DXing distant SolarEdge PV optimizer modules (or long-distance propagation of PV system QRM)

From how far away can you hear the spurious emissions from a known-noisy PV system?

Quite a racket!

Figure 1:
The spectrum of a SolarEdge PV system from several meters
away across the 6-8 MHz range showing "spurs" (clumps of
low-level carriers) at 200 kHz intervals and other places.
In the above plot the true nature of the individual peak -
the fact that each contain many carriers - is not apparent.
Click on the image for a larger version.

In a previous post (linked HERE) I described the interference produced by a SolarEdge PV (photovoltaic) system to an amateur from installations on neighboring houses.

The "take-away" from this analysis is that the current version of SolarEdge systems produce rather strong signals at 200 kHz intervals - each module on the back side of a solar panel producing its own carrier at its own frequency as depicted.  The peaks in Figure 1 show these groupings of carriers every 200 kHz (plus some additional frequencies) while the image in Figure 2 shows, in extremely high spectral resolution, many individual, narrow carriers that comprise each of these peaks.

In driving around with an HF mobile station in my vehicle I can hear these 200 kHz-spaced carrier groups almost everywhere around town during daylight hours - the roar getting much stronger in/near residential areas as you would expect.  If driving through a residential neighborhood, it is very easy to tell when you drive past a house equipped with a SolarEdge PV system - and it is easily audible from a block or two away.  Knowing the "fingerprint" of this PV system allows it to be identified uniquely - even at some distance.

Figure 2:
A "zoomed in" view of the spectrum of local SolarEdge
carriers recorded just below 7.4 MHz from my home.
See Footnote #3, below for detailed information.
Click on the image for a larger version.

Are they DX? ¹

A question arose in my mind:  Does this "grunge" produced by the SolarEdge PV systems propagate long distances?

To answer this question I checked a KiwiSDR at the Northern Utah WebSDR (link) - a site with which I am very familiar ².  This receive system is located about 3 miles (5km) from any residential area, bounded on three sides with mosquito-laden bird refuges (wetlands) and on the fourth side - the same as the closest houses - by a mountain.  Additionally, the antenna used for the reception in Figures 3 and 4 below was the TCI-530 omnidirectional log-periodic (with circular polarization) - which does not have good gain at very low radiation angles, further precluding the reception of "nearby" PV systems via "ground wave".

The quick answer to the above question is YES - the roar of SolarEdge systems is propagated when conditions are "reasonable" ⁴ as shown in the screen capture below:

Figure 3:
Propagated noise from myriad SolarEdge PV systems from the remote Northern Utah WebSDR's
remote HF receive site.  The "hump" in the middle is the combined energy of likely thousands of
SolarEdge PV systems that are being ionospherically propagated.  Amateur signals are
visible at 14.200 MHz and above.
Click on the image for a larger version.

The signals represented by the "hump" in the highlighted portion in the center of the analyzer plot in the top part of the image - and the "band" of noise on the waterfall display - between 14.199 and 14.200 MHz are the sum of the propagated low-level PV system carriers from... who knows where?  To be clear, this energy is not likely to be from just one SolarEdge PV system and its individual optimizers (one for each panel) but more likely from the many thousands of such devices that are each, individually, radiating energy.  What we are seeing is the total energy of the propagated systems, the frequency spread being centered around 14.1993 MHz.

It's worth noting that the fact that these signals do not land on exactly the same frequency ⁵ - hence the Gaussian-like distribution of energy - and this has interesting implications.  Even though the signal from each, individual optimizer is (more or less) a CW (unmodulated) carrier, the fact that there are so many of them clustered together means that, for statistical purposes, they might as well be a distribution of noise energy:  Unlike with a single coherent CW signal, the DSP filtering on modern radios will be able to do little/nothing to reduce their effects if they were to cause interference due to its similarity to white noise.

A quick power and spectral analysis of the signal above showed that if the signals above were a single, coherent CW signal, the total amount of energy contained in the "hump" in Figure 3 would have easily been at least 15-20dB above the noise in a 50 Hz detection bandwidth:  A CW signal of this strength would certainly be cause for complaints!

I also looked at other 200 kHz multiples around 14.000 and 14.400 and the same, exact types of signals were present on those frequencies - and similar bunches of energy fitting this profile were noted at least as low as 10.200 and as high as around 18.200 MHz as well (probably higher) and every (otherwise) clear frequency in between - this range being related to current ionospheric propagation at the moment that I checked (e.g. around 1845 on September 10 UTC, 2025).  ⁶

To verify that these signals were propagated and were likely from SolarEdge systems, several things were done:

• The presence at many 200 kHz multiples/intervals across the HF spectrum is telling!  Their being slightly below exact 200 kHz multiples as mentioned in Footnote 5 adds to their "uniqueness".
  
• On days with poor propagation overall, these signals were absent - or limited to frequencies commensurate with the MUF (Maximum Useable Frequency).

• These signals disappear at night.  (This test is somewhat complicated by the fact that propagation on these bands also changes at night - but sunlight is still illuminating the ionosphere well after sunset on the ground.) 
  

• An "S-meter" plot was run over the period of several minutes:  A propagated signal(s) would show variations in signal strength - but this can be foiled to a degree by the fact that many, many individual point sources would each be propagated differently and unlike a single source, would not experience as deep a fading as the plot below shows:

Figure 4:
Propagated signal strength variations caused by ionospheric variations.  This would seem to indicate
that the signals are propagated - but the magnitude of the fading would be mitigated by the large
number of point sources, each being affected individually along the signal path.
The top/bottom of this chart represents 10dB.
Click on the image for a larger verion.

As noted in the original article analyzing a system close-up (linked above) the SolarEdge optimizers produce other signals 6-10 dB weaker at various points above each 200 kHz interval - these are visible in Figure 1.  When the above plots were made these signals weren't readily apparent - but I suspect that they will be visible during "excellent" propagation conditions rather than the "mediocre-to-average" conditions that were present when Figures 3 and 4 were produced.

Conclusion:  They do get propagated!

So yes, you can DX SolarEdge PV systems - it's just that there are so many of them each doing their own radiating that you probably won't know from where those signals originate, so it's hard to know from how far away you might actually be hearing them!  To be clear, it's difficult to determine if a the radiated RF from a single optimizer would be audible via ionospheric propagation, and with many thousands of them out there this may be impossible to determine - but it is clear that the summation of many thousands of them does produce an audible signal.

Do these signals actually cause QRM ⁷ ?  As noted in the earlier post (liked above) they most certainly do if you live within a city block or two of one of the SolarEdge PV systems and operate on or near any of the frequencies occupied by the spurious radiation represented in Figure 1.  If your receive system is located well away from a SolarEdge installation, the above shows that you may still experience interference from these systems - even from a significant distance.

Figure 3 also shows that the emissions do propagate over long distances:  The 20 meter band's optimal "single skip" distance would likely place the majority of these signals in a 700-1500 mile (1100-2400 km) radius of Northern Utah - and this includes quite a few populated areas in parts of the U.S. where the number of solar installations is quite high. 

