Hello all,  I had my system installed dec 2022.  The project was three sites, three inverters , three PV arrays (2strings each) and two sets of batteries. 
Two of the inverters are side by side but the other is some 30 meters away in a different building.  The design was the remote 8kw inverter had 20KWh of batteries on it and one of the other inverters (5.5kWh) had another 20KWh.   This gave me a total charge discharge capacity of 13 ish kW to handle peak loads and capitalise on my cheap rate charging plus maximise solar storage.   My installer ran the design past the sunsynk experts and all was good. Some 12 months later the second set of batteries are to be installed. It now turns out I can’t have any batteries on the 5.5kW inverter as it is too far from the 8kW one and they have to be wired together with a cable that is probably max 1m long. This cable can’t be made longer so I’m told.  Also I’m told even if I could join these together unless they are the same size inverter I still couldn’t do it. The installer wasn’t best happy (nor was I) as he’d had the design checked at the start and again before he ordered the extra set of batteries. He checked the second time as my first batteries are 5.12kWh and the second set 5.36kWh and he wanted to ensure no probs.  So much to my annoyance I either had to scrap the idea or have all 8 batteries on my 8kW inverter. This isn’t optimal by a long way but I eventually calmed down enough to agree. So new batteries installed on my 8kW inverter 4 x 5.12 and 4 x 5.36.  With this set up the BMS drops to 20amp so the max I can charge / discharge is 1kW.  With just the old set , the BMS is 408amp and thus I can charge/discharge at the full 8kW.   The installer has been on the phone with sunsynk numerous times and no one seems to have a clue how to fix it.  So for all of Dec and nearly all of Jan I’ve had no off peak and no solar charging it has cost me a bomb. Sunsynk asked the installer to leave the new batteries in circuit incase they needed to dial in. Great I thought as it’s not costing you 2000kWh per month at 0.35 p a kWh.  I’ve heard nothing from sunsynk since before Christmas.   If there are any sunsynk experts on here can anyone tell me what’s going on ? Especially if they know how to connect the new set on one of the other inverters. I think there is maybe a software version issue in the batteries but don’t even know how to check what versions are in there.  My worry is I think I have spent £10s of thousands on a system that is never going to work. 

 

Maybe start with a description (and include a rough drawing) on how the 3 inverters are connected? Are they linked on the AC side? Are they linked together in any other way? Do you have any communication cables between the 3 inverters? If they're not linked together in any other way and in effect separate systems that merely provide AC power, each with their own PV strings, I can't see any reason why each inverter can't have their own set of batteries.

I’m away for a few days but will get a drawing done when I’m back.  All three are grid tied so connected via the property AC circuits.   No other connection between them.  What the installer said was he’s been told they would fight each other so one would see a bit of export and start charging. Another inverter would see the load and start feeding it with its batteries and you get a swing between the two.   This doesn’t make a whole lot of sense to me as the minute the first one saw the change from export to import it would stop charging….  The batteries will only charge if there is export and only feed when there is import. I could see the power swinging maybe ie a load of 5kw gets fed by one then the other then both etc. this would need so sort of power system stabiliser (laplace transforms).  Hmm maybe ct placement issue 

1 hour ago, Perfo said:

I’m away for a few days but will get a drawing done when I’m back.  All three are grid tied so connected via the property AC circuits.   No other connection between them.  What the installer said was he’s been told they would fight each other so one would see a bit of export and start charging. Another inverter would see the load and start feeding it with its batteries and you get a swing between the two.   This doesn’t make a whole lot of sense to me as the minute the first one saw the change from export to import it would stop charging….  The batteries will only charge if there is export and only feed when there is import. I could see the power swinging maybe ie a load of 5kw gets fed by one then the other then both etc. this would need so sort of power system stabiliser (laplace transforms).  Hmm maybe ct placement issue 

Seems like a kind of no go using 5.5 and 8kW units as a start. Both CAN have their own batteries but not be run in parallel as far as I know. Not sure who the consultant was to the installer. Should the installer not take some blame for doing such an installation? 

As a lay person I guess the comms cables can be long but batteries and inverters must be matched to work together. 

Not sure if one can can have a claim for cost due to a system not performing due to the different size inverters. 

This can become a very interesting system when the experienced guys start commenting. 

