Panel wiring/configuration. Converting from 12v to 24 volt battery bank

[DixieMtCR]

I have 2 racks of 6, 100w mono panels which have been in use for about 1 year for off-grid emergency power during outages when the gas generator is off at night. . I use a Renogy 3000w PSW 12v Inverter for AC power. It draws 2.5amps under no load. All this is connected to the main load center through a commercial 10-circuit 30A transfer switch with watt meters.

The panel racks are each wired 3s2p which gives me the turn on voltage for the MPPT Charge controllers in the lower sunlight of Western Oregon.

I want to change from 12v to 24v battery setup and will have to replace the currently installed inverter with a 24v model. This will cut the current to the inverter in half.

What would be the best configuration for the panels for 24vdc? It is currently 3s2p for the 12v system. The 100w panels are rated at

• Max Power Voltage(Vmp):17.48V.

Am I thinking right that I shouldn't have to change from 3s2p configuration? My MPPT charge controllers are 12/24v 40a. So they will be fine for a 24v battery bank. I change the 8, 100AHr batteries from 8p to 2s4p to get my 24v.

I have also be looking at the inverter listed below on Amazon. Do any of you have any problems or reservations against using on of this brand/model?

GIANDEL 4000W 24 Volt Heavy Duty Pure Sine Wave Power Inverter​

Thank for any experience or knowledge you would like to pass along.

Ken

 

[Rednecktek]

I want to change from 12v to 24v battery setup and will have to replace the currently installed inverter with a 24v model. This will cut the current to the inverter in half.

Yes, the current cuts in half but the wattage stays the same. At that point your wires will be oversized and you might want to downsize your fuses but that isn't a problem at all. You'll want 250a for that 4Kw inverter on a 24v setup, you should have 300a in there now. Just replace the main fuse and call it a day.

Am I thinking right that I shouldn't have to change from 3s2p configuration? My MPPT charge controllers are 12/24v 40a. So they will be fine for a 24v battery bank. I change the 8, 100AHr batteries from 8p to 2s4p to get my 24v.

Yup, just rewire the battery bank for 24v and re-program the MPPT for its 24v settings which it Might do auto-magically once you connect up the 24v battery bank. No need to mess with anything else, especially if your panels are already installed and faced.

 

[DixieMtCR]

Yes, the current cuts in half but the wattage stays the same. At that point your wires will be oversized and you might want to downsize your fuses but that isn't a problem at all. You'll want 250a for that 4Kw inverter on a 24v setup, you should have 300a in there now. Just replace the main fuse and call it a day.


Yup, just rewire the battery bank for 24v and re-program the MPPT for its 24v settings which it Might do auto-magically once you connect up the 24v battery bank. No need to mess with anything else, especially if your panels are already installed and faced.

Yes, the panels are installed and working fine. I have overloaded the 12v 3000w inverter a few times. I would rather have a 4000w 24vdc for the surges and not bring the system down.

I am still recording data on the system to see how far i can push it and still recover the next day in the sun.

Thanks for your help! Ken

 

[MichaelK]

I think the first suggestion I could make for you is to get more panels. With your new 2S4P wiring configuration, you have a 400Ah battery at 24V. Assuming you want to charge at 1/8th (0.125) of capacity (C), that works out to be 400Ah X 0.125C X 25Vcharging = 1250W, about double what you have now.

You don't necessarily buy exactly the same panels. Is your 40A controller a Voc max unit of 100V, or 150V? I know Epever made both? Is yours an Epever? Which is it? With the 150V model you can wire your 6 panels in series to get ~105VDC, and pair that with three 72-cell grid-tie panels putting out ~36V each. The two parallel strings would both be putting out about the same voltage, 105V to 108V.