Growatt 48V 12KW lnverter Split Phase and Minimum Battery

LoneRyder

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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

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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

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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
 

kromc5

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So far both of my 12k units have been perfect, no issues even at 9800+ loads.
 

JoeHam

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"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

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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

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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

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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.

Big mistake often made is thinking you have so much PV power available you don't need much AH's of battery. This is recipe for short lived batteries.

With 2p16s 280AH cells LFP (560 AH) battery in good condition, there would be about 4-5 watts of heating on each of the 32 cells for the 8 kW AC output power push even when PV is supplying all the net power.

1637929795691.png

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.

Growatt 12k is LF inverter so PV is pushed into batteries. HF inverters usually push into HV DC after battery DC to HVDC converter.

PV panels require constant load current or their output will be compromised. You don't want to have single phase AC ripple current make it to PV panels or you will lose available power. The batteries provide the filtering for the single phase AC 120 Hz ripple current when power is pushed to single phase AC output. This puts a lot of in-out ripple current on batteries even if PV net power is matching AC output power. This creates heating and loss of longevity to batteries.

On the above graph, if PV is supplying all the required power then the green DC battery current curve will drop down so average of the 120 Hz ripple is along the zero axis of graph.

Internal filter caps in inverter are nowhere near enough capacitance to make a dent in smoothing the DC ripple current at kW's of single phase AC power output.
 
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markansas

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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.
i went growatt . signaturesolar i like so far. its a good year
 

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Juan LesKar

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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.

View attachment 73568

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.
Very interesting graph.I'm thinking about trying to run my 240 V 5.5 KW electric sawmill with the 12K Growatt as it might be able to handle the 100+ Amp (AC) starting surge measured with my cheap clamp on meter. Not sure if that is peak or rms? If I used the mill while getting 3-5 KW of solar, wouldn't that ease the current demand from my 300 AHr LiFePo4 battery bank? Anybody else trying to run a single induction load this big on the Growatt 12K?
 

kromc5

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Very interesting graph.I'm thinking about trying to run my 240 V 5.5 KW electric sawmill with the 12K Growatt as it might be able to handle the 100+ Amp (AC) starting surge measured with my cheap clamp on meter. Not sure if that is peak or rms? If I used the mill while getting 3-5 KW of solar, wouldn't that ease the current demand from my 300 AHr LiFePo4 battery bank? Anybody else trying to run a single induction load this big on the Growatt 12K?
I have not run a single load this big with the 3 ton hvac, water heater, mini split its hit little over 11,500 watts at 198 amps showing on the battery side with no issues.
 
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