2 hours ago, Perfo said:

All three are grid tied so connected via the property AC circuits.   No other connection between them.

Is your incoming AC feed three phase or single phase?

If three phase, CT coils can be connected independently per phase by the meter with "non essential" loads between inverter and CT.

If single phase, CT coils should all be by the meter (30 meters extension for the one), with "non essential" loads between inverters and CT.

There will be voltage fluctuations on the AC as depending on PV production, load, export, batteries, the inverters will influence one another (single phase).

This is only possible if inverters are NOT paralleled in any way, and NO communication connections between inverters, as you have said above.

You can liken this setup to three neighboring houses all having inverters connected to the same "feed AC", and all "grid tied" with ability to export.

Depending on each neighbors load and PV the AC will fluctuate. This is not a problem, unless voltages go above limits. (All exporting excessive amounts of power)

On 2024/01/22 at 8:12 PM, Perfo said:

The project was three sites, three inverters , three PV arrays (2strings each) and two sets of batteries. 
Two of the inverters are side by side but the other is some 30 meters away in a different building.

So your three inverters feed power to three different buildings independently, but been "grid tied", you want excess power fed back to grid (export) or "non essential" loads?

Depending on single or three phase, where are the CT coils connected?

If all three inverters are independent and have no communication, all three could even have their own sets of batteries, but looking forward to the installation diagram. 👍

 

Just some thoughts and questions.🤔

Thanks Tim and Scorp.

single phase. All feeding one house.  Very simple really.    One house with a cable T’d off the incoming grid supply between the incoming fuse and the house consumer unit. This cable then goes off to one building where two of the inverters (3.6kW and 5.5kW) are then off to another building (shed) with the 8kW in.  There are various isolators and fuses etc etc but electrically all the inverters are on the same conductor connected directly to the incoming supply. All three CTs are on the incoming supply grid side of this connection point.  I’m a newb to this but worked many years in power stations and the power industry.  My closing comment about CT placements was in line with what Scorp mentioned but I had to ponder it.  The only difference between me having two system or me having one and my neighbour having one (on the same phase) is the CT placement. To the grid there is no difference. If I only charged between certain times from the grid and these times where the same for both batteries then neither could discharge (fight) during this time. Then if I set the inverters to only charge on their own solar output outside of these times they shouldn’t fight at all.   The only downside would be once one battery was full the excess solar from that system couldn’t be used to charge the other nor could the solar output from the other 3.6kW inverter but the house loads absorbs this anyway..

Please see the diagram done by little Jonny age 6. Remember it is not polite to dis someone's art work :-0

As can be seen there is no connection between any of the Inverters other than on the house mains 240AC circuits.   I have deliberately not included any isolators or meters etc etc as these don't interfere with what it looks like electrically.. As mentioned it is a pretty simple circuit really. 

It is a pain only being able to import/export 8.8kW . Over this mornings peak I was importing loads of expensive kW's from the grid as the 8.8kW inverter was maxed out even though I had 65% SOC.  It hurts.....

       It is still hurting  🙂   

On 2024/01/24 at 8:27 PM, Scorp007 said:

Seems like a kind of no go using 5.5 and 8kW units as a start. Both CAN have their own batteries but not be run in parallel as far as I know. Not sure who the consultant was to the installer. Should the installer not take some blame for doing such an installation? 

As a lay person I guess the comms cables can be long but batteries and inverters must be matched to work together. 

Not sure if one can can have a claim for cost due to a system not performing due to the different size inverters. 

This can become a very interesting system when the experienced guys start commenting. 

Hopefully someone will appear that has the definitive answers.  The new batteries are tuned off and not connected to the BMS now so are just getting old. I haven't paid for this part of the installation and obviously won't if it doesn't work. I have agreed with the installer to have them all on one inverter but that is about it on deviations from design. 

Having an electronics and power system background I can easily see why the DC cables between batteries and the inverter have to have an identical (or close enough) resistance on the power side. Having different capacity batteries on the same DC  busbar doesn't make sense in this case as no point being critical  about length of power cable and putting batteries that are almost certainly of a different resistance/impedance on the same cables. Also I really can't see the point of designing a BMS system where the length of the coms cables are also so critical nor why different inverters and battery systems can coexist on the same system. The coms between units should be able to sort out who's charging/ discharging first / last and when. Why would anyone design such a massive flaw in to modern kit ? 

