Hi,

I have a Sunsynk inverter and battery. I have 8 x 550w panels in 2 strings. The inverter is setup NOT to feed back to the grid, but to feed back to the CT Coil which is placed on the incoming live feed from the grid before the mains breaker. In other words, the inverter is limited to home. My trickle feed is set to 35W.

We have a prepaid meter which sits in the kiosk and a remote battery operated terminal in the house.

I have this recurring problem, at roughly the same time every day that the grid is cut off for short periods of time. Like 1 minute, then back on again. I have determined that this feed is being cut BEFORE coming into the house - ie at the meter. I have called the Municipality out, as I was suspecting a faulty meter.

They tell me I am feeding back to the grid. this from the error codes on the meter. But this is not the way the inverter is programmed, and this only happens between 9 and 10 am almost every day. At this time the battery is usually charging nicely. Out side these times, there is no interruption.

Any ideas?

TIA>

Hi,

We have just had pre-paid installed here at home on a rooftop system as per my signature below. Not sure if your question above can be solved by my response below.

Many months ago, when the municipality started doing this in our area, those with solar were experiencing issues with their control units for the pre-paid meters. They were simply not working when they plugged them in to a wall socket anywhere in the house.

The advise then was that a single plug point should be installed at your DB connected directly to the incoming power feed from the municipality. We installed such a plug at our DB, and when the municplaity installed pre-paid, we had no issues with the control unit communicating with the pre-paid meter outside.

Hoping that this may solve your problem.

MdF

1 minute ago, MdF said:

The advise then was that a single plug point should be installed at your DB connected directly to the incoming power feed from the municipality. We installed such a plug at our DB, and when the municplaity installed pre-paid, we had no issues with the control unit communicating with the pre-paid meter outside.

This is quite common with pre-paid meters and any sort of inverter. I recall assisting a neighbour who had the interface unit plugged into a adapter strip which, in turn, was plugged into a trolley inverter. You need to have that direct connection between the interface unit and the actual meter. And I implemented the same solution as you.

39 minutes ago, 10tpeg said:

They tell me I am feeding back to the grid. this from the error codes on the meter. But this is not the way the inverter is programmed, and this only happens between 9 and 10 am almost every day.

That's pretty regular. What's your inverter doing at that time, and is there anything programmed on your inverter for that time of day?

I can't be exact here because I don't have the same brand of inverter. You should be able to see some sort of graph showing PV coming in, loads, draws from the grid and also exports to the grid etc.

Edited October 24, 2025Oct 24 by Bobster.
punctuation

6 minutes ago, MdF said:

Hi,

We have just had pre-paid installed here at home on a rooftop system as per my signature below. Not sure if your question above can be solved by my response below.

Many months ago, when the municipality started doing this in our area, those with solar were experiencing issues with their control units for the pre-paid meters. They were simply not working when they plugged them in to a wall socket anywhere in the house.

The advise then was that a single plug point should be installed at your DB connected directly to the incoming power feed from the municipality. We installed such a plug at our DB, and when the municplaity installed pre-paid, we had no issues with the control unit communicating with the pre-paid meter outside.

Hoping that this may solve your problem.

MdF

Thanks MDF. I am aware of this issue when I helped out a neighbour with the same issue. My meter remote is completely wireless - only battery powered and cannot plug into a wall. So this would not be the issue here.

4 minutes ago, Bobster. said:

This is quite common with pre-paid meters and any sort of inverter. I recall assisting a neighbour who had the interface unit plugged into a adapter strip which, in turn, was plugged into a trolley inverter. You need to have that direct connection between the interface unit and the actual meter. And I implemented the same solution as you.

Thanks Bobster, as explained above Im aware of that issue, and that's not it. My meter remote is completely wireless, and remains connected throughout the "outage" and shows units available AND no errors, which the municipality asked to see. The actual meter is in the kiosk outside on the road.

As regards loads, graphs etc. I use Solar Assistant, and cannot find anything unusual. The only thing I can say is that it seems to happen when the sun is strong, and the battery is charging. I have tried turning on a big load and off again to see if this triggers it, but no.

@10tpeg ,

My view/theory is what you are describing is normal inverter behaviour. Refer to my usage pattern below, when adding a big load to your system.