You, too, can check for QRM at your station

If you have an HF station with a receiver with a waterfall display you might want to check the various amateur bands just below the 200 kHz multiples ⁸ during daylight hours:  If there is a SolarEdge PV system within a couple city blocks of you ⁹ you will most likely see and hear it - but don't blame me if, after finding that you can see those signals, you can't "un-see" them!

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Links to related pages (about solar power) on this blog:

• Analysis of a SolarEdge system (link) - This is the article linked at the top of the page where careful measurement was done to characterize the interference created by a SolarEdge system neighboring a local amateur.
  

• It *is* possible to have an RF quiet home PV system (link) -  On this page I describe the SunnyBoy based system at my home QTH - and the fact that it does NOT produce QRM.
  

• Reducing QRM from a Renogy 200 watt (or any other) portable solar panel system (link) - Here I describe a portable solar system that I take "car camping" and how I reduce its interference to the point of inaudibility.

• The Solar Saga Part 1: Avoiding Interference - (Why I did not choose Microinverters) - link

• The Solar Saga Part 2:  Getting the system online - link
  

• Does the Tesla Powerwall 2 produce Radio Frequency Interference? - link
  

• Reducing RFI from the Tesla Powerwall 2 - link 
  

• Tesla Powerwall susceptibility to RF Transmissions - and how to deal with it - link 

Footnotes:

1. The term "DX" means distance.  Generally speaking, if a signal is "DX" it is understood that it must be being propagated over much more than a line-of-sight distance - in this case, via ionospheric propagation at distances of hundreds or thousands of miles/km.
2. The author of this post is one of the original founders and current maintainers of the Northern Utah WebSDR which has a remote HF receive site about 80 miles (94km) north of Salt Lake City.
3. Figure 2 shows a "close-up" spectral view of the signals emitted by several SolarEdge PV systems within a mile/kilometer or two of my house - the closest system being about a block away.  The center frequency of this cluster of signals was approximately 7.39965 MHz and a 256k-point FFT with a bin width of 183 mHz (milliHertz) - along with some averaging - was used to create this plot.  Clearly visible are a large number of individual carriers along with a background "roar" of many more weaker carriers that are not individually distinguishable in this plot.  This plot was purposely done on a frequency above the 40 meter amateur band during daylight hours (the local time is visible in the image) and during this time there is no strong, long distance propagation (a fact verified by the absence of a similar set of signals on the remote Northern Utah WebSDR site) indicating that this energy is, in fact, originating from systems proximate to my own receive site.  At sunset, these carriers will gradually disappear - often "blinking" out - as the solar panels lose their light and will reappear the next morning:  This "blinking" can be heard as individual tones flicker on/off during the day<>night transition by listening on an ordinary SSB-capable receiver at one of the frequencies noted above.
4. The frequencies mentioned have also been checked when ionospheric propagation is poor (comparatively few strong signals) and the characteristic SolarEdge carriers were absent at the remote receive site.  This further illustrates the fact that the signals described above are not local to the remote receive site and reinforces the likelihood that they are, in fact, being propagated. 
5. Observation of a SolarEdge PV system at very close distance (less than 50 feet/15 meters) indicates that each, individual optimizer - a device attached to the back of every individual solar panel - will radiate the signals at 200 kHz intervals.  Due to the slight variations in oscillator frequencies (e.g. quartz crystals or MEMs devices) the precise frequencies of these signals - and their harmonics - will vary, but the mean frequency separation appears to be around 199.9901 kHz which puts them slightly below a precise 200 kHz multiple which is why the peak of the distribution shows up around 14.1993 MHz on 20 meters, 7.19965 MHz on 40 meters and so on.  As noted in the text, the actual frequency spread of the individual modules is such that it has a Gaussian-like distribution above and below the mean frequency.
6. I also checked several remote receive systems around the world during their local daylight hours and could see the same "humps" of energy at frequencies just below the aforementioned 200 kHz multiples on some of them.  One such system was that located at the University of Twente in the Netherlands:  It is not known to what degree the signals that were radiated (likely) from PV systems were propagated and which might be within a few kilometers of this receive site, but they are certainly "there".
   
7. "QRM" is a "Q" signal referring to "Man Made Interference" and the magnitude of this interference in comparison to the desired signals determines if this is harmful interference.  If QRM makes it difficult/impossible to receive a signal on frequency, that would fit the definition of harmful interference.
8. The frequencies on which the radiated signals from a SolarEdge PV system (every 199.9901 kHz) will likely land within an HF amateur band are clustered around the following:  3.5998, 3.7998, 3.9998,  7.1996, 14.1993, 21.1990, 21.3990, 28.1986, 28.3986, 28.5986, 28.7986, 28.9986, 29.1986, 29.3986 and 29.5986 MHz plus similar frequencies in the 6 meter band:  They can also be heard on non-amateur frequencies at the same 199.9901 kHz intervals as well.  As the above frequencies are the actual frequencies, you will need to tune above or below the frequencies (using LSB or USB, respectively) by 1.5 kHz or so to hear the "roar".  Of course, you will only hear these signals during daylight hours when the PV systems are active.  Note that the combination of naturally-higher noise levels on the lower bands (80, 40 meters) and the likely lower efficiency of the PV system's component ability to radiate RF there - plus the tendency for nighttime propagation on those bands (when the PV systems are inactive) - means that observing this phenomenon on those frequencies via the ionosphere is much less likely.
9. If you do remote operation like POTA or SOTA at a significant distance from any likely PV system, you might want to take a look at some of the 200kHz-interval frequencies mentioned above during daylight hours and good propagation:  You'll probably see the propagated PV signals there, too.
   

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This page stolen from ka7oei.blogspot.com

[END]

Analysis of interference from a SolarEdge PV (solar) electric system.

Comment:

This article - while it centers about the investigation of a SolarEdge PV (PhotoVoltaic) system - the discussions of techniques and strategies should be generally useful when investigating interference from any make or model of PV system - or even interference from other sources.

* * *

Follow-up:

There is a follow-up on this article where I note that the signals emitted by multiple systems can be propagated over great distances via the ionosphere - link HERE. 

Several months ago I got a call from a local amateur who was very concerned about a sudden rise in his noise floor across the HF spectrum (3-30 MHz).  This increase in noise seemed to be coincident with the installation and commission of a 5 kW PV (Photovoltaic, or "Solar") electrical system on the house of an adjacent neighbor.  I suggested that he talk to the manufacturer of the PV system to discuss the situation - and to request from them possible solutions.

A few weeks ago, he got back to me and he had, in fact, talked to the manufacturer and an online meeting was arranged in which they would remotely idle the neighbor's system while we were monitoring via the amateur's receive antenna.

Out of curiosity - and as sort of a practice run - I went over the weekend before the online meeting to get a better idea as to the spectral signature of this system - a SolarEdge series string system with optimizers - when it was operating normally.  The amateur had obtained permission from the neighbor to allow us to enter their yard to make very "close in" measurements (e.g. within a few inches/cm of the equipment, conductors) to obtain spectral "samples" of the system, thereby excluding external signals.

