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Add another inverter to a house which already has an inverter

Jer_@

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May 25, 2022
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Hello All,
Some advice needed on adding another PV inverter to a house that already has a PV system installed


I have an existing Solar PV system installed (6.4kW panels; 5kh inverter; 10kWh battery; 230v AC system).
Its feeding the grid and house but can be switched over to off-grid in the event of a power cut. The system is a rebranded KSAR BluE-S-5000D (https://www.kstar.com/HybridInverter/17419.jhtml) which was professionally installed.

I have put an additional 2 strings of solar panels on my roof and want to get an inverter for these that can co-exist with the existing Solar PV system.

The additional Solar panels are 2 strings: (5 x 275W) and (4 x 275W) totalling about 2.5kW.
The solar panels are Trinasolar TMS-275PE05H https://www.trinasolar.com/sites/default/files/EN_TSM_PE05H_datasheet_B_2017.pdf



Question:
I want to utilise the additional 2.5kW of solar panels.

A)
if I get another pure sine wave hybrid inverter will it happily coexist with the current system.
[My own thinking is that it shold as neighbouring houses can have inverters of different types - and I'm assuming that each inverter will be self-synchronising its sine wave output the the grid]

Has anyone done this before - is a special specification of inverter needed [I cannon change the existing inverter, its not a new install where I could have gotten ones which are apecitied to be able to work in parallel]?

B) I was considering getting a Growatt 5000W Off-Grid OR a Growatt 3500W Off-Grid Solar Solar Hybrid Inverter 48V to 230V.
If you think this will do the trick - do let me know
OR if you think there is a better option of invetrter do suggest it please.

Thank you
Jer
 
Hello All,
Some advice needed on adding another PV inverter to a house that already has a PV system installed


I have an existing Solar PV system installed (6.4kW panels; 5kh inverter; 10kWh battery; 230v AC system).
Its feeding the grid and house but can be switched over to off-grid in the event of a power cut. The system is a rebranded KSAR BluE-S-5000D (https://www.kstar.com/HybridInverter/17419.jhtml) which was professionally installed.

I have put an additional 2 strings of solar panels on my roof and want to get an inverter for these that can co-exist with the existing Solar PV system.

The additional Solar panels are 2 strings: (5 x 275W) and (4 x 275W) totalling about 2.5kW.
The solar panels are Trinasolar TMS-275PE05H https://www.trinasolar.com/sites/default/files/EN_TSM_PE05H_datasheet_B_2017.pdf



Question:
I want to utilise the additional 2.5kW of solar panels.

A)
if I get another pure sine wave hybrid inverter will it happily coexist with the current system.
[My own thinking is that it shold as neighbouring houses can have inverters of different types - and I'm assuming that each inverter will be self-synchronising its sine wave output the the grid]

Has anyone done this before - is a special specification of inverter needed [I cannon change the existing inverter, its not a new install where I could have gotten ones which are apecitied to be able to work in parallel]?

B) I was considering getting a Growatt 5000W Off-Grid OR a Growatt 3500W Off-Grid Solar Solar Hybrid Inverter 48V to 230V.
If you think this will do the trick - do let me know
OR if you think there is a better option of invetrter do suggest it please.

Thank you
Jer

The inverter side of the AC outputs are NOT self-syncronizing, and the only way they can co-exist on the same circuit is if they are compatible parallel stackable inverters which use a sync cable to keep their sine waves in sync.

The only type of exception to that is if the person has a grid-tie capable inverter and connects the AC output of one inverter to the AC input of the grid tie inverter, then this topology is more of a series integration. Some people do this on their main house, and send AC power out to a barn or something, and plug the grid tie inverter in out there (maybe it has panels but no batteries), so they can get battery power from the house out to the barn when solar isn't present.

Anytime you use a grid-tie inverter, it is assumed that there is a master source, creating the 60 Hz sine wave that the grid tie inverters would sync to on the grid side connection.

But that concept is different than parallel stacking inverters onto the same AC output bus.
 
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Thank you for your help.

What is confusing me a little is that the AC Input/Output of the Solar PV hybrid-inverter is connected to the mains like a stub.
The mains does not flow through the inverter, so any power coming out of the inverter must (I think) phase-synchronise with the mains.

I've attached a few diagrams from the inverter manual to help explain.

So I think I can add in another PV hybrid-inverter to the system [but it may be a special type ??] - but as you say I've heard also that inverters in parallel should be of the same type and use a synchronising cable, so I'm just not clear on how to solve the issue.

