Fronius inverter instead. It\'s quiet - with the extra ferrites I had
installed in it, it\'s super-quiet.

Can any RFI be prevented by used ferrite clamps like those on mains
leads?
Click to expand...

Can\'t vouch for Enphase, but for $1000 worth of ferrites and a lot of
trouble it\'s possible to make a SolarEdge system quiet. See the cover
story on that in April 2016 QST magazine. It\'s what convinced me I
didn\'t want to go that way.

Clifford Heath.
<https://www.dropbox.com/s/oifv0dnoohatucg/QST-Amateur-Radio-Solar-Power.pdf?dl=0>
 
On Wed, 28 Oct 2020 22:23:02 +1100, Clifford Heath wrote:

On 28/10/20 8:47 pm, Mat Nieuwenhoven wrote:
I am considering having solar panels installed. The main non
serial-string-of-panels systems seem to be SolarEdge and Enphase.
Solaredge apparently causes RFI; that system uses switching DC-DC
converters on the panels and a DC-AC converter inside.

I said \"no thanks\" to SolarEdge and installed passive panels with a
Fronius inverter instead. It\'s quiet - with the extra ferrites I had
installed in it, it\'s super-quiet.

Can any RFI be prevented by used ferrite clamps like those on mains
leads?

Can\'t vouch for Enphase, but for $1000 worth of ferrites and a lot of
trouble it\'s possible to make a SolarEdge system quiet. See the cover
story on that in April 2016 QST magazine. It\'s what convinced me I
didn\'t want to go that way.

Clifford Heath.
https://www.dropbox.com/s/oifv0dnoohatucg/QST-Amateur-Radio-Solar-Power.pdf?dl=0
Click to expand...

Thanks, good reading. I think I avoid Solaredge.

Mat Nieuwenhoven
 
On Wed, 28 Oct 2020 03:34:08 -0700 (PDT), Bill Sloman wrote:

On Wednesday, October 28, 2020 at 8:47:19 PM UTC+11, Mat Nieuwenhoven wrote:
Hi,

I am considering having solar panels installed. The main non
serial-string-of-panels systems seem to be SolarEdge and Enphase.
Solaredge apparently causes RFI; that system uses switching DC-DC
converters on the panels and a DC-AC converter inside. Enphase has
micro-inverters that produce the mains voltage straight on the solar
panel.
As these must be switchers, has anyone experience with these with
regards to RFI? I am mostly concerned for noise in the range 0-30 Mhz
general, and 77 kHz specifically (clocks).

Everybody has run into switching power supplies that generate radio-frequency interference. Quite a few of us have worked out how to design them and lay them out so that they don\'t generate much. If you are stuck with other peoples designs, there are ways of confining most of the interference to the immediate vicinity of the power supply itself.

Can any RFI be prevented by used ferrite clamps like those on mains leads?

Ferrite clamps can can reduce the amount of high frequency current travelling down mains leads, but nothing prevents that reduced current from radiating. It\'s not the only way the radio-frequency interference gets out of inverters. I\'ve run into an inverter that had to be wrapped in a grounded flywire enclosure (Faraday cage) to stop it from interfering with everything else electronic in the same rack.

There\'s one excellent book on the subject - Ralph Morrison\'s \"Grounding and Shielding Techniques in Instrumentation\"

https://www.amazon.com/Grounding-Shielding-Techniques-Instrumentation-3rd/dp/0471838055

I\'ve got a copy of the fourth edition. You could buy the sixth edition.

You\'d be much better off finding exactly how much interference the switching inverters that you are thinking of buying spew out, and how they spew it out, but that isn\'t easy to find out.
Click to expand...

I spoke today to a saleman of a company installing solar systems
using the Enphase system, and not only did he confirm that those
micro-converters generate \"some noise\", but he immediately said they
can fix that using ferrites. I was impressed. I shall get more
details, especially after reading the QST article Clifford kindly
mentioned. Apparently the panels themselves can also act as antenna
somewhat.

Mat Nieuwenhoven
 
On 29/10/20 1:50 am, Mat Nieuwenhoven wrote:
On Wed, 28 Oct 2020 03:34:08 -0700 (PDT), Bill Sloman wrote:

On Wednesday, October 28, 2020 at 8:47:19 PM UTC+11, Mat Nieuwenhoven wrote:
Hi,

I am considering having solar panels installed. The main non
serial-string-of-panels systems seem to be SolarEdge and Enphase.
Solaredge apparently causes RFI; that system uses switching DC-DC
converters on the panels and a DC-AC converter inside. Enphase has
micro-inverters that produce the mains voltage straight on the solar
panel.
As these must be switchers, has anyone experience with these with
regards to RFI? I am mostly concerned for noise in the range 0-30 Mhz
general, and 77 kHz specifically (clocks).

Everybody has run into switching power supplies that generate radio-frequency interference. Quite a few of us have worked out how to design them and lay them out so that they don\'t generate much. If you are stuck with other peoples designs, there are ways of confining most of the interference to the immediate vicinity of the power supply itself.

Can any RFI be prevented by used ferrite clamps like those on mains leads?

Ferrite clamps can can reduce the amount of high frequency current travelling down mains leads, but nothing prevents that reduced current from radiating. It\'s not the only way the radio-frequency interference gets out of inverters. I\'ve run into an inverter that had to be wrapped in a grounded flywire enclosure (Faraday cage) to stop it from interfering with everything else electronic in the same rack.

There\'s one excellent book on the subject - Ralph Morrison\'s \"Grounding and Shielding Techniques in Instrumentation\"

https://www.amazon.com/Grounding-Shielding-Techniques-Instrumentation-3rd/dp/0471838055

I\'ve got a copy of the fourth edition. You could buy the sixth edition.

