Quite a racket!
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| Figure 1: The spectrum of a SolarEdge PV system from several meters away across the 6-8 MHz range showing spurs at 200 kHz and other places. Click on the image for a larger version. |
In driving around with an HF mobile station in my vehicle, I can hear these 200 kHz carriers 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.
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 - a site with which I am very familiar. 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 by a mountain. Additionally, the antenna used for the reception in Figures 2 and 3 below was the TCI-530 omnidirectional log-periodic (with circular polarization) - an antenna that 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" 2 as shown in the screen capture below:
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| Figure 2: 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 "hump" in the highlighted analyzer plot in the top portion of the image - and the "band" of noise between 14.199 and 14.200 MHz are the sum of the propagated low-level 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 in a semi-Gaussian distribution.
It's worth noting that the fact that these signals do not land on exactly the same frequency 3 - 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 a single coherent CW signal, the DSP filtering on modern radios will do little/nothing to reduce their effects if they were to cause interference.
A quick 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 2 would have easily been 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 around 14.000 and 14.400 the same, exact types of signals were present on those frequencies - and similar bunches of energy were noted as low as 10.200 and around 18.200 MHz as well - this range being related to current ionospheric propagation at the moment that I checked (e.g. around 1845 on September 10 UTC, 2025). 4
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!
- On days with poor propagation overall, these signals were absent - or limited to frequencies commensurate to 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 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:
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| Figure 3: 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 (linked above) the SolarEdge optimizers produce another signal 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 2 and 3 were produced.
Conclusion:
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!
Do these signals actually cause QRM 5 ? 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 - albeit from a significant distance.away.
Figure 2 also shows that the emissions do propagate - likely over long distances: The 20 meter band's optimal "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.
If you live in a quiet location and have a receiver with a waterfall display you might want to check the various amateur bands just below the 200 kHz multiples 6 during daylight hours: If there is a SolarEdge PV system within a couple city blocks of you, you will most likely hear it!
Footnotes:
- 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.
- The frequencies mentioned have been checked when ionospheric propagation is poor (comparatively few strong signals) and the characteristic SolarEdge carriers were absent. 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.
- 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 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 is such that it has a Gaussian-like distribution above and below the mean frequency.
- I also checked several remote receive systems around the world and could see the same "humps" of energy at frequencies just below the aforementioned 200 kHz intervals. One such system was that located at the University of Twente in the Netherlands: It is not know 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".
- "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.
- The frequencies on which the 200 kHz spurious signals from a SolarEdge PV system will likely land within an HF amateur band are: 3.6, 3.8, 4.0, 7.2, 14.2, 21.2, 21.4, 28.2, 28.4, 28.6, 28.8, 29.0, 29.2, 29.4 and 29.6 - and remember that the cluster of carriers will be just below these frequencies and if present, will be clearly audible if you tune to any of the above frequencies (particularly 40, 20 and 15 meters where they seem to radiate most easily) using LSB (Lower Sideband). Of course, you will only hear these signals during daylight hours when the PV systems are active!
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This page stolen from ka7oei.blogspot.com
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