As you say "Anytime you use a grid-tie inverter, it is assumed that there is a master source, creating the 60 Hz sine wave that the grid tie inverters would sync to on the grid side connection."
So I'm wondering if the first inverter syncks to the main master phase then the second inverter should see only one signwave and sync to it as well?
Thanks for your help
Jer
 

Attachments

  • Diagram from inverter user manual_v1.pdf
    131.5 KB · Views: 21
I had a hard time opening the attachment and since you are using the term Mains and 230 volts I presume you are not in North America?
In either event the least expensive inverter would be Grid Dependent (Grid Tie) inverter that would sync to the grid. It would not work when the grid is down unless the existing hybrid battery inverter can AC couple. The terms and standards may be different if you indeed are not in North America so all I can do it talk about the high level concept.
 
Thank you for your help.

What is confusing me a little is that the AC Input/Output of the Solar PV hybrid-inverter is connected to the mains like a stub.
The mains does not flow through the inverter, so any power coming out of the inverter must (I think) phase-synchronise with the mains.

I've attached a few diagrams from the inverter manual to help explain.

So I think I can add in another PV hybrid-inverter to the system [but it may be a special type ??] - but as you say I've heard also that inverters in parallel should be of the same type and use a synchronising cable, so I'm just not clear on how to solve the issue.

As you say "Anytime you use a grid-tie inverter, it is assumed that there is a master source, creating the 60 Hz sine wave that the grid tie inverters would sync to on the grid side connection."
So I'm wondering if the first inverter syncks to the main master phase then the second inverter should see only one signwave and sync to it as well?
Thanks for your help
Jer

When I read on the link for the unit you have above, I mean, it looks like they could sync on the grid side fine (to get power and put power to the grid), but I don't see any indication that the inverter output side (backup power AC side), could be bridged (it's not indicating they are a parallel stackable unit)...
 
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Thank you Samsonite, Ampster, I'm in Ireland, we've 230v (mains grid supply) Domestic supply, so you can kill yourself at home but we tend to use 110v on building sites so that there is less chance of seriously electrocuting yourself at work :).

Anyhow Yes we have regulations here that you must completely disconnect from the grid before applying the backup power to your house.
So for the AC backup output this is connected to one side of a manual switch which selects between a) AC backup output from the inverter and b) Mains grid supply to feed to the house. [awkward but the electricity supply company don't want someone sending 220v back into the mains grid during a power cut and prescribe a very 'robust' means of preventing this.


I just found this Post on the forum:

"Ok, the verdict is in! I got through to a technical support person at SMA who understood my scenario and in whom I feel very comfortable with his explanation.

Using multiple grid-tie inverters is not a problem. As he explained, a grid-tie inverter is designed to sync to the grid; therefore, if I have three grid-tie inverters, all three of them are looking for the frequency of the grid power, and they have no visibility that any other inverter exists.

When it comes down to actually wiring things up, he said it's perfectly normal to take each of the AC outputs (from the inverters) and wire each of them to a breaker (in a dedicated subpanel), where they get combined to one conductor (actually two conductors since its 240v) headed to the main power panel."

This makes sense to me and I'm only guessing but the synk cable in stackable inverters might actually be managing the Power outputs rather than synchronising the sine wave outputs, - (this is just a guess).
 
B) I was considering getting a Growatt 5000W Off-Grid OR a Growatt 3500W Off-Grid Solar Solar Hybrid Inverter 48V to 230V.
If you think this will do the trick - do let me know
OR if you think there is a better option of invetrter do suggest it ple
This is a good option. Just add another consumer unit on the output. And move some of your loads to it.
Put it in SUB mode, and it will take care of what it can. Everything else will pull from your existing inverter.
And anything extra will be exported to the grid.
 
Thank you all for your help - I will get on with it now and make it happen :)
 
I'll let you know when I get it installed -
I think the reason for specifing stacking in an inverter is to synchronise power output and to achieve the combined power output.
If your not looking fofr the combined power out put or are forced to use different inverters then I think they will happly live on the same house grid.
 
If your not looking for the combined power out put or are forced to use different inverters then I think they will happly live on the same house grid.
As long as they are grid-tied models. Off-grid models will assume that they are the only source of voltage and will not synchronize to anything. Magic blue dust ensues.
 
Awesome, thanks. Both of my inverters are Grid-Tie, SunnyBoy 6000 and PV2500. So they should co-exist in the sameUS household breaker panel?
 
Hi Sorry for not getting back sooner.
- just wanted to say that the two hybrid grid tie inverters are working in the same house.
There seems to be no issues so far. Both go about their business unaware of the other's existance.
One is a K-Star 5kW with 10kWh of battery; the other is a Solaris 3.5kW with 3.5kWh of battery.

Just to say thanks to those who helped answer the questions I had, thank you again.
 
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