Viable Growatt Setup?


New Member
I'm planning to run an auxiliary AC unit during peak sun. Any adjustments you would make to this setup? Have I missed anything?



Solar Enthusiast
Will the inverter start the AC unit? AC units need a large starting current for the compressor and some inverters balk at that.


New Member
I'm curious if it would be better to get 9 panels and go 3S3P. Maybe I need more headroom than 150 OCV with the Growatt?


I See Electromagnetic Fields!
The 250W SanTan panels are cheapest $/W, but for a higher price you can get more watts per unit area, saving on mounting hardware and labor as well. Other panels still have UL labels, a good idea if mounted on a house.

8 x 250W = 2000W STC, maybe 85% = 1700W actual. Seems reasonable for 900W load.
Power production is a curve. You show 4s2p array, so orient 4s South East, other 4s South West. This drops peak to about 0.7 as much (1190W actual) and extends hours, a flatter curve so PV directly powers A/C more of the time.

Go larger PV array if space and inverter permit. PV is cheaper than batteries, OK to waste production on good days so you have enough on bad days.

Design PV series/parallel considering Voc of panels, temperature coefficient of Voc, record cold temperature for your location, max voltage in spec for Growatt. And then Vmp over temperature and MPPT range of Growatt.

Do you have the AC yet? Consider inverter-drive mini-split which would have no starting surge.
I've measured a window air conditioner with oscilloscope and current probe. Plan on starting surge 5x nameplate rating.

You show plugged into the wall. What is purpose of inverter and batteries? To keep running if grid fails?

BMS 24V 150A = 3600W
At least for no-name imports, people recommend derating by 50% for continuous load. This one may be better.
Check its surge rating vs. what motor takes to start.
Recalculate continuous using low-battery disconnect voltage, lowest efficiency of inverter, 25% headroom for margin, 12% extra for ripple current (because it won't draw steady DC from battery.)

Class T fuse at battery, because shorted lithium battery can dump 20,000A


I See Electromagnetic Fields!
I'm curious if it would be better to get 9 panels and go 3S3P. Maybe I need more headroom than 150 OCV with the Growatt?

"Open circuit voltage (VOC): 37.6 V"

37.6Voc x 3 = 113Voc (at 25 degrees C)
150V/113V = 1.33
Plenty safe, no cold temperature will boost voltage 33%
Temperature coefficient of Voc (given on data sheet, Trina for "SanTan"?) is typically -0.2% to -0.4% per degree C.
When margin is less than 20%, get the correct parameters and record cold temperature of your location, do the calculation to confirm.

For 3 or more strings in parallel, use fuses on each series string (15A specified for this panel, like most.)


I See Electromagnetic Fields!
Looking good.
Add a class T fuse for battery.

I'd still upgrade those panels. $450 for PV panels and how much for inverter and battery?
Those "white label" panels are best for someone who is going dirt cheap.


New Member
Inverter $520
Battery $750
Panels $450
BMS $140
Hardware and cables $200

$2060 for the entire system. I may upgrade the panels down the road, but these are so much cheaper than other panels I figure it's worth giving them a shot.


New Member
Bit of a snag though. I just realized all 18000 BTU AC units are 220v in the US. Looks like I'm going to either have to go with a 12000 BTU unit or get an inverter that outputs 220v.


I See Electromagnetic Fields!
Now you're in the range of, "Will it start that big A/C motor, or won't it?"
Is it inverter drive, so very soft start?

Traditionally we put battery fuse on positive lead, shunt (if used) on negative. That goes along with negative grounding, since positive wires can short to chassis or earth.

Is that a 115/230V split-phase inverter? If not you might get such a transformer so you can power other things too.
Is this going to be disconnected from grid, or does it have grid input?
There are European model 220V inverters with one hot and one neutral. US split-phase units have relays with both hots disconnecting.


New Member
Follow up question. If I were to purchase a hybrid inverter like the one below that outputs 230vac single phase would I be able to safely run an air conditioner designed for 220vac split phase? I'm not concerned about running any appliances other than the air conditioner.



I See Electromagnetic Fields!
Anything from 220V to 240V would work for appliances in that range. 50 Hz vs. 60 Hz probably OK, although an A/C designed for 50 Hz only might have trouble trying to spin 20% faster on 60 Hz due to more load. The inverter says "auto sensing", but that would only be if line voltage/frequency connected.

If an appliance also requires 120V (like my home unit with 240V to A/C and 120V for furnace fan), then it would require a transformer. If a window unit, probably 3-prong plug having ground and two hots, then OK.

If running off-grid so it provides 230V single-phase (one hot wire), should be OK.

If you want to connect its input to 120/240V split phase (two hot wires) there is a problem that is may only isolate the one wire it expects to be hot, leaving what it expects to be neutral connected to utility grid. This could be a shock hazard.

Note also the web page says only some types of PV panels can be used because it is a non-isolated inverter. What voltages are connected, for instance from grid, appear on the PV terminals. I think most common PV panels are compatible. I have some transformerless inverters with similar restrictions.

"Surge power 6000VA 10000VA"
That should start motors in appliances rated up to 1200W, 2000W for the bigger one. That bigger ought to be good enough for a (non-inverter drive) 1.4 kW A/C, smaller is questionable. If you get an inverter drive A/C, should be soft start and not a problem.

A hybrid inverter of this wattage for between $400 and $500? Maybe it is OK. You'll find out after using it. Some loads are less stressful than others.
Another guy got a hybrid to power lights for a tourist place, also welding. It worked a few weeks and blew up. So he got a different model. He was able to have the original one repaired to use elsewhere.

Watch the "OH NO its a smoke" link (from gnubie's signature)
Those of course are trying to start an induction motor, not one with built in inverter drive and slow ramp up of speed.

Brett V

Solar Addict
I have two of those mini split units. They are inverter based models and always soft start and slowly ramp up in current.


New Member
I don’t have any answers for your questions as I am new to all of this myself. I must ask though, what are you using to make your schematic of your system?