High frequency oscillation noise

Long story short:

A few weeks ago on a rare sunny evening I had some guests over. One of them was a 21 year old. Immediately we went out into the garden he asked what the loud high pitched sound was. I am much older and couldn't hear it.

A few days later, my next door neighbour mentioned that he could hear a (similar) noise too; and said that he heard it most evenings. Our first thought was of a rodent deterrent. We have asked all the near neighbours - and there are none around.

It was then suggested that the problem was my solar installation - which was installed a year ago. I said I thought this was highly unlikely. The installation is standard:- two sets of panels (east and south) with optimisers , battery and a Givenery invertor (5 G3).

My profession was in the audio industry, so I have some knowledge of audio below 24 kHz. I installed a real time spectrum analyser on my phone - not expecting much; but it seems to do the job well enough.

I then asked the neighbour to let me know when he heard the noise again. When he did, outside of my house, I could definitely see the noise on the analyser measuring a meaningful peak at just below 10 kHz. If the typical noise floor in the audio spectrum was about -110 dB , then the whistle could measure anything up to 30 dB above that. The signal being loudest on the solar panel side of the house.

I have been taking sporadic readings throughout the day for some weeks now. I have never seen the problem during the day, and not every evening either. But there is a definite pattern of increased activity at around 19:30 ish - if it appears at all. My early bird neighbour says that he has heard the noise at 05.00 in the morning.

The inverter is inside of my house (not outside, or in a garage). Using the analyser right next to the housing, the most obvious noise is a pretty constant peak of frequency at about 19kHz at all times. Normally this is about 10 to 20 dB above the noise floor, but I have seen it get up to 40 dB above the noise floor. When the lower frequency noise is present outside, I can see it at the housing too.

When measuring outside the this audible whistle is (as I said) just under 10 kHz, but the frequency can vary slightly. It rarely lasts for more than 90 secs or so, and then after a random interval it will reappear again. When I turn the isolator to the inverter off, the high 19 kHz signal remains, but the lower frequency one disappears. Occasionally I can see other harmonics - especially when turning the isolator back on - as it settles down. Even down to 6 kHz - which I can hear!

A friend who is a professional electronics engineer has told me that if is theoretically possible for such audible frequencies to be "transmitted" from the inverter through the cabling going up to the panels.

So I have some questions:-

1) Has anyone come across this problem before? (My internet search doesn't show much up. And most posts about noise from invertors talk about fan noise and other unrelated noises.)

2) The $10,000 question:- why is this an late evening (and maybe early morning) problem? If there's a general problem of somehow low generation causing the effect, why doesn't it seem to happen during the day when it's cloudy?

3) If indeed the noise is coming from my 'system', why has it started to do this now? It's possible that it's always been there of course, but I am doubtful. Caused by a system update??

Thanks to anyone who can shed any further light onto this problem and/or suggest a solution. My friend has suggested installing a filter/suppressor made by Schurter at the inverter.

Odd one. I think there's been maybe 1 person on here before regarding noise from an inverter, and that was specifically relating to the inverter and not audible outdoors. Sounded more like coil wine from an inductor.
Only thing I can suggest is (the rather difficult) collect up people who can hear it, find a time when it's doing it, and then switch everything off.
If it immediately stops, then:
1 by 1 restart it, giving it 5 mins between each step,
so AC power first with PV & Battery isolator off.
Then turn on the PV on.
Then the battery.

At which point does it come back. This may help track down the source - is it say a battery board when the battery is charging off PV at low power, or when the battery is providing power, or some other time purely based on what the MPPT tracker is doing.

I can't say I've heard more than a faint high pitch fuzz/white noise from mine if I pretty much have my ear on it. Nor have I ever heard anyone else's PV make a noise while simply walking around places. So it is an odd one. (Although I've spent nearly 2 decades working around turbines so probably not the best source of that)

I did this image to explain something else to someone but the fact you can hear it outside suggests it to be atleast on the DC side, so the battery and PV stuff is joined together it could be either party - although equally the filtering may be poor so it could be some sort of harmonics not being filters from AC side... I've never taken a gen3 apart.

Could it be something to do with batteries being fully charged at the time of the noise and the panels still generating but nowhere for the energy to go? My friend has a small yacht and uses a small turbine to charge his comms equipment battery. When the batteries are full and the wind is blowing, he says the turbine gets into "tizz"

Thanks for your replies. I am sorry not to have answered before, but I am getting measurements that don't form any reliable pattern to report.

I wonder if someone can do me a favour? If you have an android phone can you download the spectrum analyser "Spectroid". It's free and has no adverts. Change the display from log to linear.
If I put my phone within inches of the inverter I can see pretty constant peaks at 19 kHz and 16 kHz. (The noise floor above about 7.5 kHz upwards on my phone is about -120dB. The peaks are 20 dB or more above this.)

A friend who has the same inverter says he can't see these peaks. But maybe he has a noisier audio circuitry on his phone.

When switching the AC isolator off and on, the inverter puts out harmonics below 15 kHz once it's fully 'engaged' again - and they take a while to settle down and disappear.

Thanks.

Not sure what I'm looking at but if it helps you.
Taken 6 inches away from a Gen3 5Kw hybrid inverter.
I can't hear anything but I am over 60, however it looks noisy!

Thanks very much Robgy

That's very similar to what I see at times. (And just to reassure others, this pattern is only measurable within a couple of meters from the cabinet.)

What really bugs me is that the noise, when it's audible outside, is usually at precisely that first peak at around 9 kHz. Is that a coincidence or not?!

I am now pretty sure that the outside noise only occurs when the output from the panels is very low:- below 100 W.

Given that there are five chopper circuits in the hybrid inverters (4 DC-DC and one DC/AC -DC/AC) it's quite possible that, on occasion, there will be heterodyning between them in the noise the inverter makes.

I don't think it's worth a picture, but I can confirm that my inverter emits those frequencies WHEN THE BATTERY IS DISCHARGING. This is probably why you are only hearing it from the panels in the evening. You can test this in two ways. During the day turn a a big load in you house (like an electric heater or oven) so that the generation is exceeded and the battery discharges. Does that cause the sound to occur? Secondly, when the sound is detected in the evening try switching off eco mode and see if the sound stops.

The signal is only generated when the battery is discharging and will only be transmitted to the panels when current is flowing through them. This seems to fit your description of the symptoms.

The more interesting question is why do your solar panels (or their wiring) emit sound? The wiring is copper and the frames are aluminium specifically to avoid this. Are the panels roof mounted? Is the roof standard tiles on wooden rafters? Is there any metal in the roof construction? Are the panels mounted on properly certified rails (such as Renusol) designed for the purpose? Have the correct panel fixings been used? Do you have a giant magnet in your loft? 🙂

Do you have a giant magnet in your loft? 🙂