Just before 8, I switched the kettle on. The inverter supplies the load, but despite having some powerful processor, the Solar production is not instantaneous. It takes a few seconds to ramp up solar production, thus it takes the shortfall from grid, but just for a few seconds (couple of seconds - my monitoring system has a 4 seconds update frequency). At 8, I add more load (warming milk in the Microwave). When the kettle load drops (@8h02), the solar panels don't stop producing energy, but because the load had dropped, the energy has to go somewhere. That somewhere is again the grid. The graph clearly indicates this behaviour. For the life of me I can't think why inverters can't pull/push this energy from/to the battery. Above my pay grade!

Not to long ago, when solar started getting popular, prepaid meters could not handle these "feedbacks", and tripped, and you had to get the Municipality to come and reset the meter. You seem to be very lucky that your particular pre-paid meter does "self reset". Nevertheless, still a bit of a nuisance. You could attempt to get your Municipality to replace your meter with a more tolerant one.

Maybe also try and check your system if my theory is 100% correct, as I suspect that this will only occur when you drop a big load, like a kettle or geyser. Maybe play around with the timing of that, so see if my theory holds.

The Landis Gyr + models of pre-paid meters seem to be very tolerable to feedback.

@Sidewinder , Thanks for the detailed reply, and the sensitivity of the meter lines up with my thinking. I will try convince them to swop out for a Landis Gyr meter.

2 hours ago, 10tpeg said:

@Sidewinder , Thanks for the detailed reply, and the sensitivity of the meter lines up with my thinking. I will try convince them to swop out for a Landis Gyr meter.

Just make sure by placing your settings here. You have to have 2 settings correct not just the do not export to grid. The solar selling setting must also be disabled. This could be the problem. I would start by checking on the inverter itself if any power is exported and not just via SA. One way of also checking is look on the inverter screen the moment you switch of a high load. But not only high loads can export when it should not. Variable speed drives like used on top loader washings machine also go past the CT but very low quanties that even over a month it does not add up to much although one can see in real time if there is any power exported due to a negative reading on the inverter screen.

I can confirm that the latest Conlog used as prepaid does not trip the power even at a 1000W. However if exporting this 1000W export is measured as consumed by you.

5 hours ago, Sidewinder said:

My view/theory is what you are describing is normal inverter behaviour. Refer to my usage pattern below, when adding a big load to your system.

Just before 8, I switched the kettle on. The inverter supplies the load, but despite having some powerful processor, the Solar production is not instantaneous. It takes a few seconds to ramp up solar production, thus it takes the shortfall from grid, but just for a few seconds (couple of seconds - my monitoring system has a 4 seconds update frequency). At 8, I add more load (warming milk in the Microwave).

You may be onto something.

I see the PV taking time to ramp up. I have a Goodwe. So it may be a fact of solar life that PV takes a second or two to ramp up in the face of sudden demand. My system doesn't always draw from grid though, sometimes from grid, sometimes from battery, some times a bit of both. I'd rather it used battery but I can't control what it does.

I see this especially when the iron is in use. That sucker can draw 2kW, and the thermostat is turning it on and off all the time.

5 hours ago, Sidewinder said:

When the kettle load drops (@8h02), the solar panels don't stop producing energy, but because the load had dropped, the energy has to go somewhere. That somewhere is again the grid. The graph clearly indicates this behaviour. For the life of me I can't think why inverters can't pull/push this energy from/to the battery. Above my pay grade!

The inverter has to juggle PV, battery & grid. As you note, some of these react more quickly than others. Grid, of course, is always there. I don't see too much of this going on at night, because it's always drawing from the battery. But if it's charging and then load goes up, maybe it takes time to "turn around"?

But there's things I can't understand. At 6:00 my heat pump turns on. There is no useful PV and the system starts drawing from the battery. But then about 20 to 30 minutes later it takes a quick slurp from grid without the load seeming to change a lot. A couple of minutes later it's using battery again.

So IDK.

But @10tpeg you may still get a clue from looking at the graph, especially if you have lots of samples per minute instead of (like me), several minutes per sample.

I serendipitously caught this this morning

That's my inverter pushing a small amount back to the grid, despite the "no export" setting.