For these measurements, I used an amplified, shielded magnetic ("H") loop antenna (about 18"/50cm) in diameter as the "sense" antenna and an HP/Agilent/Keysight spectrum analyzer, recording the plots electronically - although a Tiny SA "Ultra" would likely have sufficed as well.  None of the readings were to represent "absolute" signal levels as all that we were really interested in were relative measurements, and as such all that we needed to do was keep our measurements consistent - that is, being able to precisely repeat the conditions between subsequent measurements.  These readings would allow us to understand the nature of the RF energy that it was creating - its "signature", if you will.

Note:  For information about the H-field loop used for this testing - and using an inexpensive spectrum analyzer such as the "Tiny SA" or, better yet, the "Tiny SA Ultra", see a previous blog entry "RFI Sleuthing with the Tiny SA" - Link.

The nature of this QRM:

The interference observed by this amateur - now known for certain to be signature of this model of SolarEdge PV system - was evident as two general types of signals:

• Moderate to strong clusters of carriers every "even" 200 kHz.  At 200 kHz intervals (e.g. 7.0, 7.2, 7.4 and 14.0, 14.2 and 14.4 MHz) from below 3 MHz through at least 30 MHz could be heard a melange of closely-spaced carriers within about 500 Hz of each other on the lower bands.  While these carriers sounded like mostly CW (unmodulated) signals, there was also evidence of low rate data signalling buried in the cacophony as well as additional lower-level carriers.  (The actual interval is very slightly smaller than 200 kHz so these "bunches" of carriers will be a centered a few hundred Hz below exact, even 200kHz multiples, the difference increasing with frequency.)
  

• Background "white" noise amplitude-modulated at the mains frequency.  If you were just casually listening at this amateur's QTH on the HF bands - say 40 meters - you might be forgiven in the short term for presuming that nothing was wrong.  In reality the noise floor had been elevated several "S" units by the PV system - the result sounding superficially like plain, old white noise:  Switching from SSB to AM reveals the loud "hum" that is riding on the noise - modulation that is almost "invisible" if one is listening only using SSB.

While the appearance of the above interference coincided with the activation of the neighbor's system, that fact that it disappeared at night further pointed to a PV system as the source of the QRM.

"Close-in" measurements

Placing the sense antenna right at the main inverter on the back of the neighbor's house, we wanted to take a snapshot of the spectrum at that location:

Figure 1:  0-30 MHz sampled right at the main inverter

With each horizontal division representing 3 MHz, this 0-30 MHz plot shows a high concentration of noise in the 3-9 MHz area from a location right at the inverter.

Because Figure 1 represents the spectrum at the inverter, we wondered what it would look like at one of the solar panels so we placed the sense antenna right against one of the solar panels:

Figure 2:  0-30 MHz sweep with sense antenna placed next to a solar panel

Figure 2 is in the same frequency and amplitude scale as Figure 1 - but with the "reference level" adjusted by 20 dB to move the trace "up" a bit - and we can see that the spectrum next to the panel looks quite different from that sampled right at the inverter.  This isn't unexpected as Figure 2 would likely represent more of the noise that is emitted from the DC (input) side of the optimizer whereas the spectrum represented in Figure 1 would be more likely to show that of the DC output of the optimizer plus whatever noise was riding on the conductors carrying the DC input and AC output of the main string inverter.

Although it is difficult to be sure, the 0-30 MHz plots taken from a greater distance (10 meters or more) had the general appearance of the noise spectra shown in Figure 2 more than that of Figure 1 leading me to believe that a significant portion of the QRM may be being radiated from the panels themselves rather than just the conductors going from the optimizers  to the main inverter - but certainly, both are likely involved.

Note:  For both of these plots, the RF energy from the PV system was many 10s of dB above the typical background noise floor - in this case, 40-50dB for Figure 1 and at least 30dB for Figure 2 in the area around 7 MHz.

As the 0-30 MHz sweep does not have enough resolution to visualize the narrower 200 kHz signals, the analyzer was readjusted as depicted in Figure 3 - again with the sense antenna next to the panel:

Figure 3:  From near the panel, a "zoomed in" spectral sweep showing narrowband birdies.

In this spectrum plot we can see not only the "white" noise on the floor of the sweep representing the "hummy hiss", but also the much stronger signals every 200 kHz - plus a number of weaker signals in between:  It is these signals that are the most obvious to the casual operator and appear to be unique to a SolarEdge system of this model/type.

On this same day we waited until after sunset - monitoring the groups of carriers at 7.2 MHz and hearing them "flicker" out of existence as it got dark and we re-did the "next to the panel" measurements - this time the spectrum was devoid of the 200 kHz-spaced carriers (they were no longer audible on the amateur receiver, either) and the 0-30 MHz plots were 10s of dB lower than in the daylight. 

Important:  The 2 MHz sweeps in Figures 3-7 use a resolution bandwidth of 10 kHz which is almost exactly 4 times wider than the typical SSB bandwidth of an amateur receiver of about 2.5 kHz making their apparent level above the background noise appear lower than it is actually is.

What this means is the coherent signals - such as the 200 kHz carriers - appear to be another 6 dB farther above the noise floor in an SSB bandwidth than what the analyzer plots show.

Plots from a distance

Having captured some "close-in" plots, we now had an idea as to what the signals emitted by the PV system looked like.

A few days after we made the above plots we were in a virtual meeting with the manufacturer of the PV system (SolarEdge) from the ham's shack.  Having reconfigured the feed to his main radio, we could quickly switch the feedline from the antenna feeding the radio and the spectrum analyzer.

At this time we also learned that there was a second SolarEdge system south of this amateur's QTH - about 150 feet (45 meters) away across the cul de sac - and that the neighboring system and the one across the street would but remotely shut down, in that order, to determine how much QRM was emanating from each.

While we captured 0-30 MHz plots of each stage of system shutdown, for the purposes of this article we'll show just the "narrow" plots in 2 MHz sweeps as depicted in Figure 3 as the presence of the 200 kHz signal are generally representative of the presence of the broadband noise as well and these signals were easily identifiable and now known to be indicators of QRM from this type of PV system.

First, here's the plot from the amateur's 40 meter inverted Vee antenna with both systems on:

Figure 4:  6-8 MHz plot from the 40 meter antenna showing the 200 kHz peaks - and a bit of broadband noise as well.

 

The next plot shows the effects when the neighboring system was turned off, but the one across the street still on:

Figure 5:  The neighboring system off - but the one across the street still on.

As can be seen, the broadband noise floor around the 40 meter band (approximately one horizontal division below and above the marker) has dropped visibly - around 3-4 dB - and the amplitude of the carrier at 7.2 MHz has dropped about 6 dB - and the 200 kHz signals have disappeared almost entirely below about 6.5 MHz.  The system across the street was then shut off and the only remaining signals were those that happened to be on the 40 meter band.  (No trace is available for this configuration, unfortunately.)

As the 40 meter inverted Vee is oriented to favor east-west signals it was not necessarily the best candidate to test the effects of the PV system across the street, so we switched to a 20 meter antenna which was responsive in that direction and this trace shows the plot between 13 and 15 MHz:

Figure 6:  This plot of the 20 meter band and surrounding frequencies shows only propagated signals, with no sign of PV system QRM.

