Growatt 48V 12KW lnverter Split Phase and Minimum Battery

LoneRyder

New Member
The Growatt 48V 12KW inverter is on my short list for purchase for off grid/UPS use. In the manual it recommends at least 400Ah of battery capacity. Knowing I won't get full performance out of the system my question is: What is the minimum battery capacity for this system to operate? I am considering an EG4 LiFePO4 100Ah battery to start with then add additional units. I emailed SignatureSolar last week but no response yet. FYI my ground mount solar array is 30 of the SanTanSolar white label 250W 60 cell panels.
 

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TNOFUBMGOW

New Member
Hi folks. My 48v 12KWH Inverter has arrived. Along with a 48V 25A 120V Batter charger. Awaiting LiFePoe 100AH EG4 pro batteries. Would enjoy collaborating together as we build these things. I have an Amazon cart full of cables, fuses, etc but no ready to order until I'm certain I have spec'd properly. Your help would be great. Thank you
 

MrM1

I'm Here, But I'm Not All There
Preordered through Signature Solar. Expected arrival date is mid November. We'll see with all those container ships backed up on the West Coast.
Ours arrived a few days ago. Won't be able to start construction until the pole barn is built
 

JoeHam

Photon Sorcerer
"I don't want to go on the cart "

🤣


Feeling much better? Want to go for a walk??

Monty Python jokes aside, if you want to be sure you have the right cables/fuses in your amazon cart you’ll have to reveal what’s in there.
 

RCinFLA

Photon Sorcerer
Beside the obvious battery consumption life and maximum AC power provided, the batteries provide the 'filtering' of the PV generated power so the amount of PV power you can use is limited with small AH batteries.

A sinewave inverter, for 60 Hz AC, has large 120 Hz ripple current that peaks at over twice the average DC current, as read by a battery monitor. When solar power is being generated, the PV power current is relatively constant current based on PV illumination level.

The batteries provides the fill when 120 Hz peak ripple current is greater then PV DC current and when 120 Hz ripple current is in its cyclic valley the PV current charges the battery. Even when PV power exactly equals the net AC output power there is significant ripple current on batteries. This requires a minimum battery AH size for given PV array power provided to prevent damage to batteries due to excessive push-pull ripple current smoothing.

One of the greatest misperceptions and damaging assumption is the opinion that you don't need much battery capacity because you have so much PV array power available.
 
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Hedges

I See Electromagnetic Fields!
Well, 12kW/48V = 250A rms, 353A peak.
correction, 250A (mean) average, because 48V DC. Plus more due to inverter inefficiency.
If current ripple gets down to zero A at the bottom, the RMS current (which causes I^2 x R heating) is 11% higher.
Figure battery would have to deliver that, minus current from PV.
Also, battery has to accept charge current from PV peaking at 100% of PV.
The BMS and fuses will carry these pulses of current, which causes heating (a bit more than average current would suggest).
How the battery itself handles it, I'm not sure. I understand ohm's low better than chemistry.
 
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RCinFLA

Photon Sorcerer
The SolArc 12k is two 4kW 120vac inverters, so max continuous AC power is 8 kW or 4.8 kW continuous on either 120vac side when fed from batteries.

Battery AH size per kW of solar depends on battery type which is important factor in how much peak current the battery can take. LFP can take higher ripple current than lead-acid batteries.

For LFP battery with about 51vdc delivered to inverter input, for 8 kW AC power consumption, at 92% efficiency, at power factor = 1, will have average inverter DC input current of 170.6 amps and peak DC input current of 342.1 amps.

Assuming PV is matching AC output power there would be +/- 171 amps of ripple current on battery. It is your call how rough you want to treat your battery but I would say about 500 AH minimum if it was my battery. If you push to grid or AC load for extended time I would have an even larger AH battery for this amount of ripple current.

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Most 48v inverter manufacturers recommend 100 AH per kW of PV power for minimum battery sizing but this is more of a lead-acid battery number.
 
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