 

Edited January 30, 20242 yr by Perfo

I'm not sure if I understand your situation entirely, but here's some of my comments:

There should be nothing stopping you from having a bank of batteries connected to the 8kw inverter and another bank of batteries connected to the 5kw inverter. I don't think you should have the same bank of batteries connected to two inverters though. Yes, you might have a situation where there's extra solar capacity on eg. the 8kw inverter when its bank of batteries is fully charged and the 5kw bank is not charged yet, but it could always provide that extra power on the AC side to run the house.

The DC cables between batteries should be as close as possible to the same length/resistance if you're using a battery bus-bar. If you're not using a bus-bar, you should connect the positive cable to the one end of the bank of batteries and the negative to the other end of the bank, but you will need thicker cables for that since cables in a daisy chain setup will carry more current.

The only limit to communication cables are whatever that protocol's limit is, eg. CAN and RS485 limits, depending on how you handle inter-battery and battery-inverter communication. I'm using CAN between inverter and battery and RS485 between the batteries, but mine are all close by and not in different buildings like yours. However, I have no idea whether communication between different model inverters can work and whether they can run in parallel. Sunsynk should be able to answer that. My two are the same unit and hence they run in parallel but even then I see some odd behaviour at times.

I'm not sure if I understand your situation entirely, ask away if I can explain anything better...  but here's some of my comments:

There should be nothing stopping you from having a bank of batteries connected to the 8kw inverter and another bank of batteries connected to the 5kw inverter. I don't think you should have the same bank of batteries connected to two inverters though.

I totally agree having the same set of batteries connected to two inverters would be problematic.  My ideal is four batteries on the 8 kw and 4 on the 5 kw with no DC side  coupling between each set. I'm told that Sunsynk state on a single phase system this wont work even though my installers state Sunsynk said it would during the design phase.

Yes, you might have a situation where there's extra solar capacity on eg. the 8kw inverter when its bank of batteries is fully charged and the 5kw bank is not charged yet, but it could always provide that extra power on the AC side to run the house. I'm not that worried about this element. It would be good to be able to utilise all available solar energy on any battery but that's not a major concern of mine. 

The DC cables between batteries should be as close as possible to the same length/resistance if you're using a battery bus-bar. It is in Bus bar connection and all cables are the same pre made length going back to a single connection point (well two, one for pos one for neg). If you're not using a bus-bar, you should connect the positive cable to the one end of the bank of batteries and the negative to the other end of the bank, but you will need thicker cables for that since cables in a daisy chain setup will carry more current.

The only limit to communication cables are whatever that protocol's limit is, eg. CAN and RS485 limits, depending on how you handle inter-battery and battery-inverter communication. I'm using CAN between inverter and battery and RS485 between the batteries, but mine are all close by and not in different buildings like yours. CAN bus between batteries and as yet nothing between inverters. I've used rs485 on other projects way above the distance needed to go between the 8kw and 5kw the protocol allows over a 1km if the right cable is used and my distance is 20m maybe. Sunsynk sent a connection cable in the box and the installer where told they had to use that to connect between the inverters. As mentioned before this was maybe 1m in length. However, I have no idea whether communication between different model inverters can work and whether they can run in parallel. This is the odd bit as I'm led to believe two different size inverters can't communicate and run in parallel !!! Why would this be the case ? It's digital so this should be a pretty simple and straight forwards thing to do. The SunSynk design team must be pretty much top notch so I can't see why they would design it like this ? So as I find it hard to believe I'm thinking there must be a way.  Sunsynk should be able to answer that. They have about four times, twice saying yes it'll work no probs and twice saying no it definitely wont work. I am only getting this info from my installers so second hand but the installer are local and pretty good chaps so if they say this is what they've been told I tend to believe them.  My two are the same unit and hence they run in parallel but even then I see some odd behaviour at times.

I knew when I set out on this project that I may have to run another Cat 5E cable for the coms between the inverters but this isn't an issue. 

25 minutes ago, Perfo said:

I totally agree having the same set of batteries connected to two inverters would be problematic.  My ideal is four batteries on the 8 kw and 4 on the 5 kw with no DC side  coupling between each set. I'm told that Sunsynk state on a single phase system this wont work even though my installers state Sunsynk said it would during the design phase.