As both systems were off, the trace was quite clear - only showing signals that actually were on or near the 20 meter band, propagated from elsewhere in the world.  The folks at SolarEdge then turned on the system across the street with the following result:

Figure 7:  Same as Figure 6, but with only the PV system across the street activated.

The effect is clear:  In the vicinity of the 20 meter band, the appearance of rather strong signals every 200 kHz is apparent - and there is an obvious 2-4 dB increase in the noise floor indicating that this system, too, is causing harmful interference.

Readings on the radio:

It would seem that the folks at SolarEdge had worked with more than one amateur radio operator on similar issues and I was pleasantly surprised when they asked for some "S-Meter" reading comparisons with the neighbor's system on and off.  Using a calibrated signal generator, I'd already determined the signal level (in dBm) that correlated with the S-meter readings for the Icom radio - and here are the results for 40 meters:

Both systems off:

S1 (<= -84 dBm) - no carrier groups every 200 kHz.

Neighbor system on:

S4 (-78 dBm) - white noise between 200 kHz carriers.

S9 (-67 dBm) - carriers at 7.2 MHz.

This shows that at 40 meters, the degradation to noise alone was on the order of 6 dB (most Japanese radios are calibrated for 3dB per S-unit) and that the cluster of carriers on 200 kHz intervals was far more destructive, rising a bit short of 20dB out of the noise floor.

As our time with the SolarEdge folks in the virtual meeting was limited, we were not able to do similar "S-meter" tests on 20 meters, but we can use the 40 meter results along with the relative strength of the 200 kHz-spacing carriers  and correlate them with the 40 and 20 meter spectrum analyzer traces and determine that the severity of QRM from the PV system on 20 meters on the receiver would have been roughly comparable to that on 40.

Analysis of these readings and implications:

As mentioned earlier, there are two types of interfering signals produced by these SolarEdge PV systems:

• Moderate to strong clusters of carriers every "even" 200 kHz.  These are very obvious, easy to identify, and quite strong compared to the noise with a few weaker signals in-between that were also clearly audible.
  

• Background "white" noise amplitude-modulated at the mains frequency.  This is also present, but it borders on insidious as the average amateur may not be able to quantify its existence - let alone its effects - as its effects may be obscured if one only listens for it using SSB modes.

"Will my radio's DSP help?"

The quick answer is "No".

While you might think that modern receivers' ability to "notch out" tones might help alleviate the effects of the signals every 200 kHz, you would be wrong.

It appears that each, individual optimizer module (there is one for every solar panel) produces these signals - and being based on individual oscillators, their frequencies will be slightly different from each other meaning that instead of needing to notch just one tone, your DSP would have to notch out dozens emanating from a single PV system - and it just cannot do that!  What's worse, these carriers are also modulated by the low-rate data used to communicate to/from each, individual module which broadens their spectrum as well.

As for the "white" noise, it is unlikely that noise reduction would help much, either:  The source of this appears to be an artifact of the actual voltage converters themselves and as it is random, it is as difficult to reduce in its effects as the normal background noise of the bands.

As each optimizer module contains is own switch-mode power converter to maximize panel efficiency, they, too - like any switch-mode supply - will produce harmonic energy.  It would appear that SolarEdge uses switch-mode controllers that employ "spread spectrum" clocking so that instead of having a myriad of harmonics and birdies all throughout the RF spectrum, that energy is "smeared" all over the place making it somewhat less obtrusive.

The use of spread-spectrum clocking is very widely used these days for the reasons noted above - and for the fact that it also enables the exploitation of a quirk when a device is subjected to testing for regulatory (FCC) compliance:  Aspects of that testing specify the maximum amount of signal energy that may be present in a given bandwidth - but by "spreading" it over a much wider bandwidth, that same amount of energy would be diluted and make the readings obtained during the testing appear lower.  This is perfectly legal and commonly done - but this technique does nothing to reduce the total amount of energy radiated - only filtering can do that!

It is apparent that in this particular case, both the neighboring system and the one across the street contribute a magnitude of interference that would be considered to be "harmful" in that it is perfectly capable of submerging weak-to-moderate signals into locally-generated noise - and if such signals happened to land near a 200 kHz harmonic rather than the elevated noise floor in between the effects are >10dB more destructive.

It is also apparent that the radiated noise extends - at the very least - from the 40 meter to 20 meter bands (7-14 MHz) but the 30 MHz plots imply a significant amount of RF energy above and below this:  The limited time permitted a semi-detailed analysis of only the interference around the 40 and 20 meter bands.

After the meeting:

At the conclusion of these tests, the analyzer readings that took were forwarded to the folks at SolarEdge for their analysis - and it is still too soon to know of any conclusions that would indicate what sort of actions that they might take.  We were, however, heartened to know that they seemed to understand and were sympathetic to the plights of amateurs affected by neighboring systems that might be adversely affect amateur radio operation.

The folks at SolarEdge themselves offered the best hope of resolution:  They noted that they have a special version of PV hardware (e.g. optimizers) that has additional filtering that could be retrofitted into an existing system to reduce the potential for interference.  As this retrofit would be done on their "dime" - and it would be rather expensive - they understandably want to be sure that they have identified only systems that are of their manufacture that are causing interference.

Is a system near you?  You can listen for yourself!

Somewhat ominously, I have since tuned to 14.2 and 14.4 MHz (and at 7.2 MHz) on my mobile HF station while driving around residential and interstate roads in my local area (Salt Lake City, Utah) during my normal commute/business:  I can, in many places, hear the characteristic "roar" of narrow carriers every 200 kHz - likely from SolarEdge PV - systems, and these carriers seem to disappear during the hours of darkness.

I have heard this characteristic signal even in locations that appear to be several city blocks from any structure that might be equipped with a PV system.  They may also be heard on other bands - including 40 meters - but the signals emitted on the higher bands (e.g. 20 meters) seem to be emitted with greater efficiency.

It would seem that these 200 kHz-spaced groups of carriers really get out!

"I have interference from a PV system - what should I do?"

At this point I will not reiterate in detail remediation methods that might be undertaken by a radio amateur affected by this type of PV system:  The June, 2016 QST article (link) discusses attempted mitigation using ferrite devices in detail. (Note:  This article also refers to experiences with a SolarEdge system - but the spectra of the system described there is different from what I found on the systems described here likely due to it being a now-older system.)

 I will only mention in passing that there's the possibility that a degree of mitigation may be possible with the use of "noise cancelling" antennas of the sort offered by Timewave, MFJ and others - but their utility is also somewhat limited owing to practical concerns:   Such techniques work best on distant "point sources" of interference rather than very nearby, spread-out (in terms of subtended agle) radiators in the near field.

If you have interference from a PV system, it is up to YOU to do your due diligence to determine that it is, in fact, a PV system that is causing the issues and NOT other devices in your house or those of your neighbors that is causing the problem.  If you own a PV system - or have one installed on your house - that you suspect is causing a problem, making detailed measurements with it on and off on various frequencies would be a suggested first step.

