Add grid-based UPS function to off-grid system?

[marcfest]

What kind of additional component(s) are required to turn the off grid solar system whose specs are below into a UPS-like system that powers connected AC devices via the batteries/solar but switches to powering the AC devices through the grid when the solar-powered batteries falls below a certain level?

Thank you.
Marc

SPECS

250V / 100A Victron charge controller
4000W Giandel inverter
4 Battleborn 100Ah / 12V batteries in 2S2P 24V config

10 Mission Solar panels in 5S2P config:
Watts (STC) 345W
Max Power Voltage (VMPP) 33.37 V
Max Power Current (IMPP) 10.34 A
Open Circuit Voltage (VOC) 41.0 V
Short Circuit Current (ISC) 10.92 A
Max System Voltage (UL) DC 1000 V

 

[Sirtate]

What about running the system like a telephone office?
Charge the batteries from solar and the grid, and run everything off the inverters...

(you would just need to keep the grid from charging the batteries when the solar is working)

 

[marcfest]

What about running the system like a telephone office?
Charge the batteries from solar and the grid, and run everything off the inverters...

(you would just need to keep the grid from charging the batteries when the solar is working)

What components could I add to my system to achieve this?

 

[Sirtate]

Just a grid powered battery charger, sized to keep things afloat...

You want solar to do most of the work, with utility power to pick up any slack during many days of foul weather, correct?

Your new utility powered battery charger would just be set at a slightly lower voltage than your solar charger, so it won't do anything until battery voltage drops down low enough to warrant charging...

 

[marcfest]

This sounds really interesting. I have four Battleborn 12V 100Ah batteries in a 2S2P 24V system. I'm thinking about adding four more of these batteries to this. Can you recommend a grid charger that would be suitable for charging all eight batteries? Thanks again.

 

[12VoltInstalls]

This sounds really interesting. I have four Battleborn 12V 100Ah batteries in a 2S2P 24V system. I'm thinking about adding four more of these batteries to this. Can you recommend a grid charger that would be suitable for charging all eight batteries? Thanks again.

You would need to create a voltage-controlled response to grid-down for UPS functions. There are $15 voltage control relays on Amazon with the switched relay at ~10A AC. You could use one to control a higher-current relay but there’s a few other things/parameters to worry about.

??Q: doesn’t victron have components that do this ?

The easiest way I can think of is one of the MPPSolar AIO units; I have a smaller one that is the same in function as the larger units. It works flawlessly as a grid backup. I have only had two ‘actual problems’ which is that several weeks apart and a few months back it “forgot” to enable grid charging during a cloudy period. Twice. Pass-through was functioning. Of course this time of year the amount of sun hours pretty much eliminates grid needs…
Turning the inverter off then on ‘fixed it’ and it began charging. From reading around this is a rare but reported issue that apparently basically never recurs. I think that machine or its brethren are awesome for the money.

The option I used last winter was an automatic dial adjustable infinitely variable volts and amps battery charger. It would reduce amps and ramp down to not charging with adequate sunshine. The fan is variable speed and you could hear it slow down and stop fully automatically as solar input ramped in. They have a 24V model that I wish I’d bought but for the current system the 17.5V is more than enough.
Neither may provide enough amps for you if your draw is higher than mine.