I can't think why this would NOT work?! Surely they would be separate systems, each with their own set of PV panels and batteries. So it will run as if they it was the only unit there, except that they will share the same AC "network". Yes, the one inverter might feed a little a bit more power compared to what's needed in the house but that's why you have separate CT's, so each inverter can sense when you're feeding back to the grid and throttle back its output.

26 minutes ago, Perfo said:

It is in Bus bar connection and all cables are the same pre made length going back to a single connection point (well two, one for pos one for neg).

Bus-bar is the best solution in my opinion, as long as you have enough fuses for safety (between battery and bus-bar AND between bus-bar and inverter). Each battery's BMS will handle its own charging.

32 minutes ago, Perfo said:

CAN bus between batteries and as yet nothing between inverters. I've used rs485 on other projects way above the distance needed to go between the 8kw and 5kw the protocol allows over a 1km if the right cable is used and my distance is 20m maybe. Sunsynk sent a connection cable in the box and the installer where told they had to use that to connect between the inverters. As mentioned before this was maybe 1m in length.

I would put a communication cable between the inverter and its bank of batteries so the inverter knows what the SoC is for its bank of batteries as well as communication cables between each battery. AFAIK these are normal CAT5 type cables so quite easy to source/make.

39 minutes ago, Perfo said:

This is the odd bit as I'm led to believe two different size inverters can't communicate and run in parallel !!! Why would this be the case ? It's digital so this should be a pretty simple and straight forwards thing to do. The SunSynk design team must be pretty much top notch so I can't see why they would design it like this ? So as I find it hard to believe I'm thinking there must be a way.  Sunsynk should be able to answer that. They have about four times, twice saying yes it'll work no probs and twice saying no it definitely wont work. I am only getting this info from my installers so second hand but the installer are local and pretty good chaps so if they say this is what they've been told I tend to believe them.  My two are the same unit and hence they run in parallel but even then I see some odd behaviour at times.

I knew when I set out on this project that I may have to run another Cat 5E cable for the coms between the inverters but this isn't an issue. 

Yes, it is my opinion as well (maybe I didn't phrase it correctly in my previous answer) that different models/sizes CAN'T be connected in parallel. Note that with parallel I meant one model connected to the same model with a communication cable in-between so they sort-of run as a unit. Agreed that Sunsynk should be able to do that given that they know the communication protocol between the units but it sounds that even Sunsunk themselves don't know whether that's possible or not. 🙄 I'm fairly sure running units separately as in your case without any communication in-between should be able to work but I hope there's maybe there's some expert in the group who can confirm that since I'm by no means an expert.

1 hour ago, Perfo said:

I'm not sure if I understand your situation entirely, ask away if I can explain anything better...  but here's some of my comments:

There should be nothing stopping you from having a bank of batteries connected to the 8kw inverter and another bank of batteries connected to the 5kw inverter. I don't think you should have the same bank of batteries connected to two inverters though.

I totally agree having the same set of batteries connected to two inverters would be problematic.  My ideal is four batteries on the 8 kw and 4 on the 5 kw with no DC side  coupling between each set. I'm told that Sunsynk state on a single phase system this wont work even though my installers state Sunsynk said it would during the design phase.

Yes, you might have a situation where there's extra solar capacity on eg. the 8kw inverter when its bank of batteries is fully charged and the 5kw bank is not charged yet, but it could always provide that extra power on the AC side to run the house. I'm not that worried about this element. It would be good to be able to utilise all available solar energy on any battery but that's not a major concern of mine. 

The DC cables between batteries should be as close as possible to the same length/resistance if you're using a battery bus-bar. It is in Bus bar connection and all cables are the same pre made length going back to a single connection point (well two, one for pos one for neg). If you're not using a bus-bar, you should connect the positive cable to the one end of the bank of batteries and the negative to the other end of the bank, but you will need thicker cables for that since cables in a daisy chain setup will carry more current.