You\'d be much better off finding exactly how much interference the switching inverters that you are thinking of buying spew out, and how they spew it out, but that isn\'t easy to find out.

I spoke today to a saleman of a company installing solar systems
using the Enphase system, and not only did he confirm that those
micro-converters generate \"some noise\", but he immediately said they
can fix that using ferrites. I was impressed. I shall get more
details, especially after reading the QST article Clifford kindly
mentioned. Apparently the panels themselves can also act as antenna
somewhat.
Click to expand...

The panels will only act as an antenna if they have a signal to radiate.
You will need ferrite between each micro-inverter and its panel to stop
that.

The biggest radiator from a rooftop system is the large loop of wire
that joins the string. In the QST article, you will see a recommendation
that the outbound and return wires should be twisted together, or at
very least, run parallel.

Regulations here in Australia require that the return wire is tied to
the mounting rail - but my installer wanted to install the
panel-to-panel links directly between the panels, about 250mm from the
rail. I insisted that each link was returned (as a pair, preferably
twisted) to the rail, then twisted along the return wire to the next
panel (where it meets the link from a further panel, etc). As it turns
out, the message got lost in translation and they didn\'t do that - but
because the panels are passive there is no significant signal to radiate.

In the QST article, the strings were installed twisted like that, but
using odds-and-evens, with even panels on the way out and odd panels on
the return wire. I have no idea if that would make a difference, but it
makes the wiring more difficult to install. It means the wiring is
all-links, and each link spans two panels - which doesn\'t suit the
prefabricated link leads used by my installer (they do however have
enough extra length to return to the rail).

With an HF sniffer loop on my spectrum analyser, I can see no signal on
the roof, and none at 2m from the inverter. It only breaks the noise
floor when I hang the loop directly against the inverter body - and
that\'s likely to be near-field coupling from the magnetics.

If you want RF quiet, passive panels are the way to go. I\'m lucky to
have no partial shading to worry about, so micro-inverters or power
optimisers would be no advantage in any case.

Clifford Heath.
 
On Wed, 28 Oct 2020 10:47:12 +0100 (CET), \"Mat Nieuwenhoven\"
<mnieuw@zap.a2000.nl> wrote:

I am considering having solar panels installed. The main non
serial-string-of-panels systems seem to be SolarEdge and Enphase.
Solaredge apparently causes RFI; that system uses switching DC-DC
converters on the panels and a DC-AC converter inside. Enphase has
micro-inverters that produce the mains voltage straight on the solar
panel.
As these must be switchers, has anyone experience with these with
regards to RFI? I am mostly concerned for noise in the range 0-30 Mhz
genaral, and 77 kHz specifically (clocks).
Can any RFI be prevented by used ferrite clamps like those on mains
leads?
Click to expand...

Ferrite beads can help quite a bit but will never eliminate RFI
completely. I think you\'ll find the Enphase is the lesser of the
available two evils.

Palomar Engineers: Solar System RFI
<https://palomar-engineers.com/rfi-kits/solar-system-rfi>
Notice at the bottom of the page, they sell an RFI suppression kit for
Enphase M190/M215/M240/M250/etc micro-inverters. There are other
vendors selling these, or you can just buy the parts directly. They
use type 75 ferrite, which is a good choice. The catch is that it
only works from 200 KHz to 30 MHz. If the switching frequency is
below 200 KHz, it will go through the filter like it wasn\'t even
there. To cover 77 KHz and 1-30MHz, you might need two cores, from
two different materials. Type 75 for the HF and type 76 for the LF.
<https://www.fair-rite.com/materials/>
You\'ll need filters on both the input and output cables to/from the
Enphase inverters.

At 77 KHz, I suspect you\'ll find far more sources of EMI/RFI than your
proposed solar power system. Typically, you\'ll find plenty of devices
with switching power supplies, most of which operate between 40KHz and
150KHz. On a spectrum analyzer, what you\'ll see is broadband hash as
many power supply switchers include \"spread spectrum\" modulation that
reduces the peak power, but smears the average power of a wide
frequency range. Chances are good one of these will land in the vary
narrow frequency spectrum used by digital clocks at 77 KHz. An easy
experiment is to setup a 77KHz resonant loop antenna and plug it into
an oscilloscope input. If you\'re lucky, you\'ll see DCF77 on the
scope, usually between midnight and 6AM. Now, start turning off
electronics and watch what happens to the noise on the scope. If it\'s
like my house, it will slowly go down, but never quite disappear. I
suspect you\'ll need to put as much effort into suppressing EMI/RFI
from these sources, as you might need to put into suppressing EMI/RFI
from your proposed Enphase micro-inverters.

LF (77 KHz) is not radiated by the electronic components. It is
conducted by the power lines or magnetically induced by these same
wires. The trick is to isolate the noise source (electronics) from
the antennas (power wires). One way it to twist the wires together to
reduce any differential mode radiation from the wires. Another way it
raise the inductance, and therefore the impedance, of the power cables
by installing a common mode choke. That\'s what the toroids in the
Palomar kit and the QST article are doing.
<https://www.eetimes.com/designing-external-cabling-for-low-emi-radiation/>

Actually, I just realized that filtering 77 KHz with ferrite cores are
not going to work for Enphase. Enphase micro-inverters use signaling
on 144 kHz. Installing ferrite cores, that blocks communications
between devices, is going to cause problems.
<https://enphase.com/sites/default/files/Power_Line_Filter_Single-Phase_TechBrief.pdf>
That means you can probably block RF from 1-30 MHz, but not 77KHz
unless you contrive a way to pass 144 KHz through (or rather around)
the filters.





--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
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