How do two inverters work together?

[rob3000]

I accepted a quote for 23 x Jinko panels, a 8 kw Solar edge inverter and a 13.5kw Tesla battery. The DNO was rejected and they said my system had to be restricted to 3.68kw export and 7.36kw total generation, no idea why.
The new proposal is to have two 3.68kw Solaredge inverters and a 10kw solaredge battery.
Apparently there is not a lot of difference between the two systems. How do the inverters work together?

 

[johnb2713]

I'm not sure why you would want to go with 2 smaller inverters, just restrict the export to 3.68 kW. I also don't see how the DNO can restrict your generation either, the only effect it will have on them is to lower the demand on the grid feed to you.
Hopefully one of the knowledgeable guru's on here will give us chapter and verse on the regulations.

 

[Mrjmegson]

Doesn't an 8kw inverter require three phase?

I also don't see how the DNO can ask you to restrict generation, export yes, but not generation. As long as your equipment is upto dealing with that level of generation.

And I'm assuming you do mean restricting generation to 7.36kw (power) and not 7.36kwh, as you total generation. Either way I'm pretty sure they can't dictate that.

 

[Mrjmegson]

If you did go for two inverters, you link then with an rj45 cable, in settings on each inverter, you set one as the master and one as the slave, then they talk to each other and work together to do what ever is needed.

Mine share their power, so will put pretty even power into what ever they are doing, powering the house, charging the batteries, etc.

Hope this helps.

 

[johnb2713]

Mine share their power, so will put pretty even power into what ever they are doing, powering the house, charging the batteries, etc.

If theyre so balanced, why do you have a 5/3 battery split?

 

[Mrjmegson]

If theyre so balanced, why do you have a 5/3 battery spli

Funnily I've just explained this on another thread.

When I set the system up I didn't realise the inverters would work like that, in fact I wasn't intending on linking them at all. So I worked out from estimated solar production that 5/3 was the best split of the batteries to keep them charged, so I split them.

Then when I started the system running, the inverters started to fight each other, they were charging each others batteries from their batteries, and generally just falling out, so I linked them, and they now play very nicely together and evenly share all power. So if I'm producing 3kw from one array and 1kw from the other, both battery banks will charge with 2kw (not quite as there is always some sort of load, but you get the idea)

So if I'd known this, I would have split them evenly. Can't be bothered messing around now though.

 

[binky]

Then when I started the system running, the inverters started to fight each other, they were charging each others batteries from their batteries, and generally just falling out, so I linked them, and they now play very nicely together and evenly share all power. So if I'm producing 3kw from one array and 1kw from the other, both battery banks will charge with 2kw (not quite as there is always some sort of load, but you get the idea)

That's interesting, multiple solar inverters work quite happily together, but then they are just generating. I've always wondered how voltages from other inverters differentiate between grid volts and inverter output voltages, to which I have never found a technical explanation. I have heard from DNO guys about housing association estates where every house has had PV installed having grid voltages rising too high and causing problems.

Hybrids and batteries I can imagine fighting each other because of the current flow monitoring.

 

[Mrjmegson]

Mine are Hybrid with batteries, that's the basis of John's question.

 

[johnb2713]

That's interesting, multiple solar inverters work quite happily together, but then they are just generating. I've always wondered how voltages from other inverters differentiate between grid volts and inverter output voltages, to which I have never found a technical explanation. I have heard from DNO guys about housing association estates where every house has had PV installed having grid voltages rising too high and causing problems.

Hybrids and batteries I can imagine fighting each other because of the current flow monitoring.

I must admit I was concerned adding the Victron and Battery to my Existing Growatt Solar PV & Battery. I was assured on the Victron forum it would be fine and when I switched it on, it was LOL.
If you consider them two independent systems it's easy to see how it would work. The growatt sits on the grid and ramps it's voltage up and down and only exports when there is an excess of PV. The Victron also does the same following its CT, if it sees export it will lower it's output voltage, if it gets to minimum and export is still happening (from the Growatt), it then ramps the charger up to keep export at zero if possible.
It all works way better than I expected.

 

[johnb2713]

So if I'd known this, I would have split them evenly. Can't be bothered messing around now though.

Is it not just the case of setting the DIP switches and plugging in data and DC cables?

 

[bladerunnerpv]

Doesn't an 8kw inverter require three phase?

I also don't see how the DNO can ask you to restrict generation, export yes, but not generation. As long as your equipment is upto dealing with that level of generation.

And I'm assuming you do mean restricting generation to 7.36kw (power) and not 7.36kwh, as you total generation. Either way I'm pretty sure they can't dictate that.

There are a few high rated single phase inverters around

Hybrid (DC coupled)
https://midsummerwholesale.co.uk/buy/solax/solax-x1-g4-hybrid-7-5(NB requires HV batteries)

String
https://midsummerwholesale.co.uk/buy/SolarEdge/solaredge-10000-home-wave-benhttps://shop.krannich-solar.com/de-.../solar-inverters/4142/primo-8.2-1-not-de?c=63https://midsummerwholesale.co.uk/buy/solax-inverters/solax-x1-8-smart
AC coupled
https://midsummerwholesale.co.uk/buy/solax/solax-x1-g4-fit-7-5

 

[bladerunnerpv]

For the OP:
- The original quote is for an AC coupled system?
- I'm not too familiar with solaredge or tesla kit, but the 8kw inverter would be a string inverter? So there should be an additional AC inverter connected to the tesla battery, or is the tesla a so-called AC battery which includes an AC-DC converter built-in as an all-in-one unit?

- Would be helpful to have a full list of items on the quote(s) to understand better.

- Multiple inverters can be linked together for some manufacturers, e.g. via ethernet cable. Givenergy AC coupled inverters can 'talk' to one another via a connecting cable. I've seen this linking facility advertised more commonly on PV string inverters and AC coupled inverters, seems quite rare for DC coupled inverters.

Agree with others, can't see how DNO can quibble with generation potential (the kWp of the panels), it's what connects to the grid which needs to be right.

Which DNO form was submitted ?

 

[Mrjmegson]

Is it not just the case of setting the DIP switches and plugging in data and DC cables?

What, to make it an even split? If so, yes if I physically move one of the 5 to be next to the 3s, but as the inverters sort everything out between them, there's no point now.

 

[johnb2713]

What, to make it an even split? If so, yes if I physically move one of the 5 to be next to the 3s, but as the inverters sort everything out between them, there's no point now.

But if theyre sharing load in both charge and discharge surely the inverter with the 3 batteries will charge up first and discharge first having a lower capacity?

 

[Mrjmegson]

I obviously can't watch them at all times, but when I have checked the app, they are always charging with similar power, there are always a few watts between them, but as you say, they must vary this, because they always seem to reach 99-100% within a short time of each other, and when I've noticed, it seems to be the smaller bank that gets there last, the opposite of what you'd expect. That's the slave bank.

As for discharging, I've seen everything, sometimes they are discharging at the same rate, other times totally different, sometimes one bank is discharging while the other is not discharging at all. I think they seem to discharge at the same rate with large loads, but not smaller loads.

I genuinely have no idea how they do it. All I know is that when I first commed them together they didn't share at all, each battery bank only charged on what it's array was producing, I hadn't checked discharge at that time. Then my supplier got involved after me moaning that despite having export set to zero, they were still exporting 2-3kwh a day. They messed with them remotely for about a week, and at the end of it the systems played very nicely with each other.

If I can stop this 200w min load rubbish (which hopefully your solution will work), then this system will be pretty near perfect.