The only limit to communication cables are whatever that protocol's limit is, eg. CAN and RS485 limits, depending on how you handle inter-battery and battery-inverter communication. I'm using CAN between inverter and battery and RS485 between the batteries, but mine are all close by and not in different buildings like yours. CAN bus between batteries and as yet nothing between inverters. I've used rs485 on other projects way above the distance needed to go between the 8kw and 5kw the protocol allows over a 1km if the right cable is used and my distance is 20m maybe. Sunsynk sent a connection cable in the box and the installer where told they had to use that to connect between the inverters. As mentioned before this was maybe 1m in length. However, I have no idea whether communication between different model inverters can work and whether they can run in parallel. This is the odd bit as I'm led to believe two different size inverters can't communicate and run in parallel !!! Why would this be the case ? It's digital so this should be a pretty simple and straight forwards thing to do. The SunSynk design team must be pretty much top notch so I can't see why they would design it like this ? So as I find it hard to believe I'm thinking there must be a way.  Sunsynk should be able to answer that. They have about four times, twice saying yes it'll work no probs and twice saying no it definitely wont work. I am only getting this info from my installers so second hand but the installer are local and pretty good chaps so if they say this is what they've been told I tend to believe them.  My two are the same unit and hence they run in parallel but even then I see some odd behaviour at times.

I knew when I set out on this project that I may have to run another Cat 5E cable for the coms between the inverters but this isn't an issue. 

My ideal is four batteries on the 8 kw and 4 on the 5 kw with no DC side  coupling between each set. I'm told that Sunsynk state on a single phase system this wont work even though my installers state Sunsynk said it would during the design phase.

Ask Sunsynk if you and the house next door is on the same phase each with their own Inverter (8&5kW) does that mean one of the 2 will not work? 

 

Yep there is a Can bus connection between the 8kW inverter and the first battery then daisy chained from this battery in to the next etc.    There are four ports on each battery. I'm not at home at the moment but I seem to remember the front two on the right is the can bus connection then the the back left is daisy chain out and back right is daisy chain in. I'm guessing these daisy chains maybe rs485 but definitely Ethernet RJ45 style.  There seems to be some confusion at SunSynk end about what is parallel and what isn't. As you say two units side by side connected together via coms lead can operate as one unit and this is classed as in parallel. That seems sensible and quite clear and it also makes sense that connecting two completely different sized inverters together in this way could be more difficult. However two inverters only linked on the AC side they are also calling parallel when my installers talk to them but I'm maintaining they are not in parallel they are T'd in to the same AC cable not parallel or series or anything as there is no other connection. 

 

As for different houses on the same phase. This is slightly different to one house with both. It is one circuit but the CT's will be in different points in that circuit so will see a different "system". But as far as I can see this is the only difference between me and a neighbour having one each or me having two.  I'm not speaking to Sunsynk direct as I don't really want to become a middle man the dispute is between the installer and them.   

If I put one battery on one invertor and the other on the other where could the most likely problem arise ?  I agree one invertor battery maybe quicker than the other so may be the first to start supplying load if it sees a house load. But the most that would happen is this one flattens first then the other battery cuts in. 

I only charge from the grid during the cheap period so at this time both inverters will be importing and charging so will not be affected by the other inverter.

When charging for solar they are only charging from their own solar and not back feeding via the AC side so again they can do this without a concern of what the other inverters is doing. 

Load in the house gets turned on. Sys1 spots it and starts feeding.  Sys2 sees no import so does nothing or carry's on charging if it has excess solar or it sees the load and also starts feeding but the import has already started dropping due to sys1 so at most if supplies a bit of it and sys1 supplies a bit. They wont both go flat out and flip to start exporting as this situation is exactly the same as a load coming in and out. 

Load in the house gets turned off. Sys1 spots is and backs of its feed. Then goes back to either charging if there is excess solar or doing nothing. Sys 2 will also see no import even if it was sharing some of the load with sys one  so backs off. 

Can anyone see a flaw in this thinking ? 

6 hours ago, Perfo said:

Yep there is a Can bus connection between the 8kW inverter and the first battery then daisy chained from this battery in to the next etc.    There are four ports on each battery. I'm not at home at the moment but I seem to remember the front two on the right is the can bus connection then the the back left is daisy chain out and back right is daisy chain in. I'm guessing these daisy chains maybe rs485 but definitely Ethernet RJ45 style.  There seems to be some confusion at SunSynk end about what is parallel and what isn't. As you say two units side by side connected together via coms lead can operate as one unit and this is classed as in parallel. That seems sensible and quite clear and it also makes sense that connecting two completely different sized inverters together in this way could be more difficult. However two inverters only linked on the AC side they are also calling parallel when my installers talk to them but I'm maintaining they are not in parallel they are T'd in to the same AC cable not parallel or series or anything as there is no other connection. 