As this article relates only to the SolarEdge PV system that I investigated, I cannot possibly offer advice to another brand of system that uses other brands of equipment in regards to interference potential - but if you suspect that you or your neighbor(s) have this brand of PV system that is causing interference, I would suggest the following checks during daylight and hours of darkness as appropriate:

• Are there signals every 200 kHz?  Common frequencies where this would be observed include 3.6, 3.8, 4.0, 7.0, 7.2, 14.0, and 14.2 MHz.  This is definitely one of the hallmarks of a SolarEdge system of the same/similar model - but it similar artifacts may be produced by others.
  

• Does the "hiss" that is elevating your noise floor have an obvious "hum" to it when you switch to AM?  You can't easily hear this when you are in SSB mode.  Listen for this on frequencies in the vicinity of 60, 40, 30 and 20 meters on a frequency devoid of other signals.
  

• Does the "hummy hiss" greatly reduce when it gets very cloudy?  The "hummy hiss" - which appears to be a property of the voltage converters - seems to become more intense with increased output from the PV system.
  

• Do the 200 kHz signals and the "hummy hiss" go away after sunset and return only after sunrise?  Not unexpectedly, this is hallmark of many PV systems' noise generation.
• Be aware that some models/brands (although not the one discussed in this article) can produce RF interference if either solar illumination OR mains voltage is present and that it takes the removal of BOTH to silence them (e.g. turning of the mains breaker feeding the system at night.)

If you believe that you are being affected by a PV system, it is up to YOU to be prepared to take all appropriate measures to document the interference, do your own testing, and make repeated observations prior to reporting them to the manufacturer, a regulatory agency, club or national organization.  A few things to consider:

• Treat this as if you were causing interference to someone else.  Just as if a neighbor complained that you were causing problems to their equipment, it is incumbent on YOU to determine if the problem is on your end.  There are likely many, many devices in your house that can cause similar types of interference so be sure that you have ruled those out - and DO NOT forget that you may have devices running on UPSs or battery back-up that may still make noise even if you shut off your power.  (Many UPSs are known to be noisy in their own right!)  In other words, be certain that your house is clean before involving them as this will not only make determining the magnitude/nature of interference from a PV system easier, but it shows good will and competence on your part.
  

• Document the issue over the period of days, weeks or even months.  Many sources of interference come and go - but if it's a PV system, it will be there day in and day out.  Noting over time the consistency of the noise may give you a clue if it's some other type of device - and if it, in fact, related to a PV system: GOOD documentation will only help your case.
  

• Once you have ruled out everything else, go ahead and contact the manufacturer - but be nice!  If you are confident that your own house is in order (e.g. you have ruled out other devices) then contact the manufacturer.
• If you have been following the above steps, you will already have some documentation which makes your specific case more solid.
• The manufacturer may schedule an online meeting to discuss the issue and run tests.  Be sure that you have the ability to use Zoom or Google Groups - or find someone who does.
• If the manufacturer runs tests, they will likely turn on/off suspected systems so YOU should be ready to document changes in noise floor - and of the signals every 200 kHz (in the case of a SolarEdge system of the type investigated here).  If you have already been taking notes/documenting, you should be already familiar with your local signal environment and be able to expedite the running of these tests - and have a basis of comparison as well.
• If the manufacturer decides that they wish to help remedy your situation, remember that they may be doing it at their own expense:  It is incumbent on YOU to be cooperative, competent, courteous, accurate and honest when you are dealing with them and their requests.
• If you feel the need to do so, you may wish to enlist the help of one or more friends to help you with these tasks that may be more experienced - and having a second or even third pair of eyes on the problem is always a good idea.  If you are not comfortable doing so, I would suggest have someone else - familiar with your problem - who can talk "nerd" be your spokesperson when dealing with the manufacturer!
• You should be clear to the manufacturer to define "interference" differently from "harmful interference".  If you can just hear weak birdies that don't really cause any issues, this could be considered just plain, old "interference" and you may not get as much sympathy or action as you like.  "Harmful interference" is that which - when present - obliterates even moderately strong signals that would otherwise be quite usable and thus, they should be taken more seriously.
  

While this article is rather specific to the SolarEdge PV system as described, this is likely be applicable to other manufacturers and models in more general ways.

Good luck!

* * * * *

P.S.  Overall, I was pleased with the knowledge and responsiveness of the SolarEdge folks with respect to interference to amateur radio stations.  After they have had time to digest the information supplied and executed their plan of action I hope to do a follow-up to ascertain the results of their mitigation efforts.

Myself and several other local amateur radio friends have PV (solar) at our own QTHs and experience ZERO interference.  As we had chosen to take an active part in our PV system design, we had installed SunnyBoy series-string systems which are known (and proven!) to have zero interference potential on any LF, MF or HF amateur band as described in the link(s) below.  Unfortunately, some installers will not entertain the use of this type of system if it is not in the suite of products that they offer.

Other local amateurs that I know have microinverter-based PV systems using Enphase IQ modules and have reported minimal or no interference.  As I have not (yet) had the opportunity to carefully analyze the spectral signature of this product, I can only go by their assertion that their own system has not caused them obvious problems.  I hope to do a careful analysis of a modern Enphase system and if so, I'll report the findings on this blog.

Follow-up - post mitigation:

In the late fall of 2024 the folks at SolarEdge - at their expense - swapped out the "standard" optimizers with special versions that are "RF Quiet".  This amateur reported that while the QRM has been reduced, it is still quite obvious:  I have not returned to his QTH to do any comparative measurements.

While it's good that SolarEdge has done work to mitigate the interference, it's unfortunate that the "fix" (swapping out the optimizers and possibly other things) didn't result in extinction of the interference.  The fact that SolarEdge has a "normal" and "RF Quiet" version of this product is also a bit disturbing in it's own right! 

Please post in your comments your experiences with PV systems - but please do so in the context of having fully read this article and at least perused the articles linked below.

  * * * * *

Other articles at this blog on related topics:

• It *IS* possible to have an RF-quiet home PV (solar) electric system - link
  
• The Solar Saga Part 1: Avoiding Interference - (Why I did not choose Microinverters) - link
  
• The Solar Saga Part 2:  Getting the system online - link
• Does the Tesla Powerwall 2 produce Radio Frequency Interference? - link
• Reducing RFI from the Tesla Powerwall 2 - link 
• Tesla Powerwall susceptibility to RF Transmissions - and how to deal with it - link 
  

Other articles related to this topic:

• Solaredge Found in Breach of Swedish Electromagnetic Rules

 

Stolen from ka7oei.blogspot.com

[END]

 

The solar saga - part 1: Avoiding interference (Why I did not choose microinverters!)

Part 2 of this article (August 22, 2016) is online - to read it, click here: "The Solar Saga - Part 2:  Getting the system online". 

Back in November I decided to get some solar (photovoltaic) "grid tie" power generation installed at my house. I decided that the best place to install this was on the roof of my detached garage because:

• The roof area of the garage was comparable to that of the house.
• Much less tree shading than on the house.
• Because it was not an occupied structure with no finished attic space, it was exempt from certain requirements (e.g. walkways around the panel areas, etc.) that would have reduced the available area for the installation of the panels.
• It already had an existing, high-current circuit that was capable of being used for both source and sink of electrical current.

