Growatt 5000es AC voltage detected on PV input!

[omarfar]

Hi. I have two growatt 5000es hybrid inverters connected in parallel. All connections are correct as per instructions:
For each inverter:
AC input: 230v L and N and ground
Ac output: 230 v L and N and ground
So ground of input and output are connected to same ground wire.
PV input: 300V array to each inverter connected to PV+ and PV -

Everything is running as it should (no problems with parallel operation of the two inverters (they share the load...etc..)

However, I was working on the DC breaker between PV and the inverter and I got an electric shock! It was at night so no PV voltage. I tested the PV input of the inverter and both PV + and PV - (of both inverters) have 230 volts AC on them! (Test screw driver lights up and also by multimeter I measured 23O volts AC between PV + and ground and between PV - and ground. So both PV + and PV - have the same 230V AC on them. I am sure this voltage is coming from the inverters and not the PV panels because the DC breakers are off (and no voltage measured at PV side. Only at inverter side.).

This seems very serious. Is this normal?? If so, isn't this bad for the PV panels? (Feeding AC into the panels) Also it seems like a major safely concern.
If only one inverter was behaving like this I would suspect a malfunction but since both are doing it, I am wondering if this is normal.
Please let me know if this is normal.
Thank you very much.

 

[omarfar]

A quick follow up to my previous post. After posting my question, I contacted a few people who do repairs on inverters (including growatt inverters). And they all said it is normal to measure an AC voltage at the PV input of the inverter even if there is no PV connected...
I don't understand this... why would there be a voltage (230 V AC in my case) at the PV in terminals?!!
I still would really appreciate any input on this issue... your experiences. Your interpretation of why this is happening.
Thank you.

 

[octal_ip]

I'm not so sure this is normal. I've just checked the PV input to my Growatt SPF while solar was isolated, and there was no substantial AC voltage present. As a sanity check I placed a 12v light bulb across the PV inputs, and it didn't light up. This was while the inverter was operating, connected to mains power and providing power to a load from batteries.

Are you sure you don't have some other issue like a ground/earth fault?
If you have a clamp meter, it'd be interesting to see if you can measure any current (DC or AC) back-feeding into the solar panels at night.

 

[omarfar]

I'm not so sure this is normal. I've just checked the PV input to my Growatt SPF while solar was isolated, and there was no substantial AC voltage present. As a sanity check I placed a 12v light bulb across the PV inputs, and it didn't light up. This was while the inverter was operating, connected to mains power and providing power to a load from batteries.

Are you sure you don't have some other issue like a ground/earth fault?
If you have a clamp meter, it'd be interesting to see if you can measure any current (DC or AC) back-feeding into the solar panels at night.

Hi. I already checked and there is no AC or DC current back feeding into the panels at night. Also, I just wanted to clarify something in case it wasn't clear in my original post. Both the PV+ and PV - inputs of the inverter give a reading of 230V AC compared to ground. They are both at the same potential. So if you measure the voltage between PV + and PV - it is zero Volts. I even tried putting a jumper between the PV input (for example PV+) and ground to see if any current flows and I got an initial spark and my clamp meter read 8 amps AC flowing from PV+ input to ground!!!
I also asked a few people I know who install PV systems and they all immediately replied saying what I am experiencing is totally normal.. that it is a known fact that one can get an electric shock if he/she touches the PV inputs of the inverter even if PV is isolated.
I still find this weird. And I would appreciate as much input from others. Thank you.

A quick note: the country I live in has 230V AC (L is at 230 V and N is zero V like ground)

 

[octal_ip]

Hi. I already checked and there is no AC or DC current back feeding into the panels at night. Also, I just wanted to clarify something in case it wasn't clear in my original post. Both the PV+ and PV - inputs of the inverter give a reading of 230V AC compared to ground. They are both at the same potential. So if you measure the voltage between PV + and PV - it is zero Volts. I even tried putting a jumper between the PV input (for example PV+) and ground to see if any current flows and I got an initial spark and my clamp meter read 8 amps AC flowing from PV+ input to ground!!!
I also asked a few people I know who install PV systems and they all immediately replied saying what I am experiencing is totally normal.. that it is a known fact that one can get an electric shock if he/she touches the PV inputs of the inverter even if PV is isolated.
I still find this weird. And I would appreciate as much input from others. Thank you.

A quick note: the country I live in has 230V AC (L is at 230 V and N is zero V like ground)

Ah yes, I misunderstood you, thanks for clarifying. I've checked again and can confirm it's the same for my setup.
Thanks for posting this, it's not at all something I would have expected. Scary stuff.

 

[chupamyth]

That is interesting. I didnt know that. Do you have and RCD upstream the inverter AC input? I was wondering if that will trip. scary indeed

 

[Bud Martin]

There EMI safety capacitor coupling between the PV input circuit and the AC side.
You can make a test setup (Resistor- Capacitor) to perform the leakage between PV input and Ground to find out how much the AC leakage current is.

 

[Quattrohead]

Not normal and scary that anyone thinks it is.
I just checked this on an SP6548 and there is no voltage on the PV or battery connections when they are not in use.

 

[Quattrohead]

There EMI safety capacitor coupling between the PV input circuit and the AC side.

Between PV and ground not anything AC surely ???

 

[omarfar]

Hi, everyone. Thank you for reactivating the discussion on this topic. After posting my original question, I also posted it on a different forum. I got a very detailed answer from someone who seemed to know what he is talking about. I will copy his reply here so everyone can benefit from it:

**********************
Yes. It's a "feature" of all transformerless inverters with high PV voltage. It's because the Solar Charge Controller is a boost converter that feeds the DC bus, so it's referenced to the DC bus negative end. Neutral (which is or should be at earth potential) is connected to either the negative or positive end of the DC bus, depending on whether the generated AC waveform is positive or negative respectively.

So PV- typically has a square wave at 50 Hz at near zero and about -380 V. When PV is connected, the PV+ will obviously be hundreds of volts positive with respect to that. So with PV at 190 V, PV+ would be roughly symmetrical (± 190 V) with respect to earth. When the PV voltage is higher than the bus voltage would otherwise be, it pushes the bus voltage even higher, making the square wave at PV- have even higher amplitude.

This square wave is slightly filtered, but still this can cause significant Radio Frequency Interference from the PV wiring. Also, any leakage to earth due to rain and/or dust can cause problems, sometimes pushing up the bus voltage and even causing faults codes to be thrown.

The 145 V max PV models use a buck converter connected directly to the battery. The battery is isolated from the AC input and output, so these models don't have this problem.

 

[dusan]

Hi Omarfar!

I have the same scenario as you, so how did you solve this in the end? When i was installing over voltage surge protector on the pv side i got a nice shock too.

br

 

[octal_ip]

Hi Omarfar!

I have the same scenario as you, so how did you solve this in the end? When i was installing over voltage surge protector on the pv side i got a nice shock too.

br

As this behaviour is "by design", there is no solution. Its just emphasises the need for normal safety measures, including but not limited to: properly earthing all your panels and mounting equipment, double-insulating everythig else, and never working on an energised system. This would apply to any high voltage system, regardless of the inverter type.