 

As for different houses on the same phase. This is slightly different to one house with both. It is one circuit but the CT's will be in different points in that circuit so will see a different "system". But as far as I can see this is the only difference between me and a neighbour having one each or me having two.  I'm not speaking to Sunsynk direct as I don't really want to become a middle man the dispute is between the installer and them.   

If I put one battery on one invertor and the other on the other where could the most likely problem arise ?  I agree one invertor battery maybe quicker than the other so may be the first to start supplying load if it sees a house load. But the most that would happen is this one flattens first then the other battery cuts in. 

I only charge from the grid during the cheap period so at this time both inverters will be importing and charging so will not be affected by the other inverter.

When charging for solar they are only charging from their own solar and not back feeding via the AC side so again they can do this without a concern of what the other inverters is doing. 

Load in the house gets turned on. Sys1 spots it and starts feeding.  Sys2 sees no import so does nothing or carry's on charging if it has excess solar or it sees the load and also starts feeding but the import has already started dropping due to sys1 so at most if supplies a bit of it and sys1 supplies a bit. They wont both go flat out and flip to start exporting as this situation is exactly the same as a load coming in and out. 

Load in the house gets turned off. Sys1 spots is and backs of its feed. Then goes back to either charging if there is excess solar or doing nothing. Sys 2 will also see no import even if it was sharing some of the load with sys one  so backs off. 

Can anyone see a flaw in this thinking ? 

With each inverter having its own CT to measure if it must throttle to prevent feeding back will be no different to 2 different houses on the same phase. It won't matter where the CTs are installed as long as they are on the grid side. Even if they are next to each other. 

9 hours ago, Perfo said:

My ideal is four batteries on the 8 kw and four on the 5 kw with no DC side coupling between each set. I'm told that Sunsynk state on a single phase system this wont work even though my installers state Sunsynk said it would during the design phase.

This will work, as you have shown in "little Jonny's" picture. This layout will then allow battery "export" of 12 kW, as now you are limited to 8 kW only. Put another set of batteries on the 3.6 kW machine too, and "export" another 3 kW of battery power to grid. Note, all three SunSynk inverters and batteries must be independent and have no inter communication.

On 2024/01/22 at 8:12 PM, Perfo said:

It now turns out I can’t have any batteries on the 5.5kW inverter as it is too far from the 8kW one and they have to be wired together with a cable that is probably max 1m long.

Looking at your first post again, my goodness, those "experts" need to be fired.😲

You must treat each inverter as an independent install. Communication only between each inverter and it's own set of batteries. No DC coupling whatsoever.

As said in my first reply, expect Voltage fluctuations in the AC line as your inverters "export". As each inverter exports it must raise the Voltage, and the more power you export the higher the Voltage. As grid tied machines the frequency will always track the incoming frequency, and "export" has nothing to do with frequency, only voltage.

I'm no expert = (ex = has been - spurt = spray of water), just a normal person like most.😂

Hope you get your systems wired up soon, and start saving some money.

If able, max out your PV, as over there you don't have to many sun-hours.👍

Why not sell the 3.6KW and 5,5KW then get a 8,8KW 

Parallel the 8,8KW next to each other with same battery and CT on the master 

AC cables can be long if volt drop is calculated...

Some good replies there thanks Dudes... 

These are screen shots of my three SunSynk inverters.   The CT readings are a puzzle I erroneously thought they would all read the same. As can be seen one thinks I'm importing 218w the next thinks I'm exporting 281w and the third importing 27w ?   What actually is that grid input measuring ? it obviously isn't the actual grid power flow. The CT's are all orientated the same way and next to each other on a straight bit of cable. 

 

@Scorp007With the me vs neighbour thing. Yep I'm not saying it would work or not but if the CT is on the neighbours property then it could be flat-out importing whilst mine is flat-out importing and any swings on his is not going to be seen by mine and visa versa.  So I'm merely pointing out two inverters in different houses wouldn't be the same as two inverters in the same house purely due to the CT in one house wont be affected by changes in the other.  Again I'm only pointing out there is a difference not if it will work or not... 