The only thing that I really had to do in the garage was to replace the 70's vintage Zinsco breaker panel with a more modern "load center" as a sub panel:  Doing so was a straightforward job that took only a few hours and cost less than $125 for all of the parts.

Unfortunately there was a significant snag to the "electrical" side of getting it connected to the utility grid via "Net Metering" (it's not "online" yet...) but that will have to wait for a later installment and that is covered in part 2 of this article - see the link at the top of the page.

What kind of solar system?

In residential, grid-tie installations, two types of solar systems are most commonly found:

• Series string.  This is where the panels are tied together and go to one, large power converter.  Many of these inverters have inputs for at least two, separate strings for redundancy, to accommodate different illumination profiles (e.g. "east versus west") and also to (statistically) increase efficiency.
• Microinverter.  In this approach each, individual panel has its own, "private" power converter.

The series string approach is a bit older technology and its popularity is being overtaken by the microinverter approach since the latter is touted with the ability to extract more energy from the entire solar plant since the output from each, individual panel is optimized rather than relying on the "weakest link" from the bank of panels comprising the series string. With modern panels that are intrinsically well-matched, the "weakest link" issue is not as significant as it once was, but that's a topic for a later discussion.

I will say right now that I chose the series string approach for a very practical reason:

Radio Frequency Interference (RFI).

Interference from microinverters:

Let me spin time back to mid 2013 when I saw on an email group a plea from a local amateur (Ham) radio operator for help to analyze a problem that he was having.

He'd had installed a sizable solar plant (approx. 3 dozen panels), each with an Enphase M190 microinverter and suddenly found that he faced a tremendously increased noise floor on both HF and VHF.  By the time that he and I "connected" he had come to some arrangement with the manufacturer and/or installer to install "ferrite beads" (at their expense) on the microinverters' leads in an attempt to mitigate the problem.

He asked me to come over to verify the nature of the interference and its approximate magnitude, prior to the installation of the ferrite devices, and I arranged to do so.

When I arrived, he demonstrated the problem:  When receiving on his HF dipole, which spanned over a portion of his roof and solar panel farm, he experienced 4-6 S-units (20-40dB) of additional noise from the microinverters, depending on frequency.  The noise was that of typical AC mains-coupled switching supplies, being grouped in spectral "bunches" every 10's or hundreds of kHz or so (I don't recall the spacing) on the lower bands (75, 40 meters) and by the time one got to 15 meters it was pretty much just an even "smear" of noise across the spectrum.  By switching to AM, it was apparent that the noise itself had an amplitude-modulated component related to the mains frequency that was not readily apparent when listening on SSB.

The problem was also apparent on 2 meters where low-level spurious signals emanated by these devices were intercepted by his rooftop antenna and would open the squelch and/or mask weaker signals - including those of some of the more distant repeaters.

Analyzing the problem:

For this visit I'd brought along with my FT-817 portable, all-band, all-mode transceiver with a small 2 meter Yagi antenna, a small shielded "H" field loop for localizing signal sources and a specialized 2-meter DF antenna/receiver, to be used with the Yagi, and in switching to 2 meter SSB mode using the rubber duck antenna on the FT-817 I could hear a myriad of low-level carriers as I tuned up and down the band.

Stepping out onto the roof we approached the solar system and I wielded my other gear:  The DF receiver/antenna combination showed the source of the signals - on any random 2 meter frequency - to be that of the solar array. Switching to the combination of the FT-817 and the small, shielded H-loop I was able to localize the conductors from which the energy was being radiated:  Not only did it seem to be coming from the AC power mains cables connecting everything together, but also the frames and the front surfaces of the solar panels themselves, indicating likely egress on both the AC and DC sides of the microinverters.

Part 15 compliance?

At this point one might ask how such a product appeared on the market if it caused interference:  Doesn't FCC Part 15 "protect" against that?

No!

First of all, it is worth re-reading a portion of the text from Part 15 that I'm sure that you have noted somewhere on a device or in a manual that you have laying around.  Quoting from FCC Part 15, section 105 subpart (b):

This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation.

This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications.

However, there is no guarantee that interference will not occur in a particular installation.

(The emphasis is mine.)

The above speaks for itself!

It should be observed that while Part 15 limits the amount of incidental RF energy that can be emitted/radiated/conducted from electronic devices to a certain level, that level is NOT zero!  The fact is that a device may be perfectly legal in its amount of emission, but still be detectable, under the right circumstances, from a significant distance.  In this particular situation, there were at least three things going against our solar system owner:

• He was in very close proximity to the microinverters and solar panels.  As noted previously, his antennas for HF and VHF were either on the roof, or crossed part of it.

• HF operation, by its nature, involves rather weak, narrowband signals.  This makes it even more likely that similar low signals emanated from devices would be noticeable and obvious and that broadband noise could be quite apparent.

AND

• His solar system comprised approximately three dozen panels.  What this means is that each of those microinverters is, by itself, radiating its own, set amount of interference.  If you take the number as 36, this means that as a system, the total amount of energy being radiated by all of those microinverters put together will be increased by nearly 16 dB - that's nearly 3 S-units!  Practically speaking those inverters nearest the antenna(s) will cause the most problem due to proximity, but you can certainly see that many devices in one location are likely to exacerbate the issue overall.

I had no way to accurately measure the emitted signals from the microinverters to determine if they were compliant with part 15 or not, but I'm willing to believe that a widely-sold product such as an Enphase M190 microinverter had been tested and found to be in compliance by reputable people.

Figure 1:
A look inside the newer, Enphase M250, a model newer than the M190's
described as causing interference problems.  At the moment the jury is still
out if the M250 (or M215) is much "cleaner" than the older M190 in terms
of radiated energy.  While some decoupling - possibly filtering - is visible
on the AC mains connection at the bottom, no inline chokes are
apparent from the top-of-board view on the DC (solar panel) side - only
some capacitors that appear to bypass it to ground (e.g. the case.)
This M250 was given to me by an installer after it had failed in the field.
Click on the image for a larger version.

We discussed what it would take to make this microinverters completely quiet and I knew a way:  Completely enclosing each microinverter in a metal box with L/C Pi filters on both the DC input and AC output leads.  Proper L/C filtering of the input and output along with appropriate capacitive bypassing so that not only does RF energy not escape from the unit, but it also offers little/no potential for RF currents generated within to appear differentially between the DC input and AC output leads.

I have discussed similar interference-elimination measures related to switching power supplies in my August 18, 2014 post, "Completely Containing Switching Power Supply RFI" - link.  This method can be completely effective in reducing the interference level of such devices to undetectable levels.

It would have been nice if if there was available a weathertight box into which each microinverter could be mounted, along with a separate set of filtered input and output power connections.  The design of such a device would be slightly complicated by the fact that the Enphase units communicate via their powerline connections, but it was likely that this could be accommodated in the filter design.

I was quite sure that such an after market product did not exist at the time and even if it did, it would be prohibitively expensive, particularly when multiplied several dozen times!

My host asked me if I thought that the installation of ferrites on the input and output leads would help:  I thought that it might help a little bit on VHF and UHF, but that I couldn't see it having any useful effect on HF - but I hoped that I was wrong!