But the meter didn't trip. The current meter was installed about 18 months ago. It is from African Meter Systems (this is what COJ are installing at present). The previous meter was an iTron, and the interface unit, but not the meter itself, was constantly tripping during the day whilst PV was being generated. So not all brands trip, and anybody who thinks their meter is tripping should check if it's the actual meter or just the interface unit (@10tpeg has already confirmed that it is the actual meter). The AMS meter is completely unbothered by feeding back of AC (I suspect that it reduces the credit any time current flows through it) but it won't load a token unless it is plugged into a socket that is not connected to the inverter. (I had one such socket installed inside)

Edited October 26, 2025Oct 26 by Bobster.
Extra detail

On 2025/10/24 at 10:22 AM, 10tpeg said:

Hi,

I have a Sunsynk inverter and battery. I have 8 x 550w panels in 2 strings. The inverter is setup NOT to feed back to the grid, but to feed back to the CT Coil which is placed on the incoming live feed from the grid before the mains breaker. In other words, the inverter is limited to home. My trickle feed is set to 35W.

We have a prepaid meter which sits in the kiosk and a remote battery operated terminal in the house.

I have this recurring problem, at roughly the same time every day that the grid is cut off for short periods of time. Like 1 minute, then back on again. I have determined that this feed is being cut BEFORE coming into the house - ie at the meter. I have called the Municipality out, as I was suspecting a faulty meter.

They tell me I am feeding back to the grid. this from the error codes on the meter. But this is not the way the inverter is programmed, and this only happens between 9 and 10 am almost every day. At this time the battery is usually charging nicely. Out side these times, there is no interruption.

Any ideas?

TIA>

When a large household load is suddenly switched off, PV string current still exists for a short time. The inverter/MPPT must either reduce PV operating voltage/current (MPPT retune), or instantly put the excess power into the battery or a local dump/load. If the MPPT loop or inverter control takes longer than the mechanical/electrical transient, a short reverse current pulse can appear at the CT/meter. Prepaid meters and their protection logic can be very sensitive to short reverse-flow spikes and will log an export / trip even if it’s only for a few seconds. The timing (same time each day) can be explained by a repeatable event (e.g., a scheduled load switching, or battery state/household behaviour at that hour) that coincides with high PV production. Normally the pre-paid meter agent(installer) can change setting on the plc(master switch) in the kiosk to accept some backfeed without going into protection mode.

Ensure you have System Mode 2 set as per attached screenshot.

Edited October 26, 2025Oct 26 by TaliaB
Changed screenshot

13 hours ago, TaliaB said:

When a large household load is suddenly switched off, PV string current still exists for a short time. The inverter/MPPT must either reduce PV operating voltage/current (MPPT retune), or instantly put the excess power into the battery or a local dump/load. If the MPPT loop or inverter control takes longer than the mechanical/electrical transient, a short reverse current pulse can appear at the CT/meter. Prepaid meters and their protection logic can be very sensitive to short reverse-flow spikes and will log an export / trip even if it’s only for a few seconds. The timing (same time each day) can be explained by a repeatable event (e.g., a scheduled load switching, or battery state/household behaviour at that hour) that coincides with high PV production. Normally the pre-paid meter agent(installer) can change setting on the plc(master switch) in the kiosk to accept some backfeed without going into protection mode.

Thanks for this great explanation. It is exactly what I am seeing on my inverter. But I can run that inverter in off-grid mode. If I put it into that mode I am telling it there is no grid connection and it will not even try to interact with the grid.

What happens in off-grid applications. The same situation can still apply - there is excess PV power for a short period of time. So now if the battery is full, and the power can't be dumped to the grid what happens? Is there some local load built into the inverter for this purpose?

I have not been able to reply for a few days, but I seem to have had some success.

Further info is that this is NOT solar related. We had a day of rain yesterday, and the issue persisted while the panels were not producing anything worthwhile, and the house was not drawing anything large and the batteries were not charging.

Someone advised that increasing the grid trickle feed figure would solve this problem. They said to increase it to say 80W, and monitor and to reduce it slowly every day until the problem occurs again to find the best setting for the meter. I set it to 80W this morning, and have had no interruptions in the grid supply, so maybe this bears the theory out.

@TaliaB your info on the meters is great, thanks. The discussion I had with the municipal technician leads me to believe that he cannot/is not prepared to change anything on the meter, and I had in mind to request a change from a Conlog Meter to a Lansdis Gyr. if they will entertain it...

My settings below, and I am happy with them. I am not exporting solar, but am exporting up to the CT coil placed on the incoming feed - ie, I am feeding my non essentials when I need to. This is why limit to load only is not ticked. Pic taken before the change to 80w grid feed.