@TimCam That was my intention. I wanted to minimise export by getting as much in to the batteries in a short a time as possible (when the sun shins) and minimise import by being able to source at least 13kW.  13kW isn't enough to capture all spikes but will be enough for a vast majority.  When I started on this journey this seemed a simple thing to do and I'm still convinced it should work. However as there is a dispute going on and it is a fair few £ to get the batteries moved I'd have to be 100% sure it would work. I'd be going against the recommendations of my installer as they say it wont work and they are going off what Sunsynk told them , so a big risk to me if I over ride them and tell them to move the batteries then it still doesn't work and I'm stuck like that with them telling me I told you so..  I normally do all these projects myself but sometimes in moments of madness I pay the money and get experts to give me a turn key system , it almost never works out like that. Every project like this reminds me why I should just do it myself. 

@Yuri  I have thought of that as well. But the physicality's are a problem. The large PV array is on the tractor shed  so the 8kW has to go there (or have very long DC cables) . The Cable feeding this shed is an underground cable good for at least 12kW but not much more. Before I worked this out I was thinking I could change the 8kW for a 16kW but the cable wouldn't take it. I could change the 8kw for two 5.5 kW and put them next to each other and paralleled up this would cure the battery problems and give me a max feed of about 10kW so better than 8kW but not really good enough to warrant another inverter (or two). I can't swap out the 3.6Kw or 5.5kW with another 8kW as these are too far from the other 8kW to parallel up anyway and I can't move it to the other site as the DC cables going to the PV's would be getting a bit long.  I can run extra cables of course but that would be hassle as they are underground across my garden and if that was the only way then so be it but I'd still have the distances between the solar arrays to contend with so it would always be sub optimal. 

 

10 minutes ago, Perfo said:

The CT readings are a puzzle I erroneously thought they would all read the same. As can be seen one thinks I'm importing 218w the next thinks I'm exporting 281w and the third importing 27w ?   What actually is that grid input measuring ? it obviously isn't the actual grid power flow. The CT's are all orientated the same way and next to each other on a straight bit of cable. 

How close are those CTs next to each other? Are they maybe not interfering with each other? If you space them a bit more, do you get the same odd readings? 

Ok I'll give that a go but being the type of split CT clamp they are they should be pretty impervious to magnetic fields not in the core.. but easy test to do so I'll do it when I get home. 

Do you think this reading should be the grid power flow and thus all read the same ? 

12 minutes ago, Perfo said:

These are screen shots of my three SunSynk inverters.   The CT readings are a puzzle I erroneously thought they would all read the same. As can be seen one thinks I'm importing 218w the next thinks I'm exporting 281w and the third importing 27w ?   What actually is that grid input measuring ? it obviously isn't the actual grid power flow. The CT's are all orientated the same way and next to each other on a straight bit of cable. 

I see you posted screen grabs from the Sunsynk web site. Those stats are only updated every 5 minutes, or maybe 60 seconds if your installer asked Sunsynk to give you quicker updates. You'll see the same when using the Sunsynk app, since it uses the same data as the web site. Also the stats are often delayed by hours when Sunsynk experiences issues with their data store. You'll see more up to date stats when you use the inverter screen or your own monitoring solution.

@p_i  Good point I have set it to the minimum scan time but this is still 60 seconds. On another thread in this forum I'm trying to get a ModBus thing working so I get quicker access direct.   Do you know the story of "clocks and more clocks" this is what is like trying to compare things on the screens of my inverters. The writing is too small and I have to go up a floor to read one then even if I get a right sweat on it still takes me 30 seconds to cross the field and compare the other 🙂  They do read different on the panels as well unfortunately.  I'll probably have to get my bestest wife on the job and thus be in two places at the same time just to confirm once and for all... 

My own monitoring solution is giving me updated data every 5 seconds, without having to get up to walk to an inverter, so the modbus route is the best way in my opinion. Even with quicker stats you will still observe stuff that seems slightly off since no CT/meter will be 100% accurate, but you'll get better stats than the Sunsynk options. But unfortunately we're still at the mercy of the people coding the Sunsynk firmware...

have you seen my other thread ? 

Home Assistant Sunsynk modbus project

Are you doing it like that ? I'd like to know if anyone has got this working but it doesn't seem to be a very popular approach.