As I left this ham's house I had my FT-817 connected to my vehicle's antenna, listening in SSB mode on 2 meters and I could hear the low-level signals from his solar array from a distance of nearly two blocks, line-of-sight.

Post ferrite installation:

A few weeks later I got an email from this same ham stating that the ferrites had been installed on the microinverters.  To do this, it was necessary to (practically!) un-install and re-install the entire system as very few could be reached from the roof, requiring a lift to access.

Did it help?

Not that he could tell.

Is his situation unique?

Apparently not.

There are many anecdotes of amateur radio operators facing terrible interference issues after they - or their neighbors - install a microinverter-type solar system.  Once such instance is documented in the following thread on Reddit:

Neighbors just got solar - They gifted me with S-9 RFI  - link

Another case was documented several years ago on the "Ham Nation" Web TV show (Episode #65) where the only way to reduce the problem to a tolerable level was to relocate the antenna some distance away from the house-mounted microinverter system, at the far end of the lot.

A link to the webcast of Ham Nation episode #65 may be found here:  Link  (The relevant portion starts at 16:40.)


Since the original posting of this article a write-up appeared in the April, 2016 QST magazine that details another ham's battles with RFI from a solar electric system.  While this system was not microinverter-based, it used devices called "optimizers" that work on similar principles to the microinverters in that high-frequency switching supplies are used to maximize the amount of power available from the array.

Why the ferrites didn't/won't work:


There is a misconception amongst some that loading wires with ferrites will stop the ingress/egress of RF signals.

This does not happen.

By putting a piece of ferrite on a conductor one increases the effective impedance at a given frequency, but that impedance is not infinite, and the effectiveness of the ferrite depends on several things:

• The characteristic impedance (real, complex) of the conductor on which it is placed at specific frequencies (it varies all over the map!) 
• The size of the ferrite (length, diameter, etc.)
• The material type (permeability)
• The frequency
• How many "turns" of the conductor may be passed through the ferrite.

For retrofits, the answer to last one is generally easy:  One turn, as that is all that may be accommodated with a typical "split core" ferrite that is installed simply by placing it over a wire.  As was certainly the case with the Enphase units, the connecting wires were simply too short to allow additional turns of wire even if the ferrite device were sized to allow it.

In general, ferrites have greater efficacy with increasing frequency, but this is not surprising since their mechanism is generally that of adding a bit of inductive reactance to the conductor on which they are placed - but this also explains why "snap on" or split ferrites are part of a futile attempt when one attempts to solve HF-related noise issues:

Simple snap-on/split ferrite devices simply cannot provide enough reactance to attenuate by the needed 10-30dB to solve most severe interference situations at HF!

Figure 2:
The outside of the same Enphase M250 as shown in Figure 1,
above, showing connecting cables:  Not much room
to place large ferrites on these - much less multiple turns!
(The cables on the M190 are of similar length.)
Click on the image for a larger version.

The reason for this is immediately apparent if one studies the specifications of a typical snap-on ferrite such as the Amidon 2x31-4181p2 link.  Here are some typical specifications for this rather large piece of ferrite:

• I.D:  0.514" (13mm);  O.D.:  1.22" (31mm) ;  Length:  1.55" (39mm)
• Material type:  31 (1-300 MHz, typical)
• Reactance of device, typical:  25 ohms at 1 MHz, 100 ohms at 10 MHz, 156 ohms at 25 MHz, 260 ohms as 100 and 250 MHz

As you can see, the impedance is stated as 100 ohms at 10 MHz.  Being generous, let us apply that figure to the 40 meter band where we can see that if this were applied to a line that had a 50 ohms characteristic impedance, we might (theoretically, simplistically) expect to see somewhere in the area of 8-16dB of additional attenuation caused by the loss induced by this device - but that is only 1-3 "S" units, and that represents only a "good case" scenario.  In the case of the aforementioned situation it would have taken several more "S" units to reduce the noise to the point where it was not highly disruptive.

What is more likely to happen is that the interconnecting wires will have wildly varying impedances at different frequencies - some higher, some lower - and the this will have a dramatic effect on the efficacy of this reduction.  In the case of the ham that I had visited I would not have been surprised that if a plot had been taken of the noise versus frequency, its "shape" would have been dramatically altered by the addition of the ferrite devices and, overall, the amount of radiated energy (interference) would have been measurably reduced.  The problem was that the level was so high to begin with that knocking it down by, say, 90% (10dB, or just under 2 S-units) still represented a terrible situation!

The Amidon device noted above is a rather large device and at least three of them would be required for each microinverter (one for each DC lead, one for the AC connection) and the expense of these devices - not to mention the installation (36 microinverters would require 108 ferrite devices!) - could really add up!

It should go without saying that a smaller ferrite - although less expensive - will have even less effect than a larger one!

Comment:

Ferrite devices such as described are often more useful for preventing RF from getting into devices:  Increasing the impedance on the connecting leads and wires may not only improve the efficacy of already-existing RFI protection devices such as bypass capacitors, but they can also break up loops through which high RF currents induced by a local transmitter might be passing "through" a device.  In these case the moderate effect of their added impedance may well be enough to adequately mitigate RF ingress issues.

Remember:  With RF ingress it is often the case that knocking down the RF energy by 6-12 dB will be enough to mitigate the issue.  Conversely,the amount of "hash" emitted by the microinverters would likely need to be reduced by more than 20 dB to make it undetectable.

"Grounding" won't help either:

Reading some of the correspondence in the Reddit posting (above) there is mention of "grounding" to eliminate/reduce RFI from these units:  To assume that "grounding" would likely solve or mitigate this problem would be to assume incorrectly!

The problem, again, is that RF energy appears to be conducted from the input and output (DC and AC, respectively) coupling wires which, themselves, can act as antennae:  "Grounding" the case - which would also "ground" the safety ground on the AC output - is not really going to help.

If the unit is installed according to code, there should already be a "ground" attached at the panels, anyway - but this wire connection, which is likely to be 10's of feet (several meters) between the roof and the Earth or grounding point is going to look like a "ground" only at DC and low frequencies - such as those found on the AC mains!

Any wire that is several feet long - grounded or not - is going to act as an antenna.

What this means is that it is entirely possible that at least some of the RF interference being radiated by the inverter is going to be conducted along the grounded metal structures (such as the solar panels and the frames) and wires in addition to the AC mains wiring.

Again, the proper way to contain such RF energy within the confines of the circuitry was discussed above:  Proper L/C filtering of the input and output along with appropriate capacitive bypassing so that not only does RF energy not escape from the unit, but it also offers little/no potential for RF currents generated within to appear differentially between the DC input and AC output leads.

The upshot:

If you are getting interference from a microinverter system - either your own, or your neighbors, is there anything you can do?

Since the installation of ferrites will have minimal effect on HF, the answer would seem to be "No, not really", aside from converting to a series-string system, or installing a series-string system, instead.

In the case of the ham operator that I visited, he mitigated the situation somewhat by moving his HF antenna as far away from his house as he could (which wasn't very far considering that he had limited space on his city lot) which helped slightly.  Nighttime was the only time during which he could completely quell the interference by turning off the breaker feeding the solar array, but during the day there was nothing he could do:  If either solar illumination or AC mains power was available to the microinverters they seemingly caused the same amount of interference, whether they were under load or not!

