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SMA Sunny Island: parallel to the grid or islanding?

carlabudar

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Jun 22, 2022
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4
Hi!

I have a Sunny Boy 3.0 + 3kW PV installed. I also have contract with local distributor for selling extra energy to the grid. Now i purchased Sunny Island 8.0H-13 and I'm trying to find out the proper way of connecting it to the grid.
My main goal is to have battery backup with AGM batteries rather than reducing energy costs. Some day maybe i will use it for cut energy costs as well

While looking at the documentation , forums, web i noticed that there are two ways of connecting SI to the grid:
1) parallel to the grid (like SB): in this case i would need to have Home Manager for regulating energy flow to the grid(if i want to limit it), disconnector from the grid (in the case grid goes down) + i can connect generator to AC1 as extra source if necessary
2) grid is connected to AC1: loads and SB are connected to AC2 in separate local grid + i can add generator to AC1 (trough transfer switch because grid is also connected to the AC1).

I guess in the 2) case i don't need to have extra disconnector from the grid because it is allready implemented inside SI?

Also, i guess in 2) case SI would use more energy even if in backup mode because energy flows trough it all the time?


Does anyone have suggestions about this dilema, or there is no dilema at all and there is only one right way to do this?


Thank you all in advance.
 
Might get better responses with a more concise question.
I'd like to help but don't know where to begin.
 
Hi!

I have a Sunny Boy 3.0 + 3kW PV installed. I also have contract with local distributor for selling extra energy to the grid. Now i purchased Sunny Island 8.0H-13 and I'm trying to find out the proper way of connecting it to the grid.
My main goal is to have battery backup with AGM batteries rather than reducing energy costs. Some day maybe i will use it for cut energy costs as well

While looking at the documentation , forums, web i noticed that there are two ways of connecting SI to the grid:
1) parallel to the grid (like SB): in this case i would need to have Home Manager for regulating energy flow to the grid(if i want to limit it), disconnector from the grid (in the case grid goes down) + i can connect generator to AC1 as extra source if necessary
2) grid is connected to AC1: loads and SB are connected to AC2 in separate local grid + i can add generator to AC1 (trough transfer switch because grid is also connected to the AC1).

I guess in the 2) case i don't need to have extra disconnector from the grid because it is allready implemented inside SI?

Also, i guess in 2) case SI would use more energy even if in backup mode because energy flows trough it all the time?


Does anyone have suggestions about this dilema, or there is no dilema at all and there is only one right way to do this?


Thank you all in advance.
Wow. Just keeping this thread handy since I am looking hard at a Sunny Island... and have a net metering contract that I want to keep. I am guessing that AC1 and AC2 refer to 110v and 220v but something someone on here will off the top.
 
Hi,

sorry for not answering on your replies, i have totally forgot that i send messages on this forum (i never got any notifications on my email).

@littleharbor2
"I think you need a larger SB to work with the SI. The 3.0 is too small. Hopefully, in your case I'm wrong."
I think it is other way around. If SB is too powerful then it might be a problem for smaller SI to handle this power. In my situation SB3.0 gives maximum output of 3kW and SI8.0 can charge batteries with max 6kW, it can give up to 6kW on AC1 output and it can handle up to 11kW if connected parallel (AC2) to the grid.
If SI had less power then SB then i guess you will need some kind of synchronization between them to lower the output of SB so SI can handle it.

@ArtDeco
Look below.

@Maitake
"Might get better responses with a more concise question"
You are right, i will try again.
My main question was why are there two ways of connecting loads and grid/generator to the SI?
In the meantime i think i figured out but i will really like if someone can confirm it.

AC1:
this AC connection is used to connect only loads to the SI, it is used to form a stand alone grid. It can be used in off-grid system which is independent of the grid connected to the AC2 (if used). For SI8.0 max output is 6kW.
AC2:
it is used to connect generator or regular grid. It is not for grid forming (SI will not try to form a grid on this connection as on AC1), but SI will synchronize with this grid. It is bidirectional, it can take energy and transfer it to AC1 or charge batteries and it can return energy to it from batteries or other sources connected to AC1. For SI8.0 max power is 11kW.

Possible configurations:
Config 1 (Main grid (max 11kW), generator (max 5kW), loads < 6kW)
Main grid (max 11kW) and generator (max 5kW) are connected via manual transfer switch to the AC2. SB and loads are connected to the AC1. This works well if all my loads and SB are < 6kW. If there is power outage, all my loads will get power from batteries connected to SI, SB will also work because it is connected to AC1. Also i don't need additional disconnect from the main grid (when outage) because i have separate grid on AC1. That means if an outage occurs and generator/grid if feed_in power is 0, then internal ATS will disconnect SI from the grid and energy will not be transferred to it.
Config 2 (Main grid (max 11kW), generator (max 5kW), loads > 6kW)
Main grid (max 11kW) and generator (max 5kW) are connected via automatic transfer switch (ATS) to the AC2. All loads (>6kW) are also connected to AC2 because AC1 cannot handle this power.
SB (max 3kW) can be connected either to AC1 or AC2. If connected to AC1, then if SI is out, the energy from SB could not be used. But if connected to AC2 then if SI disconnected (e.g. for maintenance) SB will still work if main grid is still operational.
When there is outage then SI will start to generate AC power from batteries on AC2 (if generator/grid feed_in power > 0 ) as well on AC1(if used). This means that i need to disconnect the main grid from my system (this is why i need ATS) because if grid is down i cannot return energy to it (i could kill someone if there is maintenance guy repairing the grid). This configuration is more expensive/complicated because i need to build ATS.

Right now my loads are <6kW but they will probably go up if i (and i plan to) buy EV.
So right now Config 1 is better option, but in a year or two AC2 will probably be better because of greater load power.


There is one thing that i cannot figure out:
How does SI figure out that there was an outage on the main grid that is connected to the AC2?
As i understand, SI is synchronizing with the grid connected to the AC2, and it can feed energy in main grid via AC2. But when main grid go down, then first it needs to sense it somehow and then it switches from synchronous to non-synchronous mode?
But in that case i think the power cannot be bigger than 6kW because it cannot drain batteries more than that?
Also if in the moment of outage SI is not generating AC power from batteries but all energy for loads (connected to AC2) is used from the main grid (connected to AC2) then will there be a drop of voltage until SI figures out that there was anoutage and start to generate power from batteries?



Thank you in advance for all your comments.
I would appreciate if someone can give me some advice or comment
 
AC2 is AC from grid or generator
AC1 is AC from loads/Sunny Boys.
See diagram.
 

Attachments

  • SI Layout 01.JPG
    SI Layout 01.JPG
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There is one thing that i cannot figure out:
How does SI figure out that there was an outage on the main grid that is connected to the AC2?
As i understand, SI is synchronizing with the grid connected to the AC2, and it can feed energy in main grid via AC2. But when main grid go down, then first it needs to sense it somehow and then it switches from synchronous to non-synchronous mode?
But in that case i think the power cannot be bigger than 6kW because it cannot drain batteries more than that?
Also if in the moment of outage SI is not generating AC power from batteries but all energy for loads (connected to AC2) is used from the main grid (connected to AC2) then will there be a drop of voltage until SI figures out that there was anoutage and start to generate power from batteries?
SMA has a technical note where they explain it. Basically you need a relay that is OPEN when the grid is present and CLOSED when grid power is lost. That way the SI knows when is is using grid power or generator power and will not backfeed a generator.
 

Attachments

  • TechNDIGIN-HUS123112.pdf
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