SMA SI 5048US 2008 VINTAGE

[SolarisPower]

Hello Forum members, this is my first post and I am looking for assistance reconnecting my SMA SI 5048US inverters to my solar system using SOK 48/100 LiFePo4 batteries.
Here is a description of my solar system:
2 X SMA Sunny Boy 5000US grid tied inverters.
2 X SMA Sunny Island 5048US battery inverters.
26 REC 370W solar modules
48V backup battery system
1 X SMA Sunny Webbox.
1 X Generac 14kW whole hose standby generator.
1 X Generac 200A Nexus Smart auto transfer switch.
My system is grid tied net metering. The grid tied function has never been a problem however I have never been satisfied the performance of the battery backup side. The original batteries were FLA and as they aged they became problematic. I was working internationally at the time and the system shut down completely several times while I was away due to low battery voltage with the FLA batteries, to over come this problem I replaced the FLA batteries with AGM batteries but they became unreliable after 1 battery developed an internal fault (2012). Since I was still working internationally at the time I removed the SI’s and the batteries from the system and went grid tied only with no battery backup. My system has operated reliably grid tied since. In 2009 hurricane Laura damaged my original REC modules which were 44 REC 215W panels and roof. My standby generator ran for 37 days continuous except for maintenance before grid power was reestablish. Now that I have replaced my roof and panels and retired I wish to add the SMA Sunny Islands back to the system with 5 X SOK 48/100 Batteries. My 2 SMA Sunny Islands are Circa 2008/2009 and were built pre lithium batteries with BMS. I have corresponded with SMA on the issue of using early SI’s with lithium batteries and the best advice I received was yes you can in open loop if you are using batteries with BMS which I am, and you must upgrade the Firmware which SMA has supplied. I have received my batteries and they are now racked and connected in parallel and fully charged. I am ready to reconnect the batteries to the Sunny Boys and now asking Forum members especially those who my have a similar systems for guidance and assistance. One additional correction I want to make is move the standby generator two wire start from the Generac Nexus switch to the Master Sunny Boy. This is how the original installer wired it and I left it wired this way because I was not aware the SI’s could control the generator start until I started researching to repowering the SI’s. Here is how I plan to proceed:
1. Check with utility RE: net metering agreement. Done, no concern on their part as this is not an increase in original net metering agreement capacity.
2. Check with city permit office for electrical concerns, Done, call for inspection when batteries are replaced for visual inspection and approval.
3. Reconnect batteries to the DC side of SI’s Reconnect Sunny Sunny boys to the AC side of Si’s, reestablish comms between SI’s and Sunny Boys.
4. Wake up Si’s with 48V battery power. Question is should I use the Quick Configuration Guide to view and change parameters and accept the previous defaults as this is a battery change only. Also I plan to select VRLA battery parameter as I will not have the parameter LION with BMS function. The SOK batteries charging voltage range is 57.6 to 58.4 Vdc. I know that I have to make changes first in the Slave SI first then the Master. To prevent overloading this post I will close it with this information and wait for a response from forum members especially regarding specific SI’s parameters I should be concerned for this this setup and being grid tied with batteries and backup generator.

Thanks to all in advance for review and comments.

 

[Hedges]

I haven't used lithium batteries with Sunny Island, but others here know about it. @the_colorist may be able to help.

I think the earlier Sunny Islands may be updateable with identical firmware as new, to communicate with compatible BMS. I don't know if yours are.

People do also use Sunny Island with lithium batteries and VRLA settings adjusted to match them. Which would include zero temperature coefficient.

 

[Hedges]

Transfer switch - When an inverter (Sunny Boy or Sunny Island) is switched from one operating AC source to another (e.g. between grid and generator), make sure the switch is off for 5 seconds after disconnecting from first source, before connecting to second. That is so inverter will disconnect, not be feeding power and suddenly connected out of phase.

Consider a resistor to precharge inverter capacitors before connecting to lithium battery. Lithium batteries can deliver considerable current into a short (discharged capacitors on input of inverter), and 5 in parallel much more. I don't know if SOK has any precharge mechanism built it, don't think many batteries do.

"I know that I have to make changes first in the Slave SI first then the Master."

You just tell the slave it is "slave 1" (or 2, or 3). All parameters are set in the master.

In the event max or min voltage (per 2V lead-acid cell) doesn't reach the battery voltage you want, rather than setting 48V battery you might set to 46V or 52V.

 

[SolarisPower]

Hedges,

Thank you for both replies. I will message @colorist for his responses. You have clarifies some of my concerns, very helpful. The SOK 48/100‘s do have a BMS and that is why I chose they as I may have to run them open loop.

Thanks again for the replies.

 

[Hedges]

Of course all lithium batteries require a BMS to detect if one cell runs to its voltage limits while pack voltage (seen by inverter/charger) is still OK.

What is desired is a BMS that talks to inverter, so charge is slowed and voltage held while balancing occurs. Good well matched cells may remain close enough that over/under voltage disconnect by BMS doesn't happen at least during its youth. Since SOK is reported to be of better quality than most, maybe it will work well just with suitable VRLA settings.

REC is one BMS available for DIY, with a model that does talk to Sunny Island.
Due to its price, more cost-effective for 280 Ah 16s than for multiple strings of 100 Ah cells. Some people assembly batteries with multiple cells in parallel e.g. 4p16s.

 

[Calvin98]

SMA has a TECHNICAL NOTE Topic : Sunny Island 4548-US, 5048-US, 6048-US :: Grid Backup with Generator :: Digital Input
that will help with the relay. Basically it tells the SI if it is connected to the grid or not. If not, and you need more power (something you can set in the SI) it can turn the generator off and on depending on the settings. If batteries are low the SI can turn generator on say at 40% and then off again at 80%. You need to install a relay like in the diagram.