Are newer microinverters better/quieter?

It has been reported that the Enphase M190 microinverter has been obsoleted and has been replaced with newer models that are more reliable and more "RF Quiet".  On this second point, the jury seems to be out:  Anecdotally, there seem to be about as many reports of the newer models (from various manufacturers) causing interference as not, so the reports are rather confused.

I know at least two amateur operators with newer-model Enphase inverters (M215, M250) but they report other extenuating circumstances (e.g. their microinverter PV system is located some distance from their antennas and/or they already had notable interference from other sources before installing the solar power system) that they cannot say for certain whether or not there is a problem caused by their system.  At some point I hope to personally visit at least one of those installations in the coming months.


Series String inverters and interference:

While less efficient overall and somewhat less expensive up front, I decided to use a series-string inverter system.  From direct observation and reports by people that I know and trust I knew that units made by Sunnyboy and Fronius could be reasonably expected to cause little or no interference on their own.  Additionally, were an interference issue to arise, having a single point at which to filter (e.g. one large box with a relatively small number of input and output leads) I was quite confident that it would be possible to add additional filtering if necessary.

To be sure, one might (theoretically) lose up to 10-20% or so peak efficiency with a series-string system as opposed to a Microinverter that optimizes for each, individual panel, but considering the comparatively low cost of panels these days and the lower "up front" cost for a series-string inverter system, one can usually afford to "up size" the system slightly to compensate.

(Comment:  As noted previously, series string "optimizers" have been observed to cause significant RFI since their basic principle of operation would lend to them tendencies to produce unwanted "hash" unless well-designed.)

Maintaining the various systems:

Anecdotally, from both owners and maintainers of microinverter-based systems, it is not uncommon to experience the failure of several of the microinverters after a only few years, the rate-of-failure (apparently) following somewhat of a "bathtub" curve:  Several die early on, there is often a period of relative stability, and then they start to fail in greater numbers after several more years.

While these devices (microinverters) seem to have a good warranty, the issue comes about replacing the microinverter that is in the "middle of everything" on the roof.  On a roof with a moderate-to-steep pitch it may be necessary to use equipment such as a lift to be able to safely access the failed inverter - and it may be necessary to "de-install" several of the surrounding panels to gain access.  In other words, it will likely be many times the cost of the microinverter itself ($125-$300) in equipment rental, time and labor just to replace it.  For this reason it seems that many people simply allow several of them to fail before "calling out the troops":   Having several panels (effectively) offline at a time is something that detracts from the proclaimed efficiency benefit of the Microinverter scheme!

The large, series-string inverters appear to be extremely reliable, having excellent track records (at least for Fronius and Sunnyboy - the two brands with which I have any familiarity).  The obvious down side is if there were a failure with the converter, it would likely take a large portion - or all - of the production off line, but the replacement of the device is comparatively easy and would likely not be more than a couple times the total cost (parts plus equipment rental plus labor) of replacing a small handful of microinverters!

What about failures of solar panels?  Modern panels contain diodes that "wire around" sections that have failed or shaded, so unless a catastrophic failure occurs that completely removes it from the circuit, one will lose, at most, the capacity of the entire panel:  This is true with both microinverter and series-string configurations.

Fortunately solar panels have been around for decades and have been proven to be quite reliable and rugged in terms of durability.  If a failure in a solar electric system is going to occur, the solar panel itself is less likely to be the problem unless the problem is actual, physical damage which again, is a common point in both series-string and microinverter-based systems.

(Note:  There may be warranty coverages or service plans that mitigate the costs related to such maintenance, but since they vary wildly with installers and manufacturers, they are not covered here.)

A note about "Optimizers":

It is common in series string - with a single, main inverter - to use an "optimizer" on each solar panel - particularly if the series string consists of solar panels at various angles covering a complex roof where the availability of just two MPPT inputs per main inverter is not sufficient to serve many "sub-strings" of panels mounted at those different orientations.

It has been observed (See the April 2016 QST article, "Can Home Solar Power and Ham Radio Coexist" pp. 33-37) that many models of optimizers - notably certain models made by "SolarEdge" - produce noise in a manner similar to that of microinverters.  This is not too surprising considering that an optimizer and microinverter are quite similar in many ways - notably the fact that both use high-frequency switching converters for voltage and current transformation.

In the aforementioned QST article it was noted that while the RF noise generated by the optimizers in the solar installation could be reduced significantly with proper wiring configuration and the implementation of hundreds (or maybe more) of dollars of ferrite, it could not be completely quashed:  The author of the article reported that he would simply shut down the system if the noise floor was too high to work the "weak ones".

In short:  As of the time of this writing, both Microinverters and Optimizers share the same issues when it comes to being "RF Noisy".

Final comments:

Each system has its advantages and trade-offs:  In my case a primary concern was the avoidance of interference.  Since the advent of digital TV - and because fewer people listen to the radio or even have off-air TV these days - they likely wouldn't notice (or would care!) about interference issues that appear to be common with the microinverter (and "optimizer") approach.

One can always hope that newer microinverters will become increasingly quiet, but for now that seems not the case - if not in reality, certainly in perception.

Semi-Update:

While the Enphase M190 was known to be a strong emitter of spurious RF signals across the RF spectrum (from at least 3.5 MHz through 450 MHz) it would seem that the later Enphase M215, M250 and IQ series are much quieter - at least to the point that some amateurs that have them have found their situation to be acceptable in terms of generated noise.

What is not known at the time of this update (March, 2017) is if they are "RF quiet" to the point of practical undetectability (as in the case of my SunnyBoy series string inverter) or if they are just "much quieter" than their predecessors.

What seems to be clear is that Enphase has made gains toward the reduction of interference potential of their products - definitely a move in the right direction!

(I have no new information on other manufacturers' microinverters or optimizers at this time.)

* * *

In the next installment I talked a bit more about the installation of my system - trials and tribulations...  Part 2 of this article (August 22, 2016) is online - to read it, click here: "The Solar Saga - Part 2:  Getting the system online". 



Update - May, 2024:

It has been about eight years since the above system was installed and I have had ZERO maintenance issues during the entire time other than occasionally trimming back tree branches that block/hang over panels.

I have since had a Tesla Powerwall 2 installed as well as increased the solar production to 10 kW - again using a SunnyBoy series string inverter, still with no interference from my own solar and only very slight interference from the Powerwall 2 when it was running on some of the lower bands:  If you want more details on this and other solar-related topics at this blog, peruse the links below.

* * * * *

Other articles at this blog on related topics:

• It *IS* possible to have an RF-quiet home PV (solar) electric system - link
  
• The Solar Saga Part 2:  Getting the system online - link
• Does the Tesla Powerwall 2 produce Radio Frequency Interference? - link
• Reducing RFI from the Tesla Powerwall 2 - link 
• Tesla Powerwall susceptibility to RF Transmissions - and how to deal with it - link 

[End]

This page stolen from "ka7